Transthoracic Echocardiography: Beginner's Guide with Emphasis on Blind Spots as Identified with CT and MRI

Abstract

Transthoracic echocardiography (TTE) is the primary initial imaging modality in cardiac imaging. Advantages include portability, safety, availability, and ability to assess the morphology and physiology of the heart in a noninvasive manner. Because of this, many patients who undergo advanced imaging with CT or MRI will have undergone prior TTE, particularly when cardiac CT angiography or cardiac MRI is performed. In the modern era, the increasing interconnectivity of picture archiving and communication systems (PACS) has made these images more available for comparison. Therefore, radiologists who interpret chest imaging studies should have a basic understanding of TTE, including its strengths and limitations, to make accurate comparisons and assist in rendering a diagnosis or avoiding a misdiagnosis. The authors present the standard TTE views along with multiplanar reformatted CT images for correlation. This is followed by examples of limitations of TTE, focusing on potential blind spots, which have been placed in seven categories on the basis of the structures involved: (a) pericardium (thickening, calcification, effusions, cysts, masses), (b) aorta (dissection, intramural hematoma, penetrating atherosclerotic ulcer), (c) left ventricular apex (infarcts, aneurysms, thrombus, apical hypertrophic cardiomyopathy), (d) cardiac valves (complications of native and prosthetic valves), (e) left atrial appendage (thrombus), (f) coronary arteries (origins, calcifications, fistulas, aneurysms), and (g) extracardiac structures (primary and metastatic masses).

Online supplemental material and the slide presentation from the RSNA Annual Meeting are available for this article.

^©RSNA, 2021

SA-CME LEARNING OBJECTIVES

After completing this journal-based SA-CME activity, participants will be able to:

• ■ Describe the standard TTE views.

• ■ Recognize the primary strengths and limitations of TTE with an emphasis on blind spots.

• ■ Identify the primary blind spots as seen at CT or MRI.

Introduction

Transthoracic echocardiography (TTE) is the primary initial imaging modality in evaluating the anatomic structure and function of the heart. It allows real-time noninvasive quantification of cardiac chamber volume and function, which—along with widespread availability, portability, low cost, and safety (lack of ionizing radiation)—make it a mainstay of cardiac imaging (1).

Appropriateness criteria for use of TTE have been published by the American College of Cardiology in collaboration with multiple other organizations, providing helpful guidance for the most common clinical scenarios. These include valvular heart disease, coronary artery disease, cardiomyopathy, heart failure, arrhythmias, stroke or transient ischemic attack, and pericardial disease (2). Despite its widespread use and many strengths, it is not without limitations, such as operator dependence, limited tissue characterization, and narrow field of view. Additional challenges also arise in evaluating patients with large body habitus, comorbidities (eg, emphysema), and recent trauma or surgery (3). As a result, additional imaging with transesophageal echocardiography, electrocardiographically (ECG) gated cardiac CT angiography (CTA), or ECG-gated cardiac MRI is often pursued for further and more detailed evaluation.

Heart disease, a common indication for TTE, is prevalent in the United States—affecting approximately 30 million adults, according to the National Center for Health Statistics—and is currently the leading cause of death in the nation (4,5). Advances in CT technology now allow the temporal and spatial resolution necessary to render some cardiac diagnoses at routine nongated examination of the chest. While cardiac findings are generally best evaluated with ECG-gated cardiac CTA or cardiac MRI, in some instances a cardiac finding that was not present or not noticed at prior TTE may be apparent at nongated chest CT or MRI. Given the increasing interconnectivity of picture archiving and communication systems (PACS), radiologists now have greater access to TTE images for comparison. Therefore, it is now imperative that radiologists develop a basic level of understanding of TTE, including its strengths and limitations, to enable confidence in their diagnosis and avoid the alliterative error prevalent in diagnostic imaging by not relying solely on the echocardiography report (6,7).

In this article, we review the basic echocardio-graphic technique and normal US appearance of the heart. In doing so, a number of anatomic blind spots will be highlighted, which warrant special attention when reviewing TTE studies in conjunction with either ECG-gated (cardiac CTA or cardiac MRI) or nongated (CT or MRI) examinations of the chest. These blind spots have been divided into seven categories based on the structures involved: the pericardium, aorta, left ventricular (LV) apex, cardiac valves, left atrial appendage (LAA), coronary arteries, and extra-cardiac structures. This article can be used as a primer for either general or subspecialty radiologists who wish to incorporate comparison TTE images into their practice.

Transthoracic Echocardiography

To understand the limitations and blind spots of TTE, we first provide a basic overview to include transducer selection, windows, and scan planes.

Transducer Selection

A phased-array transducer is typically selected for TTE, which utilizes multiple transducer elements that are fired in a precise sequence to create a sector (fan-shaped) image, allowing a relatively wide field of view in relation to the small transducer footprint. This sector scanning method is ideal for echocardiography, in that its fast frame rate allows evaluation of cardiac motion and the small transducer footprint enables evaluation in small acoustic windows, such as the intercostal spaces (8). Typical transducer frequencies used in TTE range from 2.0 to 5.0 MHz, with the higher frequencies offering better spatial resolution but lacking the tissue penetration of lower frequencies, which are reserved for evaluating deeper structures (9). Further pre- and postprocessing image optimization and other techniques (eg, use of Doppler and three-dimensional imaging) are outside the scope of this review, but further details can be referenced in recently published American Society of Echocardiography (ASE) guidelines (9).

Standard Views

For image acquisition, the window is defined as the position of the transducer on the patient. The four standard windows used in TTE are the parasternal, apical, subcostal, and suprasternal windows (Fig 1) (9). The image plane refers to the orientation of the transducer in relation to the axis of the LV. The four standard planes are the long-axis, short-axis, apical four-chamber, and apical two-chamber planes (Fig 2) (9). Slightly off-axis planes may be acquired by gently tilting the transducer.

Figure 1.

Standard echocardiographic windows in transthoracic echocardiography (TTE). The four standard windows are parasternal, apical, subcostal, and suprasternal. The parasternal and apical windows are generally used from the left side. The third or fourth intercostal space is most often used for the parasternal window, and the fifth intercostal space is most often used for the apical window. AO = aorta, LV = left ventricle, PA = pulmonary artery, RA = right atrium, RV = right ventricle. (Reprinted, with permission, from reference 9.)

Figure 2.

Standard imaging planes. Drawing shows the four standard planes: long axis, short axis, apical four chamber, and apical two chamber. The long-axis plane corresponds to images acquired in the parasternal long-axis view, and the short-axis plane corresponds to images acquired in the parasternal short-axis view. The apical plane (both four chamber and two chamber) corresponds to images acquired from the apical window. (Reprinted, with permission, from reference 9.)

The combination of the window, the plane, and the structures evaluated defines the echocardiographic view. Notably, there is some overlap in use of the terms plane and view, and at times they may be used interchangeably. The ASE published guidelines in 2019 for a comprehensive TTE examination that contain detailed descriptions and images of the essential views for a complete examination (9).

In this article, we present the standard views alongside multiplanar reformatted cardiac CTA images in the same plane for correlation. Details regarding the orientation and position of the transducer for each view are outlined later. In addition, graphic overlays are placed in the upper left corner of the TTE images, along with a summary figure to assist the beginner with orientation (Fig E1) (10). These standard views, as well as their main strengths and limitations, are further detailed and summarized in Table E1. While the clinical scenario may require additional TTE windows or transition to transesophageal echocardiography, this is outside the scope of this article, and the interested reader can find further examples not shown here in the ASE guidelines (9).

Parasternal Window.—The parasternal long-axis (PLAX) LV view is typically one of the first images obtained during a comprehensive TTE examination. It is obtained by placing the transducer to the left of the sternum in the third or fourth intercostal space while the patient lies in the left lateral decubitus position. The primary structures visualized are the left atrium (LA), LV, LV outflow tract (LVOT), and aortic root (AR) (Fig 3). The mitral valve (MV) and aortic valve (AV) are also visualized on this view, with magnified images of each additionally obtained.It should be noted that while it may appear that the true LV apex is visualized, this view actually represents an oblique image through the antero-lateral wall.

Figure 3a.

Normal parasternal long-axis LV view at TTE (a) and correlative cardiac CT angiography (CTA) (b). AR = aortic root, DAo = descending aorta, IVS = interventricular septum, LA = left atrium, arrow = mitral valve, arrowhead = aortic valve, _* = LV outflow tract.

Figure 3b.

Normal parasternal long-axis LV view at TTE (a) and correlative cardiac CT angiography (CTA) (b). AR = aortic root, DAo = descending aorta, IVS = interventricular septum, LA = left atrium, arrow = mitral valve, arrowhead = aortic valve, _* = LV outflow tract.

The parasternal long-axis right ventricular (RV) inflow view is obtained by moving the transducer toward the apex and orienting the probe toward the RV. The tricuspid valve (TV) is in the center of the image, with visualization of the right atrium (RA) and RV (Fig 4). The right atrial appendage (RAA) is rarely seen at TTE. A parasternal long-axis RV outflow view can also be obtained by moving the transducer toward the base and angling laterally, which shows the RV outflow tract (RVOT), pulmonary valve (PV), and main pulmonary artery (MPA).

Figure 4a.

Normal parasternal long-axis RV inflow view at TTE (a) and correlative cardiac CTA (b). IVC = inferior vena cava, arrow = tricuspid valve, arrowhead = eustachian valve, _* = coronary sinus.

Figure 4b.

Normal parasternal long-axis RV inflow view at TTE (a) and correlative cardiac CTA (b). IVC = inferior vena cava, arrow = tricuspid valve, arrowhead = eustachian valve, _* = coronary sinus.

The parasternal short-axis (PSAX) view is obtained by rotating the transducer approximately 90° clockwise from the parasternal long-axis view. The probe is then angled from superior to inferior to obtain views at the levels of the great vessels, aortic valve, mitral valve, papillary muscles, and LV apex. At the aortic valve level, all three aortic valve leaflets and nearby surrounding structures are shown (Fig 5). Additional dedicated views of the aortic valve, tricuspid valve, pulmonary valve, and main pulmonary artery can also be obtained. At the mitral valve level, separate anterior and posterior leaflets are displayed, with the so-called “fish mouth” appearance of the mitral valve during diastole (Fig 6).

Figure 5a.

Normal parasternal short-axis view at the aortic valve level at TTE (a) and correlative cardiac CTA (b). LAA = left atrial appendage, LC = left coronary cusp, MPA = main pulmonary artery, NC = noncoronary cusp, RC = right coronary cusp, arrow = tricuspid valve, arrowhead = pulmonary valve.

Figure 6a.

Normal parasternal short-axis view at the mitral valve level in diastole at TTE (a) and correlative cardiac CTA (b). Arrow = anterior mitral valve leaflet, arrowhead = posterior mitral valve leaflet.

Figure 5b.

Normal parasternal short-axis view at the aortic valve level at TTE (a) and correlative cardiac CTA (b). LAA = left atrial appendage, LC = left coronary cusp, MPA = main pulmonary artery, NC = noncoronary cusp, RC = right coronary cusp, arrow = tricuspid valve, arrowhead = pulmonary valve.

Figure 6b.

Normal parasternal short-axis view at the mitral valve level in diastole at TTE (a) and correlative cardiac CTA (b). Arrow = anterior mitral valve leaflet, arrowhead = posterior mitral valve leaflet.

At the papillary muscle level, the anterolateral and posteromedial papillary muscles are seen in cross section (Fig 7). The LV should have a circular appearance at this level. Although the LV may look slightly elliptical during diastole or if the probe is not positioned orthogonal to the LV's long axis, a noncircular morphology during systole is compatible with myocardial disease (8). Finally, at the apical level, a cross section through the apical third of the LV is shown. It should be noted that the parasternal short-axis apical-level view is not the best view for evaluating the true LV apex, since it is not seen in its entirety (Fig 8).

Figure 7a.

Normal parasternal short-axis view at the papillary muscle level at TTE (a) and correlative cardiac CTA (b). Arrow = anterolateral papillary muscle, arrowheads = posteromedial papillary muscle.

Figure 8a.

Normal parasternal short-axis view at the LV apex level at TTE (a) and correlative cardiac CTA (b). In this example, the RV is visible in addition to the LV, although this is not required.

Figure 7b.

Normal parasternal short-axis view at the papillary muscle level at TTE (a) and correlative cardiac CTA (b). Arrow = anterolateral papillary muscle, arrowheads = posteromedial papillary muscle.

Figure 8b.

Normal parasternal short-axis view at the LV apex level at TTE (a) and correlative cardiac CTA (b). In this example, the RV is visible in addition to the LV, although this is not required.

Apical Window.—For the apical window, the transducer is placed in one of the intercostal spaces (usually the fifth) near the point of maximal impulse (9). The views from this window are typically excellent for assessment of cardiac motion, morphology, presence of mass lesions, and presence of a pericardial effusion, although not without limitation, as discussed later (11). This window is also most frequently used for Doppler evaluation and interrogation of valvular stenosis, regurgitation, cardiac output, cardiac index, and intracardiac pressures, although this is outside the scope of this article.

The apical four-chamber (A4C) view is the first view obtained in the apical window, with both atria and ventricles visualized (Fig 9). Magnified images of the LV and RV can be obtained for further detail. This view is optimal for evaluation of septal and other wall motion abnormalities such as ventricular interdependence (9). This view is also relied on heavily for atrial volumetric assessment and evaluation of Chiari networks and RV leads.

Figure 9a.

Normal apical four-chamber view at TTE (a) and correlative cardiac CTA (b). Owing to the parallel orientation of the interatrial septum to the ultra-sound beam, an atrial septal defect may be simulated where no actual defect is present. Additionally, valve leaflets may be difficult to visualize on cardiac CTA images. Straight arrow = mitral valve, curved arrow = tricuspid valve.

Figure 9b.

Normal apical four-chamber view at TTE (a) and correlative cardiac CTA (b). Owing to the parallel orientation of the interatrial septum to the ultra-sound beam, an atrial septal defect may be simulated where no actual defect is present. Additionally, valve leaflets may be difficult to visualize on cardiac CTA images. Straight arrow = mitral valve, curved arrow = tricuspid valve.

However, detailed assessment of the atria is limited with this view owing to their position further from the transducer. In addition, the parallel position of the interatrial septum in relation to the ultrasound beam makes evaluation for atrial septal defects inaccurate with this view (8). It is also important that the transducer be positioned as close to the apex as possible to avoid foreshortening of the LV, as this can result in misdiagnosis (8).

Anterior angulation of the transducer reveals the aortic valve and aortic root in addition to the four chambers and is therefore termed the apical five-chamber (A5C) view (Fig 10). If the transducer is tilted further anteriorly, the RV outflow tract and pulmonary valve may be visualized, although this is not an essential part of a typical TTE examination (8,9). A more posteriorly angulated apical four-chamber view can also be obtained, which shows the coronary sinus.

Figure 10a.

Normal apical five-chamber view at TTE (a) and correlative cardiac CTA (b). Arrowhead = aortic valve, _* = LV outflow tract.

Figure 10b.

Normal apical five-chamber view at TTE (a) and correlative cardiac CTA (b). Arrowhead = aortic valve, _* = LV outflow tract.

Rotating the transducer 90° counterclockwise from the apical four-chamber view produces the apical two-chamber (A2C) view, with visualization of the LA, mitral valve, and LV (Fig 11). This view allows direct visualization of the true anterior and inferior walls of the LV (12). An additional dedicated image focused on the LV can also be obtained with this view.

Figure 11a.

Normal apical two-chamber view at TTE (a) and correlative cardiac CTA (b). Arrowhead = mitral valve, * = left atrial appendage, arrow = pulmonary vein.

Figure 11b.

Normal apical two-chamber view at TTE (a) and correlative cardiac CTA (b). Arrowhead = mitral valve, * = left atrial appendage, arrow = pulmonary vein.

The apical three-chamber (A3C) view, also known as the apical long-axis view, is obtained after rotating the probe approximately 60° counterclockwise from the apical two-chamber view. This view is similar to the parasternal long-axis LV view, although the resolution of the mitral valve and aortic valve is typically worse on this view owing to the greater image depth (Fig 12) (8). However, the LV apex is best visualized on this view (8,13). As with the apical two-chamber view, a dedicated image focused on the LV can also be obtained.

Figure 12a.

Normal apical three-chamber (long-axis) view at TTE (a) and correlative cardiac CTA (b). AR = aortic root, straight arrow = aortic valve, curved arrow = mitral valve.

Figure 12b.

Normal apical three-chamber (long-axis) view at TTE (a) and correlative cardiac CTA (b). AR = aortic root, straight arrow = aortic valve, curved arrow = mitral valve.

Subcostal Window.—The subcostal window utilizes the liver as an acoustic window to obtain additional images of the heart. The patient is often lying supine, with the knees flexed to relax the abdominal musculature and inspiration held to allow improved image acquisition (8,9,12,13).

The subcostal four-chamber (SC4C) view is similar to the apical four-chamber view, with a few key advantages. First, this window is excellent for use in infants and small children. Second, it may be the only suitable window for evaluation of the heart in a patient in the intensive care unit or with a traumatic thoracic injury (12). Third, the interatrial and interventricular septa are positioned perpendicular to the ultrasound beam, which allows them to better reflect the beam and provides a more confident evaluation of septal defects (Fig 13) (8,9,12,13).

Figure 13a.

Normal subcostal four-chamber view at TTE (a) and correlative cardiac CTA (b).

Figure 13b.

Normal subcostal four-chamber view at TTE (a) and correlative cardiac CTA (b).

By rotating the transducer approximately 90° counterclockwise from the previous subcostal four-chamber view and angling the transducer inferiorly, the inferior vena cava (IVC) can be visualized along its long axis entering the RA, producing the subcostal IVC view (Fig 14). The diameter of the IVC can be measured on this view, and the collapsibility index can be calculated to estimate central venous pressure (9). An additional view of the hepatic veins can also be obtained by angling the transducer to the right and rocking it superiorly (9).

Figure 14a.

Normal subcostal inferior vena cava (IVC) view at TTE (a) and correlative cardiac CTA (b). Arrowhead = eustachian valve.

Figure 14b.

Normal subcostal inferior vena cava (IVC) view at TTE (a) and correlative cardiac CTA (b). Arrowhead = eustachian valve.

Suprasternal Window.—With the patient lying supine and the neck extended, sometimes with the help of a pillow positioned behind the shoulders, the transducer is placed in the suprasternal notch (SSN) and angled toward the right nipple to produce the suprasternal long-axis view of the aortic arch. On this view, the origins of the major aortic arch branch vessels, portions of the ascending and descending thoracic aorta, and a cross section of the right pulmonary artery inferior to the aortic arch can be seen (Fig 15). This view can be particularly helpful for evaluation of aortic coarctation. It should be noted that because this is an oblique view of the thoracic aorta, rather than a true short-axis view, accurate measurement is difficult.

Figure 15a.

Normal suprasternal long-axis view at TTE (a) and correlative cardiac CTA (b). Ao = aorta, BC = brachiocephalic artery, LCC = left common carotid artery, LSC = left subclavian artery, RPA = right pulmonary artery.

Figure 15b.

Normal suprasternal long-axis view at TTE (a) and correlative cardiac CTA (b). Ao = aorta, BC = brachiocephalic artery, LCC = left common carotid artery, LSC = left subclavian artery, RPA = right pulmonary artery.

Blind Spots

There are a number of anatomic blind spots at TTE that warrant special attention when reviewing in conjunction with CT or MRI. These blind spots have been divided into seven categories, which include those involving the (a) pericardium, (b) aorta, (c) LV apex, (d) cardiac valves, (e) LAA, (f) coronary arteries, and (g) extra-cardiac structures (Table). A few miscellaneous blind spots (eg, the small septal defects referenced in the Table) along with additional pitfalls and limitations, such as masses and mass mimics, are outside the scope of our discussion. The interested reader is encouraged to review an excellent previous publication in RadioGraphics by Malik et al (13) on this topic.

Blind Spots at TTE

Pericardium

A wide variety of disease processes can involve the pericardium, including pericarditis (acute or chronic), effusions of varying composition (with or without tamponade), cysts, masses, and congenital abnormalities. Evaluation of the pericardium at TTE is inherently limited owing to its generally thin nature, relatively low echo-genicity, and poor tissue contrast against the adjacent myocardium and lungs (14). CT and MRI generally show the pericardium better owing to the much higher tissue contrast resolution of the pericardium in relation to the surrounding fat and air in the lungs at CT. Potential pericar-dial blind spots that may be difficult to visualize or are located outside the standard field of view at TTE include pericardial effusions (which can be loculated or distributed within the pericardial recesses), pericardial thickening and calcification (such as is seen in constrictive pericarditis), pericardial cysts, and pericardial masses.

Thickening, Calcification, and Effusions.—Constrictive pericarditis is the sequela of an end-stage inflammatory process that takes months to years to develop. Over time, patients develop pericardial thickening, fibrosis, and calcification. Although there are several findings at TTE that are specific for constrictive pericarditis, such as ventricular interdependence, identifying features of constrictive pericarditis at cardiac CTA or cardiac MRI may suggest the diagnosis when not previously suspected.

Pericardial thickening can be focal or diffuse. TTE has limited accuracy in assessing pericar-dial thickness (14–17). Its reported sensitivity in identifying pericardial thickening greater than 5 mm in patients with constrictive pericarditis is 37%, whereas cardiac CTA and cardiac MRI have been shown to demonstrate pericardial thickening of as little as 3–4 mm in 72% and 77%–93% of patients with constrictive pericarditis, respectively (15,18).

Pericardial calcification, even when small and localized, strongly suggests the diagnosis of constrictive pericarditis. However, calcifications may not always be apparent at TTE or even cardiac MRI and are best visualized at CT (particularly cardiac CTA) (15,18). Close attention should be paid to areas such as the atrioventricular groove, as calcifications tend to occur in locations with a relatively higher proportion of pericardial fat (Fig 16). While pericardial thickening and calcifications are best depicted on ECG-gated studies, these findings can also be seen on nongated CT studies of the chest. Therefore, these areas should be routinely evaluated, even on nongated studies.

Figure 16a.

Pericardial calcifications in a 57-year-old man with chronic orthopnea and dyspnea, suggestive of constrictive pericarditis. (a, b) Axial (a) and coronal (b) cardiac CTA images of the chest show pericardial calcifications, most notable along the RV (arrow) and adjacent to the mitral valve (arrowhead in a). (c) Apical four-chamber TTE view shows a hyperechoic lesion (arrow) adjacent to the mitral valve, which was seen only in retrospect. The echogenic appearance is most consistent with calcification, although prominent fat in the atrioventricular groove can have a similar appearance. The true extent of pericardial calcification is visualized much better at CT.

Figure 16b.

Pericardial calcifications in a 57-year-old man with chronic orthopnea and dyspnea, suggestive of constrictive pericarditis. (a, b) Axial (a) and coronal (b) cardiac CTA images of the chest show pericardial calcifications, most notable along the RV (arrow) and adjacent to the mitral valve (arrowhead in a). (c) Apical four-chamber TTE view shows a hyperechoic lesion (arrow) adjacent to the mitral valve, which was seen only in retrospect. The echogenic appearance is most consistent with calcification, although prominent fat in the atrioventricular groove can have a similar appearance. The true extent of pericardial calcification is visualized much better at CT.

Figure 16c.

Pericardial calcifications in a 57-year-old man with chronic orthopnea and dyspnea, suggestive of constrictive pericarditis. (a, b) Axial (a) and coronal (b) cardiac CTA images of the chest show pericardial calcifications, most notable along the RV (arrow) and adjacent to the mitral valve (arrowhead in a). (c) Apical four-chamber TTE view shows a hyperechoic lesion (arrow) adjacent to the mitral valve, which was seen only in retrospect. The echogenic appearance is most consistent with calcification, although prominent fat in the atrioventricular groove can have a similar appearance. The true extent of pericardial calcification is visualized much better at CT.

Pericardial effusions can be simple or complex and may be free flowing or loculated. Although effusions are typically well seen at TTE, loculated effusions or small effusions that freely shift throughout the pericardial space may be first detected at CT or MRI (Fig E2). CT or MRI also allows better characterization of pericardial effusions as they evolve and change consistency over time. For example, acute blood products in a hemopericardium will initially be visualized as anechoic or complex hypoechoic fluid. With time, the blood products will organize into a more homogeneous hypoechoic ef-fusion, which can later become isoechoic to the myocardium and thereby invisible to the sonographer and interpreting clinician (16,19).

Cysts and Masses.—Pericardial cysts and masses include lesions such as simple pericardial cysts, diverticula, hematomas, primary neoplasms (benign or malignant), and metastatic disease (17). Even an experienced imager can overlook these lesions at TTE owing to their peripheral location, in addition to the other limitations of TTE discussed earlier (Fig 17). Cardiac CTA or cardiac MRI is often required to further evaluate these lesions, owing to limited tissue characterization and limited evaluation of involvement with adjacent structures at TTE (14,20). However, these can be detected incidentally at nongated CT or MRI of the chest. A detailed analysis of these lesions is beyond the scope of this article.

Figure 17a.

Pericardial cyst incidentally detected in a 67-year-old man without an acute complaint who underwent TTE and noncontrast chest CT within 2 weeks of each other. (a) Axial noncontrast chest CT image shows a circumscribed simple fluid-attenuation mass (arrow) at the right anterior cardiophrenic angle. No definite pericardial cyst was seen at TTE. (b) Apical four-chamber TTE view shows a questionable subtle hypoechoic structure possibly representing a cyst (arrow), which was seen retrospectively.

Figure 17b.

Pericardial cyst incidentally detected in a 67-year-old man without an acute complaint who underwent TTE and noncontrast chest CT within 2 weeks of each other. (a) Axial noncontrast chest CT image shows a circumscribed simple fluid-attenuation mass (arrow) at the right anterior cardiophrenic angle. No definite pericardial cyst was seen at TTE. (b) Apical four-chamber TTE view shows a questionable subtle hypoechoic structure possibly representing a cyst (arrow), which was seen retrospectively.

Aorta

TTE is advantageous in assessment of the thoracic aorta in that it can be performed at bedside in patients who are hemodynamically unstable (21). Generally, the aortic root, sinus of Valsalva, sinotubular junction, and ascending aorta can all be visualized on the first set of images obtained with the parasternal long-axis LV view (sometimes referred to as the scout view), with measurements made after decreasing the depth. Additional standard TTE views such as the parasternal short-axis, apical four-chamber, and apical two-chamber views can be used to visualize the ascending and mid to distal descending aorta. With addition of the suprasternal view described earlier, the aortic arch and proximal descending aorta can also be visualized (22).

Using a combination of these views, the entirety of the aorta can be visualized in up to 71% of patients (23). As with other views at TTE, these views are susceptible to limitations created by patients with larger body habitus, pulmonary emphysema, or chest wall deformities. Not surprisingly, owing to the technical difficulty with the suprasternal view and the obliquity of image acquisition, the measurements of the aortic arch and descending aorta have been reported as less accurate and less consistent compared with those of ECG-gated CTA and MR angiography (MRA) of the aorta, making this area a relative blind spot at TTE (24).

Acute Aortic Syndrome.—Acute aortic syndrome includes aortic dissection, intramural hematoma (IMH), and penetrating atherosclerotic ulcer (PAU). It requires rapid and definitive diagnosis to allow prompt medical or surgical intervention (23). TTE is advantageous in assessing the aorta in patients with suspicion for acute aortic syndrome owing to its widespread availability and portability.

At TTE, acute aortic dissection is classically seen as an intimal flap dividing the aorta into a false lumen and true lumen. TTE can often rapidly aid in determination of the true lumen and false lumen at the bedside by using Doppler techniques, providing information regarding branch vessel involvement, valvular involvement, and end-organ perfusion (25). However, in addition to the limitations of TTE in evaluating the transverse and descending aorta mentioned earlier, TTE may not adequately show the extent of the dissection, including vital preoperative findings such as coronary artery involvement (26). For example, the sensitivity of TTE in evaluation of Stanford type A dissections—which involve the ascending thoracic aorta up to the level of the brachiocephalic artery—ranges from 78% to 90%, whereas the sensitivity for Stanford type B dissections—which occur in the aorta distal to the brachiocephalic artery—drops substantially to 31%–55% (27,28). Specificity for Stanford type A and type B dissections is 87%–96% and 60%–83%, respectively (25,26).

With the addition of contrast-enhanced TTE, sensitivity and specificity have improved to 93% and 97% for Stanford type A dissections and 84% and 94% for Stanford type B dissections, respectively (25). For comparison, the reported sensitivity and specificity for CTA of the aorta are 90%–100% and 87%–100%, respectively (29,30). Similarly, the reported sensitivity and specificity for MRA of the aorta are 92%–100% and 94%–100%, respectively (29,30). Therefore, although TTE may be used for rapid diagnosis of dissection, ECG-gated CTA or MRA of the aorta should always be performed as a confirmatory test for definitive assessment of dissection and extent of involvement of the aorta and its branches, even in the setting of a normal TTE result (Fig 18) (21,25,31,32).

Figure 18a.

Aortic dissection in a 71-year-old man with a medical history significant for hypertension who presented to the emergency department (ED) with severe acute back pain. (a) Axial CTA image of the aorta shows an aortic dissection involving the aortic root and descending aorta (arrows) with extension to the large branch vessels (not shown). (b) Parasternal long-axis TTE view obtained earlier in the ED shows no gross abnormality. In particular, there is no dissection flap identified in the aortic root (arrow). LVOT = LV outflow tract.

Figure 18b.

Aortic dissection in a 71-year-old man with a medical history significant for hypertension who presented to the emergency department (ED) with severe acute back pain. (a) Axial CTA image of the aorta shows an aortic dissection involving the aortic root and descending aorta (arrows) with extension to the large branch vessels (not shown). (b) Parasternal long-axis TTE view obtained earlier in the ED shows no gross abnormality. In particular, there is no dissection flap identified in the aortic root (arrow). LVOT = LV outflow tract.

TTE can additionally be used to assess for the other two components of acute aortic syndrome: IMH and PAU. IMH is seen as circular or crescentic thickening of the aortic wall greater than 5 mm, and PAU appears as a defect with irregular margins in the aortic wall (25). The sensitivity and specificity for detection of IMH and PAU are similar to those of dissection. However, addition of contrast material to TTE does not improve sensitivity for detection of IMH (26). The European Association of Echocardiography states that TTE should not be relied on for evaluation of IMH or PAU, underscoring the importance of CTA or MRA for their evaluation (25).

LV Apex

A variety of disease processes can affect the LV apex to include infarcts (with or without aneurysm or thrombus formation) and apical variant hypertrophic cardiomyopathy (HCM).

Visualizing the apex at TTE can be challenging owing to its generally thin composition, position near the chest wall, proximity to the transducer, limited visualization between rib spaces, patient body habitus, or disease states that produce poor sonographic windows. In addition, as mentioned earlier, foreshortening of the LV during image acquisition occurs secondary to slight variations in transducer positioning, causing the imaging plane to miss the true LV apex. One must be careful to avoid this pitfall, as it can lead to not only distortion of the LV morphology but also incomplete visualization of the true LV apex (33). Cardiac CTA or cardiac MRI can resolve some of these limitations by providing a standardized full field of view without distortion, along with the ability to create multiplanar reformatted images (13). It is important to note that although cardiac CTA and cardiac MRI are used to fully assess for LV apical thrombus or aneurysm, these can be incidentally detected at nongated contrast-enhanced CT or MRI of the chest performed for a nonrelated reason.

Aneurysm or Pseudoaneurysm.—In the setting of prior infarction, the weakened myocardium can become stretched during contraction of the adjacent viable myocardium, leading to ballooning (aneurysmal dilatation) of the LV apex (34). When the LV apex becomes aneurysmal, the finding can be missed at TTE, as the true apex will often extend beyond its usual visualized location (Fig 19) (35). Although the apex is seen best on the apical three-chamber view and to some degree on the apical two-chamber view, the interpreting physician might be overconfident in their visualization of the true LV apex and may miss an aneurysm extending beyond the field of view. Similarly, infarcted myocardium can lead to necrosis and a full-thickness contained rupture, otherwise known as a pseudoaneurysm, which may be outside the standard field of view at TTE. This life-threatening condition requires urgent evaluation and is usually differentiated by the thin neck connecting to the intraventricular cavity.

Figure 19a.

Apical aneurysm in a 69-year-old man with a history of coronary artery disease and prior myocardial infarction. (a) Axial steady-state free-precession (SSFP) MR image shows apical myocardial thinning and ballooning (arrow), consistent with an LV apical aneurysm. (b) Apical two-chamber TTE view obtained 2 days later shows no definite apical aneurysm or thinning (arrow).

Figure 19b.

Apical aneurysm in a 69-year-old man with a history of coronary artery disease and prior myocardial infarction. (a) Axial steady-state free-precession (SSFP) MR image shows apical myocardial thinning and ballooning (arrow), consistent with an LV apical aneurysm. (b) Apical two-chamber TTE view obtained 2 days later shows no definite apical aneurysm or thinning (arrow).

Thrombus.—In addition to apical aneurysm and pseudoaneurysm, prior myocardial infarction can lead to impaired contractility with relative stasis of blood flow within the LV. This stasis creates an environment conducive to thrombus formation, which will often layer in the LV apex (36). Apical thrombus is important to diagnose to prevent future embolic events. When apical thrombus forms, particularly when it is large, it can become relatively isoechoic to the myocardium and conform to the LV wall, masking itself partially or completely at TTE (Fig 20) (37).

Figure 20a.

Apical thrombus in an 81-year-old man with a history of coronary artery disease and prior myocardial infarction. (a) Axial SSFP MR image shows a flat hypointensity (arrow) in an otherwise morphologically normal LV. (b) Apical two-chamber TTE view obtained 1 day earlier shows a questionable area of hyperechogenicity (arrow) near the LV apex, without a definite apical thrombus visualized.

Figure 20b.

Apical thrombus in an 81-year-old man with a history of coronary artery disease and prior myocardial infarction. (a) Axial SSFP MR image shows a flat hypointensity (arrow) in an otherwise morphologically normal LV. (b) Apical two-chamber TTE view obtained 1 day earlier shows a questionable area of hyperechogenicity (arrow) near the LV apex, without a definite apical thrombus visualized.

Hypertrophic Cardiomyopathy.—Lastly, apical HCM is an important but less common HCM variant that affects the midchamber and apex of the LV. The diagnostic criteria include (a) maximal LV apical thickness greater than or equal to 15 mm and (b) ratio of apical to posterior wall thickness greater than or equal to 1.5 (38). As mentioned earlier, TTE can not only provide false assurance in evaluation of the apex but also lead to inaccurate apical measurements, thereby causing the diagnosis to be missed (Fig E3).

Cardiac Valves

A variety of diseases affect the native or prosthetic cardiac valves, with our primary discussion here focused on the aortic valve.

Endocarditis.—Endocarditis is an infection of the endocardium that commonly involves the valve leaflets and chordae tendineae. It can be complicated by valvular stenosis, leaflet perforation, perivalvular leak, dehiscence of prosthetic valves, pseudoaneursym, or perivalvular abscess formation (39). Echocardiography is a primary tool used for evaluation of endocarditis—as well as all valvular disease—given its excellent resolution and ability to quantify real-time physiology such as valve motion, stenosis, and regurgitation (9). Although transesophageal echocardiography is the current standard of reference for definitive evaluation of endocarditis and its associated complications, TTE has been suggested as a screening modality—despite its relatively low negative predictive value—owing to its low cost and noninvasive evaluation (40).

When evaluating for complications of endocarditis, studies have shown that cardiac CTA is more sensitive and specific for diagnosing pseudoaneurysms and leaflet perforations than TTE (41). In addition, cardiac CTA is much more sensitive than TTE for evaluation of perivalvular abscess (81% vs 36%) and only marginally less specific (90% vs 95%), respectively (42). Furthermore, cardiac CTA has been shown to be more sensitive and specific in evaluating vegetations and perivalvular complications, even when compared with both TTE and transesophageal echocardiography combined (Fig 21) (42).

Figure 21a.

Aortic valve vegetation in a 58-year-old man with septicemia and a history of prior septic emboli to the brain. (a) Axial CTA image of the aortic valve shows an irregular vegetation of the noncoronary cusp (arrow). (b) Sagittal oblique (three-chamber) white-blood SSFP MR image shows the irregular vegetation involving the noncoronary cusp (arrow). AR = aortic root. (c, d) Parasternal long-axis (c) and short-axis (d) TTE views through the level of the aortic valve (arrow in c, AV in d) show normal-appearing leaflets without definite thickening or vegetation. The imaging findings in this clinical setting are consistent with infective endocarditis. LVOT in c = LV outflow tract.

Figure 21b.

Aortic valve vegetation in a 58-year-old man with septicemia and a history of prior septic emboli to the brain. (a) Axial CTA image of the aortic valve shows an irregular vegetation of the noncoronary cusp (arrow). (b) Sagittal oblique (three-chamber) white-blood SSFP MR image shows the irregular vegetation involving the noncoronary cusp (arrow). AR = aortic root. (c, d) Parasternal long-axis (c) and short-axis (d) TTE views through the level of the aortic valve (arrow in c, AV in d) show normal-appearing leaflets without definite thickening or vegetation. The imaging findings in this clinical setting are consistent with infective endocarditis. LVOT in c = LV outflow tract.

Figure 21c.

Aortic valve vegetation in a 58-year-old man with septicemia and a history of prior septic emboli to the brain. (a) Axial CTA image of the aortic valve shows an irregular vegetation of the noncoronary cusp (arrow). (b) Sagittal oblique (three-chamber) white-blood SSFP MR image shows the irregular vegetation involving the noncoronary cusp (arrow). AR = aortic root. (c, d) Parasternal long-axis (c) and short-axis (d) TTE views through the level of the aortic valve (arrow in c, AV in d) show normal-appearing leaflets without definite thickening or vegetation. The imaging findings in this clinical setting are consistent with infective endocarditis. LVOT in c = LV outflow tract.

Figure 21d.

Aortic valve vegetation in a 58-year-old man with septicemia and a history of prior septic emboli to the brain. (a) Axial CTA image of the aortic valve shows an irregular vegetation of the noncoronary cusp (arrow). (b) Sagittal oblique (three-chamber) white-blood SSFP MR image shows the irregular vegetation involving the noncoronary cusp (arrow). AR = aortic root. (c, d) Parasternal long-axis (c) and short-axis (d) TTE views through the level of the aortic valve (arrow in c, AV in d) show normal-appearing leaflets without definite thickening or vegetation. The imaging findings in this clinical setting are consistent with infective endocarditis. LVOT in c = LV outflow tract.

Prosthetic Valves.—Prosthetic valves provide a unique challenge for TTE owing to their intrinsic physical properties. There are two main types of prosthetic valves: bioprosthetic and mechanical. Bioprosthetic valves are derived from pig or bovine heterografts or pulmonary valve allografts. Mechanical valves are available in a wide variety of designs that vary by manufacturer (43). The various types and designs of valves are beyond the scope of this article.

However, they all contain a metallic component that can produce posterior acoustic shadowing and obscure findings or limit the reader's ability to visualize the valve (41). Limitations in complete visualization of prosthetic valve components due to posterior acoustic shadowing can be overcome by using both cardiac CTA and cardiac MRI as adjuncts in evaluation of patients with prosthetic valve replacements.

For example, hypoattenuating leaflet thickening (HALT), or subclinical leaflet thrombosis, is a known complication of transcatheter aortic valve replacement (TAVR). HALT is defined as a focal area of hypoattenuating leaflet thickening that begins at the leaflet insertion on the valve frame. There is concern that it may compromise valvular durability and increase the risk of thromboembolism, stroke, and transient ischemic attack (44). While this is a relatively new diagnosis and the true clinical implications are not fully understood, it remains an important finding that must be communicated to the referring clinician (45). Owing to the limitations of TTE in evaluation of prosthetic leaflets, HALT is strictly a cardiac CTA diagnosis and an important area of focus in patients who have undergone TAVR (Fig 22).

Figure 22a.

Hypoattenuating leaflet thickening (HALT) in a 62-year-old woman with a history significant for transcatheter aortic valve replacement (TAVR) secondary to aortic insufficiency. (a) Axial oblique CTA image of the aortic valve shows a metallic TAVR with appropriate positioning (arrowhead). The noncoronary leaflet is notably thickened with hypoattenuating material (arrow) present. (b, c) Parasternal short-axis (b) and long-axis (c) TTE views through the aortic valve show poor characterization of the valve prosthesis secondary to the echogenic nature of metal and posterior acoustic shadowing (arrow) without definite correlation with the CT finding. The patient had no clinical signs of infection and was subsequently diagnosed with HALT.

Figure 22b.

Hypoattenuating leaflet thickening (HALT) in a 62-year-old woman with a history significant for transcatheter aortic valve replacement (TAVR) secondary to aortic insufficiency. (a) Axial oblique CTA image of the aortic valve shows a metallic TAVR with appropriate positioning (arrowhead). The noncoronary leaflet is notably thickened with hypoattenuating material (arrow) present. (b, c) Parasternal short-axis (b) and long-axis (c) TTE views through the aortic valve show poor characterization of the valve prosthesis secondary to the echogenic nature of metal and posterior acoustic shadowing (arrow) without definite correlation with the CT finding. The patient had no clinical signs of infection and was subsequently diagnosed with HALT.

Figure 22c.

Hypoattenuating leaflet thickening (HALT) in a 62-year-old woman with a history significant for transcatheter aortic valve replacement (TAVR) secondary to aortic insufficiency. (a) Axial oblique CTA image of the aortic valve shows a metallic TAVR with appropriate positioning (arrowhead). The noncoronary leaflet is notably thickened with hypoattenuating material (arrow) present. (b, c) Parasternal short-axis (b) and long-axis (c) TTE views through the aortic valve show poor characterization of the valve prosthesis secondary to the echogenic nature of metal and posterior acoustic shadowing (arrow) without definite correlation with the CT finding. The patient had no clinical signs of infection and was subsequently diagnosed with HALT.

Calcification.—The presence of calcification on the aortic valve leaflets at both gated and nongated CT of the chest has been shown to be highly associated with aortic valve stenosis (46). By reporting these calcium score values at CT, it may assist the physician interpreting the TTE images in evaluating notoriously difficult studies such as low-flow low-gradient aortic stenosis. A heavily calcified aortic valve can also be detected at routine nongated CT of the chest in patients in whom aortic stenosis was not previously suspected; the presence of this finding strongly suggests some degree of aortic stenosis (Fig E4). This emphasizes the importance of assessing this area in all CT studies of the chest.

Left Atrial Appendage

Although of relatively little value to myocar-dial function, the LAA is a critically important contributor to cardiovascular disease and its sequelae. It is well recognized that approximately 90% of the thrombi that form in the LA in the setting of atrial fibrillation originate from the LAA (47). This has led to creation of novel techniques to ligate or occlude this portion of the LA, such as LAA exclusion systems performed with open heart surgery and the LAA closure devices inserted percutaneously.

However, the LAA can be difficult to visualize at TTE owing to its posterior location. Although generally much better visualized with transesophageal echocardiography, it still remains difficult to visualize in some patients. Cardiac CTA has been shown to provide a reliable alternative to transesophageal echocardiography in assessment of LAA thrombus in the setting of atrial fibrillation. Both cardiac CTA and cardiac MRI have also become the imaging modality of choice in evaluation of pulmonary vein and LAA anatomy before invasive procedures such as pulmonary vein isolation and are increasingly being used in evaluation of Watchman Left Atrial Appendage Closure Device (Boston Scientific) implantation (48–50).

Coronary Arteries

Owing to its noninvasive nature, lack of ionizing radiation, and availability, TTE can be used as a first-line study in assessment for major coronary anomalies. The coronary artery origins can be visualized at TTE in up to 98% of the pediatric population and 91% of the adult population (51,52). In the remaining 8%–9% of adults, the coronary origins are a blind spot for TTE, usually secondary to aortic root calcifications or poor acoustic windows produced by the patient's body habitus (52).

Cardiac CTA is a good alternative imaging modality in this patient population, as the sensitivity for detection of anomalous coronary arteries at cardiac CTA has been reported to be as high as 100% (53). Although the sensitivity for detection of coronary artery anomalies at nongated CT is invariably lower than with ECG gating, these abnormalities can be detected, especially with newer-generation CT scanners in patients with slower heart rates, making this a location that warrants close attention at all imaging studies of the chest (Fig 23). Aside from assessing the proximal origins of the coronary arteries, the role of TTE in assessing the individual coronary arteries is limited. Additional abnormalities such as coronary artery aneurysms and fistulas are also more readily detected at cardiac CTA and, in some instances, can even be detected at routine nongated CT of the chest (Fig E5).

Figure 23a.

Anomalous coronary artery in a 63-year-old woman who underwent TTE for a 2-month history of chest pain. (a) Parasternal short-axis TTE image at the level of the aortic valve shows that the origins of the coronary arteries can be difficult to identify at TTE. The remainder of the TTE was notable only for borderline concentric LV hypertrophy and mild LA enlargement. LC = left coronary cusp, NC = noncoronary cusp, RC = right coronary cusp. (b, c) Reconstructed axial oblique (b) and volume-rendered (c) images from cardiac CTA of the coronary arteries show anomalous origin of the right coronary artery (straight arrow in b, RCA in c) from the left coronary cusp with an interarterial course. AR = aortic root, curved arrow in b = left main coronary artery, arrowhead in b = pulmonary valve, LAD in c = left anterior descending coronary artery, LCx in c = left circumflex coronary artery. (d, e) Selected images from subsequent nongated CTA of the chest, abdomen, and pelvis show the anomalous origin of the right coronary artery (black arrow in e) from the left coronary cusp. AR = aortic root, _* = RV outflow tract, arrow in d = left main coronary artery, white arrow in e = left circumflex coronary artery. This case highlights the fact that anomalous coronary arteries may not be detected at TTE and are occasionally discovered at nongated chest CT.

Figure 23b.

Anomalous coronary artery in a 63-year-old woman who underwent TTE for a 2-month history of chest pain. (a) Parasternal short-axis TTE image at the level of the aortic valve shows that the origins of the coronary arteries can be difficult to identify at TTE. The remainder of the TTE was notable only for borderline concentric LV hypertrophy and mild LA enlargement. LC = left coronary cusp, NC = noncoronary cusp, RC = right coronary cusp. (b, c) Reconstructed axial oblique (b) and volume-rendered (c) images from cardiac CTA of the coronary arteries show anomalous origin of the right coronary artery (straight arrow in b, RCA in c) from the left coronary cusp with an interarterial course. AR = aortic root, curved arrow in b = left main coronary artery, arrowhead in b = pulmonary valve, LAD in c = left anterior descending coronary artery, LCx in c = left circumflex coronary artery. (d, e) Selected images from subsequent nongated CTA of the chest, abdomen, and pelvis show the anomalous origin of the right coronary artery (black arrow in e) from the left coronary cusp. AR = aortic root, _* = RV outflow tract, arrow in d = left main coronary artery, white arrow in e = left circumflex coronary artery. This case highlights the fact that anomalous coronary arteries may not be detected at TTE and are occasionally discovered at nongated chest CT.

Figure 23c.

Anomalous coronary artery in a 63-year-old woman who underwent TTE for a 2-month history of chest pain. (a) Parasternal short-axis TTE image at the level of the aortic valve shows that the origins of the coronary arteries can be difficult to identify at TTE. The remainder of the TTE was notable only for borderline concentric LV hypertrophy and mild LA enlargement. LC = left coronary cusp, NC = noncoronary cusp, RC = right coronary cusp. (b, c) Reconstructed axial oblique (b) and volume-rendered (c) images from cardiac CTA of the coronary arteries show anomalous origin of the right coronary artery (straight arrow in b, RCA in c) from the left coronary cusp with an interarterial course. AR = aortic root, curved arrow in b = left main coronary artery, arrowhead in b = pulmonary valve, LAD in c = left anterior descending coronary artery, LCx in c = left circumflex coronary artery. (d, e) Selected images from subsequent nongated CTA of the chest, abdomen, and pelvis show the anomalous origin of the right coronary artery (black arrow in e) from the left coronary cusp. AR = aortic root, _* = RV outflow tract, arrow in d = left main coronary artery, white arrow in e = left circumflex coronary artery. This case highlights the fact that anomalous coronary arteries may not be detected at TTE and are occasionally discovered at nongated chest CT.

Figure 23d.

Anomalous coronary artery in a 63-year-old woman who underwent TTE for a 2-month history of chest pain. (a) Parasternal short-axis TTE image at the level of the aortic valve shows that the origins of the coronary arteries can be difficult to identify at TTE. The remainder of the TTE was notable only for borderline concentric LV hypertrophy and mild LA enlargement. LC = left coronary cusp, NC = noncoronary cusp, RC = right coronary cusp. (b, c) Reconstructed axial oblique (b) and volume-rendered (c) images from cardiac CTA of the coronary arteries show anomalous origin of the right coronary artery (straight arrow in b, RCA in c) from the left coronary cusp with an interarterial course. AR = aortic root, curved arrow in b = left main coronary artery, arrowhead in b = pulmonary valve, LAD in c = left anterior descending coronary artery, LCx in c = left circumflex coronary artery. (d, e) Selected images from subsequent nongated CTA of the chest, abdomen, and pelvis show the anomalous origin of the right coronary artery (black arrow in e) from the left coronary cusp. AR = aortic root, _* = RV outflow tract, arrow in d = left main coronary artery, white arrow in e = left circumflex coronary artery. This case highlights the fact that anomalous coronary arteries may not be detected at TTE and are occasionally discovered at nongated chest CT.

Figure 23e.

Anomalous coronary artery in a 63-year-old woman who underwent TTE for a 2-month history of chest pain. (a) Parasternal short-axis TTE image at the level of the aortic valve shows that the origins of the coronary arteries can be difficult to identify at TTE. The remainder of the TTE was notable only for borderline concentric LV hypertrophy and mild LA enlargement. LC = left coronary cusp, NC = noncoronary cusp, RC = right coronary cusp. (b, c) Reconstructed axial oblique (b) and volume-rendered (c) images from cardiac CTA of the coronary arteries show anomalous origin of the right coronary artery (straight arrow in b, RCA in c) from the left coronary cusp with an interarterial course. AR = aortic root, curved arrow in b = left main coronary artery, arrowhead in b = pulmonary valve, LAD in c = left anterior descending coronary artery, LCx in c = left circumflex coronary artery. (d, e) Selected images from subsequent nongated CTA of the chest, abdomen, and pelvis show the anomalous origin of the right coronary artery (black arrow in e) from the left coronary cusp. AR = aortic root, _* = RV outflow tract, arrow in d = left main coronary artery, white arrow in e = left circumflex coronary artery. This case highlights the fact that anomalous coronary arteries may not be detected at TTE and are occasionally discovered at nongated chest CT.

Furthermore, as mentioned earlier, calcifications are much more readily identified at CT than at TTE. The utility of coronary artery calcium (CAC) scoring is well established and now carries a level 2A indication for assessment of cardiovascular risk from the American College of Cardiology and American Heart Association (54). TTE for semiquantitatively assessing coronary calcium has been explored but is not widely used (55). While traditionally obtained with ECG-gated noncontrast studies of the heart, CAC scores obtained with nongated examinations have been shown to correlate well with scores obtained with ECG-gated examinations (56). This knowledge may lead to more aggressive primary prevention efforts, resulting in an overall reduction in major adverse cardiovascular events (57). CAC scoring alone may be potentially reported in approximately 7.1 million annual diagnostic noncontrast CT examinations in the United States (58).

Extracardiac Structures

TTE is designed to provide a detailed morphologic and physiologic evaluation of the heart. However, as in other radiologic examinations, there may be incidentally visualized structures beyond the confines of the heart that must be evaluated and can serve as blind spots. In a study by Khosa et al (59), 7.5% of all TTE examinations showed an extracardiac finding, at least in retrospect. These ranged from benign findings, such as hepatic cysts and cholelithiasis, to more worrisome findings, such as pleural effusions, ascites, and malignancy, to include metastatic disease. Fortunately, the majority of these findings were either known from a prior comparison study or better characterized with other imaging modalities (59).

Given that TTE is not designed to evaluate extracardiac spaces, the majority of the literature regarding extracardiac findings at TTE has been case reports. Throughout these case reports, none of the incidentally detected extracardiac abnormalities were definitively diagnosed at TTE, and all had to be further evaluated with other imaging studies (20,60–65).

Mediastinal masses can be missed at TTE but are occasionally seen owing to their close anatomic relationship to the heart. Given the standard TTE views, anterior mediastinal masses are the most frequently identified and account for 58% of incidentally imaged lesions (Fig 24). Middle, superior, and posterior mediastinal lesions are less frequent, accounting for 25%, 13%, and 4% of incidentally detected lesions, respectively (65). As mentioned earlier, TTE is nonspecific when evaluating mediastinal masses; therefore, any mediastinal mass visualized at TTE requires further evaluation with contrast-enhanced CT or MRI.

Figure 24a.

Anterior mediastinal mass. (a) Axial contrast-enhanced T1-weighted MR image shows a large avidly enhancing anterior mediastinal mass (arrow) with displacement of the heart secondary to mass effect. (b) Axial T2-weighted black-blood MR image shows the anterior mediastinal mass (arrow) with prominent internal hypointense flow voids. AR = aortic root, MPA = main pulmonary artery. (c, d) Axial (c) and sagittal (d) CTA images show the avidly enhancing anterior mediastinal mass (arrow) with an associated pericardial effusion (_*). AR = aortic root, MPA in c = main pulmonary artery, RPA in d = right pulmonary artery. (e) Digital sub traction angiogram shows prominent contrast blush in the region of the mass (arrow) near the right coronary artery (arrowhead). (f) Parasternal long-axis TTE view retrospectively shows but incompletely characterizes the large anterior mediastinal mass (arrowhead), which is partially seen as a complex heterogeneous hypoechoic mass in the lateral aspect of the field of view. LVOT = LV outflow tract. Surgical biopsy yielded histologic findings consistent with a paraganglioma.

Figure 24b.

Anterior mediastinal mass. (a) Axial contrast-enhanced T1-weighted MR image shows a large avidly enhancing anterior mediastinal mass (arrow) with displacement of the heart secondary to mass effect. (b) Axial T2-weighted black-blood MR image shows the anterior mediastinal mass (arrow) with prominent internal hypointense flow voids. AR = aortic root, MPA = main pulmonary artery. (c, d) Axial (c) and sagittal (d) CTA images show the avidly enhancing anterior mediastinal mass (arrow) with an associated pericardial effusion (_*). AR = aortic root, MPA in c = main pulmonary artery, RPA in d = right pulmonary artery. (e) Digital sub traction angiogram shows prominent contrast blush in the region of the mass (arrow) near the right coronary artery (arrowhead). (f) Parasternal long-axis TTE view retrospectively shows but incompletely characterizes the large anterior mediastinal mass (arrowhead), which is partially seen as a complex heterogeneous hypoechoic mass in the lateral aspect of the field of view. LVOT = LV outflow tract. Surgical biopsy yielded histologic findings consistent with a paraganglioma.

Figure 24c.

Anterior mediastinal mass. (a) Axial contrast-enhanced T1-weighted MR image shows a large avidly enhancing anterior mediastinal mass (arrow) with displacement of the heart secondary to mass effect. (b) Axial T2-weighted black-blood MR image shows the anterior mediastinal mass (arrow) with prominent internal hypointense flow voids. AR = aortic root, MPA = main pulmonary artery. (c, d) Axial (c) and sagittal (d) CTA images show the avidly enhancing anterior mediastinal mass (arrow) with an associated pericardial effusion (_*). AR = aortic root, MPA in c = main pulmonary artery, RPA in d = right pulmonary artery. (e) Digital sub traction angiogram shows prominent contrast blush in the region of the mass (arrow) near the right coronary artery (arrowhead). (f) Parasternal long-axis TTE view retrospectively shows but incompletely characterizes the large anterior mediastinal mass (arrowhead), which is partially seen as a complex heterogeneous hypoechoic mass in the lateral aspect of the field of view. LVOT = LV outflow tract. Surgical biopsy yielded histologic findings consistent with a paraganglioma.

Figure 24d.

Anterior mediastinal mass. (a) Axial contrast-enhanced T1-weighted MR image shows a large avidly enhancing anterior mediastinal mass (arrow) with displacement of the heart secondary to mass effect. (b) Axial T2-weighted black-blood MR image shows the anterior mediastinal mass (arrow) with prominent internal hypointense flow voids. AR = aortic root, MPA = main pulmonary artery. (c, d) Axial (c) and sagittal (d) CTA images show the avidly enhancing anterior mediastinal mass (arrow) with an associated pericardial effusion (_*). AR = aortic root, MPA in c = main pulmonary artery, RPA in d = right pulmonary artery. (e) Digital sub traction angiogram shows prominent contrast blush in the region of the mass (arrow) near the right coronary artery (arrowhead). (f) Parasternal long-axis TTE view retrospectively shows but incompletely characterizes the large anterior mediastinal mass (arrowhead), which is partially seen as a complex heterogeneous hypoechoic mass in the lateral aspect of the field of view. LVOT = LV outflow tract. Surgical biopsy yielded histologic findings consistent with a paraganglioma.

Figure 24e.

Anterior mediastinal mass. (a) Axial contrast-enhanced T1-weighted MR image shows a large avidly enhancing anterior mediastinal mass (arrow) with displacement of the heart secondary to mass effect. (b) Axial T2-weighted black-blood MR image shows the anterior mediastinal mass (arrow) with prominent internal hypointense flow voids. AR = aortic root, MPA = main pulmonary artery. (c, d) Axial (c) and sagittal (d) CTA images show the avidly enhancing anterior mediastinal mass (arrow) with an associated pericardial effusion (_*). AR = aortic root, MPA in c = main pulmonary artery, RPA in d = right pulmonary artery. (e) Digital sub traction angiogram shows prominent contrast blush in the region of the mass (arrow) near the right coronary artery (arrowhead). (f) Parasternal long-axis TTE view retrospectively shows but incompletely characterizes the large anterior mediastinal mass (arrowhead), which is partially seen as a complex heterogeneous hypoechoic mass in the lateral aspect of the field of view. LVOT = LV outflow tract. Surgical biopsy yielded histologic findings consistent with a paraganglioma.

Figure 24f.

Anterior mediastinal mass. (a) Axial contrast-enhanced T1-weighted MR image shows a large avidly enhancing anterior mediastinal mass (arrow) with displacement of the heart secondary to mass effect. (b) Axial T2-weighted black-blood MR image shows the anterior mediastinal mass (arrow) with prominent internal hypointense flow voids. AR = aortic root, MPA = main pulmonary artery. (c, d) Axial (c) and sagittal (d) CTA images show the avidly enhancing anterior mediastinal mass (arrow) with an associated pericardial effusion (_*). AR = aortic root, MPA in c = main pulmonary artery, RPA in d = right pulmonary artery. (e) Digital sub traction angiogram shows prominent contrast blush in the region of the mass (arrow) near the right coronary artery (arrowhead). (f) Parasternal long-axis TTE view retrospectively shows but incompletely characterizes the large anterior mediastinal mass (arrowhead), which is partially seen as a complex heterogeneous hypoechoic mass in the lateral aspect of the field of view. LVOT = LV outflow tract. Surgical biopsy yielded histologic findings consistent with a paraganglioma.

In addition to mediastinal pathologic conditions, primary (Fig 25) and metastatic (Fig E6) pulmonary neoplasms can be incidentally detected but are frequently missed at TTE. It is important for echocardiographers and radiologists to understand this limitation of TTE. To our knowledge, no large-scale reviews have reported on the ability of TTE to allow effective evaluation of extracardiac disease processes, such as malignancy. This is in large part due to limitations such as poor acoustic windows, technical difficulties from lung disease, and patient conditions, including obesity and other postoperative changes (66).

Figure 25a.

Extracardiac mass in an 81-year-old man who presented to the emergency department with acute chest pain and underwent CT pulmonary angiography (CTPA). (a) Axial CTPA image shows a large heterogeneous mass (_*) in the left upper lobe that abuts and invades the pericardium, as well as a moderate-sized left-sided pleural effusion (arrowhead) and adjacent atelectasis. (b) Apical four-chamber view from TTE performed 2 weeks earlier shows the large hypoechoic mass (*) adjacent to the LV; the mass was seen only in retrospect. CT-guided biopsy demonstrated primary lung squamous cell carcinoma.

Figure 25b.

Extracardiac mass in an 81-year-old man who presented to the emergency department with acute chest pain and underwent CT pulmonary angiography (CTPA). (a) Axial CTPA image shows a large heterogeneous mass (_*) in the left upper lobe that abuts and invades the pericardium, as well as a moderate-sized left-sided pleural effusion (arrowhead) and adjacent atelectasis. (b) Apical four-chamber view from TTE performed 2 weeks earlier shows the large hypoechoic mass (*) adjacent to the LV; the mass was seen only in retrospect. CT-guided biopsy demonstrated primary lung squamous cell carcinoma.

Conclusion

Incidental cardiac findings will likely be encountered by radiologists who interpret chest images, as heart disease affects upwards of 30 million Americans. TTE is an excellent imaging modality and is frequently the first choice for evaluating the heart. However, like all imaging modalities, it is not without limitations, including blind spots. In some instances, incidental cardiac findings at CT or MRI may not be apparent at TTE owing to an inherent blind spot or because they were inadvertently overlooked.

Given that many patients who undergo chest CT or MRI (particularly cardiac CTA or cardiac MRI) will have undergone prior TTE, radiologists who interpret these images should have a basic understanding of TTE and its blind spots to correlate with their findings. This review article provides an overview of the major echocardio-graphic views at TTE and reviews the seven major blind spots of TTE, including the pericardium, aorta, LV apex, cardiac valves, LAA, coronary arteries, and extracardiac structures. Through a basic level of understanding of TTE, including its strengths and limitations, radiologists will improve confidence in their diagnosis and avoid misdiagnosis by not relying solely on the echocardiography report.