Left Atrial Mural Thrombus Arising from a Left Atrial Diverticulum

Graphical abstract

Highlights

• •TEE identified a mural thrombus arising from a left atrial diverticulum.
• •The thrombus was anatomically separate from the LAA.
• •Anticoagulation led to thrombus resolution and unmasked the diverticulum.
• •Comprehensive evaluation of the entire LA wall is essential in patients with AF.

Introduction

Left atrial diverticula are relatively common anatomical variants; however, thrombus formation within them is extremely rare. Impaired left atrial function has increasingly been recognized as a contributor to thromboembolic risk. Increased left atrial volume index (LAVI) has been associated with ischemic stroke,¹ and reduced left atrial reservoir strain has been reported as a discriminator of cardioembolic stroke.² We report a case of left atrial mural thrombus (LAMT) arising in association with a left atrial diverticulum, diagnosed by multimodality imaging with transesophageal echocardiography (TEE) and contrast-enhanced chest computed tomography (CT), and successfully treated with anticoagulation.

Case Presentation

A 77-year-old man presented to our emergency department with back pain. The patient was being seen at our hospital for the first time, and atrial fibrillation (AF) was first identified at presentation. Accordingly, the patient had not been receiving anticoagulation before admission. The CHA₂DS₂-VASc score was 4 and HAS-BLED score was 2. The pain was transient and improved by the following day. There was no elevation of inflammatory markers, no neurological deficit, and no other clinical findings suggestive of systemic embolism.

Contrast-enhanced CT, performed to evaluate the back pain, revealed no abnormalities explaining the symptom; however, it incidentally demonstrated a low-density mass-like structure measuring 21 × 15 mm attached to the left atrial wall (Figure 1). Transthoracic echocardiography demonstrated a left atrial mass (Figure 2A, Video 1). In the parasternal long-axis view, the mural mass was seen attached to the left atrial wall, whereas the basal parasternal short-axis view demonstrated the left atrial appendage (LAA) but did not clearly visualize the mass (Figure 2B). Transthoracic echocardiography also showed normal left ventricular systolic function, whereas left atrial function was markedly reduced and the chamber was enlarged (left atrial ejection fraction 14%, left atrial reservoir strain 10%, and LAVI 60 mL/m²).

Figure 1.

Delayed-phase contrast-enhanced chest CT, axial (A), coronal (B), and sagittal (C, D) views, demonstrates a left atrial mural mass (arrows) located away from the LAA, which shows no definite thrombus. Ao, Aorta; LV, left ventricle; PA, pulmonary artery.

Figure 2.

Two-dimensional transthoracic echocardiography, parasternal long-axis (A) and basal short-axis (B) diastolic views, demonstrates a left atrial mural mass attached to the left atrial wall (arrow) separate from the LAA. Ao, Aorta; AV, aortic valve; LV, left ventricle; RV, right ventricle.

TEE demonstrated a mobile low-echoic mural mass attached to the left atrial wall (Figure 3A-C, Video 2). Simultaneous orthogonal displays demonstrated the mural mass and the LAA separately, with no clear continuity identified between them (Figure 3A and 3B, Video 2). Simultaneous dual displays without and with color-flow Doppler showed no internal color flow within the mass (Figure 3C, Video 3). Transesophageal echocardiography at 45° demonstrated the LAA with pectinate muscles but no definite thrombus (Figure 3D). Mild spontaneous echo contrast was present within the LAA. Because the mural mass was located along the roof of the left atrium (LA), at a higher imaging level than the LAA, simultaneous visualization of the entire mass and the LAA cavity in a single TEE plane was limited. This also supported the impression that the lesion was not clearly continuous with the LAA.

Figure 3.

Two-dimensional TEE, midesophageal simultaneous orthogonal displays at 0° and 90° (A), 90° and 180° (B), 43° (C) without (left) and with (right) color-flow Doppler (C), and 45° optimal LAA and LSPV view (D), demonstrates a large left atrial mural mass without internal color enhancement (arrow) attached to the left atrial wall and separate from the uninvolved LAA. Ao, Aorta; AV, aortic valve; LSPV, left superior pulmonary vein; LV, left ventricle; MV, mitral valve.

The differential diagnosis included LAMT and a cardiac tumor such as myxoma. Surgical excision was considered to prevent embolization; however, the lesion was considered more consistent with thrombus than tumor at presentation because it appeared as a nonenhancing low-density filling defect on contrast-enhanced chest CT, showed no internal color flow on TEE, and was attached broadly to the left atrial wall rather than presenting as a typical pedunculated atrial tumor. Anticoagulation therapy was therefore initiated. The patient was hospitalized and started on intravenous heparin followed by oral warfarin. Warfarin was selected as the initial oral anticoagulant after intravenous heparin because heparin followed by warfarin was the institutional anticoagulation strategy for suspected intra-atrial thrombus in the acute setting.

The initial contrast-enhanced chest CT included both an initial contrast-enhanced acquisition and an approximately 1-minute delayed phase acquisition. A follow-up contrast-enhanced chest CT performed 1 week later, including delayed-phase imaging, demonstrated reduction in size of the mass, further supporting the diagnosis of LAMT. Anticoagulation therapy was continued in the outpatient setting. Because renal function was normal, both TEE and contrast-enhanced chest CT were used during follow-up to improve diagnostic confidence and assess treatment response. Transesophageal echocardiography was useful for evaluating mobility, internal flow, and the relationship of the mass to the LAA, whereas CT provided complementary information regarding spatial anatomy, serial size change, and delayed-phase imaging. Serial follow-up contrast-enhanced chest CT studies, each including delayed-phase imaging, showed interval reduction in size at 1 month and further reduction at 3 months (Figure 4A-C), with complete resolution at 6 months (Figure 4D). Arterial-phase CT clearly demonstrated a residual left atrial diverticulum in the anterior-superior LA (Figure 5). Follow-up TEE at 6 months provided additional confirmation that no definite thrombus was present within the LAA on multiple views (Figure 6, Video 4).

Figure 4.

Serial delayed-phase contrast-enhanced chest CT, axial views, obtained at initial presentation (A), at 1-month (B), 3-month (C), and 6-month (D) follow-up, demonstrates progressive reduction and the resolution of the left atrial mass (arrow). Ao, Aorta; PA, pulmonary artery.

Figure 5.

Arterial-phase contrast-enhanced chest CT, focused axial (A), coronal (B), and sagittal (C) views of the LA obtained at 6 months follow-up after thrombus resolution, demonstrates an unmasked left atrial diverticulum (arrows). Ao, Aorta; PA, pulmonary artery; RSPV, right superior pulmonary vein.

Figure 6.

Two-dimensional TEE, midesophageal short-axis (43°) view obtained at initial presentation (A), demonstrates the large LAMT (arrow) for comparison to the two-dimensional TEE views obtained at 6 months follow-up, displayed in the 47° (B), 0° (C), 90° (D), and 134° (E) views, which now demonstrate resolution of the mass. Ao, Aorta; AV, aortic valve.

After CT confirmed complete thrombus resolution, the patient developed a drug eruption, and warfarin was considered the suspected causative agent. Warfarin was therefore discontinued and anticoagulation was switched to dabigatran 150 mg twice daily. Continued anticoagulation was selected as the management strategy. The patient has remained free from ischemic stroke, systemic embolism, and bleeding events during follow-up.

Discussion

Left atrial diverticula are relatively common anatomical outpouchings, reported in 10% to 40% of individuals on cardiac CT (CCT).3, 4, 5, 6 They are more frequently observed in men and typically arise in the anterior-superior region of the LA.3, 4, 5, 6 In the present case, the diverticulum was similarly located in the anterior-superior LA, consistent with previously reported anatomical characteristics. Despite their relatively high prevalence, thrombus formation within a diverticulum is exceedingly rare. This discrepancy suggests that the diverticulum itself may not be sufficient to promote thrombogenesis and that additional pathophysiological factors are required. Recent data also suggest that left atrial diverticula may have clinical relevance beyond simple anatomic variants, including a possible association with ischemic stroke risk.⁷

In our patient, the LA was markedly enlarged and mechanically impaired. Impaired left atrial function has increasingly been recognized as a contributor to thromboembolic risk. Increased LAVI has been associated with ischemic stroke,¹ and reduced left atrial reservoir strain has been reported as a discriminator of cardioembolic stroke.² Although these observations do not establish causality, they support the concept that structural and functional atrial remodeling may contribute to thrombogenesis not only in the LAA but also in other left atrial structures, including a left atrial diverticulum.

A major diagnostic issue in this case was whether the lesion represented a mural thrombus arising from the left atrial wall/diverticulum or thrombus originating from the LAA. The available TEE views did not demonstrate clear continuity between the mass and the LAA. In the 45° view, no definite thrombus was visualized within the LAA, whereas simultaneous orthogonal displays suggested that the mural mass and the LAA were spatially separate. In addition, the mural mass was located along the roof of the LA, at a higher imaging level than the LAA, which limited simultaneous visualization of the entire mass and the LAA cavity in a single TEE plane. Therefore, interpretation of the lesion was based on multimodality imaging rather than TEE alone. Contrast-enhanced chest CT provided complementary information regarding spatial anatomy, delayed-phase imaging, and serial change in size, and together with TEE supported the diagnosis of mural thrombus arising from the left atrial wall/diverticulum rather than persistent LAA thrombus.

In this context, TEE and CT served complementary roles. Transesophageal echocardiography was particularly useful for assessing mobility, internal flow, and the relationship of the mass to the LAA, whereas CT was useful for defining spatial anatomy, demonstrating interval reduction in size, and identifying the residual diverticulum after thrombus resolution. Because renal function was normal, both modalities were used during follow-up to improve diagnostic confidence and to monitor treatment response.

Current AF guidelines note that prothrombotic changes are often evident in the LA and may increase the risk of thrombus formation and stroke.⁸ In patients with AF, detection of intracardiac thrombus warrants therapeutic anticoagulation, and repeat imaging with TEE or CT is generally pursued after at least 3 to 6 weeks to assess thrombus resolution.⁸ In the present case, anticoagulation led to progressive reduction and complete resolution of the mass on serial imaging, further supporting the diagnosis of LAMT.

Although direct oral anticoagulants are generally recommended over warfarin for stroke prevention in AF, management of established intra-atrial thrombus remains less well defined.⁸ In this case, intravenous heparin followed by warfarin was selected according to our institutional strategy for suspected intra-atrial thrombus in the acute setting, and anticoagulation was later switched to dabigatran because of drug eruption. The mass resolved completely without thromboembolic or bleeding complications during follow-up.

This case underscores the importance of comprehensive imaging assessment of both the LA and the LAA when evaluating intracardiac masses in patients with AF. In particular, TEE before procedures such as cardioversion, AF ablation, or LAA occlusion should not be limited to the appendage alone, because thrombus may arise from other regions of the atrial wall. Multimodality assessment with TEE and contrast-enhanced chest CT may be particularly useful when the anatomical relationship between a left atrial mass and the LAA cannot be fully defined by a single modality. In this case, CT was performed as contrast-enhanced chest CT rather than dedicated electrocardiographic-gated CCT. Although delayed-phase imaging provided useful complementary information, dedicated electrocardiographic-gated CCT with LAA-specific contrast timing and routine delayed imaging would be preferable, when available, for more precise evaluation of LAA filling defects and to reduce motion and slow-filling artifacts.

Conclusion

An LAMT arising in association with a left atrial diverticulum is rare but should be considered in patients with AF who present with an intracardiac mass. In this case, multimodality imaging with TEE and contrast-enhanced chest CT provided complementary information for differentiating LAMT from other left atrial masses and for monitoring treatment response. Prompt anticoagulation may lead to complete thrombus resolution and reveal the underlying diverticulum without the need for surgical intervention.

Ethics Statement

The authors declare that the work described has been carried out in accordance with The Code of Ethics of the World Medical Association (Declaration of Helsinki) for experiments involving humans.

Consent Statement

Complete written informed consent was obtained from the patient (or appropriate parent, guardian, or power of attorney) for the publication of this study and accompanying images.

Funding

The authors declare that this report did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.

Declaration of Generative AI and AI-Assisted Technologies in the Manuscript Preparation Process

During the preparation of this work, the authors used ChatGPT to assist with language editing and organization of the manuscript. After using this tool, the authors reviewed and edited the content as needed and take full responsibility for the content of the published article.

Disclosure Statement

The authors reported no actual or potential conflicts of interest relative to this document.

Supplementary Data

Video 1

Two-dimensional transthoracic echocardiography, parasternal long-axis view, demonstrates normal left ventricular size and global function, dilated LA with reduced contraction, and a large left atrial mural mass attached to the left atrial wall.

Video 2

Two-dimensional TEE, midesophageal simultaneous orthogonal two-dimensional short-axis (0°; left) and long-axis (+43° through –44° sweep; right) displays, demonstrates a large left atrial mass that arises from the left atrial wall separate from the LAA.

Video 3

Two-dimensional TEE, midesophageal simultaneous short-axis (43°) views without (left) and with (right) color-flow Doppler (Nyquist limit, 23.1 cm/s), demonstrates a large left atrial mural mass without internal color enhancement.

Video 4

Follow-up two-dimensional TEE, midesophageal, selected views from a sweep of the LAA (47°, 0°, 90°, and 134° views), obtained at 6-month follow-up, demonstrates the LA and LAA with spontaneous echo contrast, but without the previously noted definitive mass.