Multidetector CT and Postprocessing in Planning and Assisting in Minimally Invasive Bronchoscopic Airway Interventions

Abstract

A widening spectrum of increasingly advanced bronchoscopic techniques is available for the diagnosis and treatment of various bronchopulmonary diseases. The evolution of computed tomography (CT)—multidetector CT in particular—has paralleled these advances. The resulting development of two-dimensional and three-dimensional (3D) postprocessing techniques has complemented axial CT interpretation in providing more anatomically familiar information to the pulmonologist. Two-dimensional techniques such as multiplanar recontructions and 3D techniques such as virtual bronchoscopy can provide accurate guidance for increasing yield in transbronchial needle aspiration and transbronchial biopsy of mediastinal and hilar lymph nodes. Sampling of lesions located deeper within the lung periphery via bronchoscopic pathways determined at virtual bronchoscopy are also increasingly feasible. CT fluoroscopy for real-time image-guided sampling is now widely available; electromagnetic navigation guidance is being used in select centers but is currently more costly. Minimally invasive bronchoscopic techniques for restoring airway patency in obstruction caused by both benign and malignant conditions include mechanical strategies such as airway stent insertion and ablative techniques such as electrocauterization and cryotherapy. Multidetector CT postprocessing techniques provide valuable information for planning and surveillance of these treatment methods. In particular, they optimize the evaluation of dynamic obstructive conditions such as tracheobronchomalacia, especially with the greater craniocaudal coverage now provided by wide-area detectors. Multidetector CT also provides planning information for bronchoscopic treatment of bronchopleural fistulas and bronchoscopic lung volume reduction for carefully selected patients with refractory emphysema. Supplemental material available at http://radiographics.rsna.org/lookup/suppl/doi:10.1148/rg.325115133/-/DC1.

© RSNA, 2012

LEARNING OBJECTIVES

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

• •. Discuss role of minimally invasive diagnostic and therapeutic airway interventions in a variety of bronchopulmonary conditions.
• •. Describe types of multidetector CT and postprocessing available for evaluation of the airways.
• •. Review role of multidetector CT and postprocessing in planning and assisting in bronchoscopic interventions.

Introduction

Conventional bronchoscopy has an established and invaluable role in the investigation of bronchopulmonary diseases. Over the past 20 years, bronchoscopic technology, anesthetic techniques, therapeutic materials, and interventional tools have all undergone important advances (1–3). These advances have synergistically enhanced the ability of the interventional pulmonologist to access more distal parts of the bronchial tree, perform increasingly sophisticated diagnostic procedures, and deliver more demanding therapeutic interventions. At the same time, the rapid evolution of computed tomography (CT), particularly multidetector CT imaging techniques, has enhanced the degree of accuracy in depicting normal and pathologic details of the respiratory system (Fig 1). Most of the multidetector CT techniques and the software required for such imaging are now available commercially. In this article, we review existing and novel bronchoscopic techniques and highlight pertinent multidetector CT and postprocessing techniques that enhance the evaluation, planning, and monitoring of such procedures for various tracheobronchial, peripheral airway, and parenchymal conditions.

A variety of multidetector CT techniques are now available for optimal visualization of the central and peripheral airways. These example images are from different patients. (a) Coronal oblique multiplanar reconstruction (MPR) image shows a cardiac bronchus (arrow). (b) Coronal minimum intensity projection (minIP) shows a tracheal stenosis (arrow). (c) Curved MPR shows an endobronchial metastasis (arrowhead) from ovarian carcinoma. (d) Static endoluminal rendering from virtual bronchoscopy (VB) shows a submucosal endobronchial metastasis (arrow) from lung adenocarcinoma. (e) Three-dimensional (3D) bronchial segmentation is shown. (f) A 3D translucent volume rendering of the lungs and airways is depicted. (g) A 3D combined lobar and bronchial segmentation is shown.

Figure 1a.

Figure 1b.

Figure 1c.

Figure 1d.

Figure 1e.

Figure 1f.

Figure 1g.

Bronchoscopic Techniques

The characteristics of the main types of bronchoscopes used in clinical practice are summarized in Table 1.

Table 1.

Characteristics of Some Commonly Used Bronchoscopes and Examples of Their Use

Rigid Bronchoscopy

Originally conceived as a tool for tracheobronchial examination and foreign body removal in 1897, the rigid bronchoscope (Fig 2) underwent modifications that secured its position as the preeminent diagnostic and interventional tool for the airways over the subsequent 70 years (2). Over time, its use as a diagnostic tool has been superseded by flexible bronchoscopy, mainly because of its limited ability to evaluate airways that lie beyond the proximal lobar bronchi, but also because it requires general anesthesia and the use of an operating room in the majority of cases. It has, however, been resurrected as a procedural tool that allows the alleviation of proximal airway obstruction with use of techniques such as airway stent insertion, bougie dilation of tracheal stenoses, and tumor debulking with laser surgery, cryotherapy, or electrocauterization. Its principal advantages include the provision of effective suction, excellent hemostatic control, and direct visualization of the proximal luminal anatomy (4).

Figure 2.

Photograph shows an example of a ventilating rigid bronchoscope and its accessories. The ventilation ports (1) are located at the distal end of the bronchoscope barrel (2), which has an internal diameter of 8.5 mm in this case. A respirator port (3) is located at the proximal end. The bronchoscopist obtains a direct view down the barrel through the viewport (4). The light channel (5), to which a prismatic light deflector (6) is attached, receives a light source; the light channel can be passed down the barrel to provide both proximal and distal illumination. A direct-viewing telescope (7) can be inserted to provide magnified views, and instruments such as a rigid forceps (8) and a suction catheter (9) are easily passed.

Flexible Bronchoscopy

The introduction of the flexible fiberoptic bronchoscope by Shigeto Ikeda in 1967 (5) paved the way for the rapid uptake and availability of flexible bronchoscopy, with more than 95% of bronchoscopic procedures now performed in this manner (1). Flexible bronchoscopy is extremely safe: overall reported major complication rates are on the order of 0.08%–0.5% (6). Flexible bronchoscopy under conscious sedation and topical anesthesia has a significantly lower major complication rate than rigid bronchoscopy (7). The ability of flexible bronchoscopy to visualize airways that are more peripherally located has been boosted by the development of an array of models with various diameters that can be used independently or in combination with a rigid instrument (Fig 3). Manipulation of a flexible bronchoscope through a rigid bronchoscope combines greater distal airway access with more robust hemostatic control. It is worth noting that even though the size of biopsy specimens obtained at rigid bronchoscopy is generally larger than those obtained with the flexible bronchoscope, no significant differences in diagnostic yield between the two techniques have, to our knowledge, been demonstrated (8).

Different types of flexible fiberoptic bronchoscopes with varying luminal diameters are available. (a) Photograph of a model that can be inserted through a rigid bronchoscope, a maneuver that enhances stability in interventional applications in which a flexible bronchoscope is required. (b) Photograph of a model that can be used independent of a rigid bronchoscope and is able to reach small, peripheral (fourth- to sixth-order) airways.

Figure 3a.

Figure 3b.

Ultrathin Flexible Bronchoscopy

Over the past 27 years, ultrathin flexible bronchoscopes that can reach sixth- to ninth-order airways, and thus permit access to and sampling of previously remote lung lesions, have been developed (9–11) (Fig 4). Such instruments incorporate fine-caliber functioning channels that lend themselves particularly well to pediatric applications, including aspiration of secretions and drug delivery. However, they have two potential disadvantages: (a) because of the smaller samples obtained from peripheral lesions, sampling errors may occur and thus compromise diagnostic sensitivity (12) and (b) visualization of the distal airways may progressively deteriorate during the examination because of impairment of the field of view by airway secretions. For these reasons, the use of CT guidance to obtain a clear “map” of the tracheobronchial tree to determine a predefined path to a peripheral lesion may help ameliorate some of these limitations.

Figure 4.

Photograph shows the tip of an ultrathin flexible bronchoscope and that of a conventional flexible bronchoscope. The external diameter of the ultrathin bronchoscope depicted here is only 2.8 mm, compared to the 4.9-mm external diameter of the standard model. Ultrathin bronchoscopes with an external diameter of only 1.8 mm have been developed. These instruments have the potential to reach small, peripheral (sixth- to ninth-order) airways. Experience with the use of such ultrathin bronchoscopes has been limited to particular centers and to descriptive reports in the literature.

In addition to the standard visualization offered by the instruments already described, novel techniques, including bronchoscopic fibered confocal fluorescence microscopy, are currently in development. These have the potential to provide virtual histologic imaging of bronchioles in vivo (2). As these and other techniques evolve, the critical role played by accurate imaging guidance in helping bronchoscopic modalities achieve their full potential will continue to expand.

Multidetector CT Imaging Techniques

The evolution of CT technology has been integral to the development of CT-assisted airway evaluation. Since the 1990s, the advent of multidetector CT scanners with 64 channels or more, combined with an increased gantry rotation speed, has allowed decreased section thickness coupled with a greater coverage along the z axis per gantry rotation, thereby increasing temporal and longitudinal resolution without a significant increase in radiation exposure (13). The acquisition of narrow-collimation datasets permits not only contiguous but overlapping isotropic thin-section reformations with a redundancy of data along the z axis. The resulting datasets enable smooth reconstructions, eliminating “stair-step” artifacts in all planes. Increased speed also allows shorter breath holds, and the resulting temporal resolution optimizes airway and parenchymal visualization with minimal distortion. For optimal airway evaluation and postprocessing, contiguous thin-section (0.625–1.25 mm) datasets with a small degree of overlap (10%–25%) are essential.

Axial CT images are usually sufficient to visualize airway and parenchymal abnormalities; however, axial images do have certain limitations: (a) They may underestimate the craniocaudal extent of disease; (b) they may suboptimally represent airways oriented oblique to the axial plane; (c) they may have limited ability to detect subtle airway stenoses or lesions; and (d) they are limited in their ability to display relationships between airways and mediastinal structures and lymph nodes in three dimensions (14). The exponentially increasing computational power that has accompanied recent generations of multidetector CT scanners has facilitated innovation of reconstruction methods that do not require added radiation exposure or scanning time. These two- and three-dimensional (3D) reconstruction methods can display airways and parenchyma in a more anatomically familiar meaningful way for clinicians. In turn, these techniques can provide a noninvasive means of preprocedural planning and postprocedural surveillance, improving success rates of complex bronchoscopic interventions. The variety of reconstruction methods is summarized in Figure 1 and Table 2. These methods serve to enhance but do not entirely replace the traditional role of the axial CT dataset as the primary means of image review.

Table 2.

Types of Two-dimensional and 3D Multidetector CT Techniques Used in the Advanced Visualization of Airways and Lung Parenchyma

Multidetector CT in Diagnostic Bronchoscopic Procedures

Transbronchial Needle Aspiration and Transbronchial Biopsy

Transbronchial needle aspiration (TBNA) and transbronchial biopsy (TBB) are bronchoscopic methods for, respectively, aspirating intrathoracic lymph nodes through the tracheal or bronchial wall and obtaining lung parenchymal tissue beyond the bronchiolar terminus. TBNA of mediastinal and hilar lymph nodes is primarily used to exclude malignant adenopathy during lung cancer staging, although its utility in showing mediastinal nodal disease in sarcoidosis (15) and human immunodeficiency virus infection (16) has also been demonstrated. TBNA of mediastinal nodes was first reported by Schieppati in 1949 (17) and modified for use with flexible bronchoscopes by Wang et al in the 1980s (18). TBNA has an overall sensitivity of 78% (range, 14%–100%) and specificity of 99% (range, 96%–100%) (19). Various factors that include operator proficiency, node size, presence of nodal metastases, number of samples obtained per node, and availability of experienced cytopathologists to perform rapid on-site cytologic examinations influence TBNA yields in lung cancer staging (20,21). However, it is inherently difficult to objectively compare different methods of invasive staging, as a preference for one mode over another is usually favored on the basis of patient characteristics and clinical staging.

Optimization of TBNA and TBB by incorporating image guidance has gained wider acceptance recently. Real-time imaging provided by EBUS-TBNA has gained prominence, particularly due to its increased diagnostic sensitivity (90%; range, 79%–95%) (19). The complementary ability of EBUS-TBNA and endoscopic ultrasonography–needle aspiration (EUS-NA), accessed through the esophagus, to increase the collective yield of all mediastinal lymph node groups is promising (19). However, the benefit of EBUS-TBNA for central node sampling may be greatest for bronchoscopists who are less experienced in “blind” nodal sampling; overall, EBUS-TBNA may have the highest overall benefit for accessing hilar and interlobar nodes.

The diagnostic success of bronchoscopy for peripheral pulmonary lesions (those not visible beyond the segmental bronchial level) with use of brushings, washings, or TBB is greatly dependent on lesion size and location, with smaller and more peripherally located targets associated with diminished yields. A recent systematic review of eight studies reported pooled sensitivities of only 33% for peripheral lesions smaller than 2 cm in diameter versus 62% for those with a diameter greater than 2 cm (22). CT guidance thus confers distinct advantages for locating intrathoracic lymph nodes, peripheral lung lesions, and diffuse parenchymal lung abnormalities for transbronchial sampling. These functions can be used for both procedural planning and as real-time assistance during the intervention.

Axial CT and MPR in TBNA and TBB

In 1994, Wang proposed a system of lymph node mapping for the staging of bronchogenic carcinoma with TBNA that integrated the standard bronchoscopic examination with axial CT information regarding suspected pathologic nodes (23). This map identified 11 nodal stations accessible by TBNA and remains in harmony with the regional classification of lymph node staging for lung cancer (Fig 5). Using the Wang system, Harrow et al demonstrated a role for CT prospectively in the procedural planning for TBNA (Fig 6). They found that performing TBNA on lymph node targets predetermined at CT precluded the need for a diagnostic surgical procedure in 29% of cases (24). Incremental positive yield was most notable for sampling of right paratracheal and subcarinal lymph nodes, compared with similar-sized nodes in other locations.

Mediastinal and hilar lymphadenopathy in a 55-year-old man undergoing staging investigations for a superficial spreading melanoma on his back. (a) Axial contrast material–enhanced CT image (section thickness, 2.5 mm) displayed with mediastinal window settings demonstrates multiple mediastinal lymph nodes. A left lower paratracheal lymph node (arrowhead) that would be designated station 4L on the Mountain-Dresler lymph node map and station 4 on the Wang bronchoscopic lymph node classification (Fig 5) appeared potentially amenable to EBUS-TBNA. (b) Sonogram obtained with a 7.5-MHz convex EBUS probe demonstrates the station 4L lymph node (measuring 0.89 cm in the short-axis diameter), in which a successful TBNA was performed. Note the position of the descending thoracic aorta (arrow), seen posteriorly, corresponding to its CT appearance. (c) A right hilar lymph node (station 10R) was also sampled at the same examination. Examination of aspirated material from both nodes revealed noncaseating granulomatous inflammation, indicative of sarcoidosis. Axial CT in this case helped identify a lymph node amenable to fine-needle aspiration, as well as to characterize the surrounding anatomy. EBUS-TBNA not only increases the yield of central mediastinal nodal sampling performed by less experienced bronchoscopists but is being used more to access peripheral nodes, including those in interlobar, lobar, and hilar locations.

Figure 6a.

Figure 6b.

Figure 6c.

Figure 5.

Lymph nodes potentially amenable to sampling by EBUS, TBNA, or EBUS-TBNA are indicated on the current lymph node map proposed by the International Association for the Study of Lung Cancer. The lymph node stations that are potentially amenable to TBNA, as originally illustrated by Wang et al (18,23), correspond to stations 4, 5, 7, 10, and 11, but TBNA is most often used to sample subcarinal lymph nodes (station 7). EUS-NA may be used to sample stations 5, 7, 8, and 9; EBUS-TBNA can be used to sample stations 2, 4, 7, 10, 11, and 12, and occasionally some high mediastinal nodes in station 1. L = left, R = right.

MPR images can now provide more anatomically familiar information for locating nodal stations and hilar lesions (25), especially in craniocaudal dimensions (Fig 7). Their utility has also been demonstrated in sampling of peripheral lesions. In a recent study, Bandoh et al evaluated the performance of MPR-guided TBNA and TBB combined with the ultrafast Papanicolaou stain (a rapid cytologic preparation technique) in solitary pulmonary nodules, compared with results from a historical group of patients in whom these techniques were not used (26). MPR provided valuable information in guiding sampling that was not available from conventional axial CT scans for 38 (38%) of their 100 cases. Their results also suggest an improved diagnostic accuracy with a reduced complication rate with use of this combination of techniques compared with results from the historical group. The yield of CT-guided TBNA or TBB of a peripheral lesion is significantly enhanced by a positive “bronchus sign,” defined as the presence in cross-section of a bronchus leading to or contained within the nodule of interest (27–29), especially up to the fifth-order bronchus (Fig 8).

Poorly differentiated non–small cell lung cancer in a 67-year-old man with a history of smoking. (a) Axial contrast-enhanced CT image (section thickness, 2.5 mm) obtained with mediastinal window settings depicts a tumor extrinsically invading and compressing the left mainstem bronchus and trachea and which is inseparable from contiguous lymphadenopathy in the subaortic, left paratracheal, and subcarinal regions. (b) Coronal oblique MPR image (section thickness, 3 mm) obtained with mediastinal window settings illustrates the relationship between tumor and airway more clearly to the bronchoscopist, who was able to obtain an unequivocal diagnostic biopsy. The inset image depicts the oblique plane of reconstruction.

Figure 7a.

Figure 7b.

Figure 8.

Solitary pulmonary nodule in a 65-year-old man with a history of smoking. Axial contrast-enhanced CT image (section thickness, 2.5 mm) obtained with lung window settings depicts a 14-mm nodule located at the end of a subsegmental branch of the anterior segmental bronchus of the right upper lobe, demonstrating a positive CT “bronchus sign” (arrow), suggesting that the target lesion has a higher likelihood of being amenable to bronchoscopic needle aspiration or biopsy. Successful bronchoscopic biopsy revealed adenocarcinoma.

Virtual Bronchoscopy in TBNA and TBB

Several investigators have postulated a potential role for VB in TBNA and TBB of both mediastinal and peripheral lung lesions. VB can assist TBNA in two ways: by generating a “roadmap” of the tracheobronchial tree for planning the optimal path for bronchoscopy and by enhancing identification of optimal sites for biopsy and then virtually simulating the direction of needle puncture so that adjacent mediastinal structures can be confidently avoided (Fig 9). McAdams et al found that in a small group of 17 patients, VB-guided TBNA of mediastinal and hilar nodes provided an overall sensitivity for diagnosing malignancy of 88% per node sampled, coupled with a reduced procedural time (30). Review of preselected VB images by the bronchoscopist often took less than 5 minutes. In a more recent analysis, Weiner and colleagues compared the “hit rate” between TBNA guided by axial CT and VB-guided TBNA and concluded that the hit rate of 58% with VB-guided TBNA was significantly greater than the 30% hit rate with use of conventional axial CT, independent of lesion size or location (31). Although such observations provide encouraging proof of concept, the wider applicability of VB to nodal staging, particularly in comparison with EBUS-TBNA and EUS-NA, remains unclear, as direct comparisons have, to our knowledge, not yet been undertaken.

Mediastinal lymphadenopathy in a 47-year-old man investigated for suspected sarcoidosis. Axial (a) and coronal (b) images (section thickness, 1 mm) were postprocessed from a VB rendering (not shown) performed on a contrast-enhanced CT dataset obtained with mediastinal window settings. An enlarged right paratracheal lymph node has been semiautomatically color-coded pink on both images. The direction of view (yellow line in a and red line in b) simulates a virtual needle and hence provides a simulated puncture path. The virtual needle (short red line with rectangles in a and short yellow line with rectangles in b) can then be placed along the direction of the puncture path, and the optimum position of the needle tip can be simulated. (Images courtesy of Bernhard Geiger, PhD, Siemens Corporate Research, Princeton, NJ.)

Figure 9a.

Figure 9b.

VB has also assisted in the sampling of peripheral solitary pulmonary nodules measuring less than 3 cm in diameter with an ultrathin bronchoscope (12) (Fig 10, Movie 1). Interestingly, Shinagawa et al demonstrated that, in addition to a proximal bronchial lesion location (up to fifth-order), the presence of both a “bronchus sign” and an “artery sign” (the presence of a pulmonary artery leading into the target lesion) were useful predictors of high sensitivity with VB-guided TBB (12). Preliminary experience with VB for delineating the optimal biopsy path for enhancing TBB yield when sampling areas of perilymphatic nodularity in sarcoidosis is also available (32) (Fig 11, Movie 2).

VB planning for ultrathin TBB of a peripheral solitary pulmonary nodule in a 64-year-old woman with a history of smoking. Images from a workstation depicting a VB sequence show a solitary lesion in the right upper lobe close to an eighth-order bronchus on axial (a) and coronal (b) CT images obtained with lung window settings. The subsequent VB fly-through movie (Movie 1) demonstrates the optimal path to this lesion. Note the direction of view (red line in a and b), and automatically designated consecutive orders of the bronchi (arrow in endoluminal view, c).

Figure 10a.

Figure 10b.

Figure 10c.

Movie 1.

Download video file ^{(7.2MB, mp4)}

VB planning for ultrathin TBB of a peripheral solitary pulmonary nodule in a 64-year-old woman with a history of smoking. VB fly-through movie created on a workstation demonstrates the optimal path to a solitary lesion in the right upper lobe, close to an eighth-order bronchus. The direction of view is demonstrated by the thin red and yellow lines in the axial (top left) and coronal (bottom left) views (section thickness, 0.8 mm) obtained with lung window settings. The lines alternate color between red and yellow as a new bronchial order is entered. The red arrows on the volume-rendered endoluminal sequence automatically designate consecutive orders of the bronchi. Note that toward the end of the movie, the segmented nodule is also depicted in 3D, outside the lumen of the adjacent bronchus, and the direction of view then functions as a virtual “needle,” enabling the bronchoscopist to visualize the best approach to the lesion.

Movie 2.

Download video file ^{(7.4MB, mp4)}

VB for ultrathin TBB to evaluate peripheral diffuse nodular lung disease in a 48-year-old man complaining of shortness of breath. VB fly-through movie created on a workstation demonstrates the virtual endoluminal sequence (top left), and axial (top right), coronal (bottom left) and oblique (bottom right) views (section thickness, 0.8 mm) obtained with lung window settings. The optimal path to the selected region of most marked parenchymal nodularity has been automatically designated and depicted by the continuous static yellow line seen with all four sequences. The alternating thin red and yellow lines are as in Movie 1. Such “diffuse” lung disease is often patchy in its distribution. VB can direct ultrathin bronchoscopy to the area of optimal diagnostic yield, potentially avoiding the need for open lung or video-assisted thoracoscopic biopsy. Ultrathin TBB with VB and real-time CT guidance demonstrated granulomatous disease consistent with sarcoidosis.

Figure 11.

VB planning for ultrathin TBB to establish the nature of peripheral diffuse nodular lung disease in a 48-year-old man complaining of shortness of breath. Screen capture from a workstation depicting a VB sequence demonstrates the virtual endoluminal view (top left) and the axial (top right), coronal (bottom left) and oblique (bottom right) CT images obtained with lung window settings. The subsequent fly-through movie (Movie 2) demonstrates the optimal path to the region of most marked parenchymal nodularity. Such “diffuse” lung disease is often patchy in distribution. VB can direct ultrathin bronchoscopy to the area of optimal diagnostic yield, potentially obviating open or video-assisted thoracoscopic lung biopsy. Ultrathin TBB using VB and real-time CT guidance in this way demonstrated granulomatous inflammation consistent with sarcoidosis.

Although the utility of VB in TBNA and TBB of lymph nodes and peripheral lesions has been largely confined to a few specific situations, its ability to depict real-time in vivo anatomy in detail makes it a powerful tool for training and for teaching advanced bronchoscopic skills.

Real-Time Guidance in TBNA and TBB

CT Fluoroscopy.—CT fluoroscopy–guided bronchoscopy is a low-dose multidetector CT technique that permits the real-time localization of the bronchoscope tip and needle, with the dual convenience of a foot pedal controlled by the bronchoscopist and a screen for live image review within the CT scanner. Such a setup eliminates the traditional reliance on the technologist during conventional CT-guided bronchoscopy, thereby facilitating a minimally interrupted procedure. This technique has been shown to be safe, fast, and reliable in TBNA of both mediastinal nodes and peripheral pulmonary lesions, with acceptable levels of radiation exposure (33,34). When considering CT fluoroscopy–guided bronchoscopy in isolation, the diagnostic yield from peripheral lesion sampling is higher in patients with CT-confirmed needle entry into the target lesion (Fig 12). However, no statistically significant benefit has been demonstrated when considering CT fluoroscopy–guided bronchoscopy overall compared with conventional bronchoscopy (35). The lack of statistical significance in this sole comparative study to date may be due to the use of conventional bronchoscopes (with their limited steering capability) rather than ultrathin bronchoscopes, potentially limiting the ability to enter the lesion despite the improved imaging offered by CT. This in turn suggests that CT-guided bronchoscopy potentially offers value only if combined with thin steerable bronchoscopes.

Figure 12.

Real-time CT fluoroscopic guidance for TBNA of a solitary pulmonary nodule performed with an ultrathin flexible bronchoscope in a 65-year-old man with no history of smoking. Successive real-time low-dose thin-section unenhanced axial CT images (section thickness, 1.25 mm) obtained with lung window settings were used to guide the tip of an ultrathin bronchoscope (arrow) into a peripherally located lesion in the right upper lobe (arrowhead). Although the technician at the control panel can acquire such CT images, they are more quickly and conveniently acquired by the bronchoscopist in the procedure room, with use of a foot pedal.

Real-Time Electromagnetic Navigation with CT and VB.—In a small study of 13 subjects, Schwarz et al (36) were the first to demonstrate the feasibility of using electromagnetic navigation for the biopsy of peripheral pulmonary lesions in humans. This system relies on five prerequisites: (a) an isotropic CT dataset, (b) a clear bronchoscopic path to the lesion at CT, (c) an electromagnetic location board placed under the bronchoscopy table, (d) a flexible bronchoscope of a suitable caliber, and (e) a sensor probe that is compatible with the working channel of the bronchoscope used (36) (Fig 13, Movie 3). Initially, a number of anatomic reference (fiducial) points within the bronchial tree are preselected by using a CT study reconstructed in axial, sagittal, and coronal planes (and incorporating VB images) ex vivo. The CT images are then overlaid on the electromagnetic field when the patient undergoes bronchoscopy, so that the sensor probe may be guided to “touch” the preselected fiducial points in vivo to acquire a coregistered map of real (anatomic) and CT data. Finally, real-time navigation to the target lesion along a predetermined path can be performed. The diagnostic yield of peripheral lesions biopsied in this manner is between 69% and 82%, regardless of lesion size (37). In a prospective study of 51 subjects, Seijo and colleagues showed that such yield correlates highly at univariate analysis with a positive CT “bronchus sign” (27). Apart from the sampling of peripheral lesions, electromagnetic navigation has also been used for TBNA of mediastinal nodes, dye marker application to enhance visualization of nodules during diagnostic thoracoscopy, and placement of radiosurgical markers to better locate tumors for targeted radiation therapy (38).

Steps involved in CT-guided electromagnetic bronchoscopic navigation. (a–c) Screen capture (a) from a commercially available electromagnetic navigation system (superDimension, Minneapolis, Minn). During the planning phase, a thin-section CT isotropic dataset coupled with VB images is loaded into a navigational computer, and the optimal pathway (purple lines) to the target lesion (color-coded green) is automatically plotted. Specific anatomic landmarks such as the carina are also chosen as “fiducial points” for coregistration of landmarks during the procedure. After the patient lies down on an electromagnetic location board (b), external tracking sensors are attached to the patient’s chest. An electromagnetic location sensor (c) with 360° steering capability is then passed through a bronchoscope and coregistration of the chosen CT landmarks with real-time bronchoscopy can be performed by touching the fiducial points. (d) Screen capture from the procedure phase in a different patient. The predesignated optimal pathway to the lesion can then be followed during bronchoscopy by using the location sensor, with multiple different views available. Once the target lesion is reached, biopsy forceps can be inserted via a working channel. This system thus has potential to increase diagnostic yield from bronchoscopic sampling of peripheral lesions but has the disadvantages, at present, of cost and limited availability (see also Movie 3). (Images and movie courtesy of superDimension.)

Figure 13a.

Figure 13b.

Figure 13c.

Figure 13d.

Movie 3.

Download video file ^{(2.3MB, mp4)}

Steps involved in planning and performing CT-guided electromagnetic bronchoscopic navigation. (Movie courtesy of superDimension.)

Multidetector CT Assistance in Diagnosis and Treatment of Obstructive Airway Conditions

Several malignant and nonmalignant obstructive conditions, chiefly of the central airways, are now treatable with minimally invasive bronchoscopic airway intervention (Table 3). Although bronchoscopy has historically been the initial modality by which such lesions were diagnosed, multidetector CT with attendant MPR and 3D virtual rendering is increasingly assuming this role, allowing bronchoscopy to be reserved for cases in which there is diagnostic uncertainty or the need for intervention. In the subsequent sections, we highlight some of these conditions and interventions, illustrated with examples from our own practice.

Table 3.

Types of Minimally Invasive Bronchoscopic Intervention Techniques Used for the Relief of Central Airway Obstruction

Note.—NSCLC = non–small cell lung cancer.

*The suitability of carcinoma in situ for ablative resection is strictly dependent on the size of the lesion and the proved absence of any nodal or distant metastatic disease.

Dynamic Airways Evaluation: Tracheobronchomalacia

Tracheobronchomalacia develops because of weakness in the airway walls or cartilage or both, leading to pathologically increased tissue compliance and resultant collapse of the central airways during expiration (39). The condition may be localized or diffuse and may arise either as a congenital or acquired form in both adults and children. Tracheobronchomalacia is an established cause of chronic cough (40) and frequently occurs in the context of other obstructive abnormalities such as emphysema. It is widely considered to be underdiagnosed. Historically, a reduction in the expiratory airway diameter greater than or equal to 50% at bronchoscopy, in combination with a suggestive clinical picture, has been accepted as diagnostic for tracheobronchomalacia (39); however, wide physiologic variations in tracheal diameter, distortion effects of the airway during bronchoscopy, and a lack of standardized characterization of the degree of expiration limit this diagnostic definition (39,41).

A ≥ 50% reduction in the expiratory cross-sectional area of the airway lumen has also been adopted as a radiologic sign of tracheobronchomalacia. This sign is best assessed at paired end-inspiratory and dynamic expiratory or forced-exhalation multidetector CT rather than static end-expiratory imaging (42); however, acknowledgment that appreciable variations in tracheal and bronchial diameter (43) can occur during forced expiration in the healthy state has compelled a critical reexamination of this “diagnostic” 50% threshold (44). Increased radiation exposure associated with image acquisition during both phases of respiration is an additional concern. Low-dose imaging techniques during the expiratory phase have been used in multidetector CT assessment of tracheobronchomalacia, apparently without sacrificing diagnostic accuracy, and so provide an acceptable dose-reduction strategy (45).

MPR image review is increasingly used when analyzing CT scans of patients with tracheobronchomalacia. With 4–detector row CT, dynamic evaluation for tracheobronchomalacia previously relied on repeated evaluation of a single section through a narrow field of coverage (approximately 0.5 cm, assuming a 1.25-mm detector width, for example) (Movie 4). The utility of this technique in examining the entire tracheobronchial tree was therefore limited. The advent of 64–detector row CT has allowed greater craniocaudal coverage of between 3.2 cm and 4 cm (assuming detector widths of 0.5 mm and 0.625 mm, respectively), and so permits cine CT during forced exhalation or coughing (46) (Movie 5, 6). More recently, 320–detector row CT with wide-area detectors that use cone-beam reconstruction are capable of even greater and more rapid coverage of up to 16 cm, while allowing simultaneous 3D and dynamic (so-called 4D) assessment of the tracheobronchial tree (47).

Movie 4.

Download video file ^{(1.2MB, mp4)}

Dynamic evaluation of the lower trachea in a 62-year-old man with a history of increasing shortness of breath and suspected tracheobronchomalacia. Two-dimensional axial cine CT obtained with lung window settings and repeated thin-section acquisition (section thickness, 1.25 mm) with four-detector-row multidetector CT during breathing. The trachea collapses by more than 60% on expiratory views, confirming the suspicion of tracheomalacia. However, the narrow field of coverage (2.5 mm in this case) allows evaluation of only a small area of the airways at a time, and so simultaneous evaluation of the bronchi was not possible.

Movie 5.

Download video file ^{(1.7MB, mp4)}

Dynamic evaluation of suspected airway narrowing in a 68-year old man with a double lung transplant. The patient had a right anastomotic dehiscence that was subsequently repaired, but he then presented with new-onset shortness of breath. Three-dimensional dynamic volume rendering of the main bronchi was performed with 64-detector-row multidetector CT to evaluate if the dyspnea was due to bronchomalacia or airway stenosis. The wider coverage provided (4 cm in this case) helps to better conceptualize the focal narrowing of the right main bronchus, which only slightly worsens with expiration. The narrowing was thought to be due to a stenosis rather than bronchomalacia and was treated with a stent. The normal left main bronchus is simultaneously demonstrated.

Movie 6.

Download video file ^{(1.9MB, mp4)}

Dynamic evaluation of suspected airway narrowing in a 68-year old man with a double lung transplant. The patient had a right anastomotic dehiscence that was subsequently repaired, but he then presented with new-onset shortness of breath. Three-dimensional dynamic volume rendering of the main bronchi was performed with 64-detector-row multidetector CT to evaluate if the dyspnea was due to bronchomalacia or airway stenosis. depicts 3D dynamic volume rendering after stent insertion, performed because of new-onset shortness of breath, demonstrating some narrowing of the right bronchial stent, a recognized complication. This was subsequently successfully treated with balloon dilation.

Inhaled Foreign Body Localization and Removal

Multidetector CT may visualize aspirated foreign bodies, even translucent objects that are not evident on plain chest radiographs in both children and adults (48). Kocaoglu and colleagues evaluated both VB and multidetector CT with MPR in the diagnosis of aspirated foreign bodies in children. They found that axial 1-mm-section multidetector CT and MPR images produced a diagnostic sensitivity of 88.9%, comparable to that of conventional bronchoscopy; VB complemented MPR imaging but did not provide additional diagnostic benefit (49). Put another way, MPR images may potentially reduce the need for diagnostic bronchoscopy in such cases. In our experience, multidetector CT can also be valuable in demonstrating aspirated foreign bodies that may be difficult to extract bronchoscopically, thus identifying patients who may require thoracotomy (Fig 14); however, an attempt at bronchoscopic removal should still be made in these difficult cases before proceeding to thoracotomy.

Accidental inhalation of a scarf pin in a 39-year-old woman. (a) Frontal chest radiograph shows the pin (arrow) in the left lower zone, but precise localization is not possible. Attempted pin extraction by means of rigid and flexible bronchoscopes failed. (b) Subsequent unenhanced axial CT image (section thickness, 2.5 mm) obtained with lung window settings identifies the location of the pin more accurately and demonstrates associated pulmonary hemorrhage. (c) Axial oblique CT reconstruction (section thickness, 1.2 mm) obtained with lung window settings demonstrates that the angle at which the pin subtends the subsegmental bronchus (arrowhead), with the proximal tip of the pin against the airway wall, makes bronchoscopic removal technically unfeasible. The pin was subsequently removed at surgery. Bronchoscopy has historically played an important role in the management of foreign body airway inhalation, and multidetector CT complements this role.

Figure 14a.

Figure 14b.

Figure 14c.

Treatment of Lesions Causing Airway Obstruction: Preprocedural Assessment and Posttherapy Surveillance

An increasing variety of techniques to ameliorate airway obstruction due to neoplastic (50,51) and nonmalignant (52–55) conditions are available (Table 3). Airway patency can be mechanically restored by insertion of an airway stent, with or without debulking with bougie dilation via a rigid bronchoscope. An array of ablative techniques are also available: Nd:YAG laser ablation, electrocauterization, and argon plasma coagulation cause rapid tissue coagulation by using thermal energy, while cryotherapy and photodynamic therapy use the sensitivity of tissue to cold and photochemical agents under light, respectively, to cause delayed tissue destruction. In broad terms, the choice of a single therapy or combined therapeutic options depends on whether there is an emergent need for rapid airway recanalization, the type and extent of the obstructing lesion, and the overall fitness of the patient.

Multidetector CT techniques provide the most convenient initial method for assessing the type and extent of airway obstruction. Compression caused by extrinsic or submucosal lesions is usually more amenable to endoscopic stent insertion or brachytherapy, while intraluminal obstruction can be treated with ablative techniques, with or without additional mechanical debulking via a rigid bronchoscope. Lesions that cause complete airway obstruction are generally unsuitable for laser ablation, but a contact mode of electrocauterization may still be used in such situations (56).

In malignant endobronchial lesions such as infiltrating non–small cell lung cancer or carcinoid, bronchoscopic techniques are usually used as alternative or complementary strategies to surgery, radiation therapy, or chemotherapy (particularly for poor surgical candidates) (57) (Figs 15, 16). In contrast, techniques such as laser resection can preferentially be used in the treatment of benign central airway conditions such as amyloidosis (52), avoiding the costs and morbidity associated with surgery (Fig 17). Because laser ablation, electrocauterization, argon plasma coagulation, and stent insertion provide more rapid relief, they are primarily used to restore airway patency, unlike cryotherapy, photodynamic therapy, and brachytherapy, which require more time to achieve recanalization after initial removal of endobronchial tissue (57). It is often necessary to combine approaches to achieve an optimal therapeutic result (Figs 15, 17). An increased understanding of the biologic behavior of both malignant and nonmalignant disease has helped to better define the choice of therapy selected, allowing the interventional pulmonologist to offer individually tailored solutions.

Bronchoscopic palliative treatment of suspected non–small cell lung cancer in a 68-year-old man. (a, b) Axial contrast-enhanced CT image (section thickness, 2.5 mm) obtained with lung window settings (a) demonstrates a predominantly endobronchial mass in the left main bronchus, causing complete obstruction at rigid bronchoscopy (b). A combination of Nd:YAG laser ablation and argon plasma coagulation was used to debulk the tumor to its origin in the left upper lobe bronchus. A cryoprobe was also used to extract fragments of coagulated tumor. (c) Postprocedure axial contrast-enhanced CT image (section thickness, 2.5 mm) obtained with lung window settings demonstrates successful recanalization of the left main bronchus. Residual tumor (arrow) is evident at the origin of the left upper lobe bronchus. (d) Postprocedure bronchoscopic image demonstrates that the basal segmental left lower lobe bronchi (the anteromedial basal, lateral basal, and posterior basal segmental bronchi are depicted) are completely free of tumor. CT plays a crucial role in the preprocedure planning and follow-up of ablative airway procedures, especially when a combination of complex techniques is required, as in this case.

Figure 15a.

Figure 15b.

Figure 15c.

Figure 15d.

Utility of multidetector CT and VB in a 38-year-old woman who presented with stridor. (a) Coronal contrast-enhanced CT image (section thickness, 3 mm) obtained with lung window settings depicts a subglottic lesion (arrow) causing obstruction. (b) Craniocaudally oriented VB endoluminal view “looks down” at the mass. (c) Caudocranially oriented VB endoluminal view from the same CT dataset allows the bronchoscopist to “bypass” the lesion and “look up” at it to get an idea of the caliber of the airway distally (note the tracheal cartilage rings). (d) The lesion was removed with Nd:YAG laser ablation and proved to be an adenoid cystic carcinoma, leaving only residual narrowing (arrow) on the postprocedure coronal CT image (section thickness, 3 mm).

Figure 16a.

Figure 16b.

Figure 16c.

Figure 16d.

CT in a 53-year-old woman with extensive tracheobronchial amyloidosis. (a) Axial contrast-enhanced image (section thickness, 2.5 mm) obtained with lung window settings demonstrates marked irregularity and narrowing of the proximal bronchi. (b, c) Coronal MPR (section thickness, 3 mm) (b) and coronal oblique minIP (section thickness, 3 mm) (c) images obtained with lung window settings more accurately depict the true craniocaudal extent of the tracheobronchial amyloid deposits. Because of the extensive distribution of the deposits, stent placement was thought to be not beneficial. (d, e) Axial (section thickness, 2.5 mm) (d) and coronal (section thickness, 3 mm) (e) images obtained with mediastinal window settings from the same study demonstrate partially calcified, predominantly posterior subglottic amyloid soft-tissue deposits (arrows) inferior to the vocal cords, causing an approximate 90% subglottic stenosis. Debulking of this abnormal soft tissue with rigid forceps, with subsequent Nd:YAG laser ablation, restored the airway lumen to 90% patency. Utilization of multidetector CT reconstructions helped in planning the appropriate therapy for this patient.

Figure 17a.

Figure 17b.

Figure 17c.

Figure 17d.

Figure 17e.

Airway Stents

Endobronchial stents were originally designed to restore and maintain airway patency for patients with malignancy deemed unsuitable for curative surgery, chemotherapy, or radiation therapy. Since the introduction of a silicone airway stent by Dumon in 1990 (58), a variety of covered and uncovered stents that are either self-expanding or balloon-expandable have been used (Fig 18), extending their versatility to include use in nonmalignant conditions (Table 4); however, the vast majority are still placed to relieve central airway obstruction due to malignancy (59). The site of obstruction is critical in evaluating the feasibility of stent insertion: Lesions beyond the main bronchi are not usually suitable for palliative stenting, and upper lobe obstruction is technically more difficult to alleviate with this method.

A variety of airway stents are available in different shapes to fit the anatomy of the tracheobronchial tree. (a) Photograph of Dumon-style silicone stents (Bryan, Woburn, Mass) of varying shapes and sizes. Silicone stents can be used for both benign and malignant conditions. Newer stents have been manufactured with coated implantable silicone to reduce adherence and thus facilitate removal. Studs (arrows) on the side of the stent can embed slightly into the airway mucosa to reduce the risk of stent migration and still allow some collateral ventilation between the stent and the airway wall. (Image courtesy of Bryan.) (b) Self-expanding metallic stents such as the Ultraflex stent (Boston Scientific, Watertown, Mass) may be uncovered (U) or covered (C). (Image courtesy of Boston Scientific Endoscopy Division, UK and Ireland.)

Figure 18a.

Figure 18b.

Table 4.

Some Indications for Central Airway Stent Insertion

In the context of central airway obstruction due to lung cancer, palliative airway stent placement helped to provide acute relief of dyspnea in as many as 58 (98%) of 59 patients in one case series (60). A recent study has suggested that stent placement may improve survival in patients with an intermediate performance status, especially if it is performed before symptomatic deterioration (61).

A high rate of successful symptom alleviation has also been reported for stent placement for benign airway diseases, including tracheal stenosis complicating prolonged endotracheal intubation or infection (62).

Long-term stent placement is associated with different complications, including airway restenosis, stent migration, stent fracture, in-stent growth of neoplastic tissue, granulation tissue formation, and stent-associated infection (59). The frequency of complications varies with the type of stent deployed: For example, a silicone stent may be easier to remove but is associated with an increased risk of migration (63). Covered stents are more likely to impede mucociliary clearance; on the other hand, the role of uncovered stents has become more limited owing to an increased rate of complications, including in-stent growth of tumor granulation tissue (57). Such stents remain useful in cases in which the primary aim of intervention is to increase airway caliber (recanalization) in the face of extraluminal compression. In view of the significant complication rate associated with stents, the decision to deploy a stent for the treatment of obstruction requires careful consideration and judicious patient selection, particularly in the context of benign tracheobronchial disease (64).

Multidetector CT with MPR, with or without VB, provides a detailed means of assessing patients for the suitability of stent deployment (Figs 19–21). Studies have demonstrated that the anatomically accurate depiction of tracheal stenosis and the degree of intra- and extraluminal central airway narrowing seen with use of MPR and VB correlate closely with bronchoscopic findings (65,66). In our experience, multidetector CT may be used in conjunction with bronchoscopic evaluation to assess the correct diameter and length of stent required, especially in pediatric cases.

Utility of multidetector CT before and after tracheal stent insertion in a 58-year-old man with tracheal stenosis secondary to prolonged intubation. (a–c) Coronal oblique minIP reconstruction (section thickness, 3 mm) (a), translucent airway volume rendering (b), and endoluminal VB rendering (c) from contrast-enhanced CT show a stenosis in the superior portion of the trachea (arrow in a and b). The patient underwent successful tracheal stent deployment but developed increasing stridor 4 months later. (d) Unenhanced axial CT image (section thickness, 2.5 mm) obtained with mediastinal window settings demonstrates granulation tissue (arrowhead) in the posterior aspect of the stent. (e) Coronal maximum intensity projection (section thickness, 3 mm) obtained with lung window settings demonstrates some stent waisting (arrow). The multiple multidetector CT techniques at the radiologist’s disposal can be used in combination to optimize visualization of various aspects of prestent assessment, stent deployment, and poststent surveillance.

Figure 19a.

Figure 19b.

Figure 19c.

Figure 19d.

Figure 19e.

Non–small cell lung cancer in a 74-year-old woman with a history of smoking. (a) Coronal fused virtual unenhanced image (section thickness, 1.5 mm) obtained from contrast-enhanced dual energy CT (100 kV and 140 kV) depicts a large bronchial adenocarcinoma (arrow) obstructing the right upper lobe bronchus and extending to the right main bronchus with distal atelectasis (arrowhead). (b) Axial image (section thickness, 3 mm) from the same CT study obtained with lung window settings shows that the bronchus intermedius remains patent. (c) Curved MPR (section thickness, 3 mm) reconstructed with lung window settings demonstrates the bronchus intermedius better and suggests that it is amenable to protective stent insertion. If a covered stent is used, it is accepted that the diseased right upper lobe bronchus will be sacrificed to preserve aeration of the residual right lung, thus providing a degree of palliation for the patient’s dyspnea.

Figure 20a.

Figure 20b.

Figure 20c.

Metastatic renal cell carcinoma in a 67-year-old man. (a) Axial contrast-enhanced CT image (section thickness, 2.5 mm) obtained with mediastinal window settings demonstrates a metastasis causing endoluminal and extrinsic compression of the bronchus intermedius. (b) Bronchoscopic image shows that the bronchus intermedius is still amenable to stent insertion. Subsequently, a 3-cm-long, 14-mm-diameter Ultraflex covered metallic stent (Boston Scientific) was successfully deployed. (c, d) Axial contrast-enhanced CT image (section thickness, 2.5 mm) obtained with mediastinal window settings (c) and a bronchoscopic image (d) after stent deployment demonstrate stent patency (arrow in c). Note that the bronchial walls are still visible through the proximal aspect of the stent, as the ends of covered stents are left uncovered. Even a central airway that appears completely occluded at CT may still be amenable to protective stent placement. Such benefit may be even greater in cases of extrinsic airway compression by tumor or nonmalignant disease.

Figure 21a.

Figure 21b.

Figure 21c.

Figure 21d.

Multidetector CT also offers a critical means of appraising the rationale and suitability for sacrificing an airway (usually an upper lobe bronchus) whose luminal integrity is directly threatened by tumor obstruction. Such a situation may mandate the placement of a stent across the origin of the airway in question to preserve patency of an adjacent lobe (Fig 20). Multidetector CT also provides versatility in assessing stent complications, comparable to that traditionally provided by diagnostic bronchoscopy (Figs 22–24). Dialani and colleagues observed that multidetector CT accurately detected 29 (97%) of 30 bronchoscopically evident complications in 21 patients who had undergone airway stent insertion, including 13 for benign indications and eight for malignant disease (67). Accurate detection of such events with multidetector CT may circumvent the need for diagnostic flexible bronchoscopy and reserve rigid bronchoscopy for cases in which intervention to restore stent patency is clinically and technically indicated.

Multidetector CT used in the detection of stent migration in a 72-year-old man with a known left upper lobe adenocarcinoma. (a) Coronal MPR image (section thickness, 3 mm) from contrast-enhanced CT performed with mediastinal window settings demonstrates the large left upper lobe tumor causing partial obstruction of the left main bronchus. The patient underwent laser debulking of the tumor, followed by stent insertion and radiation therapy. (b, c) After treatment, reduction in tumor size resulted in the stent (arrow) migrating proximally to the carina, as demonstrated on axial (b) and coronal (c) contrast-enhanced CT images.

Figure 22a.

Figure 22b.

Figure 22c.

Multidetector CT used for surveillance after stent deployment in a 77-year-old man with a history of smoking and a known history of non–small cell lung cancer, who presented with acute deterioration of respiratory function. (a) Coronal unenhanced CT image (section thickness, 2.5 mm) obtained with lung window settings demonstrates the extent of airway obstruction caused by the tumor in the left main bronchus (arrows indicate margins of the tumor). The patient underwent emergency bronchial stent placement followed by radiation therapy. (b) Coronal contrast-enhanced CT image (section thickness, 2.5 mm) obtained with lung window settings after radiation therapy demonstrates significant re-expansion of the left main bronchus. The stent is no longer seen, as the widened airway caliber led to its dislodgement and expectoration. Stents act as a useful palliative adjunct to radiation therapy in such cases; however, to avoid the complication depicted here, a case for prestent radiation therapy can be made, subject to the patient’s respiratory reserve.

Figure 23a.

Figure 23b.

Multidetector CT in the detection of narrowing of a tracheal stent placed for postintubation tracheal stenosis and increasing dyspnea in a 68-year-old woman. (a, b) Axial images (section thickness, 2.5 mm) from unenhanced CT depict granulation tissue (arrow) in the posterior aspect of the stent (a) and waisting of the stent more inferiorly (b). (c) Coronal oblique minIP (section thickness, 3 mm) obtained with lung window settings accurately depicts the narrowed trachea. (d) Coronal oblique maximum intensity projection (section thickness, 3 mm) obtained with bone window settings depicts waisting of the stent (arrow). The patient successfully underwent bougie dilation of the narrowed portion by means of rigid bronchoscopy, followed by Nd:YAG laser ablation of the granulation tissue.

Figure 24a.

Figure 24b.

Figure 24c.

Figure 24d.

Evaluation and Treatment of Bronchopleural Fistulas

A fistula connecting an airway to the pleura or to peripheral air-filled cavities is a recognized complication of thoracic surgery (eg, lobectomy or pneumonectomy) or complex infection (eg, empyema or tuberculosis). The occurrence of bronchopleural fistulas has a substantial frequency after pulmonary resection, complicating between 1.5% and 28% of cases, and is associated with high mortality (68). Central fistulas are more common in the postsurgical or posttraumatic setting, while peripheral bronchopleural fistulas may result from diverse and even coexistent conditions such as necrotizing pneumonia or tuberculous empyema (69). The treatment of bronchopleural fistulas involves surgical or bronchoscopic procedures and has had varying degrees of success, depending on the size and location of the abnormality (68). In recent years, our local experience in successful repair of peripheral fistulas with bronchoscopically instilled albumin-glutaraldehyde tissue adhesive and cyanoacrylate glue has increased (70).

The advantages of CT, and more recently multidetector CT, reside not only in its ability to depict the fistulous tract along its entire length (thereby identifying potential sites for therapy) but also to highlight possible underlying causes of the lesion (Figs 25, 26). Specific diagnosis of a bronchopleural fistula at CT requires direct visualization of a fistulous tract between the pleural space and a central airway proximal to the lobar bronchus (central bronchopleural fistula) or between the pleural space and peripheral airway or lung parenchyma (peripheral bronchopleural fistula). Indirect signs such as locules or air adjacent to the bronchial stump in a postpneumonectomy or lobectomy patient are also highly suggestive. The ability of helical single-detector CT scanners using 5–10-mm collimation to detect peripheral bronchopleural fistulas in 36%–50% of cases has been reported (71,72). In a series of 33 patients, Ricci and colleagues also found that peripheral fistulas caused by ruptured bullae were less likely to be visualized at CT than those occurring in patients with nonbullous lung disease (8% vs 52%) (72); however, they failed to find an important additional role for thin-section (1.0–1.5 mm collimation) CT, in contrast to other studies (71).

Bronchopleural fistula arising from the left main bronchus stump after pneumonectomy for non–small cell lung cancer in a 75-year-old woman. (a) Axial contrast-enhanced CT image (section thickness, 1 mm) obtained with lung window settings shows the tiny communication (arrowhead) between the stump and the air-filled pleural cavity. (b) The communication (arrowhead) is better visualized on the coronal MPR image (section thickness, 1 mm). The patient underwent successful bronchoscopic glue application. There is no current consensus on the treatment of these complications; both surgical and nonsurgical techniques have been used. In our experience, careful selection of candidates for bronchoscopy-guided fibrin or cyanoacrylate glue application has met with reasonable success.

Figure 25a.

Figure 25b.

Fistulous connection between a peripheral bronchus and a cavity in a 58-year-old man with upper lobe fibrosis secondary to parenchymal sarcoidosis, who presented with recurrent hemoptysis. (a) Axial high-resolution CT image (section thickness, 1.25 mm), from contrast-enhanced CT performed with lung window settings and a high-frequency reconstruction algorithm, depicts a mycetoma within a cavity in the left upper lobe. (b) Coronal MPR image (section thickness, 0.6 mm) obtained with lung window settings demonstrates a possible fistulous connection (arrow) between a peripheral bronchus and the cavity. (c, d) Double oblique minIP (section thickness, 3 mm) (c) and curved reformation (section thickness, 3 mm) (d) MPRs optimally show a viable path to the fistula. The patient was successfully treated with cyanoacrylate glue application via a flexible bronchoscope, which was passed through a rigid bronchoscope to provide additional stability.

Figure 26a.

Figure 26b.

Figure 26c.

Figure 26d.

In an analysis of multidetector CT for bronchopleural fistulas, Seo et al found that multidetector CT correctly demonstrated a finding suspicious for peripheral fistula in 23 (96%) of 24 patients, compared with only five (39%) of 13 patients who underwent bronchoscopy (69). Of note, one (14%) of seven central fistulas and five (29%) of 17 peripheral bronchopleural fistulas were visible on coronal MPR images alone.

Multidetector CT Evaluation for Bronchoscopic Lung Volume Reduction

Lung volume reduction (LVR) surgery has now been validated as a palliative therapy for symptomatic relief from dyspnea in patients with severe emphysema refractory to medical therapy. The role of CT in the careful selection of patients who may benefit from LVR surgery is crucial; the presence of bullous emphysema predominant in the upper lobe at thoracic CT in association with proven low exercise capacity after postpulmonary rehabilitation identifies patients who are most likely to benefit (73). This selection process has been greatly enhanced by the development of detailed quantitative and qualitative methods for radiologically characterizing emphysema in terms of its burden and distribution (74) (Figs 27–29).

Qualitative evaluation of emphysema in a 67-year-old man with a history of smoking who was being considered for LVR surgery after failing medical therapy. (a) Coronal maximum intensity projection image (section thickness, 5 mm) from contrast-enhanced CT performed with lung window settings demonstrates asymmetric large bullae in the right upper lobe. (b) A 3D translucent volumetric rendering shows the focal segment of the right upper lobe emphysema more clearly. This patient was thus an ideal candidate for LVR, as removal of the bullous change in the right upper lobe allowed the right lower lobe to reinflate. LVR can be performed surgically or endoscopically (as long as a clear endoscopic path to the lesion can be visualized) if surgery is contraindicated.

Figure 27a.

Figure 27b.

Combined qualitative and quantitative evaluation of emphysema in a 52-year-old woman with a history of smoking who was being considered for LVR surgery after failing medical therapy. (a) Axial image (section thickness, 0.5 mm) from contrast-enhanced CT performed with lung window settings, with lung and lobar segmentation. The left upper lobe, middle lobe, and lower lobes have been color-coded red, blue, and green, respectively. (b, c) Segmentation of areas of emphysema was then performed by using a threshold technique, so that the distribution of emphysema could be represented qualitatively in a 3D combined lung and lobar segmentation (section thickness, 0.5 mm) (b), as well as quantitatively (c). HAA = high-attenuation areas (percentage of lung volume that has an attenuation greater than –200 HU), LAA = low-attenuation areas (percentage of lung volume that has an attenuation less than –950 HU, MLD = mean lung attenuation, P15 = upper limit of attenuation of the lowest-attenuation 15% of lung volume (lower values indicate a greater proportion of low-attenuation emphysema), Rel.Vol. = relative lung volume (volume of the given lung or lobe as a proportion of total lung volume), Vol. = lung volume.

Figure 28a.

Figure 28b.

Figure 28c.

Steps in the multidetector CT evaluation of a 65-year-old man with emphysema who was being considered for bronchoscopic LVR after failing medical therapy. Surgery was contraindicated because of significant cardiovascular comorbidities. (a) Airway segmentation generated from multidetector CT has been performed, and areas of bullous emphysema have also been segmented and color-coded. After manual selection of the largest bulla (arrow), an automatic pathway (red line traversing the tracheobronchial tree in the region of green bullae) is generated to that bulla. (b, c) Image a can then be coregistered with the axial CT image (b) or VB image (c) to provide optimal guidance for bronchoscopic LVR, if this were to be attempted. In this case, however, LVR was deemed inappropriate, as there were too many areas of bullous disease, some of which were too small to reduce, and there was no compression of the adjacent lung.

Figure 29a.

Figure 29b.

Figure 29c.

The substantial rates of mortality and morbidity associated with LVR surgery, as well as the considerable costs, have incentivized the development of alternative minimally invasive bronchoscopic procedures to achieve LVR. A variety of techniques and devices are now at different stages of pilot evaluation. The goal of all these strategies is to reduce hyperinflation within emphysematous areas of the lung, thereby decreasing regions that are not contributing to gaseous exchange. Methods of bronchoscopic LVR can broadly be classified into those that use blocking devices (one-way endobronchial valves), reversible nonblocking devices (LVR coils), and irreversible nonblocking techniques (thermal vapor ablation, drug-eluting “airway bypass” stents, and polymeric adhesives) (75). The role of CT in preoperative evaluation for bronchoscopic LVR is thus potentially more extensive than that for LVR surgery: A clear bronchoscopic path to the targeted hyperinflated segment should ideally be visualized, in addition to computer-derived and visual evaluation of emphysema.

Conclusions

Novel bronchoscopic techniques have been developed that offer minimally invasive means of diagnosing and treating a variety of pulmonary conditions. The planning, execution, and postprocedure assessment of these methods have been complemented and augmented by multiple innovative multidetector CT techniques. A radiologist with a discerning awareness of both the possible interventions and the new and emerging postprocessing imaging techniques is a critical component of any interventional pulmonology team seeking to deliver an innovative, effective, and clinically beneficial service.