Optimizing Monitoring of Pulmonary Airway Interventions With Digital Tomosynthesis

Postintubation Tracheal Stenosis

During the peak of the COVID-19 global pandemic, reports from regions that were more profoundly affected by COVID-19 found that up to 88% of critically ill patients with COVID-19 required endotracheal intubation for a median of 18 days.¹⁴ The complications of prolonged or repeated intubation and endotracheal cuff overinflation have been well documented, including tracheal ischemia, ulceration, and necrosis.¹⁵ Such tracheal injury can lead to tracheal stenosis, resulting in chronic or progressive respiratory symptoms after extubation. Treatment options for tracheal stenosis include endoscopic balloon dilation and open surgery with partial tracheal resection and anastomosis. Mattioli et al highlighted the advantage of balloon dilation in patients with COVID-19 over the more invasive approach of open surgery.¹⁶ After treatment, patients undergo serial endoscopic examinations to assess patency and integrity of their airways. Diagnostic imaging has a role in assessing the airway in the periprocedural setting, both for the detection of tracheal stenosis, preprocedural planning, and postprocedural follow-up. Cross-sectional imaging with CT is often used to assess the severity of tracheal stenosis and is complementary to the more definitive but invasive diagnostic approach of direct endoscopic evaluation. Additionally, the use of dynamic CT and MRI has been described for further characterizing tracheal stenosis.¹⁷ However, digital tomosynthesis can be valuable in this setting, particularly when cross-sectional imaging is not available ( Figure 1 ).

Figure 1. p class="p ">Adult with COVID-19 pneumonia. Coronal CT (A) in minimum intensity projection at the level of the trachea and central airway demonstrates tracheal distention secondary to overinflated endotracheal tube cuff (arrow). Postextubation radiograph (B) is suboptimal in the assessment of the trachea due to overlapping mediastinal and osseous structures. Digital tomosynthesis (C) centered at the trachea reveals severe narrowing of the tracheal lumen (arrow). Preintervention bronchoscopy (D) confirms a smooth, circumferential tracheal stricture.

Malignant Bronchial Stenosis

Central airway stenting is a common, minimally invasive interventional pulmonary procedure performed to maintain airway patency in patients with malignant airway pathologies, including tumor invasion into the airway lumen, as well as extrinsic mass compression of the airway.¹⁸ While not curative, airway stenting relieves symptoms and improves the quality of life for the patient. Conventional radiography is often the initial imaging requested to assess the thoracic anatomy. However, due to overlapping mediastinal anatomic structures, conventional radiographs have a relatively low sensitivity for detecting central airway pathology, often resulting in suboptimal evaluation of the airways.¹⁹ Digital tomosynthesis provides an alternative or intermediate step in detecting malignant airway stenosis and determining the integrity of the airways ( Figure 2 ). Studies evaluating inter-reader diagnostic performance found increased sensitivity and accuracy for detecting airway pathologies using digital tomosynthesis over conventional radiography.¹³

Figure 2.

Adult with malignant bronchial stenosis. Chest radiograph (A) demonstrates an irregular, lobular, mass-like density projecting over the right perihilar region (arrow). Note the limited visualization of the mainstem and segmental bronchi secondary to underpenetration. Digital tomosynthesis (B) improves visualization of underlying severe stenosis of the right-sided tracheobronchial structures (white arrow). There is moderate stenosis of the left mainstem bronchus (black arrow).

Postoperative Airway Complications

Lung Transplantation

Patients with end-stage lung disease undergo an extensive assessment of transplant eligibility prior to receiving a lung transplant. Radiologists are becoming increasingly more involved in the care of these patients both before and after transplantation. In addition to assessing post-transplant infection or sequelae of transplant rejection, assessing the airway anastomosis site is critical. Central airway stenosis at the anastomotic site between the donor and recipient mainstem bronchi is one of the common post-transplant complications.²⁰ Placement of an airway stent is an important treatment option for post-transplant anastomotic strictures. However, complications may occur after the stent is placed, and follow-up imaging can help assess the possibility of stent migration and/or obstruction ( Figure 3 ). In 1 series, stent-related complications were seen in 23% to 34% of patients.²¹ In another study by Kim et al, evaluating patients undergoing airway stent placement, 47% required 2 or more procedures, with stent-related complications occurring in the first 2 to 3 months after the initial procedure.²² Digital tomosynthesis can change the treatment plan without the need for additional CT imaging.²³

Figure 3. p class="p ">Adult lung transplant patient who underwent right mainstem bronchus stent placement for postprocedural bronchial stenosis. Conventional radiograph (A ) shows poor visualization of the right mainstem bronchus owing to overlying anatomy and sternal wires. Digital tomosynthesis (B) demonstrates markedly improved visualization of the stented right mainstem bronchus (black arrow), which appears intact.

Endobronchial Valve Placement

Patients with refractory chronic obstructive pulmonary disease (COPD) owing to severe lung hyperinflation and air trapping may benefit from minimally invasive procedures, which aim to selectively reduce lung volume, improve lung function, and relieve symptoms. In fact, the placement of an EBV is a standard-of-care treatment option for advanced COPD in many countries.²⁴ After placement of an EBV, serial imaging follow-up is necessary to assess lung volume changes in addition to postprocedural complications. A pneumothorax is a common complication, with some reporting a 15% to 25% occurrence rate.²⁴ However, making the distinction between a bulla or pneumatocele, which has been shown to resolve on its own,²⁵ and a pneumothorax, for which the valves may need to be removed, may impact the patient’s clinical and treatment course. Conventional radiography may not have the resolution to definitively visualize the thin-walled cyst of a pneumatocele.²⁶ However, by scrolling through slices provided by digital tomosynthesis, the outline of the pneumatocele can be better appreciated ( Figure 4 ).

Figure 4.

Adult with chronic obstructive pulmonary disease following left upper lobe EBV placement. Conventional chest radiograph (A) following left upper lobe EBV placement. Postprocedural digital tomosynthesis image (B) following EBV placement enhances demonstration of left apical lucency consistent with postprocedural pneumatocele (black arrow). Note improved visualization of the EBV within the left upper lobe airways (white arrow). Coronal chest CT reformation (C) following EBV placement confirms the digital tomosynthesis diagnosis of postprocedural pneumatocele.

Limitations of Digital Tomosynthesis in Thoracic Imaging

The diagnostic value and added benefit of digital tomosynthesis in the monitoring of patients with a variety of airway pathologies and airway interventions are clear. However, digital tomosynthesis technology has limitations. Current digital tomosynthesis platforms are not portable, precluding their use in the intensive care unit setting. Additionally, blurring artifact may occur in patients who have difficulty cooperating with the examination, given that the acquisition requires a 10-second breath hold ( Figure 5 ); however, we are not aware of specific literature indicating a significant rate of nondiagnostic digital tomosynthesis examinations.

Figure 5.

Limitations of digital tomosynthesis. Digital tomosynthesis centered over the trachea and central airways shows blurring artifact owing to patient motion during the acquisition. As a result, there is poor delineation of the contour and luminal integrity of the trachea and central airways.