Unusual pairing: Concurrent spontaneous lung hernia and expiratory dynamic airway collapse in a patient with chronic obstructive pulmonary disease

INTRODUCTION

Chronic cough and sustained elevations in intrathoracic pressure are well-recognized consequences of advanced chronic obstructive pulmonary disease (COPD), and over time, they may impose significant mechanical stress on both the central airways and thoracic wall.^[1] This can result in structural failure at several levels of the respiratory system, giving rise to conditions that are individually uncommon and even more rarely observed in combination.

Expiratory dynamic airway collapse (EDAC) represents one such manifestation, characterized by excessive inward bowing of the membranous posterior tracheal wall during expiration, resulting in a reduction of 50% or more in airway diameter. EDAC is substantially more prevalent in patients with COPD than in healthy individuals due to altered respiratory mechanics.^[2]

Lung herniation represents a second, less frequent manifestation of mechanical failure, occurring when lung parenchyma protrudes beyond the confines of the thoracic cavity through a congenital or acquired defect in the chest wall. Intercostal lung hernias most commonly occur following trauma or surgery but can rarely develop spontaneously.^[3]

Although both EDAC and lung herniation are individually well described in patients with COPD, we did not encounter prior reports describing the coexistence of these two entities in the same patient during our review of available literature. We report a case of a COPD patient who demonstrated concurrent EDAC and spontaneous intercostal lung herniation, diagnosed on paired inspiratory-expiratory computed tomography (CT).

CASE REPORT

A 66-year-old woman with a 15-year history of COPD presented with progressive dyspnea and persistent non-productive cough. She had been treated with inhaled bronchodilators and corticosteroids and required intermittent oxygen support. She also reported intermittent dull left-sided chest discomfort precipitated by coughing and exertion. There were no acute infectious symptoms, no history of trauma, or recent thoracic surgery.

On examination, auscultation revealed diffusely diminished vesicular breath sounds, with occasional expiratory wheeze and scattered basal crackles. There is no chest wall deformity or focal tenderness noted. Routine laboratory investigations were unremarkable. Pulmonary function testing demonstrated severe obstructive physiology consistent with advanced COPD. A frontal chest radiograph obtained at presentation appeared within normal limits. Because of persistent respiratory symptoms with poor response to medical therapy, a non-contrast CT of the thorax was performed. At our institution, routine high-resolution CT evaluation of suspected COPD is performed using thin-section volumetric acquisition during full inspiration. Expiratory imaging is not routinely obtained in all patients but is selectively performed in individuals with suspected small airway disease, air-trapping, or when dynamic airway abnormalities such as tracheobronchomalacia or EDAC are suspected.

In the present case, the initial image acquisition was inadvertently obtained during expiration because of suboptimal breath-hold and demonstrated marked central airway narrowing. A repeat acquisition was immediately obtained during full inspiration, effectively providing paired inspiratory-expiratory images.

On the expiratory acquisition, there was marked narrowing of the tracheal lumen, with inward bowing of the posterior membranous wall and relative preservation of the cartilaginous anterior and lateral rings [Figure 1]. The reduction in cross-tracheal cross-sectional area was more than 50% compared with the inspiratory image, consistent with EDAC. CT also revealed a focal protrusion of the aerated lung parenchyma through a defect in the left anterolateral chest wall through the intercostal space between the 4^th and 5^th ribs, forming a well-defined, pleura-lined outpouching that remained in continuity with the intrathoracic lung [Figure 2]. No evidence of incarceration, pneumothorax, or subcutaneous emphysema was noted associated with the herniated segment. There was no imaging evidence of prior thoracic surgery or rib trauma which was consistent with the clinical history. The patient was obese, which likely reduced external visibility of the defect on clinical examination. The remaining lung parenchyma showed diffuse bronchial wall thickening and peribronchial cuffing, consistent with a chronic bronchitis phenotype of COPD.

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Figure 1:

Axial images of computed tomography (CT) thorax in (a) inspiratory and (b) expiratory phases show inward bowing of the posterior wall of trachea in expiratory phase with a reduction of more than 50% luminal diameter compared to the inspiratory phase. Virtual bronchoscopy images acquired from (c) inspiratory and (d) expiratory CT demonstrate posterior wall collapse on expiratory image.

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Figure 2:

(a) Axial, (b) coronal, and (c) 3D reformat images of computed tomography chest show focal protrusion of lung parenchyma through the intercostal space between the left 4th and 5^th ribs (arrows).

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DISCUSSION

EDAC and intercostal lung herniation represent two distinct manifestations of chronic respiratory mechanical stress. EDAC is characterized by excessive invagination of the posterior membranous tracheal wall during expiration, resulting in ≥50% reduction in cross-sectional airway area. In patients with COPD, chronic cough, loss of elastic recoil, and sustained expiratory pressure loading are thought to promote membranous laxity, while cartilaginous support remains preserved – distinguishing EDAC from tracheomalacia, in which cartilage weakness predominates.^[4,5] Although dynamic bronchoscopy remains the reference standard, chest CT has been demonstrated to be an important adjunct in the evaluation of suspected EDAC. Inspiratory images establish baseline airway anatomy, whereas expiratory images demonstrate dynamic collapse and help differentiate fixed stenosis from functional narrowing. Mosaic attenuation and air trapping, when present, further support underlying small airway disease. Expiratory CT imaging is therefore particularly useful in patients with unexplained dyspnea, chronic cough, or suspected tracheobronchial instability, particularly when routine inspiratory imaging findings fail to explain the severity of clinical symptoms.

Lung herniation refers to the protrusion of lung tissue beyond the thoracic cage through a defect in the chest wall, mediastinum, or diaphragm. Intercostal hernias are most often associated with trauma or prior thoracic surgery; however, spontaneous hernias may occur in predisposed patients with COPD, chronic cough, obesity, steroid use, or connective tissue disease.^[6] In such individuals, repetitive increases in intrathoracic pressure can strain the intercostal musculature, eventually producing a focal defect through which the lung parenchyma herniates. CT is the modality of choice for diagnosis because it can delineate the hernia neck, verify continuity with the intrathoracic lung, identify associated rib or intercostal abnormalities, and detect potential complications such as incarceration or ischemia.^[7] Management depends on symptom severity and the risk of complications. Small or asymptomatic lung hernias may be managed conservatively with observation and treatment of underlying factors such as chronic cough or COPD. However, symptomatic hernias, enlarging defects, or those associated with complications such as incarceration may require surgical repair with reduction of the herniated lung and reinforcement of the chest wall defect. Spontaneous resolution is uncommon, although small hernias may remain stable with conservative management.

The coexistence of EDAC and lung herniation in COPD, which has not been previously documented to our knowledge, likely reflects a shared mechanical substrate related to chronic cough and pressure fluctuations. Importantly, if only one process is recognized, symptoms may be inaccurately attributed and management may be incomplete.

DIFFERENTIAL DIAGNOSIS

Central airway narrowing on expiration in EDAC should be differentiated from tracheomalacia, which is characterized by primary cartilaginous weakness and demonstrates deformity or collapse of anterior and lateral walls rather than isolated posterior membranous wall bowing. Fixed tracheal stenosis can also mimic airway collapse but lacks significant respiratory phase-dependent variation. With respect to chest wall abnormalities, soft tissue masses, post-operative defects, or rib fractures can be differentiated from spontaneous lung herniation based on morphology and clinical history.

CONCLUSION

Concurrent EDAC and spontaneous intercostal lung herniation represent uncommon but clinically relevant findings in patients with advanced COPD. This case underscores the importance of maintaining a broad, systematic approach to thoracic CT interpretation that extends beyond parenchymal assessment to include central airways and chest wall, particularly when symptoms are disproportionate to routine imaging appearances.

TEACHING POINTS

1. When the severity of symptoms appears disproportionate to otherwise unremarkable routine CT findings, especially in a COPD patient, assessment of airway caliber across respiratory phases is essential, as EDAC may not be evident on routine inspiratory CT alone.

2. Systematic evaluation of the chest wall is important because spontaneous lung herniation may be clinically occult, particularly in obese individuals.