Teaching Case

A 69-year-old male presented with a recent onset fever and worsening cough for 2 weeks. He had a history of chronic cough for 40 years and had been repeatedly treated for infections without any cross-sectional imaging performed earlier because of a lack of referral to a specialist center.

The patient was admitted to our hospital as a case of community-acquired pneumonia (CAP) requiring further investigations. A High-resolution CT scan of the chest showed widened and deformed tracheobronchial tree [Fig.1,2] with extensive bilateral cylindrical bronchiectasis and reticular and cystic changes particularly affecting bilateral lower lung lobes, right middle lobe, and to lesser degrees both upper lobes. In addition to bronchial and bronchiolar wall thickening, centrilobular and peripheral subpleural nodular shadowing, ground glass opacities, and consolidative changes were present at both the lower lobes and the right middle lobe.

Subsequent bronchoscopy revealed a distorted tracheobronchial tree [Fig.3,4] with absent tracheal cartilages with exaggerated collapsibility upon coughing or expiration. Mucoid secretions were seen within the tracheobronchial lumens on both sides with no diverticula noted. The reported cytology of the bronchial wash revealed acute inflammatory cells along with squamous and ciliated cells. The patient was therefore diagnosed to have CAP and underlying Mounier-Kuhn syndrome.

Mounier-Kuhn syndrome or tracheobronchomegaly, is a rare disease mostly reported in middle-aged men. It is characterized by significant dilatation, weakness, and diverticulosis of the trachea and main bronchi secondary to complete or partial deficiency or atrophy of the elastic fibers of both the cartilaginous and membranous parts [1,2]. Such tracheobronchomegaly manifests as excessive dilatation on inspiration and enhanced collapsibility on expiration, predisposing the patient to recurrent respiratory tract infections due to stagnation of infected intraluminal secretions. The likelihood of it being congenital is supported by the fact that not all reported cases are symptomatic, and that the histology reveals the absence or deficiency of elastic fibers rather than damage secondary to inflammation. It has also been argued that it is an acquired condition because most of the reported cases are of adults with chronic pulmonary suppuration or infections [3,4]. Chronic inhalation of irritants such as cigarette smoking or occupational exposure may contribute to the development of tracheobronchomegaly. The clinical presentation is heterogeneous ranging from completely asymptomatic to severely complicated disease with chronic lung infections and respiratory failure. The diagnosis mandates a CT scan of the chest to demonstrate tracheobronchomegaly, while the modality of choice is bronchoscopy. Treatment is largely supportive and non-specific. Smoking cessation and limiting exposure to airway irritants are encouraged. Infectious exacerbations are treated with antibiotics and postural drainage.

Other causes of tracheomalacia (or dilated trachea) need to be considered in differential diagnoses of Mounier-Kuhn syndrome that can be either be congenital (certain connective tissue disorders like Marfan syndrome and Ehlers-Danlos syndrome) or acquired (prolonged intubation, chronic obstructive pulmonary disease). Imaging finding of lunate trachea with increased ratio of coronal-to-sagittal tracheal diameter is characteristic. Tracheal dilatation (coronal or sagittal widening), tracheal cartilage calcification, wall thickening, and mediastinal lymphadenopathy need to be looked for to exclude these other causes. Clinicians should consider the diagnosis in cases with recurrent chest infections and opt for imaging. 

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