Tracheobronchomegaly (TBM), also know as Mounier-Khun syndrome, is a rare disorder characterized by marked dilation of the trachea and main bronchi occasionally complicated by tracheal diverticulosis, bronchiectasis and recurrent lower respiratory tract infections. Presentation varies from incidental radiographic finding to progressive respiratory failure.
A 46-year-old male was referred with diffuse “cystic” lung lesions discovered on chest tomography (CT). He initially presented with lower respiratory tract infection requiring 14-day course of intravenous antibiotics 6-months earlier. The patient was a 27-pack-year tobacco smoker, quit 2 years prior to evaluation. He carries no significant medical or surgical diagnoses with exception to hypercholesterolemia requiring a statin therapy over the past 4 years. Review of systems revealed a 2-year non-progressive exertional dyspnea. He denied excessive mucous, cough, recurrent infections, or childhood pulmonary disorders. He further denied weight fluctuation, loss of appetite or night sweats. Furthermore, he denied joint or auricular inflammation, ophthalmologic disorders or recurrent sinusitis. He has fathered 4 children. He denied alcohol, illicit drug, HIV risk factors or suggestive occupational or environmental exposures. Physical examination revealed a chronically thin, well-nourished African American male with a body mass index of 18.8. His vital signs were within normal limits with an oxygen saturation of 97% while breathing ambient air. His lung examination revealed no obvious abnormalities. Rest of exam was normal. Spirometry showed no evidence of airflow obstruction and remained stable since his earlier study 6-months ago. Diffusion capacity for carbon monoxide showed a mild impairment (21.9 mL/mmHg/min, 74% predicted). Review of his chest roentogram revealed tracheomegaly (41 mm) without other obvious abnormalities (Fig. 1). In transaxial images, CT of his chest further confirmed the tracheomegaly in addition to bilateral bronchomegaly (Right: 25.4 mm; Left 23.4 mm) and diffuse varicose bronchiectasis extending to the fifth-order of bronchial division (Fig.2. Arrow). A closer examination of his chest CT showed proximal tracheal diverticulosis. Laboratory findings showed normal alpha-1-antitrypsin level, sedimentation rate, ANA, anti-SSA and SSB. Immunoglobulin levels (IgG) and related subclasses were within normal limits. Total IgE and IgE-specific for aspergilus were normal. Sputum culture showed no acid-fast bacteria and was negative for mycobacterium avium complex (MAC). Genetic testing for Cystic Fibrosis showed no obvious mutations.
Mounier-Kuhn syndrome is primarily a radiographic diagnosis in the correct clinical setting. The etiology remains uncertain, however evidence suggest a congenital defect or atrophy of the elastic and smooth muscle tissue of the trachea and main bronchi. Though a scant amount of literature points to a familial, recessive pattern of inheritance, the majority of cases appear to be sporadic. The disease predominantly occurs in middle age men with African American descent. Radiographically, any diameter of the trachea, right main and left main bronchus that exceeds 3.0 cm, 2.4 cm and 2.3 c, respectively, on a standard chest radiograph is diagnostic of TBM. For chest CT, the values are 3.0, 2.9, and 1.8, respectively. Treatment is limited to physiotherapy to assist in secretions and appropriate antibiotics in times of exacerbation. Scarce case reports of lung transplantation and tracheal stenting for tracheal stenosis have been reported with variable outcomes.
TBM is a radiologic diagnosis in the context of a fitting clinical presentation. Immunizations, clearance of secretions and appropriate duration and choice of antibiotics are crucial in management. Being familiar with the radiographic findings could potentially prevent unnecessary surgical and/or endoscopic evaluation. Spirometric pattern in patients with TBM is difficult to predict, however, our case is the second in the literature documenting normal spirometric findings.
Mohammad Omari, No Financial Disclosure Information; No Product/Research Disclosure Information