Mounier–Kuhn syndrome: A rare cause of bronchial dilatation: A case report

1. Introduction 

Mounier–Kuhn syndrome, or tracheobronchomegaly (TBM), is a rare clinical entity characterized by abnormal dilatation of the trachea and main bronchi. It is frequently associated with recurrent lower respiratory infection.2, 3, 4, 5, 6 We report a case of a 53-year-old male patient with refractory lower respiratory infection since childhood.

2. Case report 

A 53-year-old male patient was referred to the pulmonology department at the University Hospital Farhat Hached, Sousse (Tunisia), due to a recurrent mild amount of haemoptysis, since four days before his admission. He denied fever, wheezes, chest pain and weight loss. He never smoked and he worked as a Farmer. The patient had a history of lower respiratory infection since early childhood. The diagnosis of bronchial dilatation has been established for 15 years. Physical examination revealed a fever at 38.5°C, cutaneous paleness, hypertrophy of the upper lip, polypnea at 25c/min and diffused bronchial rales. The chest X-ray revealed a significant increase in the diameter of the trachea and of the main bronchi together with cystic lesions in both right and left lower lobes (Fig. 1). A chest computed tomographic scan confirmed an abnormal widening of the trachea and main bronchi with transversal diameters of the trachea of 50mm. There was bilateral cylindrical and cystic bronchiectasis in the lower lobes (Fig. 2). Fiberoptic bronchoscopy, for unresolving haemoptysis, revealed markedly enlarged airways and traces of bleeding arising from the right airways (Fig. 3). The patient received intravenous antibiotics and haemostatic treatment. The haemoptysis is stopped only after bronchial artery embolization with detachable coils of two bronchial arteries.

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Fig. 1 The chest X-ray revealed a significant increase in the diameter of the trachea with cystic lesions in both right and left lower lobes.

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Fig. 2 The chest computed tomographic scan confirmed the abnormal widening of the trachea (50mm).

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Fig. 3 Fiberoptic bronchoscopy revealed markedly enlarged airways and traces of bleeding arising from the right airways.

3. Discussion 

TBM is a rare disorder of uncertain aetiology while autopsy studies suggested a congenital defect or atrophy of the elastic and smooth muscle tissues of the trachea and main bronchi, resulting in dilatation.1 That was until 1932 when Mounier–Kuhn associated the endoscopic and radiographic appearance of the markedly enlarged airway with recurrent respiratory tract infection.2 TBM has been described by a variety of names, including Mounier–Kuhn syndrome, tracheal diverticulosis, tracheobronchiectasis, tracheocele, tracheomalacia, and tracheobronchopathia malacia.1, 2, 3, 4, 5, 6 The common denominator is the dilatation of trachea and central bronchi with an abrupt transition to a normal caliber of the peripheral airways.5 For an adult, an increased diameter of the trachea, the right and the left main bronchus that exceeds 3.0, 2.4, and 2.3cm, respectively, on a standard chest radiograph or bronchogram is diagnostic for tracheobronchomegaly because these are the upper limits of the means plus three standard deviations.7 The diameters in the present case were the following: 5.0cm, 3.8cm, and 3.4cm, they respectively fulfill the anatomic diagnosis of tracheobronchomegaly.

The tracheobronchomegaly is characterized by a severe atrophy of the longitudinal elastic fibers, with thinning of the muscularis mucosa, which results in a dilatation of the membranous and cartilaginous portions of the trachea and main bronchi. This increased compliance of the wall allows the development of broad diverticulum like protrusions of the redundant musculomembranous tissue between the cartilaginous rings.

Diagnosis can usually be made by measuring the tracheal diameter, using only data from chest X-rays, in which the trachea can seen in profile and thus the diameter determined. However, computed tomography of the chest, however, makes this measurement more precise.8

Radiographically, tracheobronchomegaly is manifested not only by the dilatation of trachea and bronchi but also by the protrusion of the redundant musculomembranous tissue between the cartilaginous rings. Thus, resulting in an irregularly corrugated or scalloped appearance of the air columns. Dynamic radiographic and endoscopic studies characteristically show the trachea and major bronchi distend with deep inspiration and collapse on expiration. The central airways may virtually occlude with forced expiration or cough. Retention of secretions may lead to chronic infection and some degree of chronic bronchitis, bronchiectasis, and pulmonary fibrosis. Tracheobronchomegaly has been classified into three subtypes.4 In Type 1 there is relatively subtle symmetrically diffuse enlargement of trachea and major bronchi. Type 2 has more obvious enlargement with bizarre eccentric configurations and diverticula may also be present. In Type 3 diverticula or sacculations extend to the distal bronchi.9 As in bronchiectasis, computed tomography scan has replaced bronchography to confirm the diagnosis. Routine radiographs alone may also display the tracheobronchomegaly and saccular out-pouchings. Bronchoscopy can confirm the diagnosis too.

Pulmonary function tests (PFTs) typically reveal an increase in total lung capacity, to the detriment of residual volume, occasionally with signs of obstructive ventilator disorder. Mostafa et al. had present a case of Mounier–Kuhn syndrome with normal PFTs.9

The etiology of tracheobronchomegaly is unresolved. The association of this condition with Ehlers–Danlos syndrome reported in adults10 and with acquired cutis laxa in children may suggest that tracheobronchomegaly is related to a lack of smooth muscle and elastic connective tissue in the trachea and main bronchi, leading to herniation and even to the formation of diverticula between the cartilaginous rings. A finding of bronchiectasis, such as in the case in question is uncommon.11, 12 It has been speculated that barotrauma is the primary pathophysiologic factor in neonates who have tracheobronchomegaly after receiving intensive ventilatory and oxygen support.6 In adults, inhalation of chronic irritants found in cigarette smoke and air pollution could be important in the development of tracheobronchomegaly.

Tracheobronchomegaly is believed to be extremely rare. However, the identification of some patients with minimal or no symptoms suggests the syndrome's incidence may be greater than suspected. The diagnosis is made in 75% of patients at age 29 or older. Only a few of them reported symptoms in childhood. A genetic link is suggested. The clinical manifestations of tracheobronchomegaly are nonspecific and largely indistinguishable from those of chronic bronchitis or bronchiectasis. Symptomatic Mounier-Kuhn syndrome is characterized by recurrent pneumonia, sometimes evolving to chronic productive cough, occasional hemoptysis, and progressive dyspnea as a result of the pulmonary involvement. More rarely, massive haemoptysis,13 spontaneous pneumothorax, and digital clubbing can be observed.

Asymptomatic patients with tracheobronchomegaly require no specific therapy, although smoking cessation may be helpful. Therapy is primarily limited to intensive antibiotic therapy and postural drainage. The use of permanent prostheses is reserved only for selected advanced cases since there are no precise indications for the practice.8, 14 The generalized nature of the disease limits any possible benefits of surgical resection. It is also known that smoking, chronic obstructive pulmonary disease, and repeated infections can worsen the profile. A careful evaluation of the airway anatomy is very important in patients presenting recurrent pneumonia, productive chronic cough, or incomplete response to appropriate antibiotic therapy for pneumonia. Mounier–Kuhn syndrome, although rare, constitutes a possible diagnosis in these patients and must be considered.

4. Conclusion 

Most cases of tracheobronchomegaly are probably under diagnosed. The present case is such an example. The diagnosis of tracheobronchomegaly should be considered in instances of recurrent pneumonia and mucous plugging with or without suggestive radiologic findings.

Conflict of interest statement 

None of the authors have a conflict of interest to declare in relation to this work.