Mounier-Kuhn syndrome is a somewhat controversial entity and used synonymously with tracheobronchomegaly by most authors 7-9.
Mounier-Kuhn syndrome is most frequently seen in middle-aged men before the age of 50 years 1,6.
The anatomical and physiological changes present in the airways predispose to stagnation within enlarged portions of the bronchial tree. Therefore, chronic productive cough or recurrent pulmonary infections are commonplace 1,2. Clinical features may mimic and often co-exist with COPD 4.
It is unclear whether Mounier-Kuhn syndrome is a distinct entity or whether it is simply tracheobronchomegaly in the setting of some underlying primary abnormalities. If the latter definition is used, associations include connective tissue disorders such as 2,6:
The underlying abnormality is an absence or marked atrophy of the elastic fibers and smooth muscle within the wall of the trachea and main bronchi. Although this is thought to be congenital, there is no universal agreement.
As a result of the flaccidity of the wall of the respiratory tree, there is a significant change in airway size during the different phases of respiration. During inspiration, negative intra-thoracic pressure develops leading to marked enlargement of the trachea. However, as expiration commences, the reversed intra-thoracic pressure causes collapse. In addition to this dynamic change, bronchial or tracheal diverticulosis are common, as is bronchiectasis 2.
There is also an absence of the myenteric plexus of the bronchial tree 2.
The most sensitive imaging test is a biphasic CT with images of the trachea obtained during inspiration and expiration. Two-phase chest radiographs will also demonstrate the enlargement of the trachea on inspiration and collapse during expiration, but they are clearly less sensitive.
To consider the diagnosis, the diameter of the trachea should be greater than 3 cm: this is usually measured 2 cm above the aortic arch 1,2. Other measurements that have been used to make the diagnosis include bronchial diameters of 20 or 24 mm (right), and 15 or 23 mm (left) 2,4.
Posteriorly, projecting tracheal diverticula may also be seen.
Treatment and prognosis
Treatment is usually conservative with physiotherapy and postural drainage. Acute exacerbations are treated with antibiotics. In rare instances, tracheal stenting has been used 4.
History and etymology
It was initially described by Pierre-Louis Mounier-Kuhn, a French physician, in 1932 3-5.
The differential is that of a dilated trachea.
- 1. Jannette Collins, Eric J. Stern. Chest Radiology. (2019) ISBN: 9780781763141
- 2. Computed tomography and magnetic resonance of the thorax. editors, David P. Naidich... [et al.]; contributing author, Monvadi B. Srichai. Philadelphia : Wolters Kluwer/Lippincott Williams & Wilkins, c2007. ISBN: 0781757657
- 3. Guest JL, Anderson JN. Tracheobronchomegaly (Mounier-Kuhn syndrome). (1977) JAMA. 238 (16): 1754-5. Pubmed
- 4. Falconer M, Collins DR, Feeney J, Torreggiani WC. Mounier-Kuhn syndrome in an older patient. (2008) Age and ageing. 37 (1): 115-6. doi:10.1093/ageing/afm167 - Pubmed
- 5. Mounier-Kuhn P. "Dilatation de la trachee: constatations, radiographiques et bronchoscopies." Lyon Med 1932; 150: 106–9.
- 6. Brant William E. and Clyde A. Helms. Fundamentals of diagnostic radiology. Lippincott Williams & Wilkins, 2007. ISBN: 0781761352, 9780781761352.
- 7. Webb EM, Elicker BM, Webb WR. Using CT to diagnose nonneoplastic tracheal abnormalities: appearance of the tracheal wall. AJR Am J Roentgenol. 2000;174 (5): 1315-21. AJR Am J Roentgenol (full text) - Pubmed citation
- 8. Dee PM. Chest case of the day. Tracheobronchomegaly--the Mounier-Kuhn syndrome. AJR Am J Roentgenol. 1996;167 (1): 235, 238. AJR Am J Roentgenol (link) - Pubmed citation
- 9. Shin MS, Jackson RM, Ho KJ. Tracheobronchomegaly (Mounier-Kuhn syndrome): CT diagnosis. AJR Am J Roentgenol. 1988;150 (4): 777-9. AJR Am J Roentgenol (citation) - Pubmed citation