Chronic pulmonary suppuration
Q1: What are the findings on chest radiograph and HRCT? (see p 272)
The chest radiograph and HRCT show collapse of the right lower lobe with areas of cavitation and bronchiectasis. Areas of fibrosis due to old infection are seen in anterior and posterior segments of the left upper lobe. There is an increase in the tracheal diameter suggestive of tracheomegaly.
Q2: What is the differential diagnosis and how is the diagnosis confirmed?
The differential diagnoses to be considered in a patient with chronic pulmonary suppurative symptoms include bronchiectasis, lung abscess, and cystic fibrosis, The causes of bronchiectasis can be congenital or acquired1 as shown in box 1.
On computed tomography the coronal diameter of the trachea measured 28 mm in our case and confirmed the diagnosis of tracheobronchomegaly. Three dimensional virtual reconstruction technique (3DVRT) (fig 3) further showed dilatation of the trachea and the right main bronchus. Bronchoscopy showed presence of excessive collapsibility of the trachea suggestive of tracheomalacia.
3DVRT showing dilatation of the trachea and right main bronchus.
Q3: What is the treatment of this condition and what are the likely complications?
Treatment of tracheobronchomegaly is aimed at minimising damage resulting from stasis of secretions and infections and consists of postural drainage and antibiotics. Occasionally tracheobronchomegaly may progress to extensive tracheomalacia due to softening of supporting cartilages, as in our case. In some severe cases the trachea becomes distorted and permanently narrowed resulting in diffuse tracheal stenosis and respiratory failure occurs.2 Nasal continuous positive airway pressure provides optimal splinting of the airways to prevent dynamic collapse caused by tracheomalacia. Expanding wire shunts or Y stents have been used in adults with tracheomalacia with good results.2
Discussion
Tracheobronchomegaly is a distinctive, clinicoradiological condition consisting of marked dilatation of the trachea and major bronchi associated with chronic respiratory tract infection and bronchiectasis. The syndrome is rare and often begins in childhood, although it is frequently diagnosed in the fourth or fifth decade, and is thought to be due to a congenital defect of the elastic and muscle fibres of the tracheobronchial tree.3 4 A familial form with a possible autosomal recessive inheritance has been reported.5 Acquired forms of tracheobronchomegaly may occur as a complication of diffuse pulmonary fibrosis, due to mechanical ventilation in preterm infants or in congenital immunoglobulin deficiency.3 6 However, the degree of tracheal dilatation seen with diffuse pulmonary fibrosis is usually mild,6 and diverticula formation seen in the congenital form is not seen in the acquired form of tracheobronchomegaly.
Box 1: Causes of bronchiectasis
Congenital causes
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Structural defects—for example, tracheobronchomegaly, bronchomalacia, pulmonary sequestration.
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Ciliary defects—for example, Kartagener's syndrome, Young's syndrome.
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Immunodeficiency syndromes.
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Metabolic defects—for example, cystic fibrosis, α1-antitrypsin deficiency.
Acquired causes
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Infections in childhood.
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Secondary due to bronchial obstruction due to a tumour or foreign body or hilar glands causing bronchial obstruction.
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Associated disorders of immunity—for example, autoimmune diseases.
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Bronchopulmonary aspergillosis.
Learning points
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Tracheobronchomegaly is a rare cause of chronic pulmonary suppuration.
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Tracheobronchomegaly can be of congenital or acquired aetiology.
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Computed tomography measurement of coronal diameter of trachea greater than 18.2 + 3SD (1SD=1.2 mm), in males, 15.2 + 3SD (1SD= 1.4 mm) in females is diagnostic of tracheobronchomegaly.
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Tracheomalacia with respiratory failure is a life threatening complication.
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Treatment consists of postural drainage, antibiotics, and nasal continuous positive airway pressure or tracheal splints for associated tracheomalacia.
Clinical symptoms range from asymptomatic to symptoms indistinguishable from those caused by chronic bronchitis or bronchiectasis. Stridor or respiratory failure may suggest associated tracheomalacia or tracheal stenosis. The diagnosis of tracheobronchomegaly may be missed unless specifically looked for. Hence the routine measurement of tracheal diameter on chest radiographs and computed tomograms in cases of chronic pulmonary suppuration is worthwhile. Tracheobronchomegaly is defined by an increase in transverse diameter of the trachea and mainstem bronchi of 3SDs or greater. The mean (SD) tracheal diameter on computed tomography is 18.2 (1.2) mm in males and 15.2 (1.4) mm in females.7 The diagnosis of tracheobronchomegaly can also be confirmed by bronchography, computed tomography, virtual bronchoscopy, and magnetic resonance imaging. Demonstration of excessive collapsibility of the trachea on expiration by flow volume loop, fluoroscopy, and bronchoscopy confirms associated tracheomalacia.
Final diagnosis
Tracheobronchomegaly (Mounier-Kuhn syndrome) with tracheomalacia.
