Tracheobronchomegaly

Overview

Tracheobronchomegaly, also known as Mounier-Kühn syndrome, is a rare congenital or acquired condition characterized by abnormal dilation of the trachea and main bronchi. This abnormal enlargement weakens the airway walls, leading to recurrent respiratory infections, ineffective clearance of secretions, and progressive lung damage. The syndrome was first described by Pierre Mounier-Kühn in 1932. Tracheobronchomegaly predominantly affects adult males and is often underdiagnosed due to its nonspecific clinical presentation. It may occur as an isolated condition or be associated with connective tissue disorders such as Ehlers-Danlos syndrome or Marfan syndrome.

Causes

Tracheobronchomegaly can be either congenital or acquired, with the majority of cases believed to be congenital in origin. The main causes include:

• Congenital tracheobronchomegaly: Caused by atrophy or absence of elastic fibers and smooth muscle in the trachea and main bronchi, leading to structural weakness and dilation.

• Connective tissue disorders: Conditions such as Ehlers-Danlos syndrome, Marfan syndrome, and cutis laxa may contribute to airway wall fragility and enlargement.

• Acquired cases: Rarely, chronic infections or prolonged mechanical ventilation can contribute to secondary tracheal dilation.

The exact pathogenesis remains unclear, but the loss of structural support within the tracheobronchial tree is central to the development of the syndrome.

Symptoms

The symptoms of tracheobronchomegaly are variable and often develop gradually. Common clinical manifestations include:

• Chronic cough

• Recurrent respiratory infections (e.g., bronchitis, pneumonia)

• Excessive sputum production

• Hemoptysis (coughing up blood)

• Dyspnea (shortness of breath), especially during exertion

• Wheezing or stridor due to airway collapse

• Bronchiectasis and airway obstruction in advanced cases

In some individuals, the condition may remain asymptomatic for years and only be discovered incidentally through imaging studies.

Diagnosis

Diagnosis of tracheobronchomegaly relies on imaging studies and clinical correlation. Diagnostic approaches include:

• Chest radiography: May reveal a widened tracheal shadow, but it is not sufficient for diagnosis.

• High-resolution computed tomography (HRCT): The gold standard for diagnosis. Criteria include:

  • Tracheal diameter > 30 mm (sagittal view)

  • Right main bronchus > 20 mm

  • Left main bronchus > 18 mm

• Bronchoscopy: Reveals flaccid airway walls, mucosal atrophy, and sometimes diverticula or collapsible airways.

• Pulmonary function tests: May show obstructive or mixed ventilatory defects.

It is important to differentiate tracheobronchomegaly from other causes of airway dilation or obstruction, such as tracheomalacia, bronchiectasis, or tumors.

Treatment

There is no cure for tracheobronchomegaly, and management is focused on symptom control, prevention of complications, and preservation of lung function. Treatment strategies include:

• Airway clearance techniques: Chest physiotherapy, postural drainage, and mechanical devices (e.g., flutter valves) to help mobilize secretions.

• Antibiotic therapy: Prompt treatment of respiratory infections; some patients may benefit from prophylactic antibiotics to prevent recurrent infections.

• Bronchodilators: Used in patients with coexisting obstructive airway disease.

• Inhaled corticosteroids: May reduce inflammation and improve symptoms in some cases.

• Surgical intervention: Rarely indicated; in select cases, tracheal stenting or tracheoplasty may be considered.

• Oxygen therapy: For patients with advanced disease and chronic hypoxemia.

Smoking cessation and vaccination against influenza and pneumococcus are strongly recommended to prevent exacerbations.

Prognosis

The prognosis of tracheobronchomegaly depends on the severity of airway dilation and the frequency of respiratory infections. Many patients can maintain a reasonable quality of life with supportive care and appropriate pulmonary hygiene. However, recurrent infections and progressive respiratory failure may occur in more severe cases. Long-term complications may include bronchiectasis, chronic obstructive pulmonary disease (COPD), and pulmonary hypertension. Early recognition and proactive management can help reduce complications and improve functional outcomes.