Bronchogenic Cysts

1. Definition & Embryology

• Definition: A congenital malformation of the bronchial tree representing a foregut duplication cyst.
• Etiology: Results from abnormal budding of the ventral foregut (tracheobronchial tree) between the 4th and 6th week of gestation.
• Pathology:
  • Lined by ciliated pseudostratified columnar (respiratory) epithelium.
  • Wall contains bronchial elements: Cartilage, smooth muscle, and mucous glands.
  • Filled with mucoid or proteinaceous fluid.

2. Location & Classification

They are usually solitary and do not communicate with the tracheobronchial tree (unless infected/ruptured).

1. Mediastinal (65-75%): Most common.
   • Typical site: Middle Mediastinum, near the Carina or paratracheal area.
2. Intraparenchymal (15-25%): Within the lung tissue (usually lower lobes).
3. Ectopic (Rare): Neck, pericardium, or sub-diaphragmatic.

3. Clinical Features

Presentation varies by age and size.

• Asymptomatic: Often incidental findings on CXR/CT in older children/adults.
• Symptomatic (Compression): Due to critical location near airways (carina).
  • Stridor, wheezing, dyspnea.
  • Dysphagia (esophageal compression).
  • Air trapping/hyperinflation of the affected lung.
• Symptomatic (Infection): Fever, cough, purulent sputum (if ruptured into bronchus).

4. Diagnosis

• Chest X-ray:
  • Smooth, round, well-defined opacity.
  • Usually in the mediastinum/hilar region.
  • Air-fluid level seen only if communication with airway exists (infection).
• CT Thorax (Gold Standard):
  • Homogeneous, non-enhancing mass.
  • Fluid density (0–20 HU) usually, but high protein/calcium content can mimic soft tissue density.
  • Defines anatomical relationship to trachea/esophagus.
• MRI: Useful if CT is indeterminate; cyst fluid is very bright on T2-weighted images ("Light bulb" sign).

5. Complications & Management

Complications:

• Recurrent superinfection/abscess formation.
• Massive hemoptysis (rare).
• Malignant Transformation: Rare risk of developing carcinoma or sarcoma within the cyst wall.

Treatment:

• Surgical Excision: The standard of care for all cysts (including asymptomatic ones).
  • Rationale: Prevention of infection, compression, and malignancy.
• Approach:
  • Video-Assisted Thoracoscopic Surgery (VATS) is preferred.
  • Thoracotomy for complex/large adherent cysts.
  • Note: Incomplete excision can lead to recurrence.