Bronchogenic Cyst

Bronchogenic cyst is a congenital foregut duplication cyst lined by respiratory epithelium, arising from abnormal budding of the primitive tracheobronchial tree at 3 to 7 weeks of gestation. It is the commonest primary cystic mass of the mediastinum, with an estimated incidence of 1 in 42,000 to 68,000.

About 70 to 85% are mediastinal (subcarinal and paratracheal most often), and the rest lie in the lung parenchyma (lower lobes more often), neck, pleura, diaphragm, pericardium or under the diaphragm. Cysts are usually single and unilocular, filled with mucus or serous fluid, and up to 10 cm in size, found in children or young adults, though many are found at any age.

Pathophysiology. Detachment of a bud from the ventral foregut leaves a sequestered cyst with a wall containing cartilage, smooth muscle, mucous glands and ciliated columnar epithelium. Mucus secretion enlarges the cyst slowly, and infection, bleeding or compression of adjacent structures may follow.

About half to two thirds of adults have no symptoms, and the cyst is found incidentally. Symptoms arise from compression: cough, wheeze, stridor, dyspnoea, chest pain and dysphagia, or from infection (fever, purulent sputum, haemoptysis). Infants may have respiratory distress, recurrent infection or feeding problems from a large cyst or air trapping. Rare complications are rupture, haemorrhage, pneumothorax, superior vena cava syndrome, arrhythmia, and malignant change.

Stridor, respiratory distress, cardiac compression or sudden pain with fever needs urgent assessment.

• Chest radiograph: a well defined round or oval homogeneous mass in the mediastinum or lung, possibly with air fluid level when connected to an airway or infected.
• CT chest with contrast: a smooth walled, non-enhancing cyst of water attenuation (0 to 20 Hounsfield units) in two thirds, or higher attenuation (over 20 to 100 units) when contents are proteinaceous, calcified or haemorrhagic, with a thin rim enhancement only. Lack of solid enhancing component distinguishes from tumour.
• MRI: high signal on T2, variable on T1 depending on protein content. Used when CT is uncertain, and to show relation to vessels, spinal canal and airway.
• Endoscopic ultrasound or endobronchial ultrasound: confirms a cystic structure. Needle aspiration is avoided or covered with antibiotics because of infection risk, and cytology is seldom needed.
• Pulmonary sequestration is excluded by CT angiography for a systemic feeding vessel in parenchymal cysts.
• Pathology after resection confirms the diagnosis: respiratory epithelium with cartilage and glands.
• Prenatal ultrasound or foetal MRI in congenital cases.

Differential diagnosis.

• Oesophageal duplication cyst
• Pericardial cyst
• Neurenteric cyst (vertebral anomaly)
• Congenital pulmonary airway malformation
• Pulmonary sequestration
• Cystic teratoma, lymphangioma or thymic cyst
• Lung abscess, hydatid cyst or cystic tumour

• Symptomatic cysts: complete surgical excision by video assisted thoracoscopy (or open surgery), with removal of the whole cyst wall to prevent recurrence. Segmentectomy or lobectomy for intrapulmonary cysts. Aspiration alone is inadequate since the cyst refills.
• Asymptomatic cysts: resection is usually advised even in the absence of symptoms, because infection, haemorrhage, compression and (rarely) malignant change develop over time, and the operative risk is low in children and young adults. Observation with serial imaging is reasonable for small, stable cysts in older patients or those with high surgical risk.
• Infected cyst: antibiotics first (amoxicillin-clavulanate 625 mg three times daily, or 1.2 g intravenously three times daily, for 7 to 14 days), then surgery after the infection settles, since resection in the inflamed state is harder. Children: amoxicillin 125 mg three times daily at 1 to 11 months, 250 mg at 1 to 4 years, 500 mg at 5 to 11 years.
• Percutaneous or endoscopic drainage and marsupialisation for patients unfit for surgery.
• Perioperative care: preoperative CT, and avoidance of positive pressure that can expand an air filled cyst. In infants with a large cyst, urgent resection for respiratory compromise.

Complications and prognosis. Infection, haemorrhage, rupture, pneumothorax, compression, and rarely malignancy (adenocarcinoma, rhabdomyosarcoma). Recurrence after complete resection is rare, and outlook is excellent.

Monitoring. Clinical review and chest radiograph at 3 to 6 months after surgery, and imaging at 12 months. For observed cysts, CT at 6 months and then yearly.

Referral and escalation. Refer to a thoracic surgeon, or a paediatric surgeon in children, and urgently for airway compromise.