Most common foregut cyst.

• A. Bronchogenic foregut cyst
• B. Esophageal duplication
• C. Pericardial cyst
• D. Mediastinal thymic cyst

Answer: (A)

Foregut cysts come from abnormal development of the foregut, and the bronchogenic cyst is the most common of these lesions. It arises from early abnormal budding of the ventral foregut/tracheobronchial tree during weeks 4–6 of gestation and is typically found in the mediastinum or lung. Histologically it is lined by respiratory-type epithelium and often contains cartilage, smooth muscle, and bronchial-type glands in its wall, reflecting its bronchial origin. Esophageal duplication cysts are another foregut duplication but are less common and have GI-type lining with a muscular wall, usually in the posterior mediastinum and intimately associated with the esophagus. Pericardial cysts and mediastinal thymic cysts are not foregut duplications; they arise from persistence of the pericardial coelom and thymic tissue remnants, respectively, and have different histology. Therefore, the bronchogenic cyst stands out as the most frequent foregut cyst.