Bronchogenic cysts are congenital lesions thought to result from abnormal budding of the ventral foregut that occurs between the 26th and 40th days of gestation. This abnormal bud subsequently differentiates into a fluid-filled, blind-ending pouch. Most cysts are located in the mediastinum, near the tracheal carina.

Bronchogenic cysts are sometimes found in association with other congenital pulmonary malformations such as sequestration and lobar emphysema.

Most of the cysts are asymptomatic.

The fluid within bronchogenic cysts is usually a mixture of water and proteinaceous mucus.

The typical roentgenographic appearance of a bronchial cyst is that of a solitary, round, fluid-filled mass in the middle third of the lung. The average diameter is about 5 cm, but occasionally, the diameter exceeds 10 cm. Infection of the cyst results in communication with the tracheobronchial tree, allowing air with or without fluid to enter the lumen of the cyst.

At computed tomography (CT), bronchogenic cysts typically manifest as spherical masses of either water or soft-tissue attenuation.