Solution to Unknown Case #2 – Bronchogenic Cyst

History: 40 year old male with cough.

Bronchogenic Cyst: Axial CT scan of the lung bases shows a fluid attenuation lung mass in the right lower lobe.

This is a case of a bronchogenic cyst, which is a congenital lesion thought to arise from abnormal budding of the foregut during development, and it is classified as a foregut duplication cyst along with enteric and neurenteric cysts. Many bronchogenic cysts are asymptomatic and not discovered until adulthood, as in this case. About 85% of bronchogenic cysts are found in the mediastinum, about 80% of which are in the middle mediastinum. The majority of bronchogenic cysts found outside of the mediastinum are located in the pulmonary parenchyma, as in this case.

Typically bronchogenic cysts are well defined, round, and have smooth borders. Usually they contain low attenuating liquid (as seen in the image above), and on contrast enhanced imaging show little to no wall enhancement and no central enhancement. On MRI, the liquid within the cyst may be T1 hyperintense due to proteinaceous contents.