Most mediastinal cysts are diagnosed at antenatal ultrasound scanning, postnatally most patients are asymptomatic. The differential diagnosis includes: bronchogenic cysts, oesophageal duplications, neuroenteric cysts, thymic cysts, cystic hygromas, and teratomas. Thoracoscopic excision is the preferred approach for antenatally diagnosed asymptomatic lesions. Infected cysts are more difficult to excise thoracoscopically.

The patient is positioned laterally with the affected side up and an axillary roll underneath, as for a thoracotomy. For superior mediastinial cysts, the monitor is positioned over the patient’s head and the surgeon stands at the foot of the table. The converse arrangement is used for cysts in the lower half of the chest. The first port (5-mm, optical) is inserted anterior to the inferior angle of the scapula in the adjoining intercostal space. A pneumothorax of 5–6 mm Hg with flows of 1.5–2 L/min is maintained. After lung collapse, two or three working ports are inserted under direct vision between the anterior and posterior axillary lines to achieve effective triangulation and ergonomic working. Occasionally, a port may have to be inserted more anteriorly or posteriorly to achieve these goals.