[Unusual fetal teratoma presenting as a posterior mediastinal cyst]

Mediastinal cysts are uncommon prenatal findings. As isolated and non-compressing entities, they don't compromise the course of gestation. Massive lesions can compress vital structures, resulting in fetal demise. Thus, close follow-up with sonographic monitoring is recommended until birth. Non-hydroptic fetuses can be managed expectantly. Definitive etiology is known after surgical resection only. We present the first case of posterior mediastinal teratoma associated with severe vertebral abnormalities. After CT scan and fetal MRI, medical termination of pregnancy was decided. Histological examination revealed an immature teratoma. With this unique case report, we discuss the optimal prenatal management of mediastinal cysts.