Typical carcinoid arising in mature teratoma of anterior mediastinum.

Teratoma is the second most common mediastinal neoplasm, but malignant transformation in mature teratomas is uncommon at both gonadal and extragonadal sites. A 35-year-old woman presented with an anterior mediastinal mass. Computed tomography suggested a teratoma. Meticulous pathological examination helped in detecting a neuroendocrine neoplasm (carcinoid) within the mature teratoma. Malignant transformation in a teratoma is difficult to diagnose on clinical and radiological assessment; histopathology is essential to detect the malignant nature of these neoplasms.