Teratomas are germ cell tumors that typically present as large benign or malignant (20%) mass lesions containing variable amounts of fat, soft tissue, and cystic areas. Thirty percent contain calcifications. They vary from an almost entirely cystic mass to a predominately solid mass with internal cystic components.
Benign (mature) cystic teratomas, more correctly termed dermoid cysts, are usually found in patients age 10-30 being very common in the reproductive years. They are the most common ovarian tumor in children, adolescents, and young women (<30 years) with the majority presenting in adolescents. Fifteen to 25% of cases are bilateral. Most authors differentiate Dermoid cysts from Dermoids which are predominately cystic, but the presence of mature germ cell elements give them a complex and varied appearance. Unlike mature cystic teratomas, dermoids originate from ectoderm only and may contain hair, teeth, and sebaceous glands, whereas teratomas originate from ectoderm, mesoderm, and endoderm and may contain any tissue element.

Teratomas may also be found in the mediastinum, intracranially, or anywhere rests of germ cells were left during embryogenesis. In fact, teratomas are the most common congenital intracranial tumor. Additionally, teratomas are the most common benign mediastinal germ cell neoplasm and may be cystic or solid. The cystic teratomas are more mature and more common than the solid type which is usually malignant. Although benign tumors have a slight female predominance, malignant tumors are seen almost exclusively in men. Malignant abdominopelvic teratomas may be accompanied by ascites, intraperitoneal spread, and metastasis to the liver. Malignant degeneration of mature cystic teratomas is rare and occurs in only 1-2% of cases. Common complications of dermoid cysts include torsion and hemorrhage.

The initial imaging modality is usually a sonographic study, as many patients present with abdominal pain. The mixture of sebum and hair is highly echogenic with acoustic shadowing that may totally obscure the back wall of a large mass, a finding known as the “tip of the iceberg” sign. However, calcification may not be easily detected on ultrasound and plain radiographs may be diagnostic of benign cystic teratomas by demonstrating well formed teeth or bone. A recognizable tooth within the mass is a pathognomonic finding. Plain film may also reveal a subtle well-defined mass of fat density. CT scan confirms the cystic, fatty, and calcified components and demonstrates a well circumscribed cystic mass lesion with fluid, fat, and calcification. Characterization by MRI depends on demonstration of fat by chemical shift artifact or fat suppression imaging. Fat or sebaceous material within the cyst follows the signal of subcutaneous fat on all imaging sequences. Fat-fluid levels, layering of debris, dermoid plugs (mural nodules), and calcifications are additional findings. A small percentage of cystic teratomas contain simple fluid showing low signal on T1WI and high signal on T2WI which may be diagnosed as teratomas by demonstration of small deposits of fat in the walls.