Case of the Month

Lower abdominal pain

Diagnosis

Bilateral dermoid cysts

Investigation 

Left Image: Ultrasound show a focal adnexal lesion that is echogenic anteriorly with a more strongly echogenic central region that shadows posteriorly. The former represents fat while the latter hair.

Centre Image: T1 weighted MRI shows a hyperintense left ovarian lesion with central ill defined intermediate signal centrally.

Right Image: Fat saturated T2 sequence.  The anterior component of the lesion is of low signal (black). On a non fat saturated T2 sequence (not shown), this region was hyperintense. This loss of signal with the application of fat saturation demonstrates that this component of the lesion contains fat. Posteriorly the  lesion contains high signal material, consistent with fluid. Sitting at the junction of these is an ill defined intermediate signal spherical region which represents hair floating at the fat - fluid interface.

The dermoid cyst present on the other ovary has not been shown.

Discussion

Dermoids, or mature cystic teratomas, are well differentiated tumours composed of at least two of the three germ cell layers. They are the most common ovarian neoplasm in children and typically occur in a younger population than the epithelial ovarian neoplasms. They are bilateral in approximately 15% of cases.

Dermoids are typically composed of sebaceous material, squamous epithelium, hair, muscle, bone, teeth and other tissues.

Imaging appearances reflect the typical composition of these tumours.

Ultrasound typically shows a cyst with an echogenic nodule (the Rokitansky nodule), a diffusely echogenic mass with posterior shadowing (representing hair and sebum), or fine echogenic bands (caused by hair strands).

MRI and CT show the lesion to be composed of fat, fluid and sometimes calcium, bone or teeth. The demonstration of fat within the lesion is however diagnostic of a mature cystic teratoma.