'Sack of marbles' in mature cystic ovarian teratoma.

Mature ovarian cystic teratoma (also known as ovarian dermoid cyst) is a slow growing encapsulated tumor which contains well differentiated derivations of at least two out of three germ cell layers (i.e. ectoderm, mesoderm, and endoderm). The lesion is lined by ectodermally derived squamous epithelium containing skin appendages. The cyst content commonly consists of keratin, sebaceous materials and fat. On CT images, the intracystic globules of sebum/fat could appear as multiple free floating rounded hypoattenuating nodules, giving the classical 'sack-of-marbles' appearance.