Answer: Malignant mature teratoma

Histology: This testicular lesion is composed of mature elements of cartilage and intestinal-type epithelium. There is no tissue that resembles embryonic or fetal tissue (immature elements).

Discussion: Testicular teratoma is a tumor composed of cellular components derived from two or three embryonic layers (ectoderm, endoderm and mesoderm). Mature and immature teratomas are a common component of non-seminomatous germ cell tumors. Pure teratomas are rare (2-3% of all testicular germ cell tumors). Immaturity in a teratoma is defined as tissues that cannot be recognized as normal elements and those that resemble embryonic or fetal tissue.

In a post-pubertal male, such as this patient, all teratomas, whether mature or immature, are considered malignant. Clinical management differs in that the patients receive close follow-up and are offered a retroperitoneal lymph node dissection to evaluate for metastatic disease.

The testicular dermoid cyst shares with the common ovarian dermoid the usual presence of grossly identifiable hair within a cystic tumor. On microscopic examination, there is organoid replication of skin without significant cytologic atypia or mitotic activity. It also lacks adjacent intratubular germ cell neoplasia. The typical arrangement of pilosebaceous units to an epidermal surface is a necessary feature for the diagnosis of testicular dermoid cyst. Other noncutaneous elements may be present in testicular dermoids, as in the ovary. A dermoid cyst is benign.