Answer: Malignant teratoma

Histology: This lesion consists of islands of cartilage, respiratory tissue, squamous cysts, and dense fibrosis. The cartilage has areas of increased cellularity with mild cytologic atypia.

Discussion: By definition all teratomas in post pubertal males are malignant tumors capable of metastases. The only time one would use the diagnosis of mature teratoma in a testicular lesion would be in a pre-pubertal male if the lesion lacked any immature elements. Lesions in the testes that have the histological appearance of a totally benign teratoma can metastasize as a teratoma or as other germ cell elements such as embryonal carcinoma, yolk sac tumor, etc. One does not make the distinction between immature and mature teratoma in a post pubertal male as it has no clinical significance. Similarly, one can find cytological and architectural atypia within both the epithelial and mesenchymal elements with a teratoma. Within the mesenchymal components, the atypia may resemble, for example, chondrosarcoma. Within the epithelial elements one may see, for example, glandular elements with the appearance of in situ adenocarcinoma. This epithelial or mesenchymal atypia has no clinical significance as long as the teratoma is not overrun by an overt sarcoma or carcinoma where the malignant appearing epithelial or mesenchymal elements sheet out and occupy greater than a 4X microscopic field. In cases, such as the current one, in order to prevent clinicians from thinking that this lesion is benign, I would diagnose this lesion as “Malignant germ cell tumor consisting of teratoma” or alternatively as “Malignant teratoma”.