EPIDERMOID CYST OF THE TESTIS - A REVIEW OF CLINICAL AND HISTOGENETIC CONSIDERATIONS

Objective To review the records of patients with epidermoid cysts and those with germ cell tumours to determine the most appropriate method of treatment. Patients and methods The records of the patients treated for epidermoid cysts and testicular germ-cell tumours in a period covering 22 years were analysed retrospectively. Nine specimens with an epidermoid cyst were examined by immunohistology for the presence of testicular intraepithelial neoplasia (TIN) (or carcinoma in situ of the testis). Results Ten patients with a simple epidermoid cyst and 481 patients with testicular germ-cell tumour were treated during the observation period. The relative incidence of epidermoid cysts in relation to the number of patients with testicular germ-cell tumours was 2.1% (95% confidence interval 0.8-3.35%). The mean age of the 10 patients with an epidermoid cyst was 24.1 years. The right testis was affected in seven patients and the left in three. Six of these patients received conservative surgery with excellent cosmetic results. No relapse had occurred after a median observation period of 30 months. Immunohistological staining for placental alkaline phosphatase disclosed the absence of TIN in the parenchyma surrounding the cysts. Conclusion The absence of TIN calls into question the common assumption that an epidermoid cyst constitutes a monodermal teratoma. Two distinct entities of epidermoid cyst are proposed - one occurring in conjunction with a teratoma or a germ cell tumour (a 'complex' or 'mixed' epidermoid cyst) and the other a 'simple' epidermoid cyst without TIN in the adjacent tissue and thus representing a benign neoplasm that is not a teratoma. The absence of TIN near a simple epidermoid cyst justifies testis-sparing surgery.