Abstract

A 68-year-old woman developed a scalp nodule measuring 7×5× 2cm in the cranial vault. The nodule, having been present for 3 years since she had got a bruise on the head, had increased gradually in size for the past 3 months. On physical examination, a pea-sized subcutaneous nodule was found in the left temple. Biopsy specimen of the scalp nodule showed malignancy. Both nodules were resected operatively and were examined histologically. Light microscopic examination of the scalp nodule demon-strated the proliferation of atypical polygonal and spindle shaped cells in the dermis and subcutis. The temple nodule showed metastasis in the lymph node with prolifera-tion of atypical cells corresponding to those in the scalp nodule. Hematoxylin-eosin and Fontana-Masson stains revealed no melanin pigment in the tumor cells. By immunohistochemistry, the tumor cells were positive for NSE and HMB-45, but were negative for S-100, keratin, EMA, CEA, Factor VIII and UEA-1. Electron microscopic examination revealed oval granules similar to stage II or III melanosomes in the cytoplasm of a tumor cell. This tumor possibly represents an amelanotic melanoma of the scalp soft tissue accompanied by a lymph node metastasis, although no definite diagnosis can be made. The reasons against the diagnosis of melanoma were as follows: (1) Tumor cells were negative for S-100 protein. (2) There was no irregular junctional activity. (3) Only a small number of melanosomes could be detected in the tumor cells.