Cellular blue nevus with nevus cells in regional lymph nodes: a lesion that mimics melanoma.

We report the case of a young man who had a large, firm, nodule covered by darkly pigmented skin over the outer aspect of the right ankle and palpable right inguinal lymph nodes. The mole had enlarged rapidly during the past month, contained deeply pigmented cells with increased cellularity and mitotic activity and groups of intensely pigmented nevus cells within the marginal sinus of the inguinal nodes. The excised mass with inguinal lymphadenectomy was reported as benign cellular nevus with benign nevus cell aggregates in lymph nodes. The purpose of this report is to emphasize how cellular blue nevus can masquerade as malignant melanoma and to increase clinical awareness of this benign variant of melanocytic nevus. We have attempted to elaborate its natural history and comprehensive criteria for diagnosis, so that inappropriate surgery and chemotherapy can be avoided in this lesion which occurs conceivably often enough to be more than just a curiosity.