A Rare Case of Subcutaneous Scalp Mass As the Initial Presentation of Melanoma of Unknown Primary.

Melanoma is a form of skin cancer responsible for the majority of skin cancer-related deaths. Melanoma of unknown primary origin that presents as a periosteal scalp mass without overlying skin changes is rare and diagnostically challenging. Clinically, melanoma often presents as a skin lesion that is asymmetric, has irregular borders, exhibits multiple colors, is larger in size, and shows recent changes in appearance. The patient in this case is an 89-year-old male who initially presented with a subcutaneous cyst on the posterior scalp. Pathological examination of the excised mass ultimately confirmed malignant melanoma of unknown primary origin. A positron emission tomography scan performed after surgery revealed abnormal uptake in bilateral pulmonary nodules and multiple bilateral hilar lymph nodes. This case report highlights the clinical presentation, diagnostic challenges, and possible etiologies of melanoma with an unknown primary site that has metastasized to an unusual location.