Calvarial metastasis of a renal cell carcinoma, mimicking a primary alveolar soft part sarcoma, in a young girl-a rare case report.

Renal cell carcinoma (RCC) is characterized by an unpredictable clinical behavior. It has a tendency for early metastasis, which, at times is the initial presentation and therein poses a diagnostic challenge. We present a rare case of a disseminated RCC in a 15-year-old girl, who primarily presented with an occipital soft tissue mass. Computed tomography (CT) of the head revealed a soft tissue mass in the scalp, eroding the occipital bone and extending intracranially. Biopsy examination showed overlapping features of an alveolar soft part sarcoma (ASPS) and a RCC. Immunohistochemistry (IHC) showed diffuse positivity for CD10 and focal positivity for vimentin. Cytokeratin (CK) and epithelial membrane antigen (EMA) were negative. The patient was recommended a clinical 'work-up' to rule out a possible primary in the kidneys. Her CT scan abdomen unraveled a large, lobulated, heterogeneous cystic mass, involving the middle and upper pole of the left kidney. Diagnosis of a metastatic RCC was ascertained. The present case represents a rare manifestation of a RCC metastasizing at an unusual location i.e. calvarium in the youngest patient known, so far and masquerading a primary ASPS. It also highlights the value of clinico-patho-radiological correlation, including CD10 as a useful IHC marker in diagnosing a RCC in young patients, especially when histopathological features overlap with ASPS.