Primary intracranial adenocarcinoma associated with an epidermoid cyst: a case report and literature review.

Intracranial epidermoid cysts are rare benign congenital lesions. Although malignant transformation is uncommon, most reported cases have involved squamous cell carcinoma. To our knowledge, transformation into adenocarcinoma has not previously been described. We present a 56-year-old man with a cerebellopontine angle lesion that demonstrated atypical contrast enhancement and mixed signals on SWI. The lesion was surgically resected, and postoperative histopathological examination revealed a poorly differentiated adenocarcinoma associated with a residual epidermoid cyst. Immunohistochemistry, including negative CK5/6 staining, excluded squamous cell carcinoma and common metastatic origins. Postoperative PET-CT showed no extracranial primary lesions. This appears to be the first well-documented case of primary intracranial adenocarcinoma associated with an intracranial epidermoid cyst. Careful radiologic evaluation and comprehensive immunohistochemical analysis are critical when atypical features are encountered. Further accumulation of similar cases is needed to better elucidate the mechanisms, biological behavior, and prognostic implications of this possible transformation process.