Primary Intracranial Squamous Cell Carcinoma Arising from an Epidermoid Cyst: Successful Management with Subtotal Resection and Gamma Knife Radiosurgery in an Elderly Patient.

Primary intracranial squamous cell carcinoma (SCC) arising from an epidermoid cyst is an exceptionally rare and aggressive malignancy with a dismal prognosis. Conventional management typically involves gross total resection followed by wide-field radiotherapy; however, this intensive approach is often unfeasible for elderly or frail patients. We present a case of primary intracranial SCC in a 75-year-old woman who presented with rapid cochleovestibular deterioration. Imaging revealed subtle enlargement of a long-standing cerebellopontine angle epidermoid cyst. Subtotal resection was performed to preserve critical neurovascular structures adherent to the infiltrative tumor. Given the patient's poor performance status and the risk of toxicity from broad-field radiation, adjuvant Gamma Knife radiosurgery (GKS) was selected as a focal salvage modality. Despite the limited surgical margin, the patient has maintained a progression-free status with no radiographic evidence of disease progression for 18 months without neurological decline. This case highlights the diagnostic challenge of malignant transformation disguised by radiologic mimicry and demonstrates that GKS can serve as an effective and tolerable adjuvant strategy. We propose that for high-risk patients precluded from intensive multimodal therapy, focused stereotactic irradiation offers a viable alternative to secure local control while preserving quality of life and systemic immune integrity.