Abstract
BACKGROUND: Intracranial epidermoid cysts (EC) account for approximately 0.2%-1.8% of all intracranial tumors. Extremely rare, these benign lesions may undergo malignant transformation into squamous cell carcinoma (SCC). The time frame for transformation can vary greatly, and the ideal management approach remains uncertain. MATERIAL AND METHODS: 55-year-old female patient with history of migraines was diagnosed with an incidental cystic lesion suggestive of EC in right cerebellopontine angle (CPA) since the age of 30. She experienced a sudden onset in March 2023 of auditory decline in her right ear, tinnitus, vertigo, headache, dysgeusia, and gait disturbance. Examination revealed involvement of the VIII right cranial nerve with sensorineural hearing loss and complete right facial nerve palsy. She underwent surgery in June 2023 where the cyst was resected however, the capsule of the tumor was strongly adhered to the brainstem, unable to be removed. It showed positive immunohistochemistry for p63, p40, CK5/6, CK7, D2-40, S100, PD-L1, Ki67 was positive in 20% of neoplastic cells, brachyury was negative, consistent with EC with malignant transformation to SCC. She developed few days after the surgery, dysarthria, diplopia, IV and VI right nerve palsies and right dysmetria. Neuroaxis contrast-enhanced MRI was performed with no evidence of lesion otherwise. Brainstem auditory evoked potentials, blink reflex test and facial nerve conduction tests were completed and abnormal due to axonal right facial nerve neuropathy with side-to-side ≥ 90% difference and profound right hearing loss. RESULTS: The one-month follow-up brain MRI showed the right CPA lesion with heterogeneous enhancement with increase in diameter and involvement of the auditory canal. 18FDG) PET/CT demonstrated focal hypermetabolism (SUVmax 10.3) in the right CPA indicative of progression. She underwent radiosurgery with a total dose of 30 Gy in 5 sessions (October 2023). The follow-up 18FDG PET/CT (April 19, 2024) showed no distant sites associated with abnormal hypermetabolism but persistent focal hypermetabolism that decreased compared to previous exam (SUVmax 7.2). The patient is currently 11 months apart from her diagnosis without new neurological findings. Chemotherapy or checkpoint inhibitors have not been used yet. CONCLUSION: We report a case of intracranial SCC derived from an EC, the occurrence this malignant transformation is uncommon and typically indicates a poor prognosis. Small series and case reports are to date available in the literature. After surgery, radiotherapy or radiosurgery should be considered, close follow-up is recommended, chemotherapy or immunotherapy can be used but its effectiveness remains unclear.