Malignant Transformation of Intracranial Epidermoid Tumors: A Systematic Review and Survival Analysis

Intracranial epidermoid tumors (ETs) are rare, benign lesions that often arise within the cerebellopontine angle and are typically slow-growing with favorable outcomes. Malignant transformation is exceedingly rare and poorly understood, with limited data on imaging findings, medical and operative management, and overall survival.

We conducted a Preferred Reporting Items for Systematic Reviews and Meta-Analyses-guided systematic review and pooled analysis of 68 patients from 58 studies with pathologically confirmed malignant transformation of intracranial ETs. Clinical presentation, tumor location, radiologic evolution, management, histopathology, molecular findings, and survival were analyzed. The Kaplan-Meier method was used for survival analysis.

Mean age at diagnosis was 49 years with a slight male predominance. Most tumors arose in the cerebellopontine angle (97%). Malignant transformation was associated with contrast enhancement (98%) and rapid growth (57%). Longitudinal imaging revealed heterogeneous T2 signal changes (56%) and loss of diffusion restriction on diffusion-weighted imaging (43%), termed "Loss of Fluidity" and "Flip Sign." Gross total resection was achieved in 24%; subtotal resection in 66%, often supplemented with radiotherapy (46%) and chemotherapy (21%). Median overall survival was 23 months, with 58% mortality within six months and recurrence in 63%. Immunohistochemistry confirmed squamous differentiation with high Ki-67 (mean 41%).

Malignant transformation of intracranial ETs is rare but highly aggressive. Early recognition of clinical deterioration and identifying characteristic imaging changes may enable prompt detection. Maximal safe resection remains the cornerstone of management, with multimodal approaches potentially improving outcomes. Long-term surveillance and molecular studies are essential to guide prognosis and targeted treatment.