Malignant Transformation of an Intracranial Epidermoid Cyst 25 Years After Initial Surgery: A Case Report and Systematic Review

OBJECTIVE: We report a unique case of a suspected recurrent intracranial epidermoid cyst (EDC) that was found on pathology to have undergone malignant transformation to squamous cell carcinoma (SCC) approximately 25 years after initial resection. Additionally, we performed a systematic review including 94 studies reporting intracranial EDC to SCC transformation.METHODS: Ninety-four studies were included in our systematic review. PubMed, Scopus, Cochrane Central, and EMBASE were searched in April 2020 for studies regarding histologically confirmed SCC arising within an EDC. Kaplan-Meier estimations were used to estimate time to event including survival, and log rank tests were used to test for significance. All analyses were conducted using STATA 14.1 (StataCorp, College Station, Texas, USA); tests were two-sided, and statistical significance was defined using the alpha threshold of 0.05.RESULTS: The overall median time to transformation was 60 months (95% confidence interval {CI}, 12-96). Transformation time was significantly shorter in the no surgery group (10 months, 95% CI undefined) versus the other 2 groups (60 months, 95% CI, 12-72 in surgery only and 70 months, 95% CI, 9-180 in surgery + adjuvant therapy group, both P < 0.01). Overall survival was significantly longer in the surgery + adjuvant therapy group (13 months, 95% CI, 9-24) versus the other 2 groups (3 months, 95% CI, 1-7 in surgery only and 6 months, 95% CI, 1-12 in the no surgery group, both P < 0.01).CONCLUSIONS: We report a rare case of delayed malignant transformation of an intracranial EDC to SCC, occurring nearly 25 years after initial resection. Transformation time in the no-surgery group was statistically significantly shorter as compared to the surgery only and surgery + adjuvant therapy groups. Overall survival was statistically significantly higher in the surgery + adjuvant therapy group as compared to the surgery only and no surgery groups.