Intracranial epidermoid cyst with malignant degeneration and leptomeningeal carcinomatosis: illustrative case

Nonmalignant recurrence of benign ECs is relatively common, often due to the complexity of complete resection and adherence to adjacent neurovascular structures. On the other hand, malignant degeneration of an EC is extremely rare. Any rapid change in symptoms, failure to recover following surgery, and new areas of irregular thickening and enhancement on imaging should prompt further evaluation for this process. https://thejns.org/doi/10.3171/CASE24738.