Intracranial epidermoid cyst: a volumetric study of a surgically challenging benign lesion

Intracranial epidermoid cysts are rare, benign tumors. Nevertheless, the microsurgical removal of these cysts is challenging. This is due to their capacity to adhere to the neuro-vascular tissue as well as the associated difficulties in micro-surgically peeling off their capsular wall hidden in dead angles. To better understand the rate of recurrence after surgical intervention, we have performed pre- and postoperative volumetric analysis of epidermoid cysts allowing the estimation of their growth rate after resection. Imaging data from 22 patients diagnosed and surgically treated for an intracranial epidermoid cyst between 2000 – 2022 was retrospectively collected from two European neurosurgical centers with microsurgical expertise. Volumetric analysis was performed on magnetic resonance imaging (MRI) data. Average cyst volume at diagnosis, prior to any surgery, measured in 12 patients, was 28877.6 ± 10250.4 mm3 (SEM). Estimated growth rate of incompletely-resected epidermoids after surgery was 1630.05 mm3 ± 729.95 (SEM). Assuming linear growth dynamics and normalizing to postoperative residual volume, the average postoperative growth rate corresponded to 61.5 ± 34.3% (SEM) of the postoperative residual volume per year. We observed signs of recurrence during a radiological follow-up period of 6.0 ± 2.8 years (SD) in more than 50% of our patients. Due to their slow-growing nature, epidermoid cysts can often reach a complex multicompartmental size before resection, even in young patients, thus requiring complex approaches with challenging capsular resection which implies a high risk of nerve and vascular injury per se. Tumor recurrence may be predicted based on postoperative volumetry.