Minimally Invasive Approach to Intracranial Epidermoid Cysts and Monitoring of their Resection

Introduction: Epidermoid cyst (pearly tumor) is a benign tumor-like lesion with an incidence of 0.2 to 1.8% of all brain tumors. It occurs usually in the cerebellopontine angle or parasellar region and may involve several compartments, such as basal cisterns. Its natural history is of a slowly progressive nature and is generally diagnosed in patients aged between the mid 20s and late 50s. Preoperative diagnosis can be achieved with greater confidence using modern imaging such as MRI. Recently, the diffusion MRI scan was found to be more specific in differential diagnosis from other lesions such as arachnoid cyst or low-grade astrocytoma. Methods: Complete surgical excision including the (wet tissue-paper–like) capsule can be achieved in about 70% of cases. A higher total resection rate was achieved in patients with tumors confined to the primary location with no intimate adhesions of the capsule to vital structures, that is, the brainstem or cranial nerves. It was reported that about 30% of patients with subtotal removal experienced symptomatic recurrence after 8 years and their recurrence-free survival at 13 years was 65%, compared with 95% for patients with total removal ( Neurosurgery 1998;42:242–251). Aggressive surgical removal results in transient but significant cranial nerve dysfunction. Recently, we reverted from a complex extensive skull base approach and elected to use a minimally invasive transcompartment approach coupled with microsurgical techniques, neuronavigation, and intraoperative monitoring. Excellent functional results were achieved. Conclusion: Minimally invasive transcompartmental approach with intraoperative monitoring improves the functional outcome of resection of epidermoid tumors. MRI with diffusion images became the study of choice for the diagnosis of epidermoid cysts in our practice, and represents an excellent method to evaluate the extent of their resection and monitoring for recurrence.