Posterior Fossa Midline Epidermoid Tumors: Role of the Inferior Medullary Velum and a Proposed New Imaging Classification

Neurosurgery 93:112–119, 2023

Posterior fossa midline epidermoid tumors (PFMETs) include the epidermoid tumors of the cisterna magna (CM) and fourth ventricle (FV).

OBJECTIVE: To report tumor epicenter-based classification of PFMETs and its clinical and surgical implications with outcome. METHODS: On retrospective analysis of operated cases of intracranial epidermoid tumors, 19 (N = 19) patients having tumor epicenter within FV, CM, or both were included. Cerebellopontine and prepontine cistern epidermoid were excluded. Tumor location was decided based on preoperative MRI and intraoperative findings. Major complication was defined as new onset or worsening of cranial nerve (CN) deficit, sensory motor impairment, or tracheostomy.

RESULTS: The mean (±SD) age of the patients was 42.0 ± 11.6 years (range 25-61 years), with no sex predilection (male: female: 1:0.9). The most common symptoms were cerebellar dysfunction, headache, vomiting, and diplopia. Common CNs affected were VII, V, lower cranial nerve, and VI. The PFMETs were classified based on tumor epicenter as type 1 (tumor epicenter in CM, n = 4/21.1%), type 2 (FV, n = 5/26.3%), and type 3 (involved CM and FV, n = 10/52.6%). Type 2 tumors had a higher incidence of raised intracranial pressure and only facial nerve palsy as preoperative CN deficit. Type 1 tumors had the least incidence of postoperative major complications. Type 3 tumors were the largest and had a greater incidence of brainstem adhesion and postoperative complications. The tumor size, duration of symptoms, and patient age were higher in patients with brainstem adhesion (5.3 ± 1.0 cm, 21 ± 16 months, 44.1 ± 9.2 years) as against its absence (4.8 ± 1.3 cm, 11.2 ± 7.3 months, 38.2 ± 11.7 years). Inferior medullary velum and tela choroidea have a critical role in tumorogenesis, tumor extension, and brainstem adhesion.

CONCLUSION: PFMETs can be classified into 3 subtypes based on tumor epicenter having clinical and surgical implications. Less aggressive dissection and near total excision in the presence of brainstem adhesion yield favorable outcomes.

Neurosurgical management of intracranial epidermoid tumors in children

J Neurosurg Pediatrics 4:91-96, 2009

Epidermoid tumors are benign lesions representing 1% of all intracranial tumors. There have been few pediatric series of intracranial epidermoid tumors reported previously. The authors present their experience in the management of these lesions.

The neurosurgical database at the Hospital for Sick Children was searched for children with surgically managed intracranial epidermoid tumors. The patients’ charts were reviewed for demographic data, details of clinical presentation, surgical therapy, and follow-up. Ethics board approval was obtained for this study.

Seven children, all girls, were identified who met the inclusion criteria between 1980 and 2007. The average age at surgery was 11.2 years (range 8–15 years), and the mean maximal tumor diameter was 2.1 cm. Headache was the most common presenting symptom, and 1 tumor was found incidentally. Most patients had normal neurological examinations, but meningism was found in 2 cases. There were 3 cerebellopontine angle lesions, 1 pontomedullary lesion, and 3 supratentorial tumors. Hydrocephalus developed in 1 patient after aseptic meningitis, and she underwent shunt placement. There were no operative deaths. Complete resection could be performed in 2 patients. One patient experienced a small recurrence that did not require a repeated operation, while 1 subtotally resected lesion recurred and the patient underwent a second operation.

Conclusions: Intracranial epidermoid tumors are rare in the pediatric population. Total resection is desirable to minimize the risk of postoperative aseptic meningitis, hydrocephalus, and tumor recurrence. Aggressive neurosurgical resection may be associated with cranial nerve or ischemic deficits, however. In these cases, neurosurgical judgment at the time of surgery is warranted to ensure maximum resection while minimizing postoperative neurological deficits.