Validity of the frontolateral approach as a minimally invasive corridor for olfactory groove meningiomas.

Background: Several approaches are described for olfactory groove meningiomas (OGMs) varying from a very wide bifrontal craniotomy to minimally invasive endoscopic techniques. The goal of this study was to evaluate the results of the frontolateral approach for olfactory groove meningioma. Pitfalls related to this corridor will be described. The impact of tumor size and encasement of the anterior cerebral artery complex on the degree of tumor removal will be described on the basis of experience with 18 cases.

Methods: Eighteen patients with OGM underwent microsurgical removal using the frontolateral approach. A retrospective study was conducted by analyzing clinical data, neuroimaging studies, operative findings, clinical outcome, and degree of tumor removal.

Findings: The patients were classified into group A with tumor size less than 4 cm in diameter (7 out of 18 cases, 38.9%) and group B with tumor size more than 4 cm in diameter (11 out of 18 cases, 61.1%). CSF rhinorrhea was observed in three patients (16.7%). Postoperative left frontal intracerebral hematoma occurred in one patient (5.6%) belonging to group A. In another patient (5.6%) belonging to group B, marked right frontal lobe swelling was evident after dural opening, which necessitated partial right frontal pole resection. Total tumor removal (Simpson grade 1 and 2) was achieved in 14 out of 18 patients (77.8%), while subtotal removal (Simpson grade 3 and 4) was achieved in 4 patients (22.2%). In the 14 patients in whom total removal was achieved, 7 belonged to group A (all 7 patients of group A with 100% removal), while the remaining 7 patients belonged to group B (7 out of 11 patients, 63.6% removal; one of them had anterior cerebral artery complex encasement). The four patients in whom subtotal removal was achieved belonged to group B; three of them showed anterior cerebral artery complex encasement, and one elderly patient had non-extensive paranasal sinus involvement. One patient (5.6%) in group B died from cerebral infarction after subtotal tumor removal with anterior cerebral artery injury during its dissection from the tumor capsule.

Conclusion: The frontolateral approach has the advantages of both the pterional and conventional bifrontal approaches. The frontolateral approach allows quick and minimally invasive access to OGMs less than 4 cm in diameter, and also to tumors more than 4 cm in diameter without encasement of the anterior cerebral artery complex. Tumor size more than 4 cm in diameter and encasement of the anterior cerebral artery complex are limiting factors for the frontolateral approach if radical tumor removal is considered.