Residual and Recurrent Disease after Endoscopic Endonasal Approach to Midline Anterior Skull Base Meningiomas

Introduction: Endoscopic endonasal approaches (EEA) to the anterior skull base have grown in popularity in the past several years. Despite several recent reports describing the efficacy of EEA to the midline anterior skull base, its use for meningiomas remains controversial. One of the barriers to utilizing EEA for the resection of anterior skull base meningiomas is the controversy pertaining to limitations of resection for these difficult cases as well as the role of the learning curve.

Methods: Retrospective chart review was performed for all patients that underwent EEA for resection of meningiomas originating at the olfactory groove, planum sphenoidale or tuberculum sella at our institution from July 2005 to June 2014. A minimum two-year radiographic follow up was required and patient demographics, pathology, tumor characteristics and timing of recurrence was collected.

Results: 100 patients met selection criteria and underwent chart review. Follow up averaged 46.9 months (range 24 to 100 months). 35 patients (35%) had meningiomas originating at the olfactory groove, 33 were at the planum sphenoidale (33%) and 32 at the tuberculum sella (32%). The average maximum diameter was 2.9 cm with a range of 0.5–8.1 cm. Olfactory groove meningiomas were the largest with a mean of 4.0 cm, while planum tumors averaged 2.8 cm and tuberculum tumors only 1.9 cm. 67 meningiomas (67%) were considered round in shape, while 33 (33%) were classified as lobular. Vascular encasement was seen in 11 patients (11%) and calcification was present in 20 patients (20%).

Simpson grade 1 gross total resection was achieved in 64 patients (64%), while 36 patients (36%) were found to have residual tumor. The most common location of residual tumor was the dura lining the anterior clinoid process in 11 patients (11%). Seven patients (7%) had residual tumor in the optic canal with five (5%) of these located superolateral, one superior (1%) and one medial (1%) to the optic nerve. Residual tumor was also found at the anterior falx, adherent to the optic apparatus or adherent to vascular structures in 5 patients each (5%) while 3 patients (3%) had residual tumor on the dura lining the orbital roof. In addition, the rate of residual decreased over time from 13/25 (52%) in the first quartile to 6/25 (24%) in the final quartile despite similar tumor sizes. 11 patients (11%) were found to have tumor recurrence with a mean recurrence time of 40 months. Among these, four (4%) were in the optic canal with two (2%) superolateral and one (1%) each superior and medial to the optic nerve respectively. In addition, two (2%) were at the orbital roof, anterior clinoid or adherent to an optic nerve and one (1%) at the anterior falx.

Conclusions: Meningiomas of the midline anterior skull base can effectively be approached via EEA in most patients, however, tumors extending to the anterior clinoid, anterior falx, superolateral optic canal or orbital roof may also be difficult to reach via EEA and tumors with clear involvement of these regions should be considered for another approach.