gms | German Medical Science

Objective: To evaluate the significance for outcome of meningioma invasion into the internal auditory canal (IAC) in posterior fossa (CPA) meningiomas.

Method: From April 2005 to September 2015, a total of 174 posterior fossa meningiomas have been surgically treated in our institution. Careful analysis of preoperative MRI examinations depicted in 63 cases (36%) meningioma invasion into the IAC. A retrospective analysis was done of clinical and radiological presentation, surgical findings, outcome and relevant prognostic factors. All the variables were analyzed in order to stratify the risk of complication and evaluate the surgical outcome.

Results: There were 50 females and 13 males (median age 55 y, median FU19 months). Tumors were classified according to location as: pure CPA (41 pt), petroclival (19), jugular foramen (2) and tentorial (1) meningiomas. Presenting symptoms were hearing loss (37 pt), dizziness (27), trigeminal symptoms (15), tinnitus, gait instability, dysphagia and diplopia. Despite invasion of IAC by the tumor, 20 pt had normal hearing. Intraoperative monitoring included AEP, facial nerve EMG/MEP, SEP and MEP of extremities. Gross-total resection was achieved in 67% of patients, subtotal removal in 33%. There was no mortality. CSF leak occurred in 5%. In 17 pt (27%) IAC was opened (median tumor equivalent ellipsoid volume (TEV) 9 cm³). Immediate deterioration of facial function occurred in 24% of pt, hearing loss in 12% and CSF leak in 6%. In 46 pt (73%) IAC was not opened (median TEV 14 cm³). Immediate deterioration of facial function occurred in 43% of pt, hearing loss in 13% and CSF leak in 4%. Opening the IAC, a GTR was achieved in 82% while, without opening, GTR was achieved in 61% of pt. We found preoperative TEV for GTR as 9 cm³ and 19 cm³ for STR (p<0.03). Brainstem hyperintensity in MRI T2 sequences was associated with a higher risk of complications. The brainstem shift due to tumor compression was associated with a higher risk of facial palsy and hearing loss (p<0.01).

Conclusions: Meningiomas of the posterior fossa may in one-third of the cases invade the IAC. Opening of the IAC in these cases was a crucial step for increasing the GTR. Despite the minimal increased risk of transient CSF leak, opening the IAC was not associated with an increased risk of facial palsy or hearing loss in comparison to non-opening the IAC. However, IAC opening was more frequent in smaller tumors than in large tumors.