Incidence of Surgery after Gamma Knife Radiosurgery for Parasagittal Meningiomas Is Higher than Meningiomas in Other Locations: A 10-Year Review

Background: Gamma Knife radiosurgery (GKRS) and surgical resection are a well-established and accepted potential first line treatment modalities for meningiomas. Many factors play a role in the decision making for treatment. There are certain cases which necessitate surgical intervention even after GK treatment due to continued tumor growth or patient symptoms. Evaluating the tumor characteristics in such cases can lead to improved decision making for which primary treatment is preferred, and how to better guide the patients on the options they have.

Methods: A retrospective review evaluating each meningioma receiving GKRS treatment at the Medical College of Wisconsin between 2009 and 2019. The patient’s charts and relevant imaging were reviewed.

Results: There were 132 total treatments for meningiomas on 124 different patients, 39 (31.5%) of these were parasagittal meningiomas. The female to male ratio for this group was 2.25:1 and the average age was 61 (range, 28–86). We found a 17.9% incidence of parasagittal meningiomas requiring surgical intervention after treatment with GKRS, compared with a 3.5% incidence of tumors in other locations. The average tumor size (maximum diameter) for the parasagittal meningiomas was 21.8 mm with a range of 10 to 31 mm. The average radiation treatment dose prescribed for these tumors was 14 Gy at the 50% isodose line with a range of 12 to 15 gray. The time from GKRS to open surgery ranged from 6 to 67 months with 4 patients (57%) occurring within 9 months of GKRS treatment, and the most common reason leading to surgery was increased brain edema with worsening symptoms in all seven patients. In addition, one tumor exhibited tumor growth and two patients had a new onset seizure.

Conclusion: Surgery after GKRS for parasagittal meningiomas may be more common than previously thought. This is likely a result of peritumor edema from the treatment. This information can help guide patient and physician discussion in regard to preferred first line treatment for these parasagittal meningiomas.