Metastases from WHO Grade III Meningiomas

Background: Meningioma metastases are rare, with an estimated incidence of 1 in 1000 quoted in the literature. While cases of metastases to the lungs, liver, vertebrae, distant cranial sites, and other locations have been reported, they are so uncommon that patient’s are rarely screened for metastases. Unlike WHO Grade I meningiomas, WHO Grade III meningiomas can be very aggressive, invading locally, and in our experience, metastasizing to distant cranial, as well as extra-cranial sites. Recently, patients with WHO Grade III meningiomas treated at our institution began undergoing screening PET or CT scans prior to additional intervention. Here, we report our experience with metastases from WHO Grade III meningiomas.

Methods: A retrospective review of 2,120 patients who underwent surgery for resection of meningioma from 1985–2015 meningiomas was conducted. Clinical information was extracted from the chart using electronic medical records, radiology data, and pathology data. All records of patient’s with malignant meningioma were reviewed to evaluate for metastases. Tumor volumes were calculated using tumor dimensions from pre-operative imaging studies. Survival analysis was performed with the Kaplan-Meier method.

Results: Of 2,120 patients with meningioma, 75 were WHO grade III (3.5%). Median age at diagnosis of WHO Grade III meningioma was 48.5 years and 53% were female. Median follow-up time was 5 years (range 0–30 years). Median pre-operative tumor volume was 26.4 cubic centimeters. Seventeen patients (23%) progressed from lower grade tumors to WHO grade III. Nine patients were identified with distant metastases from the primary site. The incidence of metastases was 0.4% among all grades of meningioma and 12% among WHO grade III meningioma. Median age at time of metastasis was 51.7 years, and median follow-up time for patients with metastases was 8 years (range 3–30 years). Five patients had metastases outside the central nervous system (6.6% of WHO Grade III patients), most frequently in liver (3), bone (3), and lung (2). Four patients had central nervous system/cranial metastases (5.3%), including distant skull base, drop metastasis to spinal dura, opposite sided scalp, and the subependymal layer of the lateral ventricle. Interestingly, only 18 of 75 patients were evaluated for metastases (PET scan or screening CT scan). Patients with metastases had a median 3 prior surgical resections 8 of 9 had undergone adjuvant radiotherapy. Median survival after diagnosis of metastases was 38 months.

Conclusion: Meningioma metastases are rare in our cohort of more than 2000 patients, but occur at a higher rate than previously estimated, and are surprisingly common among WHO Grade III meningiomas, occurring in 12% of patients. These numbers likely underestimate the actual incidence because patients were not screened for metastases until recently. Given these findings, we suggest that neurosurgeons consider screening patient’s with recurrent WHO Grade III meningiomas for metastases as part of the pre-operative workup for additional surgery.