Ovoid Foramen Magnum Shape is Associated with Increased Complications and Decreased Extent of Resection for Anterolateral Foramen Magnum Meningiomas.

Antero-laterally located meningiomas of the foramen magnum (FM) pose significant surgical resection challenges. The effect of FM shape on surgical resection of FM meningiomas has not been previously studied. The present study investigates how FM shape effects the extent of tumor resection and complication rates in antero-lateral FM meningiomas.  This retrospective study included 16 consecutive patients with antero-lateral FM meningiomas operated on by a single surgeon. FMs were classified as ovoid (  = 8) and nonovoid (  = 8) using radiographic evaluation.  Sixteen patients were examined: seven males and nine females (mean age of 58.5, and range of 29 to 81 years). Gross total resection was achieved in 81% of patients, with tumor encased vertebral arteries in 44%. Patient characteristics were similar including age, sex, preoperative tumor volume, relationship of vertebral artery with tumor, preoperative Karnofsky performance score (KPS), symptom duration, and presence of lower cranial nerve symptoms. The ovoid FM group had lower volumetric extents of resection without statistical significance (93 ± 10 vs. 100 ± 0%,  = 0.069), more intraoperative blood loss (319 ± 75 vs. 219 ± 75 mL,  = 0.019), more complications per patient (1.9 ± 1.8 vs. 0.3 ± 0.4,  = 0.039), and poorer postoperative KPS (80 ± 21 vs. 96 ± 5,  = 0.007). Hypoglossal nerve palsy was more frequent in the ovoid FM group (38 vs. 13%).  This is the first study demonstrating that ovoid FMs may pose surgical challenges, poorer operative outcomes, and lower rates of extent of resection. Preoperative radiological investigation including morphometric FM measurement to determine if FMs are ovoid or nonovoid can improve surgical planning and complication avoidance.