Benign Enhancing Foramen Magnum Lesions

Abstract

Benign enhancing foramen magnum lesions have been previously described as T2-hyperintense small, enhancing lesions located posterior to the intradural vertebral artery. We present the first case with pathologic correlation. These lesions are fibrotic nodules adhering to the spinal accessory nerve. While they can enlarge with time on subsequent examinations, on the basis of the imaging characteristics and location, they do not necessitate surgical resection.

FIG 1.

Multiple axial images show 2 intradural extramedullary lesions (solid arrows) at the foramen magnum posterior to the vertebral arteries, superior to their dural insertion. The lesions demonstrate hyperintense signal on T2-weighted FLAIR imaging (A), are isointense to CSF on T2-weighted imaging (B), and are avidly enhancing (C). FIESTA imaging (D) shows contact with the spinal accessory nerve (broken arrows).

FIG 2.

Intraoperative photograph demonstrates the lesion with a superficial yellow membrane over an apparent cyst with a more solid and firm component deep to that. The lesion was adherent to a lower cranial nerve, identified as the left SAN on intraoperative nerve monitoring.

FIG 3.

H&E sections of the resected specimen illustrate the densely fibrotic nodule (A), involving the arachnoid (B). Small nests of meningothelial cap cells with focal psammoma body formation are present (C), adjacent to the nodule.