Meningioma of the conus medullaris mimicking neurofibroma--possibly radiation induced

Background context: Radiation-induced meningiomas (RIMs) of the brain are the most common RIMs. However, there has been no report in the literature of an RIM of the spine. Conus medullaris is a favorite site for ependymomas, whereas it is an extremely rare location for meningiomas. Dumbbell-shaped configuration is typical for nerve sheath tumors; however, it is very rarely seen in meningiomas.

Purpose: To describe imaging findings of a possibly RIM at the level of the conus medullaris mimicking a neurofibroma.

Study design: A 60-year-old male with 6-year history of irradiated urinary bladder cancer presented with paraparesis.

Methods: Radiography, computed tomography, and magnetic resonance imaging of the thoracolumbar spine were undertaken.

Results: Radiography showed widening of intervertebral foramina at T12-L1 level. Computed tomography and magnetic resonance imaging disclosed a lobulated intradural mass at the level of the conus medullaris causing widening and scalloping of adjacent bony structures, with dumbbell-shaped configuration. Surgical biopsy of the mass was consistent with fibroblastic meningioma.

Conclusions: The reported tumor might have developed secondary to irradiation for urinary bladder cancer because meningiomas are the most common radiation-induced central nervous system tumors. Although location at the level of the conus medullaris is atypical for meningioma, and dumbbell-shaped configuration is rather characteristic for neurogenic tumors, they should not exclude a diagnosis of meningioma.