Percutaneous biopsy of a metastatic spinal nerve root nodule in a child.

Nodular deposits on lumbar nerve roots are a well recognized manifestation of metastatic spread of certain intracranial tumors, particularly medulloblastoma and ependymoma, via the subarachnoid pathway. The histologic diagnosis usually is established at the time of posterior fossa exploration. However, obtaining a diagnosis at surgery can be hazardous in some intraaxial masses that do not have an exophytic component. If subarachnoid nodular implants are present, a percutaneous biopsy may be performed to establish the exact diagnosis.