Giant intradural extramedullary spinal ependymoma, a rare arachnoiditis-mimicking condition: case report and literature review.

Ependymomas are tumours arising from the ependymal cells lining the ventricles and the central canal of the spinal cord. They represent the most common intramedullary spinal cord tumour in adults and are very rarely encountered in an extramedullary location. Only 40 cases of intradural extramedullary (IDEM) ependymomas have been reported, all of which were diagnosed pre-operatively as IDEM ependymomas on contrast-enhanced MRI. We report a 23-year old male presenting with rapidly worsening signs and symptoms of spinal cord disease. A spinal MRI demonstrated a posterior multi-cystic dilatation extended between T1 and T12. Post-contrast sequences showed peri-medullar leptomeningeal enhancement and the diagnosis of spinal arachnoiditis was made. The patient underwent surgery and the spinal cord appeared circumferentially wrapped by an irregular soft tissue. The tissue was sub-totally removed and the pathological diagnosis was ependymoma WHO grade II. The patient experienced an excellent neurological recovery and no further treatments were administered. A small residue is now stable at 2.5 years follow-up. Giant IDEM ependymomas are rare entities and pre-operative diagnosis can be challenging in some cases. Surgery represents the main treatment option being resolutive in most cases.