Arachnoiditis ossiflcans of the thoracic spinal canal: a diagnostic enigma

A 65-year-old woman presented with progressive difficulty walking and sensory disturbances of the lower extremities. Plain radiographs of the thoracic spine were normal. Interpretation of magnetic resonance imaging suggested an intramedullary thoracic spinal cord tumour. However, computed tomographic myelography revealed an intradural extramedullary cystic T10 lesion compressing the spinal cord. Intraoperatively, we found a collar-like, hard mass, with hypertrophic arachnoid, and cyst formation. Histological evaluation disclosed a mesenchymal lesion composed of dense fibrous dura and arachnoid-meningeal tissue with prominent ossification. The discrepant radiological findings [combined with the difficulty arriving at a specific pathological diagnosis] contributed to the challenging nature of this case