Spinal extradural arachnoid cyst causing paraparesis in a child.

Spinal extradural arachnoid cyst is a rare condition, commonly located in the thoracic spine. It can be asymptomatic or present with symptoms of myelopathy due to spinal cord or nerve root compression. MRI is the initial imaging modality to diagnose this condition. CT myelography is the imaging modality of choice for detecting the actual site of communication between the subarachnoid space and arachnoid cysts; hence, it plays a pivotal role in surgical planning. We describe the imaging features of a symptomatic large spinal extradural arachnoid cyst and cord changes in a 12-year-old boy, who presented with paraparesis. CT and MR myelography helped in surgical planning by delineating the cyst morphology and the dural defect. It is an uncommon cause of myelopathy and must be accurately identified through imaging.