Imaging description

Apparent anterior displacement of the thoracic cord on sagittal T2-weighted MRI with expansion of the CSF space posterior to the cord in patients with myelopathy is a frequently missed finding (Fig. 104.1). Approximation of the entire thoracic cord to the ventral aspect of the canal is a common normal finding, particularly in patients with accentuated kyphosis. When this happens in a focal area with associated cord contour deformity, radiologists should suspect a CSF-signal space-occupying structure (i.e., intradural arachnoid cyst) that is pushing the cord (Fig. 104.2) or an anterior thoracic cord herniation that is pulling the cord (Fig. 104.3). Alternatively, intradural arachnoid bands can tether the cord and result in a similar appearance (Fig. 104.4). CT myelography is often diagnostic and can differentiate between these possibilities.

Intradural arachnoid cysts are congenital cysts and they are nearly always posterior to the cord [1]. Eighty percent of them are located in the thoracic spine. Most intradural arachnoid cysts are connected to the subarachnoid space and show gradual filling on myelography, with a minority presenting as a filling defect. Intradural cysts anterior to the spinal cord are unlikely to be congenital in origin and may develop on the basis of prior subarachnoid hemorrhage and archnoiditis [2].