MR imaging of traumatic spinal arachnoid cyst.

We report a case of post-traumatic lumbar arachnoid cyst, which enlarged the spinal canal and eroded the posterior elements. Computed tomographic myelography and magnetic resonance (MR) were complementary, and both correctly characterized the cystic nature of the lesion. Communication between the cyst and the subarachnoid space was demonstrated on CT myelography, which also clearly showed bone changes in the spinal canal. Continuity of the cyst with the spinal subarachnoid space was seen clearly on sagittal MR, and the MR signal characteristics of the cyst were identical with CSF.