Diastematomyelia: hemicord and meningeal sheaths; single and double arachnoid and dural tubes.

Metrizamide computed tomographic myelography demonstrates well: partial- and full-thickness diastematomyelia; the presence, shape, and (a)symmetry of the two hemicords; focal persistence of two anterior spinal arteries, one supplying each hemicord; the single or double subarachnoid space(s), arachnoid tubes, and dural tubes which encompass the hemicords; the dural septum formed by the medial walls of the two dural tubes; the dural cleft situated between the two walls of the dural septum; the bone spur within the dural cleft; and the presence of any tethering dorsal fibrous bands or aberrant dorsal nerve roots.