When combined with a myelogram, a CT scan provides for excellent nerve detail. The myelogram adds some additional risk and expense to the CT scan but provides substantial information about the nerve roots.

A myelogram consists of injecting a radiographically opaque dye (dye that is picked up by x-ray) into the sac around the nerve roots, which in turn lights up the nerve roots.

The CT scan follows and shows how the bone is affecting the nerve roots. This is a very sensitive test for nerve impingement and can pick up even very subtle lesions (injuries) (see Figure 1).

The main risk with CT scans is that they use x-ray beams and should not be performed on pregnant women.

The main risk with a myelogram is the potential for a spinal headache. The spinal headache usually resolves in one to two days with rest and fluids, and seems to be more common for patients with a history of migraine headaches.

If the patient’s headache continues, some blood can be withdrawn from the patient's arm (antecubital vein) and then injected into the epidural space in the back (blood patch). This procedure places pressure over the site that is leaking spinal fluid to stop the leak and in turn resolve the headache.