--of lower thoracic/lumbar/sacral spine; MRI's are better at picking up nerve impingment at those levels than CT.

Also, it's entirely possible, given that the CT results were not severely abnormal (most of us have disc bulges/arthritic changes in a number of areas in the spine as we age, but not all of us encounter symptoms) that the issue is coming from farther down the leg, along the thigh (piriformis areas), at the knee (a site at which compressive neuropathies are common) or even at the lower calf/tarsal tunnel areas.

Take a look at:

http://www.myfootshop.com/detail.asp...nel%20Syndrome

http://emedicine.medscape.com/article/1234809-overview

http://emedicine.medscape.com/articl...overview#a0104