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Summer 2007

MR Neurography and CT Guide Pain-Blocking Injections

Judy Flores' troubles started three years ago, when she began having excruciating shooting pains down her left hip and leg. Her physician determined that the piriform muscle was irritating the sciatic nerve. He recommended surgery to remove the muscle. Four months after she underwent the surgery, Flores was crossing the street one day when a car struck her, hitting her in the same area that was still healing from the surgery.

"It was horrible," says Flores, 43, who works in a medical group's billing department. The double whammy of the surgery and the accident left her in chronic pain. Flores tried acupuncture and cortisone injections, but neither provided much relief. Finally, she went to see UCSF neuroradiologist Cynthia Chin, M.D., who uses a particularly effective technique for eradicating pain: a CT scan-guided nerve block.

The technique, says Chin, grew out of recognition of the limits of the standard methods for banishing chronic pain. Nerve block injections relieve pain by delivering a combination of anesthetic and steroid medication to a nerve that's been inflamed by such problems as injury, bone spurs or degenerative disease. Yet often, the doctor wielding the syringe is "operating blindly," says Chin—uncertain of the precise location of the source of the pain or the best site for the injection. Thus, intramuscular cortisone injections help only to the extent that the physician has managed to hit a spot for the injection that is close to the inflamed nerve.

X-ray-guided injections are slightly more precise. But since standard X-rays show only bone and not soft tissue, there's still a risk that the nerve block may not be delivered to exactly the right spot. Using MR neurography, a new T2-weighted MR technique that identifies abnormal peripheral nerves, neuroradiologists can actually see inflamed nerves beyond the spinal canal.

Armed with that information, Chin uses CT to accurately plan where to place the needle, the angle of entry and how deep to go to deliver the nerve block to the precise location where it is needed. "With MR and CT, we are able to increase the precision and accuracy of where we place our needle," Chin says. "The improved precision extended by CT and MR guidance decreases the risk of injury to the nerve and other surrounding structures."

The procedure is most beneficial for patients who have anatomical complications—such as scoliosis or surgical scars—that can make it difficult to determine the anatomical position of the affected nerve. Most people only need one or two treatments to resolve their pain. Flores needs them every two months because her body is still recovering from the surgery and the car accident. Still, the relief each treatment brings has made all the difference in the world. The pain starts diminishing immediately, and within two weeks it is completely gone, Flores says.

Dr. Cynthia Chin can be reached at (415) 353-1537.
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