Health Tests

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Harvard Medical School


What Happens During the Test?

Patients usually wear a hospital gown. Typically, you lie on your side with your knees curled up against your chest. In some cases, the doctor asks you to sit on the bed or a table instead, leaning forward against some pillows.

The doctor feels your back to locate your lower vertebrae and feels the bones in the back of your pelvis. An area on your lower back is cleaned with soap. Medicine is injected through a small needle to numb the skin and the tissue underneath the skin in the area. This causes some very brief stinging.

A different needle is then placed in the same area and moved forward until fluid can be injected through it into the spinal canal. This fluid is a type of dye that shows up on x-rays; this allows your doctors to get a clear picture of the fluid space around your spinal cord and to see places where the space is narrowed by bones around it. Because the needle must be placed through a small opening between two bones, the doctor must sometimes move the needle in and out several times to locate the opening. Because of the numbing medicine used in this area, most patients experience only a feeling of pressure from this movement. Occasionally some patients do get a sharp feeling in the back or (rarely) in the leg. Let your doctor know if you feel any pain.

Once the dye has been injected, the needle is removed and several x-ray pictures are taken of your back. Sometimes a CT (computed tomography) scan picture is taken instead.

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