How do a lumbar puncture and a myelogram differ?

Lumbar puncture: The spinal cord has three layers, the dura, arachnoid and the pia. The cerebrospinal fluid is sub arachnoid. A "lumbar puncture" is placing a spinal needle to access the cerebrospinal fluid. A myelogram is a diagnostic procedure usually for spine related pain that requires a lumbar puncture to inject contrast or dye into the cerebrospinal fluid after which an xray and usually ct scan are done.

See below: A LP involves withdrawing cerebrospinal fluid for study. A myelogram involves injecting a special dye for evaluation of spinal pathology. The placement and location of the needle are the same for both procedures.