Merck Manuals says that when the thecal sac is compressed, the membrane that protects the spinal cord is put under more pressure. The Free Dictionary says that effacement of the thecal sac means that the thecal sac is getting smaller.
ChiroGeek says that MRI reports for people with back pain often include the diagnoses “effacement of the thecal sac” and “compression of the thecal sac.” MRI scans are often used to help doctors figure out what is causing lumbar or radicular pain in the lower back.
Merck Manuals says that the thecal sac could be squeezed by bone, a buildup of blood, an abscess, a tumour, or a ruptured or herniated vertebral disc. Thecal sac compression could also happen if some connective tissues get harder as a person ages.
ChiroGeek says that the thecal sac could also be affected by the compression forces that come from the thickening of the ligamentum flavum.
The Back Pain Authority says that most cases of impingement on the sac get better on their own. Even though severe thecal sac compression can stop the proper flow of cerebral spinal fluid, most cases of impingement on the sac get better on their own.
Most likely to press on the thecal sac are herniated discs in the middle vertebrae. Most of the time, there are no symptoms when the thecal sac is compressed.