Compression of the thecal sac means the protective membrane covering the spinal cord is experiencing extra pressure, according to Merck Manuals. Effacement of the thecal sac means that the thecal sac is being shortened or narrowed, according to the Free Dictionary.
Effacement of the thecal sac and compression of the thecal sac are diagnoses frequently found on MRI imaging reports for patients complaining of back pain, according to ChiroGeek. MRI scans are typically performed to aid physicians in diagnosing the sources of lumbar or radicular pain in the lower back.
The thecal sac could be compressed by bone, the accumulation of blood, abscesses, tumors or a ruptured or herniated vertebral disk, according to Merck Manuals. Thecal sac compression also could result from the hardening of certain connective tissues as one ages. Compressive forces from hypertrophy of ligamentum flavum also could be impacting the thecal sac, according to ChiroGeek.
Though severe thecal sac compression may limit proper circulation of cerebral spinal fluid, most cases of impingement on the sac generally resolve without treatment, according to The Back Pain Authority. Disc herniations of the central vertebrae are most likely to impinge upon the thecal sac. Thecal sac compression usually produces no noticeable symptoms.