Terminology for CT scans and MRI scans (Lumbar region)

Spinal stenosis – This means that the spinal canal is narrowed. This is usually because the joints that are between the vertebrae, called the facet joints, have hypertrophied (become larger) secondarily to osteoarthrosis of these joints. At the same time the ligament that runs inside the spinal canal, the ligamentum flavum, has also hypertrophied and is pushing on the nerves. The third component that causes spinal stenosis is the pressure from discs that push into the spinal canal.

Facet joint hypertrophy – This is when the joints between the vertebrae become large and irregular. This is because the joints are damaged by arthritis (osteoarthritis).

Annular tear – This describes the condition where the intervertebral disc has early damage. The damage comprises of a tear in the annulus fibrosus (see the section Anatomy of the Spine). The tear causes different inflammatory substances to be released by the body and this can cause local back pain, referred pain and even radiculopathy (see the section Lumbar Slipped Disc).

Disc bulge – This describes the condition where the nucleus pulposus (see the section Anatomy of the Spine) starts to bulge through the damaged annular fibres.

Disc herniation/disc extrusion – Both these terms mean that a portion of the nucleus pulposus has now extended outside of the confines of the annular fibres into the spinal canal (see the section Lumbar Slipped Disc).

Broad-based disc herniation – This is where the disc is damaged extensively and there is usually a decrease in the height of the disc and the disc looks a bit like a flat tyre with the whole or a large part of the nucleus projecting  beyond the confines of the annular fibres.

Foraminal disc herniation – In this case the disc herniation is on the side of the spinal canal where the nerve roots leave the spinal canal through the foramina. Even relatively small disc prolapses or hernias can cause a lot of pain or even weakness, as the space is very restricted in this area.

Extraforaminal disc compression – In this instance the nerve is compressed outside of the spinal canal and outside of the foramen as it leaves on its way to the leg. This is usually caused by a broad-based disc herniation.

Central disc herniation – This is where the disc herniation is in the middle of the spinal canal. Since this is a fairly large space, the disc herniation needs to be fairly large compared with a foraminal disc prolapse before symptoms occur. In some cases the spinal canal is already partly occluded by facet joint hypertrophy and compression from the ligament inside the spinal canal – the ligamentum flavum – and even small disc herniations can cause symptoms in these cases.

Thecal sac – This is the name given for the elongated membraneous tube that extends from the brain to the end of the spine in which the spinal cord and nerve roots run. It is made up of – and is continuous with – the membrane that covers the brain.

Flattening of the thecal sac – This is a description of the situation that occurs when a herniated (slipped or prolapsed) disc has extended so far into the spinal canal that it is pushing on the thecal sac.

Nerve root – This is the nerve root that leaves the thecal sac and exit the spine through the intervertebral foramen. Most of the exiting nerve roots can be seen side-on in the axial planes as well as the coronal planes and are seen end-on in the sagittal plane.

Foraminal stenosis – This is a narrowing of the foramen and the exiting nerve root can become compressed in the foramen by either a disc herniation or a hypertrophied facet joint or a combination of both.

Spondylolisthesis – This is the term that describes a slip of one vertebra on the vertebra directly below and is secondary to a weakness in the bone that supports the facet joints that keep the spine stable.

Spondylolysis – This is frequently the cause for spondylolisthesis and is the process where the bone supporting the facet joints is weak and fractures.

Spondylosis – This is spinal degeneration and is characterised by bone spurs  (osteophytes) that develop on the vertebral bodies and are usually asymptomatic, except if they compress nerves.

Synovial cyst – The joint space of the facet joints are lined with a membrane – the synovial membrane – which allows for free and easy movement of the joint. Sometimes, as the joints become damaged, this synovial membrane can bulge out and form a cyst. The cyst is filled with synovial fluid that is usually found in the joint space for lubrication. These are completely benign (harmless) lesions and should not be confused with cancerous lesions. They can, however, cause nerve compression and foraminal stenosis.
Tarlov cyst – This cyst is filled with spinal fluid and develop in the membrane that covers the nerve roots. If it is large, it can cause nerve compression and pain. Surgery for this benign lesion can be difficult. The diagnosis is made based on the fact that the cyst is in direct contact with a nerve root.

Arachnoid cyst – This is also a benign lesion and is formed from the inner layer of the covering of the spinal cord. It is usually asymptomatic and will only require surgery if it is very large and is causing symptoms secondary to nerve compression.

Cauda Equina – This term is Latin for horse’s (Equina) tail (Cauda). It describes the nerve roots that dangle down from where the spinal cord ends and looks like a horse's tail. The spinal cord ends at approximately the level of the first lumbar vertebra. When these nerve roots become compressed the resulting syndrome of pain, weakness  and paraesthesia (pins and needles) in the legs with associated bladder and bowel dysfunction is called Cauda Equina syndrome. This is a spinal emergency and requires immediate surgery.

Conus Medullaris (Conus) – This is the name given to the end of the spinal cord. It has a tapered conical shape and the nerve roots of the Cauda Equina exit from here. It is usually at the level of the first lumbar vertebra.

Filum Terminale (Filum) – This is the continuation of the conus medullaris and is the thin cord-like structure that extends down to the end of the spinal canal.


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This website is a patient resource compiled from information from leading spinal surgeons practicing in South Africa and complements the My Spine – Lumbar and My Spine – Cervical information booklets that you can obtain directly from your spinal specialist. You will find information about spinal conditions and treatment on this website.

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My Spine – Lumbar and My Spine – Cervical information booklets are now directly available from your spinal specialist. All patients that are undergoing spinal surgery in South Africa should have access to these booklets. Please ask your specialist at your pre-operative visit about these booklets.