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 vertebraes become large and irregular. This is becasue 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 anatomy chapter) 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 chapter on lumbar disc herniation).

Disc bulge - this describes the condition where the nucleus pulposus (see the anatomy chapter) 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 chapter on lumbar disc bulge).

Broad based disc herniation - this is where the disc is damaged on a wide front 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 is projecting beyond the confines of the annular fibres.

Foraminal disc herniation - in these cases the disc herniation is on the side of the spinal canal where the nerve roots leave the spinal canal through the foraminas. Even relatively small disc prolapses or hernias can cause a lot of pain or even weakness as the spac is very restricted in this area.
Extra foraminal disc compression - in this instance the nerve is compressed outside of the spinal canal and outside of the foramen as it leaves on it’s 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 to a foramnial disc prolapse before symptoms occur. In some cases the spinal canal is already partly occluded by facet joint hypertrophy and compression from the ligamnet inside the spinal canal - the ligamentum flavum - and even small disc hernaitions can cause symptoms in these cases.

Thecal sac - this is the name given for the elongated 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 continous with - the mebrane that covers the brain.

Flattening of the thecal sac - this is a description of the situation which 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 - these are the nerve roots that leave the thecal sac and exit the spine through the intervertebral foramens. The most of the exiting nerve roots can be ssen end - on in the axial planes as well as the coronal planes and are seen end - on in the sagittal plane.

Foraminal stenosis - this is when the exiting nerve root is compressed in the formane 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 one lower down 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 that support the facet joints is weak and fractures.

Spondylosis - this describes bony overgrowths (osteophytes) that grow on the vertebral bodies and are usually asymptomatic.

Synovial cyst - the joint space of the facet joints are lined with a membrae - the synovial membrane - which allows for free and easy movement of the joint. Sometimes as the joints become damaged, this sinovial 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 are usually benign, but they can cause nerve compression and foramnial stenosis.

Tarlov cyst - these cysts are filled with spinal fluid and develop in the membrane that covers the nerve roots. If they are large, they can cause nerve compression and pain. Surgery for these benign lesions can be difficult and is somewhat controversial. The diagnosis is made based on the fact that these cysts are in direct contact with a nerve root.

Arachnoid cyst - these are once again benign lesions and are formed from the inner layer of the covering of the spinal cord. They are usually asymptomatic and will only require surgery if they are very large and causing symptoms secondary to nerve compression

Cauda equina - this term is Latin for the horses (equina) tail (cauda). It is called like this because the nerve roots that dangle down from where the spinal cord ends. Looks like a horses tail. The spinal cord ends at approximately the level of the first lumbar vertebra and the nerve roots then are left dangling downward, like a horses tail. When these nerve roots become compressed the resulting syndrome of pain, weakness and paresthesias (pins and needles) in the legs with associated bladder and bowel dysfunction, is called cauda equinal syndrome.

Conus medularris (conus) - this is the name given to the end of the spinal cord. It has a tepered 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 continouation of the conus medullaris and is the thin cord-like structure that extends down to the end of the spinal canal.