While there are differences in how stenosis can affect the anatomy, all forms of stenosis are typically referred to as simply spinal stenosis.
In general, there are three main types of spinal stenosis:
Foraminal stenosis is most common type of lumbar spinal stenosis, and may also be referred to as lateral spinal stenosis. As the nerve root is about to leave the canal through a side hole in the back of the spine, called the neuro-foramen, a bone spur (osteophyte) that has already developed from a degenerating disc, or an arthritic facet joint, can press on that nerve root.
With this type of stenosis, the emerging nerve root is trapped (for example, the L4 to S1 individual spine nerves that form the sciatic nerve). This type of spinal stenosis can easily be visualized as a pinching of the nerves.
Narrowing of the central canal (called central stenosis) in the lumbar (low back) area can compress the thecal sac. This narrowing can cause pressure on the nerve bundle at the end of the spinal cord (cauda equina), or the individual nerves within the thecal sac.
Far lateral stenosis
The individual nerves exit from the center of the spinal canal out hole in the back of the spine called the neuro-foramen. Beyond the neuro-foramen, there can also be narrowing secondary to the development of bone spurs from the facet joints, bulging discs, herniated discs, and ligamentum hypertrophy. This narrowing of the area lateral, or to the side of the neuro-foramen is called far lateral stenosis. There is often a combination of foraminal and far lateral stenosis.
If spinal stenosis surgery is to be performed, the different locations and types of compression are important to identify in order to guide the surgeon. With the proper imaging studies, the surgeon will plan a focused approach to the areas of spinal stenosis. Subtle differences between central, foraminal, and far lateral locations need to be defined, and deliberate planning is necessary to address all the potential areas.