Nerve Root Encroachment

Depiction of a herniated disc
Depiction of a herniated disc. Medical Art Inc/E+/Getty Images

Encroachment refers to the process by which spinal spaces, such as the foramina or the spinal canal, become occupied by a piece of tissue that does not belong there. Nerve root encroachment, specifically, affects the area in the foramina.

Both the spinal canal and the intervertebral foramina contain nervous tissue — the spinal cord in the spinal canal, and spinal nerve roots in the foramina. When abnormal tissue, whether it's a bone spur, a thickened ligament, migrated disc material or even a synovial cyst, takes over some part or all of the space, it moves in on the nerves that are located there.

The contact between the encroaching tissue and the nerves on which that tissue imposes will likely cause pain and/or other symptoms.

When you have nerve root encroachment, the imposing tissue compresses or irritates the spinal nerve root. The spinal nerve root is a collection of nerves that have branched off the main spinal cord and are on their way out to serve the rest of the body (by relaying sensations and impulses to move to and from the brain.) The spinal nerve roots are located in the foramina.  

Symptoms associated with nerve root compression (and therefore in many cases of encroachment) include back pain and/or weakness, numbness or electrical sensations that go down one leg.

What Causes Nerve Root Encroachment?

Nerve root encroachment is most often caused by degenerative changes in the spine.

Degenerative changes are usually associated with central canal stenosis (i.e., spinal stenosis that affects the spinal canal, described above) as well as neuroforaminal stenosis, (which is spinal stenosis that affects the intervertebral foramina, also described above.)

Should You Have Preventative Surgery for Encroachment?

Some spine specialists encourage their patients with encroachment to agree to a preventative decompression surgery. (Decompression surgery is a commonly performed back procedure that removes part of the vertebra in order to make room for the nerve material to pass unimpeded through its respective space.)  

What these surgeons are likely trying to tell you — and many truly believe this — is that even with minor trauma, your risk for spinal cord injury is higher because of the encroachment.

Spinal cord injury is a very serious injury that can result in death or paralysis. It's usually caused by trauma or impact.

A 2015 study by Chang, et. al. published in the October issue of the journal Neurosurgery looked into this issue because, the authors say, patients who have cervical stenosis but who either experience mild symptoms or none at all commonly have the decompression surgery recommended to them — again, supposedly to reduce or eliminate the risk of paralysis after a traumatic event.  

The researchers examined 55 cervical stenosis patients with an exam and an x-ray. The patients were also surveyed with questions such as:

  • Has a physician recommended neck surgery to you?
  • Has a physician ever indicated that you would become paralyzed after a traumatic event?
  • During the follow up period for this study, did you experience a traumatic event?

The researchers found that 18% of the patients did experience a traumatic event after the surgery, but none of them injured their spinal cord. The authors conclude that the "occurrence of spinal cord injury (SCI) in this patient population after minor trauma is likely smaller than many physicians surmise."

But the jury is still out on this one; it is such an important topic for patients' safety and well-being that the researchers recommend that more prospective studies be conducted.

Another thing to think about is that it's possible to injure your nerve root during back surgery. A 2016 review of studies found that some types of lumbar spine surgery were associated with higher risk for such an injury than others. The author found that depending on the exact type of surgery, the risk ranges from 0% (for open laminectomy, which is often used in cases of spinal stenosis) to 45.8% (when bone morphogenic protein-2 was used with a TFIL surgery.

TFIL stands for transforaminal lumbar interbody fusion; it is a fusion procedure in which the surgeon enters your spine from the back.)

Remember that the decision to have surgery is ultimately yours. Consider taking the time necessary to weigh your options before you consent to it.

Sources:

Chang, V. Ellingson, B.M., Salamon, N., Holly, L.T. The Risk of Acute Spinal Cord Injury After Minor Trauma in Patients With Preexisting Cervical Stenosis. Neurosurgery. 2015 Oct.

Epstein, N. More nerve root injuries occur with minimally invasive lumbar surgery, especially extreme lateral interbody fusion: A review. Surg Neurol Int. Jan. 2016. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4743267/

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