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Selective Nerve Root Block
I. Introduction
The selective nerve root block (SNRB) is a procedure that anesthetizes an individual nerve root, either within the neck (‘cervical’), or in the back (‘thoracic’ or ‘lumbar’), thought to be responsible for the patient’s pain. The nerve root sheath is injected and anesthetized with the intent of relieving this pain.
This procedure is sometimes referred to as a ‘Foraminal Block’
The SNRB procedure delivers a low volume of concentrated medication directly into the affected nerve root sleeve.
Back Pain is often multifactorial and difficult to diagnose because the symptoms overlap considerably with those of other degenerative disorders of the spine.
The SNRB is useful in both the diagnosis and the treatment of back pain; therefore, it is both a diagnostic as well as a therapeutic procedure. In other words, if we inject a medication within the suspected nerve root sleeve and the pain improves, we are fairly confident that this nerve root is responsible for the pain; conversely, if we inject a medication and the pain is no better, this implies that this nerve root is likely not responsible for the pain.
II. Nerve Root Impingement
Patients with pain from nerve root irritation often have an anatomic cause, which is usually the result of a nearby structure pushing on, or impinging on the nerve, causing irritation of that nerve.
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 Example of Normal Disc Anatomy
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The most common causes of this are either a disc abnormality or an adjacent bone spur, either of which, when in close proximity to the nerve, can irritate it and cause pain in the distribution of that nerve.
III. Radicular Pain
If there is irritation of a nerve in the back or neck, it may cause symptoms of pain, and usually this pain is in the distribution of that particular nerve (see innervation diagram). This type of pain is referred to as radicular pain.
IV. Patient Selection
SNRB is most effectively used in patients with radicular pain.
These patients should have recent imaging studies (CT or MRI scan), which in many instances help to identify the cause of pain. Not all patients will have an identifiable cause for the pain on imaging, but all should have radicular symptoms.
V. Procedure
The procedure is explained to the patient, questions are answered and informed consent is obtained.
The patient is placed prone (stomach down) on the fluoroscopic table, and the lower back is sterilely cleansed with povidone-iodine (Betadine) and alcohol.
The exact level is located with the fluoroscope, and the skin overlying this area is anesthetized (numbed) with lidocaine. This is either to the right or left of midline on the back.
A needle is sterilely advanced along the nerve root sleeve, which typically elicits a mild degree of radicular pain in the distribution of that nerve. It is important for us to know whether the pain elicited is similar to the patient’s pain (concordant response), or dissimilar (discordant response).
Typically, as small amount of water-soluble contrast (dye) is injected to confirm proper needle tip position.
Once this is confirmed, a mixture of anesthetic (lidocaine or bupivacaine) and anti-inflammatory medication (steroid) is injected.
The needle is slowly withdrawn
This procedure may be performed with either CT or Fluoroscopic guidance.
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Radiology Medical Group, Inc. (619) 849-XRAY (9729)| © COPYRIGHT 2004 All rights reserved.
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