Pudendal Nerve Blocks

See Dr. Vancaillie's comments on pudendal nerve blocks.
See Dr. Zhou's and Violet Matthew's articles on nerve blocks

How is the nerve located for a pudendal nerve block?

In the context of PNE, a nerve block involves injecting a liquid at a precise location near a nerve. For a small nerve like the pudendal nerve, that takes slightly different paths in different people, this requires more than just studying a person's body and deciding where to insert the needle, at what angle, and how deep. It requires imaging of some type, such as Xray (fluoroscopy), MRI, ultrasound, or CT scan. Without the accuracy these imaging systems provide, it is difficult or impossible to know if the needle tip is located correctly. If incorrectly located, the nerve can be damaged or the injected liquid will be too far away to have its intended effect. 

Blocks can also be delivered based upon the nerve stimulation site.  The nerve can be stimulated transvaginally and transrectally, with same latency norms.  Using different methods improves accuracy since the length of the studied portion of the nerve is short. A major problem can be overstimulation which can cause inaccuracies such as volume conduction, inadvertent stimulation of the sciatic nerve, or a false shortening of the latency since the nerve stimulation is too strong and the nerve is activated closer to the recording point.  For this type of nerve block, an experienced physiatrist or neurologist is important. 

What medication is injected?  

There are two main types of injected liquids: a local anesthetic such as marcaine, and slow-release steroids. The local anesthetic is a short term diagnostic tool. If the pain is relieved for a few hours, the location was correct and the nerve can be suspected of being a contributor or even the sole source of pain. The steroids are a long term therapeutic attempt and in some cases they will decrease the nerve inflammation. This can take days or weeks, and improvement may be temporary or permanent. This delay explains why physicians prefer a delay of several weeks between nerve blocks with steroids. If the nerve is not irritated, the steroids have no effect.  Some doctors use heparin, an anti-inflammatory medication, instead of steroids. 

Where is the medication injected?

The most common sites for injection are at the ischial spine between the sacrotuberous and sacrospinous ligaments or in the Alcock's canal.  These are not the same as the blocks carried out for childbirth pain. Several physicians give nerve blocks into a 3rd location at the dorsal penile/clitoral branch of the pudendal nerve.  

 

Are there any risks associated with nerve blocks?

In some cases the blocks may worsen the pain for a few days or weeks. For a few people who have undergone nerve blocks, there has been a long-term worsening of symptoms including increased sitting pain or a condition called persistent genital arousal syndrome, possibly due to the nerve being “nicked” by the needle, a reaction to the medication, or formation of scar tissue. 

 

What should I expect during a nerve block?  

When the nerve block is conducted under guidance, the patient is placed in the prone position. The doctor injects a local anesthetic, to make the buttocks numb prior to injecting the needle that targets the nerve. When the pudendal nerve is located, the short term diagnositc anesthetic and the steroid are injected. The procedure itself lasts approximately 30 minutes and is done on an outpatient basis. No overnight stay is required. If there is temporary relief of pain this is considered a positive response to the nerve block and the pudendal nerve is likely the culprit. If there is no temporary relief of pain after the block there are several possibilities:

1. The pain is not caused by the pudendal nerve 

or

2. The injected medication did not get close enough to the nerve to provide any relief. If this occurs and there is no loss of sensation in the distribution of the pudendal nerve, the physican may order another block to ensure that pudendal neuralgia can be ruled out.

Below are some pictures of what to expect when receiving a nerve block. The following picture is a CT guided photo that shows the optimum placement of the needle for this particular person.

 

 

For further reading on pudendal nerve blocks see this article.

 

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