Peled Migraine Surgery Blog

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THE INJURED NERVE – WHAT TO DO?

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One of the questions I find myself answering again and again is how I make the decision as to what to do with a nerve once I see it in the operating room. Do I perform a neurectomy and muscle implantation or do I stop at a decompression? There are a lot of factors that go into making that decision so I will elaborate on a few of these in the lines that follow.

To begin, there are certain ultrastructural characteristics that indicate a relatively healthy nerve. One, you should have an intact vasa nervorum – the blood vessels within the nerve. These can be seen under loupe magnification as fine red lines and indicate good blood flow to the nerve itself.   Blood flow is usually a sign of life and this nerve should be considered for decompression and preservation. Another characteristic is the feel of the nerve. A healthy nerve should feel like a soft, wet noodle. If a nerve is firm like a banjo string, it usually means that there is at least scarring of the epineurium (the outermost covering of the nerve) and often the structures contained within. In these cases, an internal neurolysis to separate the healthy from unhealthy fascicles is required and if the scarring affects too many fascicles, a neurectomy with muscle implantation is probably the better part of valor. Third, the fascicular pattern should be visible. Think of nerve fascicles like bundles of wire (e.g. the blue one vs the red one in all of those movies in which the hero is trying to defuse a bomb) within an electrical cord. Stated differently, what you’re looking at when you look at a cord plugged into a wall is a rubber tube - the actual wires are the copper fibers inside that rubber housing. Those copper wires are analogous to the individual neurons (i.e. nerve cells) and in an electrical wire, are often arranged into bundles. In a nerve, those bundles of neurons are called fascicles. However, unlike the cord plugged into the wall, in a healthy nerve, the “rubber housing” should be transparent and the fascicular pattern should be visible. If it isn’t, the nerve isn’t completely healthy and those fascicles may be permanently damaged. Take a look at the attached picture of a recent patient whose supraorbital nerve branches (multiple black lines) and supratrochlear nerve (arrowhead) are visualized. Notice how white the supratrochlear nerve towards the right of the picture is and the lack of any fascicular pattern. In contrast, the supraorbital nerve branches towards the left are pink indicating an intact vasa nervorum and the fascicular pattern is visible if you look very carefully (and likely magnify the picture on your computer). Fortunately for this patient, the vasa nervorum re-constituted and the fascicular pattern became more pronounced once the supratrochlear nerve was decompressed and a few minutes were given for the nerve to declare itself – yet another nuance of technique. Therefore, both nerves were able to be preserved in this particular case.

Yet another factor to consider when deciding what to do with a nerve in the operating room is the actual function of the nerve itself. For example, the greater occipital nerve, as its name suggests, has the largest area of sensory distribution of any nerve in the occipital region. Therefore, performing a greater occipital neurectomy would leave the patient with a relatively large area of numbness. Personally, I have a relatively high threshold for transecting the GON. By contrast, the third (a.k.a. least) occipital nerve is many times smaller than the GON and has a minimal area of sensory distribution that is often also supplied in a redundant fashion by the GON. Therefore, if the third occipital nerve is damaged, I have a lower threshold for performing a neurectomy since it is likely the patient wouldn’t have much numbness, if at all, were that nerve to be cut and buried in a muscle. Lastly, is what I would call the “x factor”, in other words clinical decision making. I’m often reminded of a saying I heard once that went something like this, “Good judgement comes from experience and experience comes from bad judgement”. In other words, experience counts and takes into account a myriad of other variables before ultimately making decision A versus decision B. What was the mechanism of injury and how long ago did it occur? What other treatments have they had that might have affected the nerve along its length (e.g. RFA or cryoablation) and how many times have those modalities been performed? How did the patient respond to the numbness from the nerve blocks? How old is the patient and how likely is it that they would tolerate a repeat procedure if decompression fails? Alternatively, how young is the patient and what is their regenerative potential? If you cut that young person’s nerve, how would they tolerate 50 years of numbness as opposed to the 70 year-old patient who may only live with it for a few years and has many other medical problems more pressing than a little hypoesthesia. The take home message is that electing to perform a neurectomy as opposed to a decompression involves a multifactorial decision making process so have a frank discussion with your surgeon about how s/he will decide which path to take.

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Tuesday, 22 May 2018

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