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|Year : 2018 | Volume
| Issue : 6 | Page : 1692-1693
Ring graft technique: A unique modification for ensuring an effective microvascular decompression
Department of Neurosurgery, Institute of Neurological Sciences, Glasgow, United Kingdom
|Date of Web Publication||28-Nov-2018|
Dr. Likhith Alakandy
Department of Neurosurgery, Institute of Neurological Sciences, Glasgow
Source of Support: None, Conflict of Interest: None
|How to cite this article:|
Alakandy L. Ring graft technique: A unique modification for ensuring an effective microvascular decompression. Neurol India 2018;66:1692-3
Microvascular decompression (MVD) is a widely accepted therapeutic option for nerve compression syndromes like trigeminal neuralgia, glossopharyngeal neuralgia, and hemifacial spasms. It is safe, effective, and in most centres, the surgical treatment of choice following the failure of medical treatment. In most cases, a neurovascular conflict responsible for the symptom can be demonstrated at surgery. The aim of the surgery is to separate the offending vascular structure from the nerve in question. Since Janetta first published his successful results in 1977 using muscle to separate the nerve from the vessel, various other modifications of this procedure have been described.
Currently, teflon patches or slings are the most commonly used material to separate the nerve from the vessels. Recurrence of symptoms is not uncommon and could be related to a number of factors, including slippage of the graft and scarring or granulation around the nerve. The authors should be commented for describing and demonstrating the technique of using a ring of teflon graft fashioned from a vascular tube graft that is used to repair blood vessels. There is no standard technique for addressing this neuro-vascular conflict and there are various proposed ways of accomplishing this, but this technique has not been previously reported.
In the standard procedure, after a small craniotomy is made at the junction of the transverse and sigmoid sinus and dura opened, microscopic cisternal dissection is performed to expose the root entry zone (REZ) of the trigeminal nerve. Once the offending vascular loop is identified, it is separated from the nerve and a teflon patch placed between the nerve and the blood vessel. Less commonly, an arterial loop is not immediately evident, but further careful examination could reveal a smaller inconspicuous branch or a vein. Some surgeon use tissue glue to ensure that the teflon graft is not dislodged, a reason recognised as a cause of recurrence. In large vascular loops, simply placing a graft material is not sufficient. Displacing the arterial loop and keeping it away from the REZ would require a sling that is used to retract the blood vessel, which is then stitched to the dura or sometimes screwed to skull.
While the superior cerebellar artery (SCA) is most common offender in trigeminal neuralgia, the posterior inferior cerebellar artery (PICA) and anterior inferior cerebellar artery (AICA) are the two arteries most commonly involved in hemi-facial spasm. The vertebral artery is also known to cause compression, but instead of direct compression on the REZ, it tends to generate indirect transmission of pulses on the REZ via other arteries, such as the PICA or AICA. Due to the larger calibre, and therefore greater elasticity, decompression of the vertebral artery (VA) can be technically challenging with the traditional application of teflon prostheses or other cushions. The presence of vertebrobasilar dolichoectasia may present additional challenges. Apart from the difficulty in placement, excessive amount of teflon could exert excessive pressure on the brainstem.
Techniques like the one mentioned in this article are sometimes necessary in cases where simply inserting teflon sponges are not going to be sufficient. Several innovative surgical techniques have been reported for such cases. Use of teflon sling is a popular way of displacing the offending vessel, but for this to be performed successfully, the sling must be anchored securely away from the REZ. One method to achieve this is by using a stich placed on the tentorium cerebelli. Aneurysm clips or dural flaps can also be used to achieve this., These manoeuvres can be technically challenging and require sufficient operative field. Depending on the nature of the offending vessel, suturing or other forms of anchoring techniques may not be possible due to space constrains. In such cases, a sutureless technique using tissue glue-coated collagen sponge (soaked with fibrin glue), which the authors call the “birdlime” technique, can be effective. In selected cases, arachnoid membrane of the cerebellopontine cistern can be used to maintain the transposition of vessels from the trigeminal nerve when the offending vessel is the SCA.
Although the use of synthetic vascular graft for transpositioning blood vessels during MVD has been described, the method described by the authors is novel. This mitigates the risk of graft slippage, and can avoid the need to anchor the blood vessel away from the nerve. The authors persuasively argue that this would reduce the risk of recurrence due to patch dislodgement, but it must be accepted that recurrence could also happen due reasons other than patch dislodgement, notably the formation of granulation tissue or adhesions, as the ring is made of the same material as the patch. The ring appears to provide a sleeve of protection around the REZ, thus also preventing vessels, which may not be obvious during surgery, either due to poor visualisation or positional variations of the vascular loops within the cranium, from contacting the REZ, thus at least theoretically increasing the chance of success. As the authors point out, it can also lessen the chances of recurrence by preventing contact by ‘new’ vessels. It is therefore plausible that this technique can improve the outcome and minimise recurrence, which the authors have demonstrated in this small series.
In conclusion, there are several techniques described to resolve the neurovascular conflicts between the vessels of the posterior fossa and the lower cranial nerves. Although the most widely used technique is a simple placement of an inert sponge between the two structures, there are situations where it may not be sufficient. A wide range of techniques are available, to help the surgeon in such circumstances. The method described by these authors in this article is one such helpful technique and can be used effectively in selected cases.
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