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Ring graft technique for microvascular decompression
Correspondence Address: Source of Support: None, Conflict of Interest: None DOI: 10.4103/0028-3886.246282
Keywords: Microvascular decompression, neuralgia, teflon
Compression of the cranial nerve from adjacent vessels, mostly an artery, presents as a nerve compression syndrome, e.g., trigeminal neuralgia (TN), glossopharyngeal neuralgia (GN), and cochleovestibular nerve compression syndrome (CNCS).[1],[2],[3] TN is the most common among all these neuralgias.[4] Initially, patients are managed by medical treatment, and those who do not respond (resistant cases) are treated by surgery. Microvascular decompression (MVD) of the concerned nerve has become the treatment of choice in resistant cases.[1],[2],[5],[6],[7] In 1932, Dr. Walter Dandy proposed the theory of vascular compression of the trigeminal nerve as a possible cause of neuralgia. Dr Janneta initially introduced MVD and popularized the technique.[8] He placed a muscle patch between the nerve and artery. Since then, various graft materials have been used for MVD such as a muscle patch, teflon, cotton, gelfoam, thread, tape, titanium plate, and glue, as summarized in [Table 1].[9],[10],[11],[12],[13] Teflon is, world-wide, the most commonly used graft material.[11] Neurosurgeons have tried various shapes of teflon to achieve maximum success. The two most commonly used shapes are a teflon patch and sling. These slings or patch grafts can, however, slip due to various reasons and may cause a recurrence of symptoms. In this study, we are reporting a series of 10 patients in whom we used the novel technique of a ring-shaped teflon graft for MVD.
Ten patients underwent MVD over a period of 3 years. The clinical and demographic details are summarized in [Table 2]. All these cases had a classical history of neurovascular compression syndrome. We considered MVD only in patients who (1) had received medical treatment in full doses for at least 6 months and there was less than 50% relief in symptoms, (2) had given informed consent, (3) had a recurrence of symptoms after undergoing a previous surgery (MVD/radiofrequency ablation/percutaneous rhizotomy). The diagnosis was confirmed based on the clinical symptomatology and radiological correlation on magnetic resonance imaging (MRI) of the brain with hyper-T2 (constructive interference in study state; CISS, Siemens®, Erlangen, Germany), fluid-attenuated inversion recovery (FLAIR), contrast T1 sequences, and time of flight (TOF) sequences.
The severity of pain symptom was analyzed using the visual analog scale (VAS) score (0–10). The score 0 was considered when there was no pain and 10 was considered when patient had the worst possible kind of pain that he/she had ever experienced. The neurovascular conflict was classified into four categories, as mentioned by Haider et al.[14]
We set the criteria for the outcome of MVD as:
Technique Each patient was operated under general anesthesia after obtaining an informed consent. MVD was done using the standard technique. A suboccipital retromastoid craniotomy was performed. The impending vessel and the nerve complex were identified. The vessel was dissected under a microscope. The ring-shaped teflon graft was harvested from the vascular tube graft [Figure 1]and [Figure 1]b, which is commonly used by vascular surgeons to repair vessels. A 1-2-mm length of the ring graft was cut out from the tube graft of 6 mm diameter. The ring was further split to open it [Figure 1]b. The split ring graft was then carefully placed around the nerve at the site of compression, as shown and explained in a case of TN [Figure 2]a,[Figure 2]b,[Figure 2]c,[Figure 2]d and HFS [Figure 3]a,[Figure 3]b,[Figure 3]c. The size of the ring was selected based upon the space available for the graft. Only one ring was used in all ten cases. The technique has been explained by a diagram to simplify it [Figure 4]a and [Figure 4]b.
Illustrative case A male patient, aged 42 years, had a history of attacks of severe, lancinating facial pain over the left lower cheek and below the angle of mouth for the last 5 years. There was precipitation of the episode of pain on washing the face, touching the involved area, chewing, or exposure to cold breeze. There was a history of left molar tooth extraction to relieve pain. He was taking carbamazepine 300 mg thrice a day and gabapentin 300 mg twice a day for the last 3 years;there was, however, no relief in the severity of pain for the last 3 months. On examination, he had no neurological deficits. Radiology Constructive interference in steady-state (CISS) sequence of MRI brain showed the loop of left SCA compressing and pushing the trigeminal nerve. Operative technique The patient underwent MVD of the trigeminal nerve. Surgery was done under general anesthesia in a sitting position. A left retromastoid suboccipital, retromastoid craniotomy was undertaken. The cerebellum was retracted. The trigeminal nerve along with aberrant SCA loop was visualized. The SCA loop was present above the trigmeinal nerve and a vein was present below it [Figure 2]a. Both were pressing and stretching the nerve near its origin. An arachnoidal dissection was done to mobilize the arterial loop and vein. A ring-shaped teflon graft (6 mm diameter and 3 mm wide) was placed around the trigeminal nerve [Figure 2]b,[Figure 2]c,[Figure 2]d to separate it from the SCA loop and vein. The patient experienced a significant relief from the repeated attacks of pain in the immediate post-operative period (VAS 1/10). There was no neurological deficit and he was discharged after 7 days. At the follow-up visit after 1 month, the patient had no pain episodes. On a serial follow-up, there was no recurrence of pain and the patient remained pain -free at the 5-year follow-up.
In this study, there were ten cases of nerve compression syndrome [Table 1] treated by MVD. Six patients had TN, 2 HFS, 1 GN, and 1 CVNCS. The compressing vessels included six SCAs, three AICAs, and one PICA. Four patients had type 1 conflict, 4 had type 2 conflict, and 2 had type 3 conflict. No patient had type 4 conflict. All patients had complete resolution of symptoms (type 1, 100% relief) after 5 years of follow-up. The patient of CVNCS developed a House and Barackmann grade II facial palsy in the postoperative period. She was taught facial muscle exercise, following which the palsy completely resolved in 4 months. No other complications were reported in the remaining patients.
The offending vessel causes pressure on the root entry zone of the nerve and precipitates neuralgia. It is initially treated by medicines such as carbamazepine, gabapentin, and amitriptyline. These medicines give relief for some time, but long-term results are poor due to worsening of symptoms and side-effects of drugs, e.g., hyponatremia and leucopenia.[4],[15] In about 50% of patients, some sort of surgical treatment is needed.[16] There are various surgical options for alleviating nerve compression syndromes, including MVD, rhizotomy and nerve blocks.[17] MVD is the most popular and effective surgical treatment. The efficacy of MVD is around 65–80%.,[1],[2],[5],[16],[17] MVD is the most popular and effective surgical treatment. The efficacy of MVD is around 65–80%., as reported by various studies.[1],[2],[5],[16],[17] MVD may fail due to slippage of the graft, development of adhesions between the vessel and the nerve, the development of a graft granuloma, or the graft placing pressure on the nerve.[18],[19],[20],[21],[22],[23],[24] Continuous research and efforts are ongoing to increase the efficacy of MVD. A polytetrafluoroethylene or a teflon graft is usually the material of choice for MVD because it is inert, well-tolerated in the nervous system, resistant to resorption, and has a lower complication rate than other materials.[11] However, recent studies have shown that it is not that inert and can form a granuloma.[14],[18],[19],[20],[21],[22] Teflon graft is generally used by making a sling around the offending vessel or nerve. The sling can, however, slip due to pulsations of the brain, cerebrospinal fluid (CSF) flow, and a poor sling memory. This results in a recurrence of symptoms. According to Cohen-Gadol, an unshredded teflon graft can get dislodged easily and hence a shredded graft should be used.[23] We also suspect that failure of MVD may occur due to the teflon patch migration as a result of CSF and arterial pulsations. According to Hana et al., failure in the surgical managment of HFS can also occur due to change of body postures and due to activities that may cause an indirect mild compression as a result of the decompression material coming in contact with the nerve, or the CSF pulsations causing displacement of the graft.[24] This results in recurrence of symptoms. To prevent the graft slippage, some surgeons use the anchoring/wrapping of graft around the artery using stitch or glue, which again does not ensure its non-migration.[10],[11],[17] Our technique of using a ring-shaped graft has the advantage of lesser chance of slippage and the single graft protecting the nerve circumferentially. This also takes care of compressions due to multiple vessels (the nutcracker contact or multiple contact). While utilizing a teflon patch graft, a delayed recurrence may occur due to compression by a new vessel at a different surface of the neve. However, the ring graft may also prevent this late recurrence by preventing contact of the REZ with the new vessel (vein or artery) due to the circumferential cover provided to the nerve surface. Due to these advantages of our technique, there was no recurrence of symptoms seen in any of the reported cases. There are a few limitations of our study. There were only 10 cases recruited in the study. There are a few reports of the formation of a teflon granuloma that causes a recurrence of symptoms.[18],[19],[20],[21],[22] In our ring graft technique also, the teflon ring graft is placed around the nerve. It might cause granuloma formation or compression of the nerve. Further long-term follow-up studies with large numbers of patients are needed to predict its success or failure.
MVD using a ring teflon graft is an alternate and safe method for the management of various types of neuralgia. A large-scale study is needed to statistically confirm its efficacy over the regular teflon patch graft for MVD. Financial support and sponsorship Nil. Conflicts of interest There are no conflicts of interest.
[Figure 1], [Figure 2], [Figure 3], [Figure 4]
[Table 1], [Table 2]
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