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 Table of Contents  
ORIGINAL ARTICLE
Year : 2021  |  Volume : 9  |  Issue : 2  |  Page : 80-83

A concise operative atlas of microvascular decompression – Different intraoperative scenarios and technical nuances


Department of Neurosurgery, Apollo Proton Centre, Chennai, Tamil Nadu, India

Date of Submission01-Dec-2021
Date of Decision12-Dec-2021
Date of Acceptance10-Jan-2022
Date of Web Publication5-Apr-2022

Correspondence Address:
Dr. Roopesh V R. Kumar
Department of Neurosurgery, Apollo Proton Centre, Chennai, Tamil Nadu
India
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/jcvs.jcvs_21_21

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  Abstract 


Background: Trigeminal neuralgia is one of the most common facial pain syndromes. Although there are many postulated hypotheses explaining the pain, microvascular compression of the root entry zone (REZ) of the trigeminal nerve is commonly accepted to be the pathology for neuralgia. Various medical and surgical treatments are available to relieve the pain and microvascular decompression of the trigeminal nerve at the REZ is considered as the most successful modality and the gold standard.
Methods: In this video atlas on operative nuances, we have described nine common scenarios that could be encountered during this surgery.
Conclusion: Thorough knowledge of the different intraoperative scenarios is crucial for a complete microvascular decompression that translates into a good post-operative outcome.

Keywords: Microvascular decompression, root entry zone, trigeminal neuralgia


How to cite this article:
Kumar RV, Karthikayan A. A concise operative atlas of microvascular decompression – Different intraoperative scenarios and technical nuances. J Cerebrovasc Sci 2021;9:80-3

How to cite this URL:
Kumar RV, Karthikayan A. A concise operative atlas of microvascular decompression – Different intraoperative scenarios and technical nuances. J Cerebrovasc Sci [serial online] 2021 [cited 2022 Aug 14];9:80-3. Available from: http://www.jcvs.com/text.asp?2021/9/2/80/342558




  Introduction Top


Microvascular decompression of the trigeminal nerve is the gold standard technique for relieving the patients suffering from intractable trigeminal neuralgia (TN).

In 1934, Walter Dandy, who described the retrosigmoid approach to the trigeminal nerve, noticed the vascular contacts of the nerve in patients with tic douloureoux and believed it to be the cause of TN.

However, it was James Gardner, in 1959, who defined the procedure of microvascular decompression (MVD) by mobilising the offending vessel away from the nerve and placing a gel foam between them.

Peter Jannetta further refined the procedure[1] and held record for one of the largest case series of MVD. He emphasised that patient selection plays a crucial role in the outcome of MVD.

A magnetic resonance imaging of the posterior fossa using constructional interface steady-state sequence (three dimensional [3D]) helps in delineating the nerve vessel conflict [Figure 1] in majority of the patients.[2]
Figure 1: CISS three-dimensional magnetic resonance imaging showing evidence of neurovascular conflict – indentation of the right trigeminal nerve by the right superior cerebellar artery

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With respect to patient positioning, a supine with head turn or a lateral position can be used depending on the preference of the surgeon. We prefer a lateral position with adequate padding of pressure points in all our patients. Supine position with undue head turn might be an issue, especially in the elderly, obese and those with a short neck. A 5 cm retro-auricular linear incision just 5 mm behind the hairline with one-fourth of the incision above the inio-meatal is made, and monopolar cautery is used to dissect the muscular tissue until the body of mastoid and digastric groove are seen. The mastoid emissary vein is a relatively constant landmark for the transverse sigmoid junction. Burr hole is placed at the emissary vein and craniotomy is extended progressively, posteriorly and inferiorly. A point just below the asterion is also a useful landmark for positioning the initial burr hole. Adequate care is taken to prevent sinus injury.

The transverse-sigmoid sinus junction exposure is mandatory to visualise the root entry zone (REZ) of the trigeminal nerve without cerebellar retraction. Any mastoid cells if opened are waxed thoroughly. A small retromastoid craniotomy is sufficient for the exposure of the trigeminal nerve REZ to perform microvascular decompression. Dura is opened in a K-shaped or L-shaped manner.

After opening the dura, the arachnoid is opened to release the cerebrospinal fluid, thereby assisting gravity-assisted cerebellar retraction. It is better to use dynamic retraction with suction cannula rather than fixed cerebellar retractors, which may result in cerebellar contusion and rarely hearing loss due to avulsion of cochlear nerve microfilaments at porus acusticus. After gentle retraction of the superolateral surface of the cerebellum, the superior petrosal vein (Dandy's vein) can be identified that has to be preserved. The trigeminal nerve (V nerve) can be identified deeper into the vein. Once the V nerve is identified, the arachnoid is opened all around with sharp microscissors from the REZ medially till it exits into the Meckel's cave.[3] This gives the access to identify all the vascular relations to the nerve.

Once the trigeminal nerve is completely freed, Teflon pledgets are placed between the nerve and offending vessel.

Dura is closed in a watertight fashion. We harvest fascia lata graft in all cases. After dural closure, a fat graft overlay is used for reinforcement.

Patients who present with episodic and lancinating pain (TN Type I) have a significantly better outcome than those who present with constant pain (TN Type II).[4]

The video atlas depicts various scenarios of microvascular decompression[Video 1] [Table 1].
Table 1: Video timeline with audio transcript

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[Additional file 1]

In the first case [Figure 2], the superior cerebellar artery (SCA) is found indenting the REZ. After separating the vessel, Teflon pledgets are placed between the REZ and the vessel [Figure 3]. One should make sure that the nerve is completely free of all the vessels from REZ till Meckel's cave.
Figure 2: Intraoperative picture of the first case scenario where the superior cerebellar artery is dissected away from the trigeminal nerve. The groove on the trigeminal nerve due to the indentation by the artery is clearly seen

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Figure 3: After making sure that the trigeminal nerve is completely free from any conflict, Teflon patches are placed between the route entry zone of the trigeminal nerve and the superior cerebellar artery

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In the second case, the nerve is found to be stretched significantly by the loop of SCA, causing thinning of the nerve so much that the vessel is seen transparently from the inferior aspect of the nerve. The arachnoid is opened sufficiently to separate the vessel, and Teflon pledgets are placed to make the nerve get back to the normal orientation.

In the third case, multiple vessels are found near the REZ. As one cannot be certain which vessel is the culprit, all the vessels must be meticulously separated from the nerve and Teflon pledgets are placed to prevent re-approximation.

In the fourth case, the nerve is indented superiorly and inferiorly by SCA and anterior inferior cerebellar artery (AICA), respectively. Both the vessels are separated from the nerve after adequate dissection and kept in place by Teflon.

In the fifth case, the problem was found near the Meckel's cave rather than REZ. Although there was a vessel close to REZ, it was not suggestive of the pathology. After dissecting the nerve distally, the AICA loop was seen indenting the inferior surface of the nerve and it was separated. If one misses that, the patient can have failed surgery and persistence of neuralgia. This emphasises the fact that a thorough dissection till the exit of the nerve laterally is imperative.

In the sixth case, the entire loop of AICA was found spread over the surface of REZ. The entire vessel along with its tiny branches could be separated and lifted away from the nerve establishing a new course of the vessel and Teflon placed between the nerve and vessel.

In the seventh case, the offending vessel was a dolichoectatic basilar artery along with the origin of AICA. After a meticulous microsurgical dissection of the origin of AICA from the REZ, two Teflon pledgets were placed so that the pressure of the large vessel does not cause recurrence of neuralgic pain.

In the eighth case [Figure 4], the offending vessels were veins (which constitutes 10%–15% of the neurovascular compression). Before contemplating the veins as the pathology, one should make all attempts to find the offending artery, which sometimes be hidden under the REZ. If the veins are small, they can be coagulated, but large veins need to be preserved and separated with Teflon pledges.
Figure 4: Venous compression as the cause of trigeminal neuralgia (eight case scenarios) is relatively rare. The large offending veins are preserved and separated from the nerves with Teflon patches

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In the final case scenario, the patient had a recurrence of neuralgia[5] after 3 years of pain-free period (a procedure done elsewhere). In view of the initial success of the procedure, a decision was taken to re-explore the nerve to perform the decompression. The REZ was found to be compressed by the granuloma formation of the muscle patch. A sharp meticulous microsurgical dissection was performed to release the REZ from the granuloma, which was also adherent to the adventitia of a branch of AICA. A small Teflon patch was used to separate the REZ from the vessel granuloma complex. There was another loop of AICA indenting the inferior aspect of the nerve, which was also dissected and separated. Redo MVD must be performed very meticulously and cautiously to prevent damage to the nerve or vessel.

An immediate post-operative evaluation with a plain computerised tomogram of the posterior fossa helps in knowing the position of the Teflon placed intra-operatively [Figure 5] and this can be used as a control for future evaluation, in the case of displacement of the pledget, causing recurrence of neuralgia.
Figure 5: Post-operative plain computed tomography brain showing the location of Teflon patch. This can be used in the follow-up period to look for any displacement of the patch as a cause of recurrence of trigeminal neuralgia

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  Discussion Top


Having a thorough knowledge of the different operative scenarios that one might encounter during microvascular decompression for TN is of paramount importance. Complete and adequate decompression of the trigeminal nerve throughout its course yields the best clinical results with minimum rates of recurrence.


  Conclusion Top


Microvascular decompression is one of the commonly performed curative pain procedures for TN. The need for careful patient selection, imaging and meticulous decompression intraoperatively could not be overemphasised.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.



 
  References Top

1.
Mistry AM, Niesner KJ, Lake WB, Forbes JA, Shannon CN, Kasl RA, et al. Neurovascular compression at the root entry zone correlates with trigeminal neuralgia and early microvascular decompression outcome. World Neurosurg 2016;95:208-13.  Back to cited text no. 1
    
2.
Prieto R, Pascual JM, Yus M, Jorquera M. Trigeminal neuralgia: Assessment of neurovascular decompression by 3D fast imaging employing steady-state acquisition and 3D time of flight multiple overlapping thin slab acquisition magnetic resonance imaging. Surg Neurol Int 2012;3:50.  Back to cited text no. 2
[PUBMED]  [Full text]  
3.
Forbes J, Cooper C, Jermakowicz W, Neimat J, Konrad P. Microvascular decompression: salient surgical principles and technical nuances. JoVE (Journal of Visualized Experiments). 2011;(53):e2590.  Back to cited text no. 3
    
4.
Ammori MB, King AT, Siripurapu R, Herwadkar AV, Rutherford SA. Factors influencing decision-making and outcome in the surgical management of trigeminal neuralgia. J Neurol Surg B Skull Base 2013;74:75-81.  Back to cited text no. 4
    
5.
Cheng J, Meng J, Lei D, Hui X. Repeat microvascular decompression for patients with persistent or recurrent trigeminal neuralgia: Prognostic factors and long-term outcomes. Medicine (Baltimore) 2019;98:e15167.  Back to cited text no. 5
    


    Figures

  [Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5]
 
 
    Tables

  [Table 1]



 

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