To the Editor: We found the case report, the video accompanying it, and the comments following the article “Side-to-Side A3-A4 Bypass after Clip Ligation of Recurrent Coiled Anterior Communicating Artery Aneurysm: 3-Dimensional Operative Video” very informative.1 It is on the A3-A4 (A-anterior cerebral artery) area. To compare this interhemispheric gutter to bit more coronally wide suprachiasmatic cistern we watched Professor Lawton's video.2 This is on the A1-M2 (M-middle cerebral artery) area. Both videos provide a unique dynamic and 3-D perspective at the site of anastomosis. We watch these operative steps and discuss few related points in principles of microneurosurgery. MODERNIZATION With the advent of endovascular neurosurgery, the indications for bypass in modern neurosurgery have come down drastically. But the pendulum has been swinging from open vascular neurosurgery to endovascular neurosurgery and back again in many places. The main reason for this being the microeconomics of treatment and neurosurgical training for neurovascular diseases. This has been already hinted by Professor Ringer in the comments of the Park et al article itself.1 Nevertheless, the classical indications for a bypass procedure are to replace the parent artery or its branches. In other words, in patients who cannot tolerate anti-platelet therapy, those who have failed endovascular/clip ligation and those ruptured aneurysms unsuitable for endovascular neurosurgery.3 ANATOMY The diameter of blood vessels was well-documented by Professor Rhoton.4 On average, the M1 diameter is around 4 mm and the A1 diameter is around 2 mm. The classification of M1-M6 is straight forward. The classification of A2-A5 is a bit more challenging. A3 (precallosal) A2 (infracallosal) comes under ascending segment and A5 (postcallosal). A4 (supracallosal) comes under the horizontal segment. Not to forget the simple classification based on branching patterns, vis a vis, A1, pericallosal artery. PROFESSOR ACLAND’S PEARLS In microscopic surgery, Professor Acland says do not pull the needle directly (Figure). Sometimes a shift in the point of holding the needle from the tip to a bit more towards the eye of the needle will help, also using the microforceps to guide the thread while pulling so as not to make a hole because of the tug.5 Advances in fine sutures and atraumatic needles can mitigate some of these problems. There may not be enough room to make the shift. Also, the delicate needle may not stay still. But, as seen in the video1 in couple of occasions, we need to play around with the direction of the bite and angle of the microforceps grip to get a perfect result. FIGURE. View largeDownload slide While passing through the tissues, the needle in the top takes the route along the curve and there is no pull on the tissues to the right of the anastomotic line. While pulling the thread, the forceps is positioned under the thread to guide it and is not allowed to tear a hole on the right side of the needle route. The wrong technique is shown at the bottom: the needle takes a straight route in the first step and the unguided thread causes more tears in the second step. FIGURE. View largeDownload slide While passing through the tissues, the needle in the top takes the route along the curve and there is no pull on the tissues to the right of the anastomotic line. While pulling the thread, the forceps is positioned under the thread to guide it and is not allowed to tear a hole on the right side of the needle route. The wrong technique is shown at the bottom: the needle takes a straight route in the first step and the unguided thread causes more tears in the second step. To compare, in a 2-D perspective, Professor Lawton seems to be pulling the tip of the needle (with a microneedle holder) in a straight line, and not taking it along its curve.2 The key is if you need to pull, you need to pull along the curve of the needle. This has been visualized by adding further dimensions to the video. ACLAND’S PEARL SIGNS AND TESTS OF PATENCY These patency signs and tests can be done just before an intraoperative angiogram. Professor Acland's 3 signs include expansile pulsation (distal to the anastomosis), wriggling (change in curvature distal to anastomosis), and longitudinal pulsation (longitudinal column of pulsation hammering against an anastomosis). Of these, the former are good signs and the last one is a bad sign indicating thrombotic block.5 Professor Acland's 2 tests of patency include the uplift test (lift the artery distal to the anastomosis and see if the artery blanches and fills up with every pulsation) and empty-and-refill test (this is a crude, traumatic test and generally not advised, basically milking the blood distally distal to the anastomosis using 2 forceps).5 ASSESSING MICRONEUROSURGICAL SKILLS Visual assessment scores, tool path, task completion time, and needle gripping force have been studied.6 But real-life situations are very different from the laboratory. Visual assessment scores become less important to a good flow across the anastomosis. Tool path might have to be restricted or altered depending on the depth and space available. Task completion time in classical surgery teaching should not be the goal, but in specific circumstances like applying a temporary aneurysmal clip microneurosurgeon needs to race against time. Microneedle holder gripping force is a valid method in assessment, but one needs to be aware that gripping edges of cut end of blood vessels is against atraumatic technique. GOALS OF VASCULAR ANASTOMOSIS One of the goals is a good histopathological anastomosis. We know there can be intimal damage, medial necrosis, initially because of the trauma of surgery (microvascular anastomosis). This can later progress to become intimal hyperplasia or subintimal hyperplasia or medial fibrosis. Suture-less surgery can mitigate some of the problems. The excimer laser assisted non-occlusive anastomosis and suture-less excimer laser assisted non-occlusive anastomosis are other newer techniques, not all of which have zero complications. An ideal suture-less anastomosis in the brain seems to be still developing.7 HUMAN CEREBRAL CORTEX MICROVASCULAR SYSTEM Strictly, A3-A4 and A1-M2 do not belong to this cerebral cortex microvascular system, but come at a level just proximal to it. All the perforators arising from this area constitute the intracerebral extrinsic microvascular compartment.8 Along with cerebrospinal fluid dynamics, this microvascular system forms the main work horse for the supply of nutrition and waste removal from the brain. Of the 3-cerebral cortex microvascular subcomponents, the blood brain barrier along with the surrounding pericytes, astrocytes, neurons, and extracellular matrix constitutes the “neurovascular unit.” CONCLUSION In both videos,1,2 the changes that might occur post bypass hemodynamically, both proximal and distal to the anastomosis, appear to be minimal considering the caliber of the vessels affected being distal to the circle of Willis. Not to forget the excellent immediate postoperative results arising out of a brilliant technique. Disclosure The authors have no personal, financial, or institutional interest in any of the drugs, materials, or devices described in this article. REFERENCES 1. Park D-H, Singh H, Silva HBD, Sekhar LN. Side-to-side a3-a4 bypass after clip ligation of recurrent coiled anterior communicating artery aneurysm: 3-dimensional operative video. Oper Neurosurg . 2018; 14( 1): 87. Google Scholar CrossRef Search ADS 2. Benet A, Yousef S, Tabani H, Griswold D, Meybodi AT, Lawton MT. Intracranial–intracranial A1 ACA-SVG-M2 MCA M2 MCA double reimplantation bypass for a giant middle cerebral artery aneurysm: 3-dimensional operative video. Oper Neurosurg . 2018; 14( 1): 84. Google Scholar CrossRef Search ADS 3. Spetzler RF, Kalani YS, Nakaji P. Neurovascular Surgery . Estados Unidos: Thieme Medical Inc; 2015. Google Scholar CrossRef Search ADS 4. Rhoton AL. The supratentorial arteries. Neurosurgery . 2002; 51( suppl_4): S53- S120. Google Scholar PubMed 5. Acland RD, Raja Sabapathy S. Aclands Practice Manual for Microvascular Surgery . 3rd ed. 2008. 6. Harada K, Morita A, Minakawa Y et al. Assessing microneurosurgical skill with medico-engineering technology. World Neurosurg . 2015; 84( 4): 964- 971. Google Scholar CrossRef Search ADS PubMed 7. De Boer B, Van Doormaal TP, Van Der Zwan A, Tulleken CA, Regli L. Towards sutureless non-occlusive cerebral revascularization. J Neurosurg Sci . 2011; 55( 2): 117- 125. Google Scholar PubMed 8. Dorovini-Zis K, ed. The Blood-Brain Barrier in Health and Disease . Vol. 1. Boca Raton: CRC Press; 2015. Google Scholar CrossRef Search ADS Acknowledgments The authors thank Mr Christos Tolias, PhD, FRCS, vascular neurosurgeon, Kings College London, for his lecture at Harley Street Clinic, London, United Kingdom and Dr Poovizhi, veterinary surgeon and director Institute of Surgical Education, Chennai, India. Copyright © 2018 by the Congress of Neurological Surgeons This article is published and distributed under the terms of the Oxford University Press, Standard Journals Publication Model (https://academic.oup.com/journals/pages/about_us/legal/notices)
Operative Neurosurgery – Oxford University Press
Published: May 23, 2018
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