Ziad A. Hage, Gregory D. Arnone, and Fady T. Charbel
Abstract
Double anastomosis using only one branch of the superficial temporal artery (STA), single-vessel double anastomosis (SVDA), describes a valuable technique of direct revascularization for moyamoya disease. A proximal side- to-side anastomosis is made, followed by a distal end-to- side anastomosis with the same STA branch used on both recipient vessels. This technique may be chosen for cases in which preoperative evaluation reveals only a single robust usable STA branch on angiogram, with more than one territory requiring flow augmentation. Additionally, the decision to proceed with SVDA bypass configuration may be made based on intraoperative flow measurements of potential donor and recipient vessels, in an effort to maximize graft potential and minimize bypass failure. This chapter discusses the technique, indications, contraindications, complication avoidance, and other considerations when performing SVDA.
Keywords: moyamoya, direct bypass, single-vessel double anastomosis, cut-flow index, extracranial-to-intracranial bypass, superficial temporal artery bypass
The first description of “moyamoya” disease was by Suzuki and Takaku in 1969.1 Three years later, professor Yasargil performed the first surgical intervention for moyamoya with a superficial temporal artery (STA) to middle cerebral artery (MCA) bypass,2 marking the beginning of an evolution in the surgical treatment of the disease. Over the next several decades and into the 21st century, novel surgical strategies have been developed to treat moyamoya disease, and operative techniques have been continually refined. Currently, various operations for both direct and indirect bypass are described to augment blood flow to multiple vascular territories, including the anterior cerebral artery, MCA, and posterior cerebral artery territories.3
While double-barrel bypass techniques with both the parietal and frontal STA branches have been described,4 the single-vessel double anastomosis (SVDA) technique is a novel strategy that involves utilizing one donor branch for both a side-to-side, and end-to-side anastomosis, provided the donor artery has sufficient flow to supply multiple bypasses. This technique can be an important addition to the bypass armamentarium in selected patients with moyamoya disease, particularly when a single anastomosis is unlikely to supply sufficient flow to multiple ischemic territories, or in cases where there is mismatch between the available flow from the donor graft exceeding the sink capacity of a single recipient bed.
Potential candidates for flow augmentation bypass surgery include patients with symptomatic moyamoya disease with poor cerebrovascular reserve as diagnosed on preoperative studies. We prefer to use a vasodilatory challenge paired with imaging studies to assess cerebrovascular reserve and identify areas at risk with impaired autoregulation stemming from a chronic oligemic state. Vasodilatory challenge normally causes a resultant increase in cerebral blood flow, though in instances of hemodynamic compromise, this response will be either dampened or absent in an impaired vascular territory compared to the normal circulation.5 The studies we utilize include quantitative MRA with use of Noninvasive Optimal Vessel Analysis (NOVA) software, with a Diamox challenge, and functional MRI (regional and global blood oxygen level dependent [BOLD] imaging) with CO2 challenge. Adequate donor and recipient vessels should be available as noted on digital subtraction angiography. The SVDA bypass configuration, in particular, can be selected as an option during preoperative work up if only a single robust usable STA branch is noted on the angiogram and more than one territory requires flow augmentation (such as with superior and inferior MCA division territories). On the other hand, the decision to proceed with SVDA bypass configuration may be taken intraoperatively based on flow measurements of potential donor and recipient vessels. If the cut flow (i.e., free-flowing carrying capacity) of the STA donor vessel is substantial enough to augment two vascular beds, an initial side-to- side anastomosis is performed. The cut-flow index (CFI) is then measured and calculated; if CFI< 0.5, the second anastomosis is completed in an attempt to get the CFI closer to 1, therefore maximizing the graft potential and minimizing type 2c error and bypass failure.6,7
Once the vascular territories in need of flow augmentation are identified based on patient symptoms (including left vs. right in bilateral disease), imaging findings, and cerebrovascular reserve testing, the skin incision and craniotomy must be carefully planned. Excessive supragaleal dissection and devascularization of the scalp can be spared if only a single branch of the STA is needed. The skin incision is tailored according to the targeted STA branch. If the parietal branch is being dissected, the skin incision will be made following its path; it can then be reflected anteriorly, distal to the superior temporal line, if a larger skin flap is needed. If the frontal branch is harvested, the incision is made to accommodate for an adequate size craniotomy while minimizing the amount of skin reflected anteriorly. The frontal STA will then be dissected from the underside of the skin flap through the galea. When performing the craniotomy and opening the dura, great care should be exercised in preserving the middle meningeal artery (MMA), as it may already provide critical extracranial-to-intracranial (EC—IC) collaterals, as often seen on preoperative angiography. Various donor/recipient vessels should be identified and different direct bypass configurations planned and selected; the surgeon should be ready to adapt and reconfigure the surgical plan based on intraoperative flow measurements. Flow-assisted surgical technique (FAST) is uti- lized,7 which involves the following: performing flow measurement for the STA cut flow; calculating CFI to predict bypass patency rate6; optimizing type 2c error (further described in Chapter 13.4.4); optimizing CFI at 1 by performing more than one anastomosis if needed; maximizing donor capacity.
13.4.1 Strengths
In contrast to indirect techniques, direct bypass allows for immediate flow augmentation and, in some cases, relief of symptoms. The development of adequate collaterals can take several months after indirect bypass, putting the patient at risk for repeated events in the interim. Specific to the SVDA technique, multiple anastomoses using a single donor vessel maximize its donor capacity while optimizing type 2c error (explained in Chapter 13.4.4 ). The technique also obviates the need to dissect a second STA branch, therefore saving time, preserving scalp blood supply for improved healing, and providing a salvage plan in case of reoperation or failure of the initial bypass.
13.4.2 Weaknesses
All EC-IC bypass procedures require temporary occlusion time of the recipient bed, putting patients at risk for ischemic events during the surgery; however, temporary occlusion time is required for multiple recipients in SVDA. Furthermore, any problem at the proximal anastomosis site may affect the distal anastomosis, and any potential issue affecting the donor compromises both recipients at once.
13.4.3 Opportunities
Techniques to reduce or eliminate temporary occlusion time will improve the safety of bypass procedures, especially when multiple bypasses are being planned as in SVDA. As such, novel suturing devices may be a target for future consideration. Additionally, the development of more advanced software that is able to accurately and quantitatively identify the amount of flow needed for augmentation in various territories with poor reserve would allow for more reliable and informed surgical planning.
13.4.4 Threats
Four main types of errors7,8 are encountered with direct bypass procedures that constitute threats to the success of this surgery.
Type 1 error, or poor patient selection, occurs when the recipient vascular bed already has adequate collaterals (good hemodynamic reserve) and bypass is unnecessary. In these cases, often times the bypass will fail because the demand is low and there will be poor flow through the anastomosis.
Type 2a error refers to a problem with the donor vessel —in the case of SVDA, the STA branch. Technical issues may be secondary to vessel injury during harvesting, or thrombosis due to inadequate flushing. Of most concern in SVDA is insufficient supply of the single branch to provide adequate flow to two recipient territories, resulting in continued ischemia of both territories. Again, intraoperative flow parameters will dictate whether or not a single STA branch is sufficient.
Type 2b error is simply an anastomosis problem. Meticulous technique and the need for continued practice cannot be understated for bypass surgery, and increasing experience should mitigate these technical issues.
Type 2c error refers to recipient or distal bed problems that may limit the outflow from the bypass. Causes include atherosclerotic disease, vessel stenosis distal to the anastomosis, small recipient vessel size, and increased distal vascular bed resistance.
Contraindications to the SVDA technique encompass the usual contraindications to bypass for moyamoya in general, including preserved hemodynamic reserve, poor quality donor vessels, and poor quality recipient vessels. Inadequate vessel length or orientation may also prevent a successful SVDA. Finally, unless the cut flow from the single STA branch is sufficient to supply two separate vascular territories, an alternative technique (double barrel, for example) must be employed.
Careful study of the preoperative angiogram will help assess the quality of donor and recipient vessels, select the adequate bypass configuration, and define the recipient territory at risk. Furthermore, it must be determined if the MMA is supplying EC-IC collaterals, in which cases one must avoid injuring the vessel during craniotomy and dural opening. Diuretics, hyperosmolar medications, and hyperventilation must not be used during the surgery because all of these techniques may compromise blood flow to an already tenuous territory during surgery and temporary occlusion time. The patient’s blood pressure should be maintained at the baseline preoperative value during the surgery and especially during anesthesia induction. The pressure should be raised during temporary occlusion time and the patient should be in burst suppression. An antiplatelet agent such as aspirin (we use 325 mg) should be given the morning of surgery and continued thereafter in order to prevent thrombosis at the graft site until endothelial healing can occur. Laboratory testing for aspirin effect (platelet inhibition) may be done postoperatively to ensure therapeutic effect.
Several pitfalls may be encountered when performing a technically demanding surgery such as the SVDA bypass. Injuring the STA during harvest or craniotomy, failing to adequately flush the donor vessel after sectioning and clamping, failing to coagulate its side branches, or dissecting the STA wall during harvest can jeopardize the donor and consequently the success of the surgery. Moreover, inadequate craniotomy size or location may prevent exposure of adequate recipient arteries, rendering a planned bypass configuration difficult to achieve. Even worse, errant craniotomy site may lead to revascularization of the wrong territory (superior vs. inferior MCA division). Injuring the MMA during craniotomy or dural opening can eliminate important existing collaterals and further the ischemic burden. In addition, poor hemostasis prior to starting the anastomosis may cause continuous blood oozing in the field, a situation that significantly impedes efforts toward an efficient and timely bypass. Injury to a recipient vessel via coagulation or arteriotomy can thwart bypass plans and exacerbate the underlying disease. Additionally, neglecting to coagulate side branches from the recipient will cause continued bleeding despite temporary clipping. Moreover, donor-recipient mismatch can be of concern, and one must take care to bevel and fish mouth the donor when necessary. Suturing the back wall of the vessel during anastomosis is yet another cause of failure. Inadequate amount of sutures will cause an anastomosis to leak briskly. If a temporary stent is used, one must not forget to remove it prior to placing final sutures. Finally, during closure, strangulation of the STA by dura or muscle reapproximation must be avoided. In addition, meticulous skin closure is key in preventing inadvertent injury of the graft.
Bypass is performed with patients under general anesthesia with the head fixed in a Mayfield head holder. Foley catheter, arterial line, and central line are inserted prior to pinning. The head should be rotated such that the surgical field is parallel to the floor, and a shoulder roll can be helpful in certain instances where the neck is not very supple. The STA stump, bifurcation, frontal, and parietal branches should all be mapped out with a Doppler probe and adequately marked. Skin incision may vary depending on the operative plan and bypass configuration. For example, if a parietal branch is planned for an SVDA, an incision over the mapped out branch may be used (Fig. 13.1). If the frontal branch is needed, a subgaleal flap can be turned anteriorly from this incision and the frontal branch can be identified from the undersurface of the flap and dissected accordingly. Burst suppression should be employed and diuretics, hyperventilation, and hypotension must be avoided at all times during surgery. The patient’s blood pressure should be maintained at the baseline preoperative value during the surgery, especially during anesthesia induction. The pressure should be raised during temporary occlusion time.
Under microscope magnification, skin incision is made as planned, depending on the chosen STA branch that was mapped out prior to prepping and draping. The STA is dissected free of the surrounding soft tissue (Fig. 13.2) and flow is measured in situ using the Charbel MicroFlowprobe (Transonic, Ithaca, NY). Next, the STA is wrapped in a papaverine-soaked cottonoid to keep it hydrated and protected during the craniotomy, and to reduce vasospasm in the donor vessel (Fig. 13.3). The microscope is removed from the field and the craniotomy is performed as planned out, depending on the location of the recipient branches and targeted revascularization. Dural tack-up sutures are placed around the craniotomy edges. The microscope is brought back into the field and the dura is carefully opened, preserving MMA branches that provide critical collaterals (Fig. 13.4). After opening the dura, the STA is laid over the brain surface to plan the anastomosis sites and final position of the donor vessel (Fig. 13.5). The STA is then sectioned and the cut flow is measured.8,9 Any lower than expected flow values should prompt a search for areas of strangulation at the STA stump, as can happen with traversing veins in the soft tissue (Fig. 13.6). Such vessels should be coagulated and the STA stump freed from obstruction. The STA is then flushed with heparinized saline and a temporary clip is placed on its proximal and distal ends. Next, the arachnoid is opened over the selected recipient vessels and a rubber dam with a small piece of gelfoam is placed under the recipient in preparation for anastomosis (Fig. 13.7).
The gelfoam helps in elevating the recipient vessel and surgical field during anastomosis. The second recipient vessel is also prepared as described and baseline flow measurements are taken at both recipient sites. The STA is then dissected free from its tissue cuff and positioned in a side-to-side fashion next to the recipient in preparation for arteriotomy and anastomosis (Fig. 13.8). Care must be taken to position the STA while preserving its baseline anatomical configuration therefore preventing any twisting or kinking of the vessel. Arteriotomy sites are marked on donor and recipient and the first arteriotomy is performed on the STA at the proximal site where the side-to-side anastomosis will take place. The side-to- side proximal anastomosis is always performed first; if the end-to side distal anastomosis were done first, occlusion of the distal anastomosis would be necessary while performing the proximal one. This would not only put both territories at risk during temporary occlusion, but would also put the initial anastomosis at significant risk of thrombosis due to blood stasis. After placing the 10-0 nylon suture on one end of STA arteriotomy, temporary clips are placed on the recipient vessel (Fig. 13.9). The arteriotomy is made on the recipient vessel to match the STA arteriotomy, and the lumen is flushed with heparinized saline. The 10-0 nylon suture is then stitched and tied to the apex of the recipient arteriotomy and the first side of the anastomosis is done in a running fashion (Fig. 13.10). The stitches should remain loose until the entire length of the vessel has been sutured, and the loops of suture are then tightened sequentially. The lumen is checked making sure the back wall is not caught and the other side of the anastomosis is then completed the same way. The temporary clips are then removed from the recipient vessel and the anastomosis site is checked for hemostasis. Flow measurements are taken on the completed anastomosis. For the end-to-side anastomosis, the cut end of the STA is beveled and fish mouthed. Two 10-0 nylon sutures are then placed, one at the toe and the other at the heel of the STA (Fig. 13.11).
Temporary clips are placed on the recipient vessel. Again, the arteriotomy on the recipient vessel is made to match the STA cut end, and the lumen is flushed with heparinized saline. The first suture—on the toe of the STA—is tied to one end of the recipient arteriotomy, followed by the second suture—on the heel of the STA—that is tied to the other end of the recipient arteriotomy. One side of the anastomosis is then completed in an interrupted fashion, making sure that the needle always pierces from in- to-out in the fragile recipient vessel wall to prevent arterial dissection. After completing the first side, the lumen is checked to ensure the back wall is not caught. The other side of the anastomosis is then completed in the same way. Temporary clips are removed from the recipient initially and then from the STA, and flow is reestablished. Flow measurements are again taken in the STA and both recipient vessels to assess the flow dynamics and cut flow indices (Fig. 13.12). Indocyanine green fluorescence can then be performed to further confirm patency of the bypass and preserved flow in the MMA and its branches. Upon closure of dura and muscle, adequate bulk should be excised to clear the path of the STA. After each step up until skin closure, flow measurements should be obtained on the STA stump to ensure that the vessel has not been inadvertently strangulated or compromised.
Postoperatively, a CT of the head without contrast is performed to monitor for hemorrhage and a cerebral angiogram is done to assess the direct bypasses and flow- augmented territories. The patient is then observed in the intensive care unit (ICU) for a minimum of 24 to 48 hours. Systolic blood pressure is initially kept between 100 and 140 mm Hg to prevent reperfusion hemorrhage in case of prior strokes or hyperperfusion syndrome, and then liberalized from 100 to 160 mm Hg after 24 hours. Aspirin is never discontinued and levels may be monitored to ensure therapeutic antiplatelet effect. While in the ICU, hourly neurological examinations are performed until stable and then every 2 hours until the patient is transferred to the step-down unit. At that time, neurological examination is performed every 4 hours. Quantitative MRA/NOVA is performed in the postoperative period to measure bypass flow and MMA flow, establishing new baselines. After discharge from the hospital, we use functional MRI with global and regional BOLD and CO2 challenge and quantitative MRA/NOVA with and without Diamox at 6 weeks and then 6 months to assess for adequacy of flow augmentation and improvement of cerebrovascular reserve. Neuropsychological testing is done preoperatively at baseline, and then at 6 months after bypass to evaluate for cognitive improvement. A followup cerebral angiogram is performed 1 year postopera- tively to assess for any indirect bypass.
Several difficulties may be encountered during this procedure. If bypass flow is not adequate and the CFI is less than 0.5, consider the following: poor patient selection— best avoided thorough preoperative hemodynamic assessment; donor problem—avoided by careful harvest, keeping the vessel hydrated and protected in the papa- verine-soaked cottonoid, flushing with heparinized saline, ensuring adequate dissection of the surrounding tissue cuff from the donor graft, and ensuring that the vessel wall is not dissected; anastomosis problem— avoided by checking the back wall during suturing or use of a stent, flushing with heparinized saline prior to completion of the bypass, ensuring a clean suture line inside the lumen, correcting any dog-ear of the vessel which may compromise the lumen and anastomosis, and ensuring good size match of donor to recipient; recipient or distal bed problem—avoided by choosing adequate vessel size, flushing with heparinized saline, and choosing an ischemic vascular bed with poor reserve.
In this technically challenging surgery, it is best to prevent an error from occurring rather than fixing it. Nonetheless, certain errors do happen occasionally. If the STA is damaged during craniotomy (caught with the drill), and the cut is distal enough, the damaged portion may be amputated to obtain a clean edge. Otherwise, the other STA branch may be harvested, mobilized, and utilized. If the bypass is not flowing after anastomosis, first check the suture line, and gently massage the vessels and the anastomosis site. If there still is paucity of flow, local thrombolytic (tissue plasminogen activator or integrillin) may be injected. Ultimately, the anastomosis may need to be opened and revised, or a new anastomosis performed on a different recipient vessel. If the bypass flow is reduced during closure of the dura or muscle layers, the closure should be reopened and revised—dura and/or muscle bulk can be excised to create enough space so that the course of the STA is unobstructed. Similarly, any strangulating craniotomy bone edge should be removed. If the bypass is punctured by a needle inadvertently, apply gentle pressure with a micro-instrument until it stops. If needed, a 10-0 suture can be placed to repair the hole.
Appropriate preoperative patient evaluation and selection cannot be understated. Exhaustive review of the preoperative angiogram, with study of MMA collaterals and planning of donor/recipient vessels and bypass configuration must be done. Donor and recipient vessels should be matched for size. Mannitol, lasix, and hyperventilation should be avoided. Anticonvulsant prophylaxis is optional but advised. Clean technique from start to end is paramount, throughout every step of the operation, from STA mapping to skin closure. The STA must be kept moist and wrapped in a papaverine-soaked cottonoid until ready for anastomosis, and must be flushed generously and repeatedly with heparinized saline. The bypass field should be elevated by placing gelfoam under the rubber dam that isolates the recipient. Do not hesitate to use a stent during anastomosis, but do not forget to remove it prior to completion! Continuously inspect the back wall of the anastomosis and the suture line prior to suturing the other side. Flow measurements during the case are critical in decision-making and evaluation. The surgeon must be prepared with troubleshooting maneuvers and alternative plans based on measurements. If leakage is observed at the anastomosis site after completion, copious irrigation is often sufficient to stop the oozing; otherwise, a stich may be added. If the bypass is not flowing well and thrombus formation is noted, local thrombolytic can be injected but one should not hesitate to reopen and revise an anastomosis. Ultimately, an anastomosis on different recipient may be performed using the same donor as salvage. Of note, in the senior author’s experience, some bypasses may be visualized angiographically 1 to 2 months after appearing nonfunctional.
References
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Suggested Readings
Amin-Hanjani S, Singh A, Rifai H, et al. Combined direct and indirect bypass for moyamoya: quantitative assessment of direct bypass flow over time. Neurosurgery. 2013; 73(6):962-967, discussion 967-968