EDUCATION CORNER

Challenging Case:
Moyamoya, a Rare Cerebrovascular Disease: Clinical Decision Making and Concerns for the Anesthesiologist

Eugenia Ayrian, MD
Candice Tay, MD 
University of the Southern California 
Contribution by Trainee Engagement Committee of SNACC

Eugenia Ayrian, MD
Eugenia Ayrian, MD
Candice Tay, MD
Candice Tay, MD

Introduction
Moyamoya disease (MMD) was described by Takeuchi and Shimizui1 in 1957 and by Nomura2 in 1961. It is characterized by progressive stenosis and occlusion of terminal portions of the internal carotid arteries and the proximal portion of the anterior and middle cerebral arteries. The formation of collaterals between the internal and external carotid on angiogram presents in a characteristic “puff of smoke” form.

MMD is an idiopathic cerebrovascular disease, but it has definite ethnic and familial (9-12% of cases)3 predisposition. It can be associated with Alzheimer’s Disease, neurofibromatosis, Down syndrome, sickle cell anemia, and Marfan syndrome. The incidence of MMD is the highest in Japan – 0.54 per 100,000 population; it mostly affects female population, with a female to male ratio of 1.8:1.4. This disease tends to be bimodal, presenting in children (mostly in Japan) and North American adults in their third and fourth decades. MMD has been described as an intimal thickening of fibrous tissue which can progress to total vessel occlusion (over a five-year period) from smooth muscle hyperplasia and luminal thrombosis. It leads to the formation of collateral vessels secondary to hypoxia. Clinically, patients usually present with transient ischemic attack (TIA), major ischemic stroke, ICH, seizures, headaches and brain aneurysms.

Treatment
Patients are treated by surgical revascularization, which immediately improves blood flow and significantly reduces ischemic sequelae. Treatment can be performed by:4

  • Direct bypass procedures – Superficial temporal artery (STA) to middle cerebral artery (MCA) bypass
  • Indirect bypass procedures
    • Encephaloduroarteriosyngiosis (EDAS) – dissection of STA free and suturing the artery to the cut edges of the opened dura (promotes angiogenesis and decreases recurrent ischemia)  
    • Encephalomyosynangiosis (EMS) – temporalis muscle is dissected and placed on the surface of the brain to promote collateral vessel formation
    • Encephalomyoarteriosynangiosis (EMAS) is a combination of EDAS and EMS
    • Temporoparietal facial flap (TPFF)– in pediatric MMD
  • Combined direct STA-MCA bypass with indirect revascularization through a pedicled TPFF, which offers direct cerebral blood augmentation from the STA and supplemental neovascularization from TPFF placed in direct contact with the brain surface.

Each method has benefits and drawbacks. Direct revascularization offers immediate and reliable blood flow supplementation, but is associated with technical challenges, hyperperfusion syndrome and stroke.  In addition, direct revascularization has a need for matching donor and recipient artery calibers. Indirect revascularization, on the other hand, is technically easier and faster, but relies on late and slow revascularization. Currently, combined revascularization is recommended as the treatment of choice for adult MMD.

The role of the anesthesiologist is crucial in handling these patients during the surgery. Management of cerebral perfusion pressure (CPP) in particular is extremely important and requires careful considerations.

Case description
A 63-year-old female with a history of two transit ischemic attacks TIAs presented with right sided weakness, slurred speech, left facial droop and severe hypertension (HTN) of SBP≈200s and DBP >100s following a Left (L) MCA ischemic infarct.

Past medical history was significant for HTN and MMD. The patient was emergently scheduled for L STA to L MCA cerebral bypass with indirect revascularization through a pedicled TPFF.   

Neurosurgical evaluation showed the patient to be exceptionally perfusion dependent, thus intraoperative HTN was instituted until revascularization was established.  Maintenance of an increased cerebral perfusion pressure (CPP) during this time required an anesthetic technique including continuous use of vasoactive agents to augment HTN and prevent further infarction.

  • Patient was transferred to OR maintaining blood pressure of 200/110.
  • An awake left radial arterial line was placed under sterile conditions.
  • Patient was induced with etomidate and fentanyl while baseline mean arterial pressure (MAP) of ~130 was maintained.
  • Anesthesia was maintained with propofol and remifentanil infusions (total intravenous anesthesia - TIVA) in order to facilitate SSEP and neuromonitoring
  • Pco2 was maintained at 38-42 mm Hg. 
  • Burst suppression with propofol was induced once cranium was open.
  • Phenylephrine infusion was titrated (20 to 120 mcg/min) to sustain permissive HTN at all times
  • After revascularization was complete, the blood pressure was decreased to MAP of 100 by discontinuation of burst suppression and support of vasopressors.

The patient was transferred to ICU intubated. Post-Op day one, the patient was extubated with partial recovery from original deficit from ischemic stroke.

Discussion
The pathophysiology and clinical questions that arose in the case presented above include:

  • What are the vascular considerations in a stable Moyamoya patient?
  • How should CPP be maintained throughout the case? What are the specifics of blood pressure management in patients with severe HTN and ischemic stroke? 
  • What are the techniques for successful brain protection during the procedure, especially at the time of anastomosis creation?
  • What is symptomatic hyperperfusion?
    • How should blood pressure be managed to mitigate symptomatic hyperperfusion?
    • What are the goals for blood pressure management?
  • Should a patient be extubated at the end of surgery?
  • How should blood pressure should be managed in the ICU after the procedure?

Perioperative Management of Moyamoya
The delicate cerebral blood supply in MMD patients put them at increased risks for perioperative morbidity due to the hemodynamic changes that occur during anesthesia. If Moyamoya is being treated electively, the recommendation is the patient should be admitted the day prior to surgery for aggressive hydration. If the patient comes from home, the patient should be given clear fluids, as dehydration may result in a decrease in cerebral blood flow (CBF). In fact, it has been suggested that overhydration may be beneficial to avoid decreases in CPP and hypotension.5 All medications, such as ASA, Ca-channel blockers, anti-epileptics should be continued. The anesthetic design focuses on optimizing outcomes during surgical revascularization and promoting favorable outcomes both immediately and in the future. If patient is admitted with ischemic stroke prior to the OR, then the anesthesiologist must be aware of the risk of further cerebral ischemia. If this is the case, then careful attention to hematocrit and oxygen carrying capacity is necessary. 

The greatest anesthetic challenge is considering the vascular implications of an altered cerebral autoregulation and management of CPP. The degree of autoregulation maintained in MMD is unclear. The limits of autoregulation in MMD patients are individualized, but considered to be narrower than the general population. At baseline, Moyamoya vessels and normal cerebral collaterals are maximally dilated, therefore, blood flow just meets oxygen demand in the awake patient with Moyamoya. Any further reduction in CBF results in increased oxygen extraction, indicating an exhausted vascular reserve.6 

The ultimate goal during surgery is to ensure adequate oxygen supply when faced with compromised perfusion. The incidence of ischemic complications, especially in the perioperative period, is significant enough to warrant optimization of perfusion under general anesthesia. CPP should ideally be maintained above baseline as autoregulation becomes pressure dependent in ischemic brain matter.7  Furthermore, in the setting of normal ICP and cerebral venous pressure (CVP), increasing MAP can be considered a surrogate for increasing CPP.

Therefore, in patients with MMD, especially when complicated by an acute ischemic stroke, avoiding hypoperfusion is critical. Multiple methods of induced HTN have been described in the literature.  Fundamental qualities of ideal agents for induced HTN should include:8

    • direct action
    • rapid onset of action
    • easy titration
    • minimal effect on ICP

Phenylephrine, dopamine, and norepinephrine are commonly cited agents in literature and practice, all of which are direct acting agents that raise the MAP by increasing systemic vascular resistance.5 Blood pressure augmentation should preferably target α1-receptors, as they are prominent peripherally, and thus effectively raise the MAP by vasoconstriction.  Cerebrally, however, α1 receptors are sparse and hence cause minimal cerebral vasoconstriction.8 Hemodynamic control should ideally maintain MAPs within 10-20% of pre-induction blood pressure during the procedure.6

Techniques for Cerebral Protection
This technique of blood pressure augmentation has still not achieved widespread use because of the perceived risks of intracerebral hemorrhage and worsening brain edema.8 Nevertheless, it has long been considered a “bridging therapy,” as in our case, until surgical intervention can take place.8 Thus, it can be concluded the therapy of induced HTN may still be considered preliminary, it stands to have a role in the early neurosurgical and anesthetic management of an acute ischemic stroke.

Another challenge is maintaining the normocapnea during the procedure to avoid compromising CBF. Hypocapnia promotes vasoconstriction, while hypercapnia may precipitate a steal phenomenon from the already maximally dilated ischemic vasculature.9

Cerebral vasodilators including volatile anesthetics, nitrous oxide, and vasodilating anti-hypertensives may exacerbate steal phenomenon.10 Therefore, the utility of propofol is of value. As a cerebral vasoconstrictor, propofol decreases cerebral oxygen consumption (CMRO2) and CBF in a dose dependent fashion, as well as decrease ICP.11 In our patient, TIVA with propofol in combination with a potent opioid remifentanil was used. During creation of anastomosis, burst suppression was used to decrease CMRO2 for brain protection.    

Maintenance of adequate intravascular volume while providing reasonable brain relaxation necessitates limited diuresis.12 Normovolemia to mild hypervolemia should be maintained using clinical parameters such as continuous blood pressure monitoring, serial hourly arterial blood gas, and electrolyte evaluation. In addition, a goal hematocrit of 30% to 42%8 also guided the fluid and transfusion triggers to promote adequate oxygen delivery while limiting viscosity through occluded vasculature. Avoiding polycythemia is important as it is associated with increased risk of cerebral infarction.

Maintenance of adequate temperature value guards against hypothermia induced cerebral vascular spasm which may increase the risk of ischemia.13 The use of heated pads, forced-air warming devices, fluid warming, and room temperature control were instituted into our practice to ensure normothermia.

Cerebral Hyperperfusion and Blood Pressure Control
STA-MCA anastomosis provides low-flow revascularization because of the relatively small diameter of the recipient artery.14 This results in cerebral hyperperfusion, which in MMD patients causes transient focal neurological deficit or delayed intracerebral hemorrhage. This is unlike post-carotid endarterectomy hyperperfusion, which normally presents as progressive headache, opthalmoplegia, and seizure.6 The symptomatic hyperperfusion is a legitimate concern after revascularization, and 38.2% of adults and 5.6% of children experience this condition.15 Therefore, decreasing the blood pressure values after revascularization should be considered. Recommendations suggest that SBP should be maintained <120 mmHg in normotensive patients and <140 mmHg in hypertensive patients for a week postoperatively.6  Calcium channel blockers postoperatively are the preferred method for blood pressure control as it also reduces vasospasm. 

Considerations for Extubation and ICU Management
At the conclusion of any neurosurgery case, evaluation of neurological function is paramount, thus early awakening is helpful. However, a patient’s baseline neurological function should influence the decision for extubation. If patient was obtunded before the procedure, it can be expected that the patient will have decreased consciousness postoperatively. In this case, keeping patient intubated is recommended in order to maintain vital signs within normal limits. Maintaining normocapnia will further avoid cerebral hyperperfusion and hypertension.  Furthermore, all normal postoperative prevention should be delivered including prevention of nausea and vomiting, shivering, pain, and hypoxia.

In the ICU the blood pressure, central venous pressure, urine output, hematocrit and oxygen saturation should be closely monitored. It is very important to avoid extreme values of blood pressure, as hypotension can cause ischemia and neurological deficit, and hypertension can cause bleeding and hyperemia. The mean blood pressure should ideally be maintained in the range of 80 to 100mm Hg.16

Conclusion
To reiterate the anesthetic management of Moyamoya surgery, the patient should be admitted the day before for aggressive hydration. All the patient’s home medications including aspirin, calcium channel blockers and anti-epileptics should be continued until the day of surgery. The patient’s hemodynamic parameters should be maintained with a smooth intravenous induction and maintenance of anesthesia by total intravenous anesthesia should be considered. Permissive hypertension achieved with an α1-receptor agonist with rapid onset of action, easy titration and minimal effect on ICP should be instituted until perfusion is reestablished. Cerebral protection is optimized with maintenance of normocapnia to mild hypercapnia, mild diuresis, burst suppression and normothermia. Hydration of the patient to achieve hematocrit of 31-42% is ideal to facilitate oxygen delivery and to avoid sludging or thrombosis. At the termination of the case and once perfusion is established, consideration of anti-hypertensives to avoid symptomatic hyperperfusion may be needed and should be closely monitored. The need for ICU monitoring for hyperperfusion and neurological complications should be considered. Post-operative intubation may be indicated if pre-operative neurological function is compromised.

References:

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  2. Nomura T. Atlas of Cerebral Angiography. Tokyo: Sgakushion, 1961192–195.
  3. Kuriyama S, Kusaka Y, Fujimara M, Wakai K, Tamakoshi A, Hashimoto S, Tsuji I, Yoshimoto T. Prevalence and clinicoepidemiological features of moyamoya disease in Japan: findings from a nationwide epidemiological survey. Stroke. 2008; 39:42–47.
  4. Ravina K, Rennert RC, Strickland BA, Chien M, Carey JN, Jonathan J Russin JJ. Pedicled temporoparietal fascial flap for combined revascularization in adult Moyamoya disease. J of Neurosurgery. 2018; 139-144.
  5. Parrat T, Martin TW, Siddiqui, S. Moyamoya Disease: A Review of the Disease and Anesthetic Management, JNA, 2011; 23(2):100-109.
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  7. Wityk, Robert J: Blood pressure augmentation in acute ischemic stroke. J of the Neurological Sciences, 2007; 261(1): 63 -73.
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  11. Kikuta K, Takagi Y, Nozaki K, Yamada K, Miyamoto S, Kataoka H, Arai T, Hashimoto N. Effects of intravenous anesthesia with propofol on regional cortical blood flow and intracranial pressure in surgery for Moyamoya disease. Surgical Neurol. 2007; 68:421–424.
  12. Sato K, Shirane R, Yoshimoto T. Perioperative factors related to the development of ischemic complications in patients with moyamoya disease. Childs Nerv System. 1997; 13:68–72.
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  14. Gesang D, Zhang D, Zhao J, et al. Laser Doppler flow meter study on regional cerebral blood flow in early stage after standard superficial temporal artery-middle cerebral artery bypass surgery for moyamoya disease. C\hin Med J. 2009;122: 2412–2418.
  15. Fujimura M, Kaneta T, Tominaga T. Efficacy of superficial temporal artery-middle cerebral artery anastomosis with routine postoperative cerebral blood flow measurement during the acute stage in childhood moyamoya disease. Childs Nerv Syst. 2008; 24:827–832.
  16. Guzman R, Lee M, Achrol A, Bell-Stephens T, Kelly M, Do HM. Clinical outcome after 450 revascularization procedures for moyamoya disease. J Neurosurg. 2009; 111:927–935.
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