17 STA–MCA Anastomosis and EDMAPS
Abstract
Superficial temporal artery to middle cerebral artery (STA–MCA) anastomosis and encephalo-duro-myo-arterio-pericranial synangiosis (EDMAPS) is one of the combined bypasses for moyamoya disease. The novel indirect bypass, EDMAPS enables us to most widely cover the frontal lobe by using the vascularized frontal pericranium. This technique can provide collateral blood flow to almost the entire territory of the internal carotid artery, including the anterior cerebral artery. Thus, STA–MCA anastomosis and EDMAPS may be named as an “ultimate” bypass for moyamoya disease. In this chapter, the author introduces the concept, surgical technique, and pitfalls of STA–MCA anastomosis and EDMAPS for moyamoya disease.
17.1 History and Initial Description
17.1.1 STA–MCA Anastomosis and EDMAPS as an “Ultimate” Bypass
Fig. 17‑1 shows the historical flow of bypass surgery for moyamoya disease at Hokkaido University Hospital. Nakagawa et al established encephalo-myo-arterio-synangiosis (EMAS) in the early 1980s. The temporal muscle and superficial temporal artery (STA) were used as the donor for indirect bypass. 1 However, the incidence of perioperative ischemic complications was not low. 2 Subsequent studies also showed that cerebral hemodynamics was impaired in the frontal lobe even several years after surgery. 3 At that time, STA–MCA (middle cerebral artery) single or double anastomosis was routinely performed, and craniotomy was extended to the frontal area in order to further supply collateral blood to the frontal lobe in the late 1980s. The temporal muscle, STA, and dura mater were utilized as the donor for indirect bypass, called as encephalo-duro-myo-arterio-synangiosis (EDAMS). As a result, the incidence of perioperative ischemic stroke markedly decreased probably because of immediate improvement of blood flow after direct bypass. 2 , 4 Postoperative blood flow studies revealed significant improvement of cerebral hemodynamics in the frontal lobe after STA–MCA anastomosis and EDAMS. Intellectual outcome significantly improved in pediatric patients. 5 However, about 10% of pediatric patients still experienced paraplegic transient ischemic attack (TIA) even after surgery probably because the temporal muscle, a main donor tissue for indirect bypass, covers mainly the MCA territory. Hemorrhagic stroke also recurred in about 20% of adult patients even after STA–MCA anastomosis and EDAMS. 6
Based on these historical observations, Kuroda et al performed STA–MCA single or double anastomosis and extended craniotomy to the medial frontal area to further improve cerebral hemodynamics in the anterior cerebral artery (ACA) territory in the late 1990s. The frontal pericranial flap was used to widely cover the medial frontal lobe in addition to the temporal muscle, STA, and dura mater. A pericranial flap has been widely used to reconstruct the anterior cranial fossa because of its simplicity, reliability, and low morbidity. As reported by Yoshioka and Rhoton, the frontal pericranium receives blood flow mainly from the supraorbital and supratrochlear arteries arising from the ophthalmic artery. 7 The indirect bypass procedure was named as encephalo-duro-myo-arterio-pericranial synangiosis (EDMAPS). As a result, no pediatric patients have experienced paraplegic TIA after surgery. Clinical results strongly suggest that the incidence of recurrent hemorrhagic stroke is much lower than before. 8 Now, we are routinely performing STA–MCA anastomosis and EDMAPS for patients with moyamoya disease. Very recently, we evaluated cumulative incidence of late morbidity/mortality among 93 patients who underwent STA–MCA anastomosis and EDMAPS and were followed up for longer than 5 years post-surgery (mean, 10.5 ± 4.4 years). As per results, 92 of 93 patients were free from any stroke or death, but one recurred hemorrhagic stroke during follow-up periods (0.10% per patient-year, submitted data). Therefore, we believe that STA–MCA anastomosis and EDMAPS would be the best choice to prevent further cerebrovascular events for longer than 10 years by widely providing surgical collaterals to both MCA and ACA territories. In this chapter, therefore, the author describes the concept, surgical procedures, pitfalls, risk, and perioperative managements of STA–MCA anastomosis and EDMAPS.
17.2 Indications and Contraindications
Direct bypass procedures can quickly improve cerebral hemodynamics after surgery, and thus can significantly lower the incidence of perioperative ischemic events, including TIA and ischemic stroke. 1 Furthermore, TIA and/or headache attack quickly decreases in frequency or disappears during follow-up periods after direct bypass procedure. These clinical results of direct bypass are supported by immediate blood flow improvement just after surgery. 2 , 3 The procedures can flexibly be modified as STA–anterior cerebral artery (ACA) or STA–posterior cerebral artery (PCA) anastomosis according to patients’ condition, such as dense ischemia in the territory of the ACA or PCA. 4 However, surgical procedure for direct bypass requires skillful technique and thus a certain surgical training, because the recipients have a small caliber (0.5–1.0 mm in diameter) and more importantly a very thin wall in a majority of patients with moyamoya disease. In addition, it should be reminded that direct bypass procedure would carry the risk for postoperative hyperperfusion, which sometime causes severe neurological sequelae and/or mortality unless appropriate managements are indicated (see Table 17.1). 5 On the other hand, indirect bypass procedures are technically simple and easy, because the vascularized donor tissues are only put onto the surface of the brain. Surprisingly, an aggressive neovascularization occurs between the donor tissues and the brain and start to provide collateral blood flow to the ischemic brain in moyamoya disease. However, indirect bypass may increase the incidence of perioperative TIA and/or ischemic stroke especially in patients with dense ischemia before surgery, because the neovascularization requires 3 to 4 months to establish collateral blood flow. 2 , 6 It is well known that surgical collaterals develop in almost all pediatric patients, although previous reports have shown that efficient surgical collaterals develop through indirect bypass in about 50 to 70% of adult patients with moyamoya disease. 7 Furthermore, surgeons should be aware that the extent of craniotomy largely determined the extent of surgical collaterals through indirect bypass. As aforementioned, it is well known that cerebral ischemia is most dense in the frontal lobe, thus craniotomy for indirect bypass should widely be extended to the frontal area. Combination of direct and indirect bypass may be the best choice for moyamoya disease because an immediate supply of collateral blood flow can compensate for the shortcoming of indirect bypass. Indirect bypass often functions as a major source of surgical collaterals in a certain subgroup of patients even after combined bypass procedure in a majority of pediatric patients and a certain subgroup of adult patients. Thus, reciprocal STA regression occurs in about 30% of the hemispheres during the transition from the postoperative acute phase to the chronic phase during indirect bypass development. 7
17.2.1 Asymptomatic Moyamoya Disease
Recent studies have shown that the prevalence of asymptomatic moyamoya disease is much higher than considered before. Based on the exhaustive survey in Hokkaido Island, Japan, about 20% of patients with newly diagnosed moyamoya disease were asymptomatic. 9 Although the natural course of asymptomatic moyamoya disease is not fully understood, previous nation-wide observational study in Japan revealed that the annual risk of any cerebrovascular events and stroke was 5.7 and 3.2%, respectively. Disturbed cerebral hemodynamics at initial diagnosis was significantly linked to ischemic episodes. Disease progression during follow-up periods also highly caused ischemic cerebrovascular episodes. However, the cohort of this study was small (n = 34). 10 Therefore, the Research Committee on Moyamoya Disease in Japan started a prospective multicenter, nation-wide observational study, called as Asymptomatic Moyamoya Registry (AMORE) in January 2012 to further clarify the epidemiology, pathophysiology, and prognosis in asymptomatic moyamoya disease. As a result, a total of 109 subjects were enrolled during 4 years, and they were carefully followed-up for 5 years. Therefore, the author believes that no bypass surgery should be indicated for asymptomatic moyamoya disease at least until AMORE study reaches any conclusion in 2020. 11
17.2.2 Ischemic-Tpe Moyamoya Disease
There are no effective medical therapies to reduce or prevent further TIA and/or ischemic stroke in moyamoya disease. Importantly, the physicians should be aware that headache attack is closely related to cerebral ischemia and should be recognized as one symptom of TIA in pediatric moyamoya disease. Most of “symptomatic” hemispheres have disturbed cerebral hemodynamics in the territory of internal carotid artery (ICA) due to the reduction of cerebral perfusion pressure (CPP), which is characterized by the most severe ischemia in the frontal lobes. In addition, the involvement of the posterior cerebral artery (PCA) may often impair cerebral hemodynamics in the occipital lobe.
When determining the indication of bypass surgery for moyamoya disease, it is quite valuable to assess the CPP by measuring cerebral blood flow (CBF) before and after intravenous injection of acetazolamide using single photon emission computed tomography (SPECT), positron emission tomography (PET), or cold xenon CT. Reduced reactivity to acetazolamide would be a key finding to identify the reduced CPP in the involved hemispheres. Therefore, STA–MCA anastomosis and EDMAPS should be indicated to the “symptomatic” hemispheres of both pediatric and adult patients who experienced TIA and/or ischemic stroke. 8
Related posts:
14 Combined STAMCA Bypass and Encephalo-myo-synangiosis
15 STAMCA Bypass and EMS/EDMS
18 STA–MCA Bypass and Encephalo-duro-arterio-synangiosis
19 Individualized Extracranial-Intracranial Revascularization in the Treatment of Late-Stage Moyamoya Disease
16 Combined Direct (STA–MCA) and Indirect (EDAS) EC–IC Bypass
7 Encephalo-duro-arterio-synangiosis: In Adults
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