Ken Kazumata and Kiyohiro Houkin
Abstract
Moyamoya disease (MMD) primarily affects the middle and anterior cerebral arteries (MCA, ACA). The MCA as well as ACA is involved predominantly in patients with MMD. Symptomatic cases can be treated successfully by using combined (superficial temporal artery) STA-MCA anastomosis and indirect bypass procedures. Direct anastomosis can be successfully achieved in cases of infantile MMD. Combined direct/indirect bypass procedures demonstrates a several advantages over indirect procedures alone. This chapter discusses these advantages as well as technical points of the combined procedure.
Keywords: moyamoya disease, STA-MCA bypass, revascularization
Combined direct/indirect bypass for the treatment of moyamoya disease (MMD) has been utilized by the Department of Neurosurgery at Hokkaido University since 1985.1 The procedure was developed because we had observed complications such as inconsistent and/or suboptimal growth of postoperative revascularization following indirect bypass alone, such as encephalo-duroarterio-synangiosis (EDAS).2 Compared with indirect procedures alone, combined superficial temporal arterymiddle cerebral artery (STA-MCA) double anastomosis and indirect bypass procedures are more complex, though direct/combined bypass is more often associated with excellent revascularization than indirect bypass.3
Patients with advanced stage of MMD (Suzuki grade III or greater) who demonstrated ischemic symptoms as well as previous history of intracranial hemorrhage are considered candidates for revascularization. In ischemia, symptomatic hemispheres are treated. Asymptomatic hemispheres with hemodynamic compromise may also be treated. Revascularization surgery is performed in bilateral hemisphere of patients with prior history of intracranial hemorrhage.
Our surgical strategy is characterized by the universal application of both direct and indirect bypass regardless of the patient’s age (Fig. 15.1). The standard procedure consists of double STA-MCA anastomosis (Fig. 15.2).
15.4.1 Strengths
Combined direct/indirect bypass immediately increases regional cerebral blood flow (rCBF) at the site of craniotomy and prevents immediate postoperative ischemic complications.3,4 Postoperative revascularization is more extensive following combined direct/indirect bypass than following indirect procedures alone.6 Repeated revascularization procedures in the posterior portion of the brain are also less frequently required when compared with indirect procedures alone.
15.4.2 Weaknesses
This procedure can be time consuming and induce hyperperfusion and brain compression due to swelling of the temporal muscle.5
15.4.3 Opportunities
Symptomatic hemispheres (ischemic attack, stroke, and hemorrhage) are the targets of the combined direct/indirect bypass.
15.4.4 Threats
Bypass occlusion immediately after anastomosis is more frequent than arteriosclerotic internal carotid artery (ICA) occlusion or vascular reconstruction in aneurysmal surgery.
Patients with multiple parenchymal lesions should be treated with indirect procedures. Patients who have experienced very recent strokes or intracranial hemorrhage should be treated conservatively for the first several weeks to allow for adequate recovery from the associated brain damage. Frequent transient ischemic attacks (TIAs) represent a major risk of postoperative cerebral infarction. We try to avoid revascularization surgery during the period in which frequent TIAs are most likely to occur.
The basic procedure consists of frontotemporal craniotomy and double STA-MCA anastomosis combined with overlaying temporal muscle on the surface of the brain, though subsequent modifications have also been performed (Fig. 15.2). For example, direct STA-ACA (anterior cerebral artery) bypass may be accomplished in addition to the standard STA-MCA bypass (Fig. 15.3).7 However, we occasionally encountered suboptimal neovascularization and skin complications using the STA-ACA/MCA bypass technique. Alternatively, indirect procedures involving the midline portion have been attempted, though the benefit of such techniques has not been clearly demonstrated with regard to postoperative stroke rates.8 Thus, we currently utilize the conventional procedure developed in 1985.
Perioperative stroke event should be informed. We observed perioperative stroke events more frequently in adults compared with pediatric patients (adults: 7.9% of surgeries; pediatric patients: 1.7% of surgeries).3 Overall, postoperative complications (stroke events) were observed in 4.7% of surgeries. A low-lying frontal branch of the STA leads to increases in the rate of postoperative facial palsy. Deformity of forehead is also observed due to the use of temporal muscle for indirect anastomosis. Postoperative hyperperfusion induces neurological symptoms such as headache, seizure, speech dysfunction, and numbness in mouth as well as in upper extremity. It can cause intracerebral hemorrhage.
Patients should be placed in supine position under general anesthesia. We instruct patients to discontinue antiplatelet and/or anticoagulant use prior to surgery. No standard regimen has been established with regard to postoperative use of antiplatelet agents.
Patients are placed in supine position. An incision line is drawn on the skin directly above the parietal branch of the STA, and a microscope is used for subsequent dissection of the STA. This maneuver likely decreases the rate of skin complications. After extensive frontotemporal craniotomy, the dura is opened while preserving the middle meningeal artery (MMA). Both the parietal branch and the frontal branch of the STA are anastomosed to the cortical branch of the MCA. The dural flap is inverted and placed on the surface of the brain to increase collateral formation (See Fig. 15.4). The temporal muscle is placed on the surface of the brain and sutured to the edge of the dura, completing encephalo-duro-arterio-myo-synangiosis (EDMAS).1,9
Frequently, bypass thrombosis occurs.
To avoid bypass occlusion and an STA pedicle, single anastomosis can be performed with the parietal branch of the STA left intact and laid over the surface of the brain (arterial synangiosis). While some surgeons may not perform indirect procedures in adult patients, we always perform the indirect procedure in addition to the direct procedure. The additional benefit of the indirect procedure has been investigated and reported elsewhere.10
The MMA should be preserved due to its significant contribution to postoperative neovascularization (Fig. 15.5). Normocapnia and normotension should be maintained throughout the surgery.
In the immediate postoperative period, rCBF increases predominantly in the basal ganglia, which is followed by a gradual increase in lateral prefrontal hyperperfusion.4 Immediate postoperative increases rCBF in subcortical structures are potentially associated with intracerebral hemorrhage following surgery. Prefrontal hyperperfusion is associated with transient neurological deterioration. Regional CBF is assessed using 123I-IMP/SPECT on postoperative day 1 and day 7. Systolic blood pressure is controlled below 140 mm Hg via continuous intravenous administration of Ca2+ antagonists, if necessary. In general, hyperperfusion is a self-limiting process, though transient neurological deficits may occur during the first 2 weeks. Necrosis along with skin incision may also be observed. Therefore, the surgical site should be monitored for proper healing after discharge from the hospital. Bypass patency can be evaluated via magnetic resonance angiography (Fig. 15.6). Immediate postoperative posterior cerebral artery (PCA) regression is observed in approximately 10% of patients (Fig. 15.7).
References
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