The superficial temporal artery to middle cerebral artery bypass is an elegant procedure that was developed and first performed by M. Gazi Yaşargil. It has been used by neurosurgeons for more than 30 years in the management of neurovascular disorders such as cerebrovascular ischemic disease, moyamoya disease, and complex intracranial aneurysms. Mastering the technique requires not only precise and fine skills but also devoted training in the microsurgery laboratory 1).
The techniques involved in performing these procedures include microdissection of the superficial temporal artery in the scalp, microdissection of the recipient middle cerebral artery branches near the sylvian fissure, and anastomosis techniques using either microvascular sutures or a microanastomotic device. The successful completion of the bypass and subsequent patency requires meticulous attention to technical details 2).
The data of 63 patients who had the symptoms of cerebral ischemia in recent 3 months, intracranial segment of internal carotid artery (ISICA) and (or) middle cerebral artery (MCA) stenoses or occlusion showed by digital subtraction angiography (DSA), and reduced cerebral perfusion displayed by CT perfusion (CTP) imaging were retrospectively collected in this study. According to the patient's choice of different treatment methods (STA-MCA bypass and drugs), these patients were allocated into two groups: Bypass group (30 cases) and Drug group (33 cases). Postoperative symptoms, anastomotic patency and hemodynamics were observed in the Bypass group. Post-treatment ischemic events and clinical outcomes were recorded in the two groups and were compared between the two groups.
RESULTS: In the Bypass group, DSA all showed anastomotic patency in 28 patients (93.3%, 28/30), and the improvement rate of CTP was all significantly higher in the patients with stage-III CTP than in the patients with stage-II CTP at post-operative 3 days and 6 months (95% vs 60%). Post-treatment ischemic event incidence (13.3% vs 48.5%) and annual stroke rate (6.7% vs 25.6%) were significantly lower in the Bypass group than in the Drug group (All P < 0.05). Pre-treatment National Institutes of Health Stroke Scale (NIHSS) score and Modified Rankin Scale (MRS) score were not significantly different between the two groups, but the NIHSS (2.87±0.19 and 2.4±0.19 vs 4.03±0.47 and 3.97±0.49) and MRS (1.13±0.09 and 1.0±0.07 vs 1.55±0.14 and 1.52±0.15) all were significantly lower in the Bypass group than in the Drug group at post-treatment 6 and 24 months (all P < 0.05).
CONCLUSION: STA-MCA bypass can improve cerebral blood perfusion and reduce the incidence of stroke in the patients who have ISICA and (or) MCA-related symptoms, 70%-100% of stenosis, and above stage-ⅠCTP. However, this conclusion remains to be further confirmed 3).
Katano et al., retrospectively analyzed the cases of 35 patients who underwent an STA-MCA anastomosis for internal carotid artery/MCA occlusion or stenosis. Patients were divided into two groups based on whether the recipient artery was precisely targeted by single-photon emission computed tomography (SPECT group) or less precisely targeted by visual assessment (Visual group). Then the bypass results in both groups were evaluated postoperatively based on changes in the regional cerebral blood flow (rCBF) and clinical outcomes.
The delineated recipient artery in magnetic resonance angiography (MRA) matched the intraoperatively selected artery in 87.6% of the SPECT group cases and 83.3% of the Visual group cases. The SPECT group's digital subtraction angiography (DSA) findings coincided with the intraoperative selection in 76.9% of cases, and the MRA findings corresponded with the DSA findings in 92.3%. The postoperative areas with increased rCBF matched the perfused areas of intraoperatively selected arteries in 80.0% of the SPECT group cases and 77.8% of the Visual group cases. Postoperatively increased rCBF areas matching totally or partially with preoperative low-perfusion areas were observed in all cases.
The present results revealed no significant differences in the change in rCBF in the low-perfusion area between the patients whose recipient arteries were selected by SPECT or visual assessment 4).
112 patients who underwent surgical treatment at the National Scientific and Practical Center for Neurosurgery in the period between 1999 and 2015. Of these, 105 patients had ICA occlusions, and 7 patients had moyamoya disease. During the main stage of EC-IC bypass placement, all patients were monitored for local hemodynamic parameters using intraoperative contact Doppler ultrasonography - 89 (72%) patients (72%) and flowmetry - 56 (50%)). In 33 (29%) cases, both techniques were used. Forty two patients underwent preoperative SCT perfusion to assess the degree of perfusion deficit. Grade 1 cerebrovascular insufficiency (acute oligemia) was detected in 6 patients; grade 2 perfusion deficit (persistent oligemia) was found in 25 patients; grade 3 perfusion deficit (chronic oligemia) was present in 11 patients. Measurements were performed before bypass placement: the blood flow direction and hemodynamic parameters in the cortical arteries were evaluated; and after bypass placement: blood flow values and directions in the cortical artery, proximal and distal to the bypass area, were assessed.
A total of 112 EC-IC bypasses were placed without perioperative complications and deaths. Bypass functioning was confirmed in 108 (96.3%) cases; bypass thrombosis occurred in 4 (3.7%) cases. The distal blood flow direction was observed in patients with ICA occlusions (105 patients) in all cases before EC-IC bypass placement. Patients with moyamoya disease had more often the proximal blood flow direction - 5 (71%) out of 7 cases. The cerebral blood flow parameters obtained in this study differed significantly, depending on the baseline degree of perfusion deficit. The blood flow rate was minimal in patients with grade 1 cerebrovascular insufficiency. After revascularization, local hemodynamics in the cortical arteries was significantly dependent on the ability of EC-IC bypass to reverse blood flow in the proximal acceptor artery. A change in the blood flow direction was observed in 86 (77%) cases. The mean volumetric blood flow in EC-IC bypass was 34.2±5.7 mL/min.
The knowledge of baseline hemodynamic parameters and their changes after revascularization plays an important role in choosing the correct surgical technique, further bypass functioning, and, as a result, improvement of the clinical outcome after surgery 5).
Matano et al, described their method of monitoring MCA pressure and report their initial data on intraoperative MCA pressure and its relationship with hemodynamics prior to and after the bypass procedures.
The results from a total of 39 revascularization procedures performed between 2004 and 2014 were analyzed. The patient group included 27 men and 12 women, and their mean age at surgery was 67.6 years (range 39-83 years). The authors investigated the MCA pressure via the STA during STA-MCA bypass procedures. After one branch of the STA was anastomosed to the MCA, the other branch was connected to an arterial line, and a clip was placed temporally on the main STA trunk to monitor the pre-anastomosis MCA pressure. Simultaneously, the radial artery (RA) pressure was determined before removing the temporal clip to measure the post-anastomosis MCA pressure. The relationship between MCA pressures and single photon emission computed tomography findings and the risk factors for hyperperfusion after STA-MCA bypass were analyzed.
The MCA/RA (%) pressure was significantly correlated with that of the resting stenotic/normal side cerebral blood flow (CBF) ratio (%) in the linear regression analysis (slope 1.200, r2 = 0.3564, F = 20.49, p < 0.0001). The intraoperative MCA pressure was 39.3% of RA pressure in patients with Powers' Stage 2 cerebral atherosclerotic disease. After 1 branch of the STA was anastomosed, the intraoperative MCA pressure increased to 75.3% of the RA pressure. The rate of increase in pressure was significantly correlated with the increase in the STA diameter in the linear regression analysis (slope 2.59, r2 = 0.205, F = 9.549, p = 0.0038). Hyperperfusion occurred in 2 cases. When mean values for these 2 patients were compared with those for the 37 patients without hyperperfusion, significant differences were found in the stenotic/normal side CBF ratio (p = 0.0001), pre-anastomosis MCA pressure (p = 0.02), rate of increase in pressure (p = 0.02), pre-anastomotic MCA/RA pressure ratio (p = 0.01), vascular reserve (p = 0.0489), and STA diameter (p = 0.0002).
The measurement of intraoperative MCA pressure may be a useful technique to assess cerebral perfusion and for predicting the risk of hyperperfusion. Monitoring MCA pressure is recommended during STA-MCA bypass procedures for atherosclerotic disease 6).