Incidence and Risk Factors of the Watershed Shift Phenomenon after Superficial Temporal Artery-Middle Cerebral Artery Anastomosis for Adult Moyamoya Disease.

OBJECTIVE: Superficial temporal artery-middle cerebral artery (STA-MCA) anastomosis is the standard surgical management for adult moyamoya disease (MMD) patients, but local cerebral hyperperfusion (CHP) and cerebral ischemia are potential complications of this procedure. Recent hemodynamic analysis of the acute stage after revascularization surgery for MMD revealed a more complex and unique pathophysiological condition, the so-called "watershed shift (WS) phenomenon," which is defined as a paradoxical decrease in the cerebral blood flow (CBF) at the adjacent cortex near the site of local CHP. The objective of this study was to clarify the exact incidence, clinical presentation, and risk factors of the WS phenomenon after direct revascularization surgery for adult MMD. PATIENTS AND METHODS: Among 74 patients with MMD undergoing STA-MCA anastomosis for 78 affected hemispheres, 60 adult patients comprising 64 hemispheres underwent serial quantitative CBF analysis by N-isopropyl-p-[123I] iodoamphetamine single-photon emission computed tomography after revascularization surgery. The local CBF was quantitatively measured at the site of anastomosis and the adjacent cortex before surgery, as well as on 1 and 7 days after surgery. Then, we investigated the incidence, clinical presentation, and risk factors of the WS phenomenon. RESULTS: The WS phenomenon was evident in 7 patients (7/64 hemispheres; 10.9%) after STA-MCA anastomosis for adult MMD. None of the patients developed neurological deterioration due to the WS phenomenon, but 1 patient developed reversible ischemic change on diffusion-weighted imaging at the site of the WS phenomenon. Multivariate analysis revealed that a lower preoperative CBF value was significantly associated with the occurrence of the WS phenomenon (20.3 ± 7.70 mL/100 g/min in WS-positive group vs. 31.7 ± 8.81 mL/100 g/min in WS-negative group, p= 1.1 × 10-2). CONCLUSIONS: The incidence of the WS phenomenon was as high as 10.9% after STA-MCA anastomosis for adult MMD. The clinical outcome of the WS phenomenon is generally favorable, but there is a potential risk for perioperative cerebral infarction. Thus, we recommend routine CBF measurement in the acute stage after revascularization surgery for adult MMD to avoid surgical complications, such as local CHP and cerebral ischemia, caused by the WS phenomenon. Concomitant detection of the WS phenomenon with local CHP is clinically important because blood pressure reduction to counteract local CHP may have to be avoided in the presence of the WS phenomenon.