Focal Cerebellar Hyperperfusion After Bypass Surgery for Vertebrobasilar Ischemia: Effect of Cerebrovascular Reactivity as a Potential Predictor of Hyperperfusion

Background: Hyperperfusion in the posterior circulation is a rare complication after surgical revascularization for vertebrobasilar steno-occlusive diseases. We report a case of symptomatic cerebellar hyperperfusion after superficial temporal artery–superior cerebellar artery bypass for vertebrobasilar ischemia. Case Description: A 59-year-old man was admitted with brainstem infarction. Angiography showed bilateral vertebral artery occlusion with poor collateral circulation. Preoperative single-photon emission computed tomography revealed that bilateral cerebellar blood flow was markedly decreased. The cerebrovascular reactivity of the bilateral cerebellum, as measured by single-photon emission computed tomography with acetazolamide challenge, showed steal phenomenon. Superficial temporal artery–superior cerebellar artery anastomosis on the right side was performed through a subtemporal approach. The day after surgery, the patient exhibited temporary disorientation and the local cerebellar blood flow increased up to 182% on the right side of the cerebellum from preoperative levels. We considered that the disorientation was caused by the hyperperfusion, and the blood pressure was strictly controlled. The cerebellar blood flow then gradually decreased to 133% over preoperative levels by 1 week after surgery. The patient did not show further neurologic worsening. Conclusions: Serial hemodynamic study is useful for early detection of hyperperfusion. Steal phenomenon in the preoperative hemodynamic study could be one of the risk factors for postoperative hyperperfusion even in the posterior circulation.