Symptomatic cerebral hyperperfusion after occipital artery-posterior cerebral artery bypass in a patient with moyamoya disease: illustrative case.

backgroundMoyamoya disease (MMD) is a progressive, steno-occlusive cerebrovascular disorder. Posterior cerebral artery (PCA) stenosis can develop after successful anterior circulation revascularization. Although symptomatic cerebral hyperperfusion (CHP) is a recognized complication of anterior revascularization, it is rarely reported following occipital artery (OA)-PCA bypass. OBSERVATIONS: The authors report the case of a 50-year-old woman with MMD who developed symptomatic hemodynamic compromise due to progressive right PCA stenosis 10 years after bilateral superficial temporal artery-middle cerebral artery bypass and indirect revascularization. She underwent OA-PCA bypass with encephalo-myo-synangiosis. On postoperative day 1, single-photon emission CT revealed focal CHP in the right parietal lobe, with cerebral blood flow (CBF) increasing to 160% of preoperative levels. The patient developed a pulsatile headache and left-sided tongue numbness. By postoperative day 7, CBF had decreased to 110%, and perfusion had improved throughout the right parietal-occipital region. With strict blood pressure control and minocycline administration, both symptoms and CHP resolved. At the 1-year follow-up, the patient remained symptom free without stroke recurrence. LESSONS: Symptomatic CHP can occur after OA-PCA bypass in MMD. Perioperative CHP management, including blood pressure control and anti-inflammatory therapy, is essential for optimal outcomes of posterior circulation bypass. https://thejns.org/doi/10.3171/CASE25486.