Background Combined revascularization is the preferred surgical management of adult Moyamoya disease. However, postoperative flap necrosis of the scalp is not an uncommon complication. We investigated the role of scalp incision design on the basis of the course of the superficial temporal artery (STA) to prevent postoperative scalp necrosis. The utility of tissue expander in wide scalp defect repair is explored. Case Description A 13-year-old female patient underwent STA-to-middle cerebral artery anastomosis and encephaloduroarteriosynangiosis due to ischemic symptoms. However, she suffered from wide scalp necrosis measuring 10.5 × 10 cm after bypass surgery. Conventional rotational scalp flap reconstruction was impossible due to the wide defect, and therefore split thickness skin graft was considered. However, aesthetic compromise or hair loss is a psychologic burden in an adolescent female. Two tissue expanders were inserted under the contralateral normal scalp, and a gradual expansion was achieved by saline infusion for 3 months. Finally, a wide scalp flap, which covered the large defect, was obtained using this procedure. The patient underwent rotational flap advancement and was discharged without any hair loss wound. Conclusions Miserable scalp flap design results in a large scalp defect during combined bypass surgery. However, tissue expanders aided the reconstruction of a large scalp defect. Reconstruction using tissue expanders and advancement of local rotation flap is recommended in case of large scalp necrosis. The procedure yields cosmetically superior outcomes due to scalp hair conservation and concealment of postoperative scar behind the hair line. Highlights • Combined revascularization is the preferred surgical management of adult moyamoya disease. • Postoperative flap necrosis of the scalp is not an uncommon complication. • The utility of tissue expander in wide scalp defect repair is explored. • Miserable scalp flap design results in a large scalp defect during combined bypass surgery. • Tissue expanders aid the reconstruction of a large scalp defect. [ABSTRACT FROM AUTHOR]