Moyamoya disease is a rare constrictive cerebrovascular condition associated with cerebral hemorrhage or infarction. Hyperperfusion syndrome is a significant complication of direct bypass surgery for moyamoya disease. Previous research has shown that an increase in cerebral blood flow (CBF) is strongly indicative of symptomatic hyperfusion syndrome. As a result, post-operative assessment of cerebral blood flow is strongly recommended. 
In the first study of a correlation between hyperperfusion syndrome and intraoperative graft flow during bypass surgery for moyamoya disease, Nakamura A et al, Dept. of Neurosurgery, Tokyo Women’s Medical Univ., Yachiyo Medical Center, Chiba, Japan sought to:
- Quantitatively analyze the relationship between intraoperative graft flow and increase in CBF.
- Evaluate the effectiveness of graft flow measurement during bypass surgery for moyamoya patients.
The study evaluated 91 surgeries in 67 consecutive adult patients with moyamoya disease (mean age: 39 years, range: 16–75 years). These patients underwent direct revascularization surgery between November 2013 and September 2018.
Prior to surgery, patients were assessed using MRI, MR angiography and conventional angiography.
Direct bypass procedures included: 77 STA-MCA single or double bypasses, 2 STA-anterior cerebral artery and MCA double bypasses, 4 retroauricular artery and STA-MCA double bypasses, and 8 occipital artery-MCA single or double bypasses.
After the anastomoses had been created, intraoperative bypass graft flow was measured in all patients with a Transonic perivascular Flowprobe (H2MB – 2 mm, H3MB – 3 mm) and dual-channel flowmeter (HT207 equipped with a personal computer interface for waveform analysis).
Postoperative CBF measurements were performed under sedation, immediately after surgery.
- Radiological hyperperfusion was defined as focal high uptake as determined by CBF imaging. • Patients were divided into two groups: radiological hyperperfusion and nonradiological hyperperfusion.
- The relationship between intraoperative graft flow and radiological hyperperfusion was analyzed.
- A receiver-operating characteristic analysis was performed to test the utility of intraoperative flow as a quantitative measure.
The study found a significant correlation between hyperperfusion syndrome and intraoperative graft flow during bypass surgery for moyamoya disease.
“There is an advantage of intraoperative graft flow measurement over a Single Photon Emission Computed Tomography (SPECT) scan. Although patients in our institution can undergo SPECT immediately postoperatively, in most other centers this is not the case due to preparation of nuclide. Our study has shown that intraoperative graft flow can provide early and easy prediction of radiological hyperperfusion,” Nakamura A et al write.
The study authors continue: “The measurement of intraoperative graft flow during bypass surgery for MMD may be an effective means of predicting postoperative hyperperfusion. Intraoperative prediction of hyperperfusion could lead to faster implementation of therapeutic interventions such as strict BP control. A larger, multicenter study is required to evaluate in further detail the optimal cutoff values for intraoperative graft flow.”