Intraoperative transit-time flowmetry of the superficial temporal artery directly predicts and may mitigate risk of postoperative hyperperfusion syndrome in moyamoya bypass surgery.
Wen Y, Wang Z, et al. • Frontiers in neurology • 2026
Intraoperative transit-time flowmetry of the superficial temporal artery directly predicts postoperative cerebral hyperperfusion syndrome in moyamoya bypass surgery, with lower STA-Cut flow rates associated with higher likelihood of CHS.
Key Findings
Results
STA flow increases dramatically after vessel cutting and anastomosis, transitioning from a low-flow in situ vessel to a medium- to high-flow graft vessel.
STA in situ flow measured 7.06 ± 3.30 mL/min prior to any intervention
STA-Cut flow (after cutting but before anastomosis) was 59.75 ± 37.49 mL/min
Flow following STA anastomosis was 36.07 ± 22.59 mL/min
Prior to closure (bonnet aponeurosis and skin), STA flow was 35.14 ± 22.93 mL/min
The STA transitions from a low-flow vessel in situ to a medium- to high-flow graft vessel immediately after anastomosis
Results
Postoperative STA flow remained substantially elevated compared to intraoperative post-anastomosis levels.
Postoperative STA flow on day one was 111.91 ± 62.06 mL/min
Postoperative STA flow on day seven was 104.47 ± 64.93 mL/min
These values represent approximately a 3-fold increase compared to intraoperative post-anastomosis flow of 36.07 ± 22.59 mL/min
STA flow stabilized at an elevated level after anastomosis throughout the perioperative period
Results
12.74% of patients undergoing EC-IC bypass surgery for moyamoya disease developed cerebral hyperperfusion syndrome (CHS).
102 hemispheres underwent revascularization through EC-IC bypass in this retrospective analysis
The cohort comprised 69 direct bypass cases and 33 combined bypass cases
CHS incidence was 12.74% across the full cohort
The study was a retrospective analysis of perioperative cerebral blood flow measurements
Results
Logistic regression analysis identified STA-Cut flow as significantly correlated with the occurrence of CHS, with lower flow rates associated with higher likelihood of CHS.
Logistic regression analysis indicated that STA-Cut flow was significantly correlated with CHS occurrence
Lower STA-Cut flow rates were associated with a higher likelihood of CHS development
STA-Cut flow was measured using a transit time ultrasonic flowmeter intraoperatively
The relationship suggests that lower pre-anastomosis donor vessel capacity may be a risk factor for hyperperfusion
Results
Surgical approach and the modified MBC scale were also related to the incidence of CHS in addition to STA-Cut flow.
A modified MBC scale was developed to evaluate the vascular network of the middle cerebral artery (MCA)
Both surgical approach (direct vs. combined bypass) and the modified MBC scale were identified as related to CHS incidence
The modified MBC scale and surgical approach were analyzed alongside STA flow measurements in logistic regression
These factors were identified as additional correlates of CHS beyond intraoperative flow measurements
Results
Variability in graft vessel flow plays a significant role in the occurrence of postoperative hyperperfusion syndrome.
The study monitored blood flow in the donor artery, graft vessels, and recipient artery at various perioperative stages
Fluctuations in donor vascular flow were observed during the perioperative period
Transit time flow measurements were used alongside Doppler ultrasound for real-time monitoring
The authors concluded that 'variability in flow within the graft vessel plays a significant role in the occurrence of postoperative hyperperfusion syndrome'
What This Means
This research studied 102 patients who underwent a surgical procedure called extracranial-intracranial (EC-IC) bypass surgery for moyamoya disease, a condition where arteries in the brain become narrowed or blocked. The surgery involves connecting the superficial temporal artery (STA), a vessel on the outside of the skull, to arteries inside the brain to improve blood flow. The researchers used a special ultrasound device called a transit-time flowmeter to measure blood flow in the donor artery at multiple points before, during, and after surgery. They found that the STA starts as a relatively low-flow vessel (about 7 mL/min) but immediately increases to much higher flow after being cut and connected to the brain's blood supply. By the first day after surgery, flow had risen to over 100 mL/min on average.
About 13% of patients developed a serious complication called cerebral hyperperfusion syndrome (CHS), where too much blood suddenly rushes into brain tissue that was previously starved of blood flow. This can cause headaches, seizures, or bleeding in the brain. The researchers found that patients with lower STA blood flow at the time of vessel cutting — before the bypass connection was made — were at significantly higher risk of developing this complication. The type of surgical approach used and a scoring system the team developed to assess the brain's existing blood vessel network (the modified MBC scale) were also linked to CHS risk.
This research suggests that measuring blood flow in the donor artery during surgery using transit-time flowmetry could help surgeons identify which patients are at greatest risk of dangerous hyperperfusion after the bypass is completed. By knowing the flow characteristics of the donor vessel before anastomosis, surgical teams may be better positioned to take preventive measures or adjust their approach. This adds a potentially practical, real-time tool to the management of one of the more serious complications of moyamoya bypass surgery.
Wen Y, Wang Z, Wang Y, Chen F, Long T, Zhang S, et al.. (2026). Intraoperative transit-time flowmetry of the superficial temporal artery directly predicts and may mitigate risk of postoperative hyperperfusion syndrome in moyamoya bypass surgery.. Frontiers in neurology. https://doi.org/10.3389/fneur.2026.1863863