Editorial for “Multidelay MR Arterial Spin Labeling Perfusion Map for the Prediction of Cerebral Hyperperfusion After Carotid Endarterectomy”

Editorial for “Multidelay MR Arterial Spin Labeling Perfusion Map for the Prediction of Cerebral Hyperperfusion After Carotid Endarterectomy” Cerebral hyperperfusion syndrome (CHS) is a clinical syndrome following a revascularization procedure such as carotid endarterectomy or stenting. Impaired cerebral autoregulation and postrevascularization changes in cerebral hemodynamics are thought to be the main mechanisms involved in the development of CHS. With an incidence of between 1.2% and 4.6% of patients following revascularization, CHS manifests as a wide spectrum of clinical symptoms ranging from headache, seizure, intracerebral hemorrhage, and possibly death. Consequently, methods to identify patients at risk for symptomatic CHS are of interest. In this issue, Fan et al report the use of multidelay arterial spin labeling (ASL) perfusion MRI at 3 T to predict radiographic cerebral hyperperfusion following carotid endarterectomy. In 79 patients with moderate-to-severe unilateral carotid stenosis who underwent multidelay ASL perfusion imaging before and after carotid endarterectomy, the authors found that multidelay ASL MRI was able to detect radiographic cerebral hyperperfusion, defined as an increase in cerebral blood flow (CBF) of more than 100% compared with baseline preoperative values. In particular, Fan et al developed an “ASL perfusion score” based on brain perfusion appearance on three acquired ASL time delays. The authors found that a poor preoperative ASL perfusion score independently predicted and exhibited the highest specificity (95.3%) for postoperative radiographic cerebral hyperperfusion, whereas preoperative CBF provided the highest sensitivity (93.3%). Moreover, a combination of the ASL perfusion score, CBF, and arterial transit time (ATT) provided a strong predictive capacity (area under the curve [AUC] = 0.95) that exceeded that of blood pressure and carotid near-occlusion status alone (AUC = 0.78). This ASL-specific model was further improved by adding blood pressure and carotid nearocclusion status (AUC = 0.98). Strengths of the study include the development of a straightforward multidelay ASL-based scoring system for predicting radiographic cerebral hyperperfusion that showed excellent interobserver and intraobserver agreement, the evaluation of multiple hemodynamic parameters (eg CBF, ATT, and relative hemispheric analogs), and the high specificity and sensitivity of the multivariable model. A key finding was that a poor ASL perfusion score was highly associated with postoperative radiographic cerebral hyperperfusion (odds ratio of 37.3, P < 0.001). As acknowledged by the authors, study limitations include the limited overall sample size considering the rarity of CHS and that only 2 of 15 (13.3%) patients with radiographic cerebral hyperperfusion progressed to clinically symptomatic CHS. This relatively modest predictive value of radiographic cerebral hyperperfusion for symptomatic CHS may ultimately limit enthusiasm for preemptive antihypertensive therapy in this at-risk subgroup and could be a metric to improve in the future. The high negative predictive value of relatively normal preoperative multidelay ASL hemodynamic parameters may help physicians identify patients who may not require aggressive antihypertensive therapy and potentially guide in-hospital disposition (i.e. need for an intensive care unit stay). Literature is scarce on the use of multidelay ASL perfusion MRI for predicting cerebral hyperperfusion following carotid endarterectomy. In a study performed at 1.5 T, Endo et al found that the regression line slope summarizing hemispheric flow asymmetry across ASL delay times predicted cerebral radiographic hyperperfusion as determined by single photon emission computed tomography (SPECT) with a sensitivity of 85%, specificity of 74%, and negative predictive value of 98%. Although the methods used in these two studies differed, an apparent advantage of the ASL perfusion score as presented by Fan et al (as compared to a slope-based analysis) is the lack of postprocessing and improved ease of interpretation. Whereas other cross-sectional imaging methods such as SPECT, contrast-enhanced computed tomography perfusion, and contrast-enhanced dynamic susceptibility-weighted MRI can be used to evaluate CHS, the proposed multidelay ASL strategy avoids the use of ionizing radiation, vasodilatory agents (eg acetazolamide, CO2 inhalation), and contrast