Normative distribution of posterior circulation tissue time-to-maximum: Effects of anatomic variation, tracer kinetics, and implications for patient selection in posterior circulation ischemic stroke

Abstract

The generalization of perfusion-based, anterior circulation large vessel occlusion selection criteria to posterior circulation stroke is not straightforward due to physiologic delay, which we posit produces physiologic prolongation of the posterior circulation perfusion time-to-maximum (Tmax). To assess normative Tmax distributions, patients undergoing CTA/CTP for suspected ischemic stroke between 1/2018-3/2019 were retrospectively identified. Subjects with any cerebrovascular stenoses, or with follow-up MRI or final clinical diagnosis of stroke were excluded. Posterior circulation anatomic variations were identified. CTP were processed in RAPID and segmented in a custom pipeline permitting manually-enforced arterial input function (AIF) and perfusion estimations constrained to pre-specified vascular territories. Seventy-one subjects (mean 64 ± 19 years) met inclusion. Median Tmax was significantly greater in the cerebellar hemispheres (right: 3.0 s, left: 2.9 s) and PCA territories (right: 2.9 s; left: 3.3 s) than in the anterior circulation (right: 2.4 s; left: 2.3 s, p < 0.001). Fetal PCA disposition eliminated ipsilateral PCA Tmax delays (p = 0.012). Median territorial Tmax was significantly lower with basilar versus any anterior circulation AIF for all vascular territories (p < 0.001). Significant baseline delays in posterior circulation Tmax are observed even without steno-occlusive disease and vary with anatomic variation and AIF selection. The potential for overestimation of at-risk volumes in the posterior circulation merits caution in future trials.

Tmax profile in computed tomography perfusion-based RAPID software maps influences outcome after mechanical thrombectomy in patients with basilar artery occlusion

“…These results may indicate that autogenerated mismatch in CTP-RAPID cannot be used in pc-stroke due to inaccurate estimation, especially for ischemic cores. Consequently, Tmax, as used in the present study, might be a reasonable independent CTP-RAPID parameter for estimating penumbral volumes, despite the overestimation 16 17. The results may also explain the high cut-off value of Tmax >6 s in our results, considering the relatively small volume of posterior circulation compared with that of anterior circulation.…”

“…CTP imaging criteria based on the tissue window benefited more patients with large vessel stroke due to the salvage of reversible tissue after reperfusion therapy. Unfortunately, to date, threshold-based perfusion selection criteria have not been applied in pc-stroke due to hemodynamic delay, anatomical imbalance and variation 16. Capasso et al 17 recently compared the diagnostic accuracy between qualitative and automatic evaluations of CTP parameters in pc-stroke.…”

Thrombectomy in basilar artery occlusion

“…30,31 A recent study suggested that tissue at risk might be overestimated in the posterior circulation, most likely due to anatomical variations. 32 In BASICS, pc-ASPECTS did not influence functional outcome, whereas in BASILAR, a pc-ASPECTS score ⩾5 identified patients with a potential benefit of TE. 33…”

“…30,31 A recent study suggested that tissue at risk might be overestimated in the posterior circulation, most likely due to anatomical variations. 32 In BASICS, pc-ASPECTS did not influence functional outcome, whereas in BASILAR, a pc-ASPECTS score ⩾5 identified patients with a potential benefit of TE. International Journal of Stroke, 17 (9) In this study, functional outcome of patients with ACLVO was worse compared to previously published RCTs in ACLVO (mRS 0-2: HERMES: 46.0%, this study: 39.9%).…”

Automated Supra- and Infratentorial Brain Infarct Volume Estimation on Diffusion Weighted Imaging Using the RAPID Software

“…For example, Garcia-Esperon et al (4) reported a sensitivity of about 25% of lacunar strokes in the VB system to be recognized by multi-modal perfusion CT. Cerebellar infarction may be larger, but a good ability of multi-model perfusion CT to detect cerebellar infarction was found only for infarcts > 4-5 ml (5,6). Small structure size, the availability and the duration of the examination (MRI), the poor spatial resolution (CT), physiological variability of cerebral perfusion in this area (7), and the technical difficulties to measure cerebral blood flow correctly in this anatomical region hinder the application of the stroke mismatch concept to a broad range of VBS.…”