PURPOSE To determine the frequency of apparent posterior cerebral artery (PCA) territory asymmetry seen on arterial spin labeling (ASL) imaging in patients with a unilateral fetal PCA, but without underlying clinical or imaging pathology to suggest true hypoperfusion. METHODS A search of radiology reports from 1/2017 through 6/2020 was performed with the inclusion term "fetal PCA." Eighty patients were included with unilateral fetal PCA confirmed on MRA or CTA, with brain MRI including ASL imaging, and without conventional imaging abnormality or clinical symptoms referable to the PCA territories. Cases were evaluated by two independent readers for visually apparent PCA perfusion asymmetries. ASL imaging consisted of pseudocontinuous ASL with 1.5 s labeling duration and 2 s post-labeling delay adapted from white paper recommendations. RESULTS Thirteen of 80 cases (16.2%) had apparent hypoperfusion in the PCA territory contralateral to the side of the fetal PCA. Agreement between readers was near perfect (97.5%, κ = 0.91). This finding was more common in patients who were older, scanned on a 3.0 T magnet, and who had non-visualization of the posterior communicating artery contralateral to the fetal PCA. CONCLUSION Apparent PCA hypoperfusion on ASL is not uncommon in patients with a contralateral fetal PCA who have no clinical or conventional imaging findings to suggest true hypoperfusion. This phenomenon is likely due to differential blood velocities between the carotid and vertebral arteries that result in differential arterial transit times and labeling efficiency. It is important for radiologists to know that apparent hypoperfusion may arise from variant circle of Willis anatomy.

中文翻译：

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动脉自旋标记 MRI 上明显的大脑后动脉区域灌注不对称是单侧胎儿大脑后动脉患者常见的非病理发现。

目的 确定单侧胎儿 PCA 患者在动脉自旋标记 (ASL) 成像中看到的明显大脑后动脉 (PCA) 区域不对称的频率，但没有潜在的临床或影像学病理学提示真正的低灌注。方法 对 2017 年 1 月至 2020 年 6 月的放射学报告进行了检索，其中包含术语“胎儿 PCA”。80 名患者被纳入 MRA 或 CTA 证实的单侧胎儿 PCA，脑部 MRI 包括 ASL 成像，并且没有与 PCA 区域相关的常规成像异常或临床症状。病例由两名独立的读者评估视觉上明显的 PCA 灌注不对称。ASL 成像由伪连续 ASL 组成，标记持续时间为 1.5 秒，标记后延迟为 2 秒，改编自白皮书建议。结果 80 例中有 13 例（16.2%）在胎儿 PCA 对侧的 PCA 区域有明显的低灌注。读者之间的一致性接近完美（97.5%，κ = 0.91）。这一发现在年龄较大、在 3.0 T 磁体上扫描、胎儿 PCA 对侧后交通动脉不可见的患者中更为常见。结论 ASL 上明显的 PCA 低灌注在对侧胎儿 PCA 患者中并不少见，这些患者没有临床或常规影像学发现提示真正的低灌注。这种现象可能是由于颈动脉和椎动脉之间的不同血流速度导致不同的动脉通过时间和标记效率。