Apparent PCA territory hypoperfusion on arterial spin labeling MRI is a common artifact in patients with a unilateral fetal PCA.

A retrospective review was performed of 50 patients undergoing MRI with pseudo-continuous arterial spin labeling (pCASL) perfusion imaging and confirmed unilateral fetal PCA. The aim is to determine the frequency of visually-apparent unilateral PCA territory hypoperfusion in patients with a contralateral fetal PCA, but without underlying clinical or imaging pathology to suggest true hypoperfusion. Eight of the fifty cases (16%) had visually-apparent hypoperfusion in the PCA territory contralateral to the fetal PCA. Given these findings, we advise caution when interpreting ASL in patients with a fetal PCA/variant circle of Willis anatomy or suggest using longer post-labeling delay times.