Left internal carotid artery (ICA) aplasia with fetal posterior communicating cerebral artery.
The most important radiologic landmark is the carotid canal. In ICA hypoplasia, the carotid canal is present but reduced in caliber. In ICA aplasia, the canal is completely absent 1.
Fetal origin of the left PCA and prominent left P1 suggest that the left MCA is being supplied primarily from the posterior circulation.