Fetal Origin of the Posterior Cerebral Artery Demonstrated on Tc-99m Hexamethylpropyleneamine Oxime Brain SPECT Balloon Occlusion Test

Fetal origin of the posterior cerebral artery is a common variant of the circle of Willis. We present the case of a 78-year-old man with a right carotid space mass who underwent a preoperative right carotid artery balloon occlusion test. Brain SPECT after injection of Tc-99m hexamethylpropyleneamine oxime demonstrated markedly decreased regional cerebral blood flow to the entire right cerebral hemisphere. Notably, blood flow to the right occipital lobe was also decreased, suggesting a fetal origin of the posterior cerebral artery, which was confirmed with angiography. Additionally, SPECT images demonstrated decreased left cerebellar blood flow, consistent with crossed cerebellar diaschisis.