Aberrant course of the petrous internal carotid artery associated with ipsilateral type 1 proatlantal artery

Purpose: To describe an extremely rare case of an aberrant course of the petrous internal carotid artery (ICA) associated with an ipsilateral type 1 proatlantal artery (PA) that was diagnosed by cerebral magnetic resonance (MR) angiography. Case report: The patient was a 64-year-old man with double vision. Cerebral MR imaging and MR angiography were subsequently performed using a 1.5-T scanner. MR angiography showed an aberrant course of the petrous right ICA that was associated with right type 1 PA. The left vertebral artery (VA) and proximal right VA were absent. Discussion: An aberrant course of the petrous ICA is rare but clinically significant, because it is dangerous during middle ear surgery. Type 1 PA is an extremely rare type of persistent fetal anastomosis between the carotid and vertebrobasilar systems. Type 1 PA is also clinically significant, because it is dangerous during craniovertebral junction surgery. We found no similar cases in the relevant English-language literature. Conclusion: Although both variations were seen ipsilaterally and were located relatively close to each other, the embryological development of these variations is quite different. In addition, no similar case has been reported previously. Thus, these may have formed incidentally.