Persistent hypoglossal artery and its variants diagnosed by CT and MR angiography

Persistent hypoglossal artery (PHA) is the second most common anastomosis between the carotid and vertebrobasilar systems and demonstrates some variations. We evaluated the prevalence of PHA on computed tomography (CT) angiography. We also evaluated characteristic features of PHA and its variants on magnetic resonance (MR) angiography. We retrospectively reviewed our database of 2,074 CT angiographic images obtained using either of two 64-slice multidetector CT scanners. We also reviewed our database of 7,646 MR angiographic images obtained using either of two 1.5-T or one 3.0-T imager. We could not determine the exact number of patients whose MR angiography included the hypoglossal canal. Most patients had or were suspected of having cerebrovascular diseases. We found six usual PHAs arising from the cervical internal carotid artery on CT angiography among 2,074 patients. On MR angiography, we also found six additional usual PHAs (total 12, right/left = 6/6, male/female = 3/9), three right PHAs originating from the external carotid artery (ECA), and two posterior inferior cerebellar arteries (PICAs) arising from the ECA without connection to the vertebral artery. The prevalence of usual PHA diagnosed by CT angiography was 0.29 %, slightly higher than that reported for angiography and may be due to selection bias in the examined patients. We propose naming usual PHA "type 1 PHA"; PHA originating from the ECA, of which we found three, "type 2 PHA"; and PICA arising from the ECA, of which we found two, "type 2 PHA variant.".