Persistent trigeminal artery–superior cerebellar artery segmental fusion diagnosed using magnetic resonance angiography

Purpose To describe a case of persistent trigeminal artery (PTA)–superior cerebellar artery (SCA) segmental fusion incidentally diagnosed on magnetic resonance (MR) angiography. Case report A 53-year-old woman with a history of facial pain underwent cranial MR imaging and MR angiography. MR angiography showed a left lateral-type PTA arising from the precavernous portion of the left internal carotid artery (ICA). PTA branched into the left distal SCA and showed segmental fusion with the proximal SCA at the distal part of the PTA. We also diagnosed an unruptured cerebral aneurysm at the junction between the left ICA and PTA. Discussion PTA is the most frequent type of carotid-vertebrobasilar anastomosis. The reported prevalence rate is 0.2% by angiography and 0.34% by MR angiography. There are two types of PTA—lateral (usual) and medial (intrasellar). SCA arising from the lateral-type PTA has rarely been reported. Further, a PTA from which the distal SCA branches and segmentally fuses with the proximal SCA at the distal part of the PTA has not been reported. Conclusion Using MR angiography, we diagnosed a rare type of PTA that fused segmentally with SCA. No similar case has been reported in relevant English-language literature.