MRI of persistent trigeminal artery.

Objective: To describe the classic appearance of persistent trigeminal artery on MR imaging with the typical MR appearance of the hypoplastic precommunal basilar artery. This finding may be used as an ancillary sign of this anomaly in subtle cases of persistent fetal carotid-basilar artery anastomoses.
Materials and Methods: Two women (46 and 19 years of age) with persistent trigeminal artery were examined. An MR imaging study using spin-echo sequences was performed. The findings were confirmed on conventional angiography.
Results: Two cases showed a hypoplastic basilar trunk flow void in the caudal posterior fossa that enlarged to a more normal caliber rostrally above the persistent trigeminal artery anastomosis. The actual anastomosis was also demonstrated in both cases, and in one of the cases the persistent trigeminal artery was shown to form a groove in the dorsum sellae.
Conclusion: A proximal hypoplastic basilar trunk below the anastomosis that enlarges to a more normal caliber above the aberrant communication is an important ancillary sign of persistent trigeminal artery and should be searched for on routine MR studies in cases with suspected carotid-basilar anastomoses.