[A Case of Pediatric C1 Dysplasia with Ruptured Aneurysm in Collateral Plexiform Arterial Network].

A 3-year-old girl was admitted to our hospital with symptoms including headache, nausea, and vomiting. Head CT scan showed subarachnoid hemorrhage in the right carotid cistern. Digital subtraction angiography revealed right internal caortid artery(ICA)malformation at the C1 segment with collateral plexiform arterial network. The right ICA branched into posterior communicating artery and anterior choroidal artery(AChoA)and the ICA was decreased in caliber. The distal portion of the C1 segment of the ICA continued to the collateral plexiform arterial network, forming a saccular aneurysm. The plexiform arterial network connected to the right AChoA and the anterior communicating artery and continued to the distal portion of the right M1 segment. Right cervical carotid artery was normal. There was no transdural collateral flow from the right external carotid artery. Genetic analysis of a variant of RING finger protein 213 was negative. We diagnosed this patient with C1 dysplasia. We performed coil embolization for the aneurysm. The patient was discharged without any neurological deficit. Four months after the surgery, recurrence of the aneurysm was observed. We suspected that the aneurysm was formed due to hemodynamic mechanism and vulnerability of the collateral plexiform arterial network.