[A Rare Case of Ruptured/Unruptured Miniature Aneurysms Originating from the Infundibular Dilatation of the Callosomarginal Artery, Branching from the Infracallosal(A2)Segment of the Azygos Anterior Cerebral Artery].

We report the first case of two de novo miniature aneurysms(ruptured/unruptured)emerging from the infundibular dilatation(ID)of the callosomarginal artery, which branches from the infracallosal(A2)segment of the azygos anterior cerebral artery(AACA), in a 36-year-old woman. The patient had previously been diagnosed with a miniature, unruptured aneurysm, occurring in the A2 segment of the AACA, detected by CT angiography(CTA)at another hospital two years ago, and had been followed up with MR angiography(MRA)every 6 months. Three months after the final check-up with MRA, which did not indicate a significant change in the aneurysm, the patient presented with subarachnoid hemorrhage. Subsequent CTA and digital subtraction angiograms revealed that the right callosomarginal artery, originating from the apex of the aneurysmal bulge, had a maximal diameter of 3mm, indicating an ID of the artery. Additionally, two miniature bleb-like aneurysms emerged from the ID, projecting in opposite directions:one projecting to the right-posterior/superior direction and the other to the left-anterior/inferior direction. Both aneurysms were successfully clipped via a right pterional approach with partial resection of the gyrus rectus, and the right-projecting aneurysm was confirmed to be ruptured during surgery. In the current report, we review previously reported cases of AACA with aneurysms, and discuss their clinical characteristics, and the possible mechanisms underlying the formation of the ID and de novo aneurysms in this extremely rare case.