左椎骨動脈の窓形成部に解離性破裂脳動脈瘤を生じた1例

Ruptured Dissecting Aneurysm of the Fenestrated Vertebral Artery:A Case Report

Ⅰ．はじめに

　頭蓋内血管における窓形成（fenestration）の発生頻度は，主に2-dimensional digital subtraction angiography（2D-DSA）で評価されていた時代には，0.03〜1.3%と報告されていた^7,14,17)．しかし近年の目覚ましい神経放射線診断機器の発達により，3 teslaのmagnetic resonance angiography（3T-MRA），computed tomography angiography（CTA），3D-DSAなどのモダリティを使用した評価では，その発生頻度が3〜28%とも言われており，実臨床で遭遇する機会は増えてきている^{2,4,6,8,16,20)}．しかしながら，頭蓋内血管の窓形成の臨床的意義についてはほとんど解明されていない．これまでの報告で，頭蓋内主幹動脈の窓形成と嚢状動脈瘤の合併例は散見されるが，解離性動脈瘤の合併例は極めて稀な病態である．今回われわれは，左椎骨動脈（vertebral artery：VA）の窓形成部に解離性破裂脳動脈瘤を合併した症例を経験したため，若干の文献的考察を加え報告する．

　Fenestration of a vertebral artery（VA）is a rare anomaly that has occasionally been associated with the formation of saccular aneurysms, whereas dissection of a limb of the fenestrated artery is an extremely rare occurrence. We report the case of a ruptured dissecting aneurysm of a fenestrated VA. A 56-year-old man presented with acute-onset headache followed by respiratory failure. Computed tomography（CT）revealed diffuse subarachnoid hemorrhage, and CT angiography（CTA）demonstrated fenestration of the left VA and a fusiform aneurysm of the dorsolateral limb of the fenestrated VA. CT after injection of contrast medium revealed dissection of a limb of the fenestrated VA. A comparison of the 3-dimensional digital subtraction angiogram obtained 2 days later with the initial CTA showed that the dissecting aneurysm had shrunk. Coil embolization of the dissecting limb of the fenestrated VA was achieved, and the patient was discharged without neurologic deficit. Further advancements in neuroimaging modalities will provide more opportunities to treat dissecting aneurysms of fenestrated VAs. The relevant clinical characteristics of VA fenestration and the treatment options for a dissecting aneurysm of a limb of the fenestrated VA are also discussed in this report.