Willis环已被切开，可以看见 3 个颅底小动脉瘤。颅底小动脉瘤中多发性动脉瘤大约为20～30%。就出生时动脉壁缺陷这一点来看，多发性颅底小动脉瘤是先天性的，但实际上动脉瘤需要数年时间才能形成，因此颅底小动脉瘤破裂最可能在青年到中年发病。
The circle of Willis has been dissected, and three berry aneurysms are seen. Multiple aneurysms are seen in about 20-30% of cases of berry aneurysm. Such aneurysms are "congenital" in the sense that the defect in the arterial wall is present from birth, but the actual aneurysm takes years to develop, so that rupture is most likely to occur in young to middle age adults.