FLOW DYNAMICS IN A FATAL ANEURYSM OF THE BASILAR ARTERY

PURPOSE: To examine the flow dynamics in a fatal aneurysm of the basil ar artery in humans. METHODS: We made transparent elastic replicas of the vertebrobasilar arteries of an elderly patient who died of a ruptu red aneurysm in the basilar artery. Using non-Newtonian fluid, physiol ogical pulsatile flow volumes and profiles, and isobaric dyes and part icles, we observed and recorded the slipstreams as they entered the an eurysm while changing relative flow in the vertebral arteries. Finally , we placed clips on the aneurysm, leaving residuals (or dog-ears), an d observed the slipstreams. RESULTS: The aneurysm originated laterally from the greater curvature of a tortuous basilar artery, measured 19 x 11 x 12 mm, and had a Murphy's teat at the apex, the rupture site. T he neck measured 10 x 4 mm, about the diameter of the basilar artery. Slipstreams joined at the confluence of the vertebral arteries, formed helical flow patterns, and entered the aneurysm violently, striking t he apex. They then passed proximally around the sac walls, then centra lly, and finally reentered the basilar artery to pass distally. Alteri ng the relative flows in the vertebral arteries could modify and preve nt slipstream now into the aneurysm. When a dog-ear was created by inc orrect placement of an aneurysm clip, slipstreams entered only dog-ear s that lay distal to the clip. Correctly placed clips excluded the ane urysm from the circulation, but did not return the flow dynamics to no rmal. CONCLUSION: High-velocity slipstreams strike aneurysms at their rupture site and have an impact on distal but not proximal dog-ears. M odifying relative flow may prevent aneurysmal filling. Further, a know ledge of flow dynamics may allow us to predict which aneurysms are at risk of enlarging and rupturing, and may help guide proper therapy.