[Parent artery occlusion therapy for giant aneurysms of the vertebrobasilar system: hemodynamic analysis by hydraulic vascular model].
Although therapeutic occlusion of the basilar artery has been an accepted treatment for inaccessible giant aneurysms, several such problems have been reported as incomplete thrombosis, growth or rupture of aneurysms, cerebral embolism originating from an aneurysmal cavity. Hemodynamic changes after occlusion therapy are suspected to be responsible for these events. It is usually difficult to solve these problems or to predict them before operation because multiple factors are related in a complex fashion in a living body. One of the effective means is to simulate these hemodynamic conditions by a hydraulic vascular model. A glass-made sphere of 2.5 cm in diameter was connected to a hydraulic vascular model of the brain and was regarded as a giant aneurysm so as to evaluate hemodynamic changes after therapeutic occlusion of the parent artery. 40% glycerol solution at 25 degrees C, having similar viscosity and specific gravity to those of human whole blood at 37 degrees C, was used as a perfusate in this study. A device to measure a half-life of the dye injected in an aneurysm was made from a stable luminous source and a Cds photocell. Good correlation was obtained between the output from the device and dye concentration in an aneurysm. Intensity change of the transmitted light was measured when the dye was injected into the aneurysm during perfusion. Half-life was calculated from thus obtained clearance curve and was regarded as an index of intra-aneurysmal stagnation. The flow volumes have been estimated in our previous study: 60 ml/min to the territory of one posterior cerebral artery (PCA) and 80 ml/min to the cerebellum and the brain stem. A. Basilar artery occlusion therapy for a basilar bifurcation aneurysm. For the simulation before occlusion therapy, the flow volume of the basilar artery (BA) was fixed to be 120 ml/min. When the BA is occluded distal to the exit of the superior cerebellar artery, a flow tangential to the aneurysmal neck occurs from the side of larger posterior communicating artery (Pcom) to the other side through P1 segment of the PCAs. Its flow volume is considered to change from 60 ml/min to 0 ml/min depending on the diameter ratio of two Pcoms. The results are as follows: 1) BA occlusion makes intra-aneurysmal dye stagnate and the half-life elongate significantly from 2.5 seconds to 16 seconds. 2) The time gradually increases as the flow volume through P1 segment decreases from 60 ml/min to 20 ml/min, below which it increases drastically. 3) The P1 flow volume less than 20 ml/min corresponds to the diameter ratio of two Pcoms lager than 0.71. 4) Thrombosis in the aneurysmal cavity would be expected when diameter ratio of the Pcoms is lager than 0.71.(ABSTRACT TRUNCATED AT 400 WORDS)
Nagayasu
S
S
Department of Neurosurgery, Faculty of Medicine, Kyoto University, Japan.
D000783:Aneurysm / Q000503:physiopathology / Q000628:therapy*; D001488:Basilar Artery / Q000503:physiopathology; D002560:Cerebrovascular Circulation; D004621:Embolization, Therapeutic; D006439:Hemodynamics; D006801:Humans; D008955:Models, Cardiovascular; D014711:Vertebral Artery / Q000503:physiopathology