Functional Anatomy of Arteriovenous Malformation (AVM)

Abstract

The surgical indication of the cerebral AVM is usually decided by its clinical symptoms and circulatory pattern as well as its size and location. The objects of this study are to enable to resect various kinds of the cerebral AVM whenever indicated and/or to develop a new operative procedure. For these purposes, the author investigates fine anatomical structure and hemodynamics of the AVM, using plastic casts obtained from surgical and autopsied specimens, fluorescein angiography during operation, and sequential subtraction angiography technique. The results obtained from this study show the findings described as follows:
1) The parent artery, so-called feeding artery of the AVM, suppl ies not only the nidus of the AVM but the brain parenchym adjacent to the AVM.
2) The circulation of the cortical surface surround ing the AVM is found to be delayed comparing with that of the AVM.
3) The parent artery gives several abnormal shaped branches on its course to the peripheral part. Here, the author designates these abnormal tributaries as proper feeder, which also form important part of the nidus.
4) The connecting vessel which has the possibility to develop into the feeder as hemodynamic change occurs, is observed between the AVM and the normal cortical artery.
5) Abnormal vascular channels within the nidus, including both the p roper feeder and the drainer in the nidus, have a complicated anatomical relationship among them, showing an appearance of diverging and connecting each other in an obtuse angle.
6) Coil-like vessel and aneurysmal dilatation are observed in r elatively fine vessels within the AVM. There is a tendency that the larger the size of the AVM is, the larger the diameter of abnormal vessel becomes.
7) It is indica ted that the ordinary circulatory pattern in the nidus of the AVM is originating from its external zone and running toward the drainer in the nidus of the AVM. In large AVMs, delayed circulation at the adjacent part of the drainer in the nidus is seen.
8) Reserve nidus or preangiomatous area is not revealed on angiogram and lo c ated in the peripheral zone of the AVM, where no main stream of AV shunt is produced. It is suspected that the peculiar circulatory pattern in these areas is the cause of failure in angiographical demonstration.
9) Large drainer in the nidus forms the centrally situated core of the nidus and drains exclusively from the AVM.
10) Superficial draining vein of the AVM receives blood both from the AVM and the adjacent normal cortex, so that the congestion and disturbance of venous return in the neighboring normal cortex can be produced by increased venous pressure.