Proximal branching patterns of middle cerebral artery (MCA) in rats and their influence on the infarct size produced by MCA occlusion.

The branching patterns of the proximal middle cerebral artery (MCA) and their influence on the infarct size following MCA occlusion in rats were studied. In the proximal part from the level of the olfactory tract, the MCA most often presented one surface branch extending anteriorly, with a variable number of surface branches extending posteriorly. We classified the branching patterns of the posteriorly extending surface branches as follows: Type 1 (57.5%), one prominent proximal surface branch; Type 2 (30.2%), no prominent branch but two or more small surface branches; and Type 3 (12.3%), no surface branches with a visible junction with the MCA but surface branches probably arising from the internal carotid artery at the origin of the MCA. When the proximal surface branches (especially that in Type 1) remained uncoagulated, the infarct size in both the cortex and striatum was significantly reduced compared with that when coagulation was proximal to the most proximal surface branch. The reduction of cortical and striatal infarct sizes was particularly prominent in the posterior portion. To increase the infarct size and reduce variability, it is suggested that the MCA trunk should be coagulated from the origin to the rhinal fissure including the surface branches.