Anatomic variation of the middle cerebral artery in the Sprague-Dawley rat.

BACKGROUND AND PURPOSE The aim of this study was to record and analyze the anatomy of the middle cerebral artery in the rat in an attempt to identify a potential source of variation of quantitative infarct measurements in commonly used models of focal cerebral ischemia. METHODS Over a period of 22 months, as part of ongoing studies, we routinely induced focal cerebral ischemia in 263 Sprague-Dawley rats. This was achieved by permanent occlusion of a length of the right middle cerebral artery approximately 1 to 5 mm distal to the point at which it traverses the rhinal fissure combined with 60 minutes of bilateral common carotid occlusion. The branching pattern of the middle cerebral artery was recorded for each animal by drawing and photography before occlusion and at the time of death. RESULTS Six distinct branching patterns were observed. The majority (82.9%) of middle cerebral arteries studied conformed to the typical bifurcating vessel commonly referred to in the literature. However, the remaining 17.1% were far more variable with major, atypical branching, introducing, we believe, unnecessary and avoidable variation into quantitative measurements of ischemia in this and similar models. CONCLUSIONS Middle cerebral artery anatomy should be routinely recorded in models of focal cerebral ischemia in which this artery is occluded distal to the olfactory tract, thus allowing improved analysis of data.