Surgical Anatomy of Supratentorial Midline Lesions

DISCUSSION
The fibers of the corpus callosum are the major connecting pathways between the cerebral hemispheres of the human brain (4, 30). Various
neurological diseases involve the corpus callosum. For instance, gliomas can arise at this site, and adjacent falcine meningiomas can cause
compression. In addition, vascular malformations and aneurysms can occur in the region of the corpus callosum. An incision into the corpus
callosum is generally required to reach the lateral or third ventricles. However, a callosal incision can result in various disorders: disruption of
interhemispheric transfer of information, interference with visuospatial transfer, difficulty in learning bimanual motor tasks, memory problems,
and other deficits, including alexia, apraxia, and astereognosis (1, 6, 21, 25, 28, 33-35).
Previous studies have dealt with only limited aspects of the anatomic features of the blood supply to the corpus callosum (2, 3, 5, 9-11,
13-16, 18-20, 22, 23, 25-29, 32-36), and very few articles have addressed the vascularity of this region as one anatomic entity (12, 17, 24, 31). It
has been the aim of the present investigation to examine the blood supply of the corpus callosum, to provide adequate information to the
neurosurgeon. This accumulation of knowledge can be applied to the recognition of anatomic landmarks and variations in arterial patterns during
surgery, which can ultimately guide the exploration to a successful outcome.
The following summarizes our findings regarding the microsurgical anatomic features of the blood supply to the corpus callosum and
indicates their surgical relevance. Three main arterial systems supply the corpus callosum: the ACoA, the pericallosal artery, and the posterior
pericallosal artery.
Contribution of the ACoA
The ACoA branches are divided into three subgroups: the hypothalamic artery, the subcallosal artery, and the median callosal artery. The
hypothalamic artery arose from the ACoA in 85% of our specimens; in the other 15%, it arose from the subcallosal artery or the median callosal
artery. In no specimen did the hypothalamic artery contribute to the blood supply of the corpus callosum.
The subcallosal artery is rarely mentioned in the literature, because of the use of a different classification for the various branches arising
from the ACoA complex (19, 34). Marinkovic et al.(19) found a subcallosal artery present in 91% of his specimens, whereas it occurred in 50%
of our specimens, always as a single dominant artery.
Previous studies have discussed the contribution of the median callosal artery to the blood supply of the corpus callosum, and the artery
was reported to be present in less than 20% of specimens (2, 11, 14, 16, 19, 23, 27, 29, 31, 34). In our observations, the median callosal artery
was present in 30% of the specimens. We identified two vascular patterns, which are based on their distal arterial distributions, and we called
these “classical" and “hemispheric." The presence of the median callosal artery and the existence of anastomoses with the various
branches of the PCA, middle cerebral artery, or ACA systems can provide an adequate source of collateral flow when temporary vessel
occlusion is needed during surgery.
In an earlier publication (34) by the senior author(M.G.Y.), the branches of the ACoA complex were classified using different terminology.
The previous terminology has been modified in this study as follows: the small third A2 is now identified as the subcallosal artery, the moderate
third A2 as the classical type of median callosal artery, and the large third A2 as the hemispheric type of median callosal artery.
Marinkovic et al. (19) classified the branches of the ACoA according to the diameter at their origin as either small (hypothalamic) or large
(subcallosal and median callosal). We have advocated classifying these arteries according to their territories of supply, because occasionally, in
different specimens, the diameter of the hypothalamic artery or the subcallosal artery was found to be equal to, or larger than, that of the median
callosal artery. Thus, when we explore the ACoA complex during surgery, we cannot conclusively identify its branches simply by comparing the
diameters at their origins.
In our study of 20 brain specimens, we did not observe the azygos variation of the ACA. However, in the literature, the incidence is
reported to range from 1 to 5% (2, 11, 13, 15, 34).
Before surgically approaching the ACoA complex in the case of an aneurysm, arteriovenous malformation, or tumor, the possible arterial
variations that may occur in this area must be carefully considered. In particular, a careful study of the angiogram is strongly indicated because
of the very high probability of the presence of a subcallosal artery or a median callosal artery, and because preserving these important vessels
during surgery is crucial to a successful outcome.
Contribution of the pericallosal artery