Central Lobe Surface Anatomy and Vasculature. A, The anterior part of the frontal lobe was removed using a coronal cut anterior to the foramen of Monro. The upper part of the superior frontal gyrus was removed to expose the course of the posterior internal frontal artery, which folds over the superior margin of the lateral surface approximately 1.5 cm anterior to the precentral gyrus after supplying the supplementary motor area. It also supplies the superior portion of the precentral gyrus on the lateral surface but not the paracentral lobule on the medial surface. B, The callosomarginal artery gives rise to the posterior internal frontal and paracentral arteries. The posterior internal frontal artery folds over the superior margin of the lateral surface and supplies the supplementary motor area (green shaded area) and the superior portion of the precentral gyrus. The paracentral artery courses inside the cingulate sulcus before turning upward to supply the paracentral lobule and a small portion of the upper part of the postcentral gyrus. Sacrificing these arteries may lead to a supplementary motor area syndrome with contralateral lower-limb weakness. C, An enlarged view of the paracentral lobule. The paracentral lobule is commonly supplied by the paracentral and superior parietal arteries. In this hemisphere the superior parietal artery is a branch of the pericallosal artery and runs in the ascending ramus of the cingulate sulcus to supply the lower and posterior borders of the paracentral lobule. The paracentral artery, a branch of the callosomarginal artery, courses in the cingulate sulcus and supplies the majority of the paracentral lobule. D–G, Other arteries have been removed to show the trajectory and area of supply of the left posterior internal frontal artery. D, Medial surface of left hemisphere. This posterior internal frontal artery arises from the pericallosal artery, runs upward and posterior to supply the posterior portion of the medial surface of the superior frontal gyrus. It folds over the superior margin of the hemisphere anterior to the paracentral lobule. E, Upper lateral surface of the left hemisphere shown in D. The posterior internal frontal artery folds around the superior border anterior to the central lobe to supply the posterior portion of the superior frontal gyrus and the upper part of the precentral gyrus. F, Medial surface of a right hemisphere. The callosomarginal artery arises from the precallosal segment of the pericallosal artery and gives rise to both the middle and posterior internal frontal arteries. The paracentral artery arises from the pericallosal artery and courses upward to reach the anterior part of the paracentral lobule. G, Superior part of the lateral surface of the right hemisphere shown in F. The watershed area between the ACA and MCA is located approximately 1.5 cm lateral to the superior margin of the lateral surface (green shaded area), where there are anastomoses between branches of the MCA and ACA. The posterior internal frontal artery runs in an anterior to posterior direction. The watershed area is supplied by the central branches of the MCA and by the posterior internal frontal, paracentral, and superior parietal branches of the ACA. (Images courtesy of AL Rhoton, Jr.)