Stepwise Dissections of the Right Insular Region. A, Lateral view of the hemisphere showing the gyri and sulci bordering the sylvian fissure, which are supplied by the cortical branches of the MCA. The cortical arteries include the orbitofrontal, prefrontal, precentral, central, anterior parietal, posterior parietal, angular, temporooccipital, posterior temporal, middle temporal, anterior temporal, and temporopolar arteries. The vein of Trolard runs between the SSV and the superior sagittal sinus. The SSV also has a large anastomosis with the vein of Labbé. B, The frontoparietal operculum has been removed while preserving the branches that form the M2 and M3 segments. The cortical arteries can be followed from their origin along the insula to the cortex. The M1 bifurcates proximal to the genu near the limen insulae. The early temporal branch, arising from the prebifurcation M1 segment, gives rise to the temporopolar, anterior temporal, middle temporal, posterior temporal, and temporooccipital arteries. The superior trunk gives rise to orbitofrontal, prefrontal, and precentral arteries along its course around the pole of the insula. The inferior trunk gives rise to the central, anterior and posterior parietal, and angular arteries. All of the cortical branches arising from the early branch, except for the temporopolar artery, course along the posterior long gyrus and inferior limiting sulcus, and contribute to the supply of these insular areas. C, Enlarged view of the insula. At the pole of the insula, the superior trunk gives rise to its first cortical branch, the orbitofrontal artery, prior to reaching the insular apex. The orbitofrontal artery courses along the most anteroinferior part of the insula and contributes to the supply of the anterior short gyrus. The prefrontal and precentral arteries arise from a common stem artery (black arrow) near the level of the insular apex. The prefrontal artery courses along and supplies the middle short gyrus en route to the anterosuperior angle of the insula. The precentral artery courses near the precentral insular sulcus. The central artery, the first cortical branch of the inferior trunk, supplies the central insular sulcus and the posterior short gyrus. The first cortical branch from the inferior trunk, the central artery, arises farther away from the MCA bifurcation than the first cortical branch of the superior trunk. The central insular sulcus does not receive a contribution from the superior trunk in this hemisphere. The anterior long gyrus is supplied by a stem artery (red arrow) from the inferior trunk that eventually gives rise to the angular and the anterior and posterior parietal arteries. D–F, Photographs obtained during stepwise dissections of another right cerebral hemisphere. D, Lateral view showing the cortical territory supplied by the MCA, which includes the majority of the lateral surface of the hemisphere, the lateral part of the orbital surface of the frontal lobe, the temporal pole, and the lateral part of the inferior surface of the temporal lobe. This territory is supplied by the following cortical MCA branches: the orbitofrontal, prefrontal, precentral, central, anterior parietal, posterior parietal, angular, temporooccipital, posterior temporal, middle temporal, anterior temporal, and temporopolar arteries. E, The frontoparietal and temporal opercula have been removed while preserving the branches forming the M2 and M3 segments. The M1 segment bifurcates proximal to the genu near the limen insulae. The first cortical branch of the superior trunk is an orbitofrontal artery that supplies the accessory gyrus. The superior trunk gives rise to the posterior parietal artery on the anteroinferior portion of the insula (black arrow) prior to reaching the insular apex. The posterior parietal artery courses along the central insular sulcus. The central and anterior parietal arteries arise at the level of the insular apex, from a common stem (red arrow) of the superior trunk that courses along the posterior short gyrus. The prefrontal and precentral arteries arise from a common stem artery above the insular apex. The prefrontal artery sends perforating arteries to the anterior short gyrus and crosses the anterosuperior angle of the insula. The inferior trunk gives rise to the angular and temporooccipital arteries. The posterior and the middle and anterior temporal arteries arise from the early temporal branch. F, Enlarged view of the same hemisphere. The orbitofrontal artery, the first cortical branch of the superior trunk, sends branches to the accessory gyrus. The posterior parietal artery arises from the superior trunk at the level of the insular pole below the apex, courses along the central insular sulcus, and sends perforating vessels to the posterior short and anterior long gyri. The stem artery (red arrow), which gives rise to the central and anterior parietal arteries, arises from the superior trunk at the level of the insular apex, supplies the posterior short gyrus and precentral sulcus, and gives rise to a large insular perforating artery near the superior portion of the insula. The prefrontal and precentral arteries arise from a common stem artery above the insular apex and send perforating arteries to the anterior and middle short gyri, respectively. The angular and temporooccipital arteries arise from a stem artery (green arrow) that originates from the inferior trunk. The stem artery supplies the posterior long gyrus and inferior limiting sulcus. Photographs obtained during the stepwise dissection of a right cerebral hemisphere (G and H), demonstrating the insular, opercular, and cortical segments of the MCA. G, Lateral view of the cortical surface bordering the sylvian fissure. The anterior horizontal ramus separates the partes orbitalis and triangularis, and the anterior ascending ramus separates the partes triangularis and opercularis. The lower end of the precentral gyrus is located behind the pars opercularis. H, The frontal and temporal opercula have been retracted to expose the insular, opercular, and cortical course of the prefrontal, precentral, central, anterior and posterior parietal, and angular arteries. The M1 segment ends and the M2 segment begins at the site of a 90-degree turn, the genu, located distal to the MCA bifurcation. The M2 segment includes the trunks that lie on and supply the insula. The M1 segment of the MCA bifurcates at the level of the limen insulae. The superior trunk gives rise to the orbitofrontal, prefrontal, and precentral arteries. At the pole of the insula, the orbitofrontal artery arises from the initial centimeter of the superior trunk, proximal to the level of the insular apex, and courses anteroinferiorly to supply the orbital gyri of the frontal lobe. The prefrontal and precentral arteries arise from a common stem artery at the level of the insular apex. The prefrontal artery courses along the middle short gyrus to reach the junction of the superior and inferior limiting sulci and sends branches to the anterior short gyrus. The precentral artery courses on the precentral sulcus. The initial portion of the inferior trunk supplies the limen insulae and gives rise to the central artery as its first cortical branch. The first cortical branch from the inferior trunk, the central artery, arises farther from the MCA bifurcation than the first cortical branch of the superior trunk, the orbitofrontal artery. The central artery courses along the central insular sulcus and sends perforating arteries to the sulcus and the adjacent posterior short and anterior long gyri. The stem artery that gives rise to the anterior and posterior parietal arteries courses along the anterior long gyrus (red arrow). An early temporal branch gives rise to the temporooccipital and angular arteries that course on the posterior long gyrus and inferior limiting sulcus. The angular artery turns laterally at the junction of the superior and inferior limbs of the limiting sulci to reach the cortical surface. (Images courtesy of AL Rhoton, Jr.)