The insular cortex: morphological and vascular anatomic characteristics.

OBJECTIVE We undertook this anatomic study of the insula to investigate its vasculature, morphological features, and surrounding cortical relationships. METHODS Under magnification of x2 to x32, 53 formalin-fixed, adult cadaver hemispheres were dissected. Overlying opercular landmarks were identified and used as guides to portions of the deeper insula. RESULTS The insula has a complex venous system; 50 (94.3%) hemispheres exhibited a combination of superficial and deep venous connections. The venous connections divide the insular cortex into the following three anatomic zones, with some overlap: subapical region (insular pole), anterior lobe, and posterior lobe. Arterial contributions to the insula originated entirely from the middle cerebral artery, predominantly via the superior division. Thirty-six (67.9%) specimens exhibited a dedicated terminal vessel to the insula; in 34 of these (94.4%), this terminal vessel arose from the middle cerebral artery branch to the central sulcus. There was never more than one terminal vessel in each insular cortex. CONCLUSION Historically, it has been reported that the insula drains primarily via the deep middle cerebral vein (DMCV). We found more complex (typically both superficial and deep) venous connections. In most specimens, the DMCV exhibited a direct venous connection to only a portion of the insular cortex. The deep drainage connections of the insula and the vessels that form the DMCV suggest that the DMCV drains primarily the lateral lenticular veins and secondarily the insula. Arterial contributions to the insula tended to be centered around the central insular sulcus, independent of the location of the middle cerebral artery bifurcation. Although the insular vascular anatomic features showed great variability, the anatomic and structural relationships described in this dissection series should facilitate safe surgical and endovascular interventions.