Anatomical variations of the insular gyri: A morphological study and proposal of unified classification.

Abstract

The locations of gyral landmarks vary among individuals. This can be crucial during local landmark-based mapping of the human cortex, so the aim of the present study was to establish criteria for classifying the morphological variability of the human insula. The study was conducted on 50 isolated, randomly-selected adult cadaveric hemispheres, fixed in 10% formalin, and preserved in 70% ethanol (24 right and 26 left hemispheres). A thorough rating system, including bifid form (i.e., divided on top), branching or hypoplasia, was used to analyze the insular gyri. The number of all insular gyri ranged from four to six (mean = 5.16, SD = 0.65). Within the anterior lobule, the number of short gyri ranged from two to four (mean = 3.3, SD = 0.54). The middle short gyrus was the most variable. It was well-developed in 25 of the 50 cases (50%). Within the posterior lobule there were one or two long insular gyri (mean = 1.88, SD = 0.32). In 48 cases (96%), the anterior long gyrus was well-developed. A complete lack of the posterior long gyrus was noted in six of the 50 cases (12%). In conclusions, the accessory, the middle short, and the posterior long gyri of the insula were the most variable. The middle short gyrus was well-developed in only half of the cases. The number of insular gyri found in horizontal sections of the brain does not necessarily indicate their true number. Clin. Anat. 31:347-356, 2018. © 2018 Wiley Periodicals, Inc.