Fax +41 61 306 12 34 E-Mail karger@karger.ch www.karger.com Laboratory Investigation Stereotact Funct Neurosurg 2009;87:385–394 DOI: 10.1159/000258079 MRI-Based Definition of a Stereotactic Two-Dimensional Template of the Human Insula Afif Afif a, b Dominique Hoffmann c Guillaume Becq d Marc Guenot a Michel Magnin e Patrick Mertens a, b a Department of Neurosurgery, Neurological Hospital, Hospices civils de Lyon, and b Department of Anatomy, Inserm U 879, Lyon 1 University, Lyon, c Department of Neurosurgery, Grenoble University Hospital, and d Laboratory of Epilepsy, Grenoble University Hospital, Grenoble, and e INSERM, U 879, Bron, France to the classical AC-PC stereotactic reference system. They furthermore allow us to quantify the probability that a given element of this structure is located at a predefined position. This should be useful in functional neuroimaging studies and in insular surgery for diagnostic and therapeutic goals. Copyright © 2009 S. Karger AG, Basel Introduction The first rough sketch of the insula by Vesalius dates from more than four centuries ago [1]. However, only at the end of the 19th century did authors produce detailed qualitative descriptions of this peculiar part of the cere- bral cortex, also called at that time ‘the island of Reil’ [1–5]. In his comparative anatomical study, Clark [3] em- phasized the marked interhemispheric variations that af- fect the insula’s intrinsic morphology. Since then, few quantitative studies on the topographic anatomy of the insula have been published, the exception being the work by Türe et al. [6] on formalin-fixed human brains. This paucity of information may result from the difficulty in accessing this structure. The insula rests deep in the syl- vian fissure, hidden by the other cerebral lobes behind the temporoparietofrontal opercula. In addition, the syl- Key Words Cerebral magnetic resonance imaging  Insula  Morphometry  Neurosurgery  Stereotaxy Abstract Objective: This study aimed to create a stereotactic two-di- mensional description of the human insula based on accu- rate radiological morphometric studies. Methods: Seventy- five normal cerebral MRIs were selected and drawings of the insula then obtained from serial sagittal slices. These draw- ings were digitalized before superimposing the anterior (AC) and posterior (PC) commissures as references. This allowed us to quantify interindividual anatomical variations in a large cohort of subjects. Results: The morphometric analysis of the insula revealed a more complex shape than previously described. This structure is delimited by four peri-insular sul- ci (anterior, superior, posterior and inferior) instead of the three sulci classically mentioned. Males have a statistically larger surface area than females, according to a correlated index. Precise measurements of the different insular compo- nents allowed us to quantify their potential interindividual anatomical variations and to define their average shapes and stereotactic locations. Conclusion: These data create a two-dimensional template of the human insula, with regard Received: October 2, 2008 Accepted after revision: March 25, 2009 Published online: November 12, 2009 Afif Afif, MD, PhD Department of Anatomy, Lyon 1 University 8, avenue Rockefeller FR–69003 Lyon (France) Tel. +33 4 78 77 71 43, Fax +33 4 78 77 71 74, E-Mail afif_acc@hotmail.com © 2009 S. Karger AG, Basel 1011–6125/09/0876–0385$26.00/0 Accessible online at: www.karger.com/sfn