Anatomic relationship between the anterior sylvian point and the pars triangularis.

The aim of this study was to show morphological sulcal variations of the pars triangularis of the inferior frontal gyrus and to provide a clearer description of the anterior sylvian point. Thirty-six hemispheres of 18 adult cadavers were studied. The hemispheres were harvested by the classical autopsy method and fixed in 10% formalin solution for three weeks. In six hemispheres, the arteries and veins were filled with colored silicone. The proximal and distal segments of the sylvian fissure, the perpendicular distance of both the anterior sylvian point and inferior rolandic point to the insular cortex and the distances between the anterior ascending ramus and the precentral, central, and postcentral sulcus were measured. The anterior horizontal and ascending rami were exposed. The sulcus located on the pars triangularis was appraised. The relationship between the anterior sylvian point and the vascular structure around the sylvian fissure was examined. The rising of the anterior horizontal and ascending ramus from the sylvian fissure defines the shape of the pars triangularis. The pars triangularis has three shapes: V, U, and Y. In V- and Y-shaped pars triangularis both rami merge but in U-shaped pars triangularis the rami do not merge. The pars triangularis was Y-shaped in 30.76% (4/13) of the right hemispheres and in 50% (7/14) of the left hemispheres; U-shaped in 20.3% (3/13) of the right hemispheres and in 35.71% (5/14) of the left hemispheres; V-shaped in 40.61% (6/13) of the right hemispheres and in 14.29% (2/14) of the left hemispheres. Minimally invasive procedures use basic anatomic landmarks intracranially to reach the targeted area; therefore, exact and detailed knowledge of the anatomy of the sylvian fissure and pars triangularis is of great importance.