The anterior sylvian point and the suprasylvian operculum

The sylvian fissure or lateral sulcus is the most identifiable feature of the superolateral brain surface and constitutes the main microneurosurgical corridor, given the high frequency of approachable intracranial lesions through this route. The anterior sylvian point (ASyP) divides this fissure in its main anterior and posterior rami and was evaluated in this study for its morphology, exact location, and sulcal and neural relationships to assess its suitability as an initial, visually identifiable landmark for further neuroimaging and intraoperative estimation of its adjoining suprasylvian structures.

This study is based on 32 formalin-fixed cerebral hemispheres. The brains were removed from the skulls of 16 cadavers after the introduction of plastic catheters through properly positioned burr holes; the number of specimens for some of the analyzed data differed because of incorrect positioning of catheters or damage to the studied structures caused by the initial steps of the study. The ASyP had a cisternal aspect in 94% of the specimens and was always located inferior to the triangular part of the inferior frontal gyrus, 2.3 6 0.5 cm in front of the inferior rolandic point. The ASyP was located underneath the 1.5-cm-diameter cranial area of the anterior aspect of the squamous suture. Its adjoining structures that compose the suprasylvian operculum have constant basic morphological configurations.

The ASyP underlies the anterior aspect of squamous suture just behind the pterion, can be easily recognized, and constitutes a reliable initial sulcal landmark for further estimation of the suprasylvian sulcal and gyral structures. The suprasylvian operculum can be understood as a series of convolutions roughly arranged as a V-shaped convolution, with its vertex constituted by the ASyP, followed by three U-shaped convolutions and one C-shaped convolution.