Where is the beginning of the sylvian cistern?

Abstract

Introduction
The sylvian cistern is the most important microsurgical avenue, used worldwide to approach lesions located in the opercula, insula, and anterior basal cisterns. Its sphenoidal segment is bounded laterally, superiorly, and inferiorly by identifiable neural structures. However, its medial boundary—formed by the medial sylvian arachnoidal membrane surrounding the middle cerebral artery (MCA) as it arises from the carotid bifurcation—remains challenging to delineate in neuroimaging, particularly in non-contrast studies. This investigation evaluates the anatomical basis and feasibility of using a sagittal plane projected from the posterior portion of the olfactory sulcus as a surrogate marker for the medial limit of the sylvian cistern.
Methods
Ten contrast-enhanced T1-weighted brain MRI scans were reviewed, yielding 20 hemispheres. Image datasets were processed using 3D Slicer (version 5.8.1), and the sagittal plane projected from the posterior portion of the olfactory sulcus was compared to the location of the internal carotid artery bifurcation.
Results
In 95% of cases (19/20 sides), the projected plane led to the carotid bifurcation and helped separate the anterior perforating substance, forming the roof of this cistern, into lateral and medial portions.
Conclusion
These findings support the use of a sagittal plane projected from the posterior olfactory sulcus as a reliable surrogate for the medial boundary of the sylvian cistern, particularly in non-contrast imaging. In contrast-enhanced studies, the carotid bifurcation remains a valid and frequently employed landmark. The integration of both approaches may enhance anatomical precision and facilitate further studies of the sylvian cistern, including volumetric studies, and their translation into the surgery.