Extended Endoscopic Endonasal Approach to the Third Ventricle: Multimodal Anatomical Study with Surgical Implications

A certain interest for the extended endoscopic endonasal approach for the management of sellar-suprasellar lesions extending inside the third ventricle has been growing in recent years. The aim of this anatomical study was to evaluate the possibilities in terms of exposure and access to the different areas of the third ventricle, with the endoscopic endonasal technique, as compared with the microscopic or endoscopic view provided via different transcranial approaches. The advantages and limitations of both surgical pathways were analyzed.

Ten human cadaver heads were dissected. In order to standardize the comparison between the endonasal and the transcranial routes, the third ventricle cavity has been divided into four areas by means of two ideal planes, one passing through the optic chiasm and the interthalamic commissure and one passing through the posterior edge of the foramen of Monro and the interthalamic commissure. Accordingly, two anterior (infundibular and foraminal) and two posterior (mesencephalic and tectal) areas have been defined.

The endoscopic endonasal approach allows for exploration and surgical maneuverability, especially in the anterior areas of the third ventricle. In the infundibular and foraminal areas the surgical maneuverability seems to be better as compared with that obtained inside the mesencephalic region, while via the endonasal route the tectal area could not be reached. In particular, the infundibular area can be explored either passing through the lamina terminalis or via the tuber cinereum; this latter trajectory enables visualization of the foramina of Monro and the floor of the third ventricle up to the pineal recess.

This anatomical study shows that the lamina terminalis and, above all, the tuber cinereum represent two safe entry points defining possible surgical corridors to be considered for the extended endoscopic endonasal approach to the third ventricle.