Most endoscopic ventricular procedures take place inside the third ventricle, which occupies a strategic area because it is the topographic center of the ventricular system. As a result of the ventricular dilatation required for endoscopic ventricular navigation, the third ventricle can be divided into anterior, middle, and posterior segments, each having several recesses (Fig. 4.1). During the preoperative planning it is important to recognize the anatomy on imaging studies, especially on sagittal T2-weighted magnetic resonance imaging (MRI) (Fig. 4.2). The gateway to the third ventricle is the foramen of Monro, and after the passage of the endoscope through this it is possible to have a panoramic view of the third ventricle segments (Fig. 4.3, 4.4, and 4.5). In the anterior segment the most important area is that between the mammillary bodies and the pituitary infundibulum, the tuber cinereum. This region is the site in which endoscopic third ventriculostomy (ETV) is performed [1, 2]. Before the passage of the endoscope through the foramen of Monro, an overview of this region is possible (Fig. 4.6). The interthalamic adhesion is generally located in the middle segment, although this segment has an extremely variable position in the third ventricle, and there are reports of the existence of a duplicate variant of this structure [3]. The posterior segment is located at the entrance of the cerebral aqueduct. Above this, in sequence from bottom to top, lie the posterior commissure, which has extremely variable size [4, 5, 6]; the pineal recess; and the suprapineal recess, which is in contact with the roof of the third ventricle and contains the choroid plexus. The pineal gland can be seen through the pineal recess. The view of such posterior segment structures is possible when the skull entry point is more anterior than the Kocher’s point; for instance, when aqueductoplasty is performed [7], or when the hydrocephalus is of large proportion, allowing a posterior orientation of the endoscope subsequently.

For the anterior segment, the endoscopic viewing angle is shown in Fig. 4.7, followed by images of this segment (see Figs. 4.8, 4.9, 4.10, 4.11, 4.12, 4.13, 4.14, 4.15, 4.16, 4.17, 4.18, 4.19, 4.20, 4.21, 4.22, 4.23, 4.24, 4.25, 4.26, 4.27, 4.28, 4.29, 4.30, 4.31, 4.32, 4.33, 4.34, 4.35, 4.36, 4.37, 4.38, 4.39, 4.40, 4.41, 4.42, 4.43, 4.44, 4.45, 4.46, 4.47, 4.48, 4.49, 4.50, 4.51, 4.52, 4.53, 4.54, 4.55, 4.56, 4.57, 4.58, 4.59, 4.60, 4.61, 4.62, 4.63, 4.64, 4.65, 4.66, 4.67, 4.68, 4.69, 4.70, 4.71, 4.72, 4.73, 4.74, 4.75, 4.76, 4.77, 4.78, 4.79, 4.80, 4.81, 4.82, 4.83, 4.84, 4.85, 4.86, 4.87, 4.88, 4.89, and 4.90). For the middle segment, the endoscopic viewing angle is shown in Fig. 4.91, followed by images of this segment (see Figs. 4.92, 4.93, 4.94, 4.95, 4.96, 4.97, 4.98, 4.99, 4.100, 4.101, 4.102, 4.103, 4.104, 4.105, 4.106, 4.107, 4.108, 4.109, 4.110, 4.111, 4.112, 4.113, and 4.114). For the posterior segment, the endoscopic viewing angle is shown in Fig. 4.115, followed by images of this segment (see Figs. 4.116, 4.117, 4.118, 4.119, 4.120, 4.121, 4.122, 4.123, 4.124, 4.125, 4.126, 4.127, 4.128, 4.129, 4.130, 4.131, 4.132, 4.133, 4.134, 4.135, 4.136, 4.137, 4.138, 4.139, 4.140, 4.141, 4.142, 4.143, 4.144, 4.145, 4.146, 4.147, 4.148, 4.149, 4.150, 4.151, 4.152, 4.153, 4.154, 4.155, 4.156, 4.157, 4.158, 4.159, 4.160, 4.161, 4.162, 4.163, 4.164, 4.165, and 4.166).

Illustrative cases are presented.