(1)
Division of Neurosurgery, Federal University of Triângulo Mineiro, Uberaba, Minas Gerais, Brazil
5.1 Introduction
The subarachnoid space below the third ventricle is reached after opening the` ependymal layer just ahead of the mammillary bodies (tuber cinereum) when an endoscopic third ventriculostomy (ETV) is performed [1]. The structure in this region that divides the space into individual cisterns is the membrane of Liliequist [2, 3]. This membrane presents a sellar portion, which is inserted in the dorsum sellae, and this sellar portion is subdivided into a posterior projection, a diencephalic portion, and a mesencephalic portion. The diencephalic portion is in close contact with the ependymal layer and extends to the mammillary bodies, and the mesencephalic portion has a posterior inferior projection, surrounding the mesencephalon [4, 5, 6]. The membrane of Liliequist limits the interpeduncular cistern. This cistern has a pars profunda, adjacent to the ependymal layer, and a pars superficialis, just below the pars profunda. The diencephalic portion of the membrane of Liliequist divides the two segments [6]. The pars profunda contains the anterior group of thalamoperforating arteries. Located in the pars superficialis is the bifurcation of the basilar artery with its two main branches, the posterior cerebral arteries (P1) and the superior cerebellar arteries (located immediately before the bifurcation of the basilar artery), and the oculomotor nerves (CN III) [6]. The lower limit of the pars superficialis is the mesencephalic portion of the membrane of Liliequist. The recess below the latter is the prepontine cistern[6] (Fig. 5.1). In most ventricular procedures it is difficult to identify this anatomy. On sagittal T2-weighted magnetic resonance imaging (MRI) it is sometimes possible to visualize these structures (Fig. 5.2). But regardless of whether or not they are in clear view, the key to the success of an ETV is the opening of the membrane of Liliequist, at least of its diencephalic portion (Fig. 5.3). In certain cases progression of the endoscope inside the prepontine cistern is possible, enabling visualization of the trajectory of the basilar artery, and the nerves that emerge from the anterior side of the brainstem, such as the abducens nerve (CN VI), in the transition between the pons and the medulla oblongata, and the hypoglossal nerve (CN XII), at the medulla oblongata (Fig. 5.4). The endoscopic viewing angle for the interpeduncular and prepontine cisterns is shown in Fig. 5.5, and the structures of this region are shown in Figs. 5.6, 5.7, 5.8, 5.9, 5.10, 5.11, 5.12, 5.13, 5.14, 5.15, 5.16, 5.17, 5.18, 5.19, 5.20, 5.21, 5.22, 5.23, 5.24, 5.25, 5.26, 5.27, 5.28, 5.29, 5.30, 5.31, 5.32, 5.33, 5.34, 5.35, 5.36, 5.37, 5.38, 5.39, 5.40, 5.41, 5.42, 5.43, 5.44, 5.45, 5.46, 5.47, 5.48, 5.49, and 5.50.
An illustrative case is presented.
Fig. 5.1
Detail of the membrane of Liliequist just below the third ventricle. Pars profunda of the interpeduncular cistern (1), pars superficialis of the interpeduncular cistern (2), prepontine cistern (3), and pia mater (4) (Reprinted from Seeger [6], with permission)
Fig. 5.2
Sagittal T2-weighted magnetic resonance imaging (MRI) depicting the membrane of Liliequist and cisterns below the third ventricle. Ependymal layer (A), pars profunda of the interpeduncular cistern (B), diencephalic portion of the membrane of Liliequist (C), pars superficialis of the interpeduncular cistern (D), mesencephalic portion of the membrane of Liliequist (E), prepontine cistern (F), insertion of the membrane of Liliequist at the dorsum sellae (G)
Fig. 5.3
Trajectory of the neuroendoscope through the pars profunda of the interpeduncular cistern. This step is mandatory for ETV success. Insertion of the mesencephalic portion of the membrane of Liliequist at the pontomesencephalic rim (a), insertion of the diencephalic portion of the membrane of Liliequist at mammillary body (b), bulging of this segment against the chiasmatic cistern (c), insertion of the membrane of Liliequist at the dorsum sellae (d), gap of the mesencephalic segment (e). Bifurcation of the basilar artery (1), posterior bundle of the thalamoperforating arteries, penetrating the posterior perforated substance (2), anterior bundle of the thalamoperforating arteries, crossing pars superficialis of the interpeduncular cistern (3), prepontine cistern (4), pars superficialis of the interpeduncular cistern (5), pars profunda of the interpeduncular cistern (6), chiasmatic cistern (7) (Reprinted from Seeger [6], with permission)
Fig.5.4
Figure depicting sellar and clivus regions, viewed from behind. It is possible to see cranial nerves II to XII and other structures. Endoscopic view is possible of the III, VI, and XII cranial nerves. Anterior intercavernous sinus (1), internal carotid artery (2), projection of the anterior clinoid process (3), posterior intercavernous sinus (4), vascularization of the dorsum sellae and the posterior clinoid process (5), projection of the internal opening carotid channel of the petrous bone (6), oval foramen (7), basilar venous plexus (8), foramen magnum (9) (Reprinted from Seeger [6], with permission)
Fig.5.5
Direction of the endoscopic vision for interpeduncular and prepontine cisterns
5.2 Interpeduncular and Prepontine Cisterns
Fig.5.6
Normal anatomy. (A) Membrane of Liliequist – diencephalic portion, (B) thalamoperforating arteries, (C) left oculomotor nerve (CN III), (D) left posterior cerebral artery (P1)
Fig.5.7
Normal anatomy. (A) Membrane of Liliequist – diencephalic portion, (B) Left posterior cerebral artery (P1), (C) Left oculomotor nerve (CN III)
Fig.5.8
Normal anatomy. (A) Membrane of Liliequist – diencephalic portion, fenestration by biopsy forceps, (B) Basilar artery, (C) Pons
Fig. 5.9
Normal anatomy. (A) Membrane of Liliequist – diencephalic portion, (B) Interpeduncular cistern, (C) Ependymal layer
Fig. 5.10
Normal anatomy. (A) Ependymal layer, (B) Membrane of Liliequist – diencephalic portion, (C) Right posterior cerebral artery (P1), (D) Bifurcation of the basilar artery, (E) Left posterior cerebral artery (P1)
