**9.1 General roles of endoscope**

The advantages of better illumination, clear views of regional anatomic features at close range and the extended viewing angles make the use of the endoscope a good adjunct or an independent alternative of microscope. Endoscope can be used in and around the operative field of aneurysms easier and safer. Furthermore, the endoscope facilitates confirmation of optimal clip positions [113].

In a cadaveric study by Chowdhury et al. the variations were identified and the authors concluded endonasal extended transsphenoidal approach can fully expose CW with brain in situ to observe the circle for variations and asymmetry (**Figures 16** and **17**) [114]. Taniguchi et al. reported in their series of 54 cases, the endoscope was used for further clarification of the detailed additional anatomy in 9 cases (16.7%). The surgeons reapplied the clip on the basis of endoscopic information which was gained after the initial clipping in 5 cases (9.3%) [115]. In a series of studies by Kalavakonda et al., the endoscope was used to observe anatomical features in 26 (33%) and clip position in 75 of 79 cases (95%). In 15 (19%) aneurysms, the important information like the neck and back wall of the aneurysm, parent artery, branches, perforators and the completeness of clipping of the neck and inclusion of the parent artery in the clip could be visualized via the endoscope. To complete the clipping of the residual neck or to avoid the inclusion of parent artery within the clip, the clip was repositioned in six cases, and to avoid compression of the optic nerve the clip position was reapplied in 1 case [116]. Fischer et al. reported, the endoscope was used to obtain additional topographic information before clipping in 150 of 180 cases (83%) [5, 117]. In 4 cases, clipping was achieved under endoscopic view. Following the clip application, endoscopic inspection was performed in 130 out of 180 procedures [113].

#### **Figure 16.**

*Endoscopic view of posterior part of circle of Willils showing a number of anatomical variations. 1-Liliequist membrane, 2-basilar trunk, 3-SCA (left>right), 4-oculomotor nerve, 5-P1 (left>right), 6-P2 (left>right), 7-fetal type of Pcom & 8-mamillary bodies.*

#### **Figure 17.**

*Endoscopic view of interpeducular fossa and posterior part of CW after mobilization of pituitary gland to right cavernous sinus area. A) 1-pituitary gland (mobilized), 2-pituitary stalk. 3-basilar artery, 4 - oculomotor nerve, 5- optic chiasma & 6-optic nerve. B) 1- pituitary gland (mobilized), 2- pituitary stalk. 3- basilar artery, 4 - oculomotor nerve, 5- optic chiasma, 6-optic nerve, 7-proximal A1 and internal carotid artery, 8-Acom complex, & 9-medial temporal lobe. C) 1-basilar artery, 2-P1, 3-oculomotor nerve, & 4- medial temporal lobe. D) 1-basilar artery, 2-P1, 3-oculomotor nerve & 4-posterior communicating artery (Pcom)).*

In general, very large and giant aneurysms gain fewer benefits from the endoscope than smaller ones in the same location, because the mass of the lesion compromises insertion and fixation of the endoscope in the operative field [118]. The endoscope is especially useful in the treatment of deeply located cerebral aneurysm. Hence the location is another important factor. The effectiveness of the endoscope for these aneurysms is limited in case of superficially located aneurysms like middle cerebral artery aneurysms and distal aneurysms such as pericallosal aneurysms [113]. The detailed approach to the aneurysms are beyond the scope of this chapter.

Endoscopic application may be associated with some disadvantages. The endoscope can cause rupture of the aneurysm during initial inspection. Blood in the operative field may make the endoscope useless and clot must be removed before proceeding. There is still a lack of instrumentation specifically designed for endoscopic surgery [116]. Three dimensional views were not available before, which has now been circumvented by newer version of 3D endoscopes.

#### **10. Microvascular decompression**

The presence of offending vessels, which often compress the relevant nerve at the root entry/exit zone (REZ) generally cause the primary trigeminal neuralgia

(TN), hemifacial spasm (HFS), and glossopharyngeal neuralgia [119–121]. Microvascular decompression (MVD) is a well-established and effective treatment supported by many studies [122, 123].

Endoscopic techniques such as endoscopic or endoscope-assisted MVD (EMVD) have been used for MVD operations. Meanwhile, as the technique matures and the surgeons attain experience with endoscopic operation, some disadvantages of Microscopic MVD (MMVD) can be overcome. Though many neurosurgeons have not find EMVD is superior to MMVD as the access for MMVD can be small and the offending vessels can be separated easily through that, several authors indicated the superior efficacy of endoscopic or endoscope assisted surgery in locating the offending site of neurovascular conflict when compared with the microscopic surgery [124–126].

Regarding TN, the lateral pontomesencephalic segment of the SCA usually runs medial to the trigeminal nerve and the nerve can be compressed in a rostromedial direction [127, 128]. Through an endoscopic approach, the lateral pontomesencephalic segment of the SCA can be transposed rostromedially and fixed at the cerebellar tentorium. An approach with the thirty degree endoscope through the lateral tentorial surface of the cerebellum via a keyhole provides excellent exposure of the trigeminal nerve from the REZ to the Meckel's cave. This can also show the course of the lateral pontomesencephalic segment of the SCA as the offending artery along the midbrain while requiring neither brain retraction nor ligation of the petrosal vein [129]. A clear endoscopic view also allows visualization of the perforators from the lateral pontomesencephalic segment of the SCA. Perforators from the lateral pontomesencephalic segment of the SCA are relatively long which helps transposition to fixation at the tentorium.

For HFS, the REZ of the facial nerve is located immediately medial to cranial nerve VIII in the supraolivary fossette, and the flocculus exits just lateral to cranial nerve VIII [127, 128]. The REZ of the facial nerve is often compressed by the lateral pontomedullary segment of the AICA from a caudal direction [127, 128]. The AICA can be transposed caudally and fixed at the petrosal dura mater by endoscopic approach. A 300 or 450 view of endoscopes through the petrosal surface of the cerebellum via a retrosigmoid keyhole clearly demonstrates the neurovascular structures and relationship around the supraolivary fossette behind the flocculus. The REZ of the facial nerve is readily identified after mobilization of the AICA as the offending artery. The endoscope also clearly demonstrates small perforators even behind obstacles [130], and secure recognition of perforators contributes to avoidance of injury during decompression procedures, especially for the transposition technique.

In the meta-analysis by Li et al., it is shown that, EMVD was superior considering the perioperative safety as with less perioperative complications [131]. Facial paralysis was significantly low in EMVD, and CSF leak and dysaudia (defective articulation stemming from auditory disability) also showed a similar trend with the previous discussions [132, 133]. Postoperative efficacy like recent remission rate, long-term remission rate, and offending vessel discovery rate was also superior to MMVD. The data from the series of Li et al. favored EMVD as the preferred method of surgery for MVD for the management of trigeminal or glossopharyngeal neuralgia and facial spasm [131].
