Translated Abstract
Background Many cranial nerves and vessels lie in CPA(Cerebellopontine Angle, CPA), and their locational relationships are very complexed. Microvascular compression syndrome mainly happened in CPA. MVD(Microvascular Decompression, MVD) is the first form of operations.While there are still some patients who were operated in vain. In this few years, with the development of optics and endoscopic technique, more and more neuroendoscopies with high clearness, multiple usage and convinence have been appearing. Neuroendoscopy-assisted MVD performs frequently, which makes microvascular compression syndrome high healing rate, low complication and recurrence. Neuroendoscopic anatomy, which is different with microscopic anatomy, is a very small local area of continuous structure and lack of stereo sense. It is easy to get lost during operation. So the study focus on neuroendoscopic anatomy and operative approach of CPA. Objective The objective of our study is to simulate three kinds of keyhole approach to CPA by neuroendoscopy, including suboccipital retrosigmoid lateral cerebellum approach, suboccipital retrosigmoid superior cerebellum approach and suboccipital retrosigmoid inferior floccular process approach. It is to define anatomic landmarks of these three kinds of approach, evaluate the feasibility and characters of these three kinds of approach in MVD, find the best approach to CPA.Methods15 specimens of adult cadaveric head were selected randomly to simulate neuroendoscopy-assisted microneurosurgery keyhole approach including suboccipital retrosigmoid lateral cerebellum approach, suboccipital retrosigmoid superior cerebellum approach and suboccipital retrosigmoid inferior floccular process approach. The anatomic structure of CPA was observed as follows: susuperior cerebellar artery, antero-inferior cerebellar artery, Ⅶcranial nerve, Ⅷcranial nerve, postero-inferior cerebellar artery, Ⅸ-Ⅺcranial nerve, Meckel cavity, internal auditory foramen , jugular foramen, the relationship between vessels and cranial nerves, define the neuroendoscopic anatomic landmarks and routes to root exit/entry zoon (REZ)of Ⅴ, Ⅶ, Ⅸcranial nerve，measure data of approach and related anatomic structure. Results In simulating operation through suboccipital retrosigmoid lateral cerebellum approach, the panorama of CPA, the REZ of Ⅴ, Ⅶ, Ⅸcranial nerve and the relationship between vessels and cranial nerves were observed. The landmarks of the approach included Meckel cavity, internal auditory foramen , jugular foramen, Ⅴcranial nerve, Ⅶcranial nerve, Ⅷcranial nerve, Ⅸcranial nerve. The distance from bone margin corresponding with middle of posterior sigmoid sinus to Meckel cavity is 58.45±0.96mm, to internal auditory foramen is 44.26±1.60mm, to jugular foramen is 42.40±0.85mm mm, to the REZ of Ⅴcranial nerve is 56.90±1.29mm mm, to the REZ of Ⅶcranial nerve is 52.24±1.36mm, to the REZ of Ⅸcranial nerve is 46.75±2.00mm.In simulating operation through suboccipital retrosigmoid superior cerebellum approach, Ⅴcranial nerve from REZ to Meckel cavity, and the relationship between vessels and cranial nerves were observed. The landmarks of the approach included Meckel cavity,Ⅴcranial nerve. The distance from bone margin corresponding with corner of sigmoid sinus to petrosal vein is 48.44±3.12mm, to the REZ of Ⅴcranial nerve is 55.22±1.55mm, to Meckel cavity is 55.94±1.56mm. In simulating operation through suboccipital retrosigmoid inferior floccular process approach, the REZ of Ⅸcranial nerve, the REZ of Ⅶ cranial nerve, and the relationship between vessels and cranial nerves were observed. The landmarks of the approach included choroid plexus of fourth ventricle, floccular process. The distance from bone margin corresponding with posterior inferior sigmoid sinus medial 1cm to the REZ of Ⅸ cranial nerve is 32.58±0.91mm, to inferior floccular process is 34.73±1.00mm, to the REZ of Ⅶ cranial nerve is 38.79±1.34mm.Conclusions 1. Suboccipital retrosigmoid approach has natural anatomic gaps including superior cerebellum gap, lateral cerebellum gap and inferior cerebellum gap, which provided possibility to CPA for neuroendoscopy. 2. Through neuroendoscopic suboccipital retrosigmoid lateral cerebellum approach, the REZ of Ⅴ, Ⅶ, Ⅸcranial nerve can be explored, and MVD can be performed. Through neuroendoscopic suboccipital retrosigmoid superior cerebellum approach,Ⅴcranial nerve from REZ to Meckel cavity can be explored, and MVD can be performed. Through neuroendoscopic suboccipital retrosigmoid inferior floccular process approach, the REZ of Ⅶ, Ⅸcranial nerve can be explored, and MVD can be performed. 3.Neuroendoscopic suboccipital retrosigmoid superior cerebellum approach is a simple route, is observed overall ,and is invasive minimally to cranial nerve compared with neuroendoscopic suboccipital retrosigmoid lateral cerebellum approach in exploring the REZ of Ⅴcranial nerve and performing MVD. Neuroendoscopic suboccipital retrosigmoid superior cerebellum approach is the best approach to MVD of Ⅴcranial nerve. 4. Neuroendoscopic suboccipital retrosigmoid inferior floccular process approach is a close route, operates conveniently, and is invasive minimally to cranial nerve compared with neuroendoscopic suboccipital retrosigmoid lateral cerebellum approach in exploring the REZ of Ⅶ, Ⅸcranial nerve and performing MVD. Neuroendoscopic suboccipital retrosigmoid inferior floccular process approach is the first form to MVD of Ⅶ, Ⅸcranial nerve. 5. It can ensure accuracy and safety of the operation to master anatomic landmarks, operative route and related anatomic data, and supply objective index for the operative approach of CPA in MVD.
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