1. Is Transcranial Extradural Posterior Clinoidectomy a Feasible Maneuver? A Cadaver Anatomical Study Asem Salma MD, Song Wang MD, Mario Ammirati MD MBA Department of Neurological Surgery, The Ohio State University Medical Center, Columbus, Ohio

2. NASBS Presenter Disclosure Slide Asem Salma MD Song Wang MD Mario Ammirati MD, MBA Nothing To Disclose

3. Introduction In this anatomical study, we explored the feasibility of performing a transcranial extradural posterior clinoidectomy via a subtemporal route between V2 and V3 with skeletonization of the sphenoidal part of the medial wall of the cavernous sinus. This was accomplished by integrating the surgical microscope and the endoscope.

4. Materials and Methods Cadaver characteristics and surgical tools 10 dissections were carried out in 10 fresh cadaver heads. Standard operating microscopes and 0 and 30° endoscopes were used. 10 dissections were carried out in 10 fresh cadaver heads. Standard operating microscopes and 0 and 30° endoscopes were used.

5. Surgical technique After an extended orbitozygomatic craniotomy was performed a two stage dissection to remove the posterior clinoid process was executed

6. Stage one (microscopic stage) was conducted using an operating microscope

7. the area between V2 and V3 was exposed

8. microscopic view illustrating the flattening of the floor of the middle cranial fossa and the widening of the foramina rotundum and ovale (V2= maxillary nerve, V3= mandibular nerve, mm=middle meningeal artery, mcf = middle cranial fossa

9. Microscopic view showing that the bone at the junction of the anterior one third and posterior two thirds of the distance between V2 and V3 has been drilled all the way to the sphenoid sinus cavity (V2= maxillary nerve, V3= mandibular nerve, mm=middle meningeal artery, sph.s = sphenoid sinus).

10. This drilling was conducted at the plane that intersects the long axis of V2 at a 45 degree angle

11. microscopic view showing that the bone underneath Meckel’s cave and the beginning of the lateral portion of the carotid sulcus has been removed. (V3= mandibular nerve, gg= gasserian ganglion, sph.s = sphenoid sinus).

12. Stage two (endoscopic stage) was performed using the endoscope Stage two (endoscopic stage) was performed using the endoscope

13. The drilling was continued to remove the carotid sulcus, then, the endosteal layer of the dura lining the carotid sulcus was dissected from the bone (ca= carotid artery, cs = carotid sulcus, gg = gasserian ganglion, sph.s = sphenoid sinus).

14. At the end of this stage, the dura reflection that forms the posterior part of the pituitary capsule was exposed along with the base of the posterior clinoid process

15. Endoscopic view showing the removal of the posterior clinoid process (ca= carotid artery, pcp= posterior clinoid process, sph.s= sphenoid sinus).

16. Finally, the dura was opened to confirm the removal of the posterior clinoid process.

17. Results: We were able to remove the posterior clinoid process in all specimens. This study reveals the feasibility of transcranial resection of the posterior clinoid process extradurally. It also highlights a neurosurgical path that could afford an extra dural access to the posterior clinoid.

18. Conclusions: Keeping in mind the inherent limitations of any cadaver study, - This new neurosurgical maneuver could be incorporated into orbitozygomatic osteotomy, mainly when dealing with basilar tip aneurysms that are located posterior to the posterior clinoid process. - This new neurosurgical maneuver could be incorporated into orbitozygomatic osteotomy, mainly when dealing with basilar tip aneurysms that are located posterior to the posterior clinoid process. - This maneuver could decrease the risk of third cranial nerve or posterior communicating artery injuries that could occur when the posterior clinoid is drilled intradurally - This maneuver could decrease the risk of third cranial nerve or posterior communicating artery injuries that could occur when the posterior clinoid is drilled intradurally

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