Extended Endoscopic Endonasal Approach To The Midline Ventral Skull Base: Anatomic Study

PartⅠExtended Endoscopic Endonasal Approach to the Anterior Skull Base: Anatomic StudyObjective: The aim of study was to describe the endoscopic anatomical landmarks and extent of exposure to the anterior skull base by extended endoscopic endonasal approach, which was essential to better understand the complex anatomical relationships of the structures involved in the approach, and further to discuss the feasibility of exposing the anterior skull base, the indication of the approach and prevention of complications. Methods: Ten formalin-fixed adult cadaver heads whose arterial system was injected with red latex were dissected for the anatomical studies. Endoscopic dissections were performed with the adjunct of neuronavigation using a rigid endoscope (Karl Storz) that was 4 mm in diameter, 18 cm in length, and equipped with 0°, 30°and 45°lenses. An extended endoscopic endonasal approach to the anterior skull base was made through two nostrils in all cases to measure the distance between main anatomical landmarks and area of exposure.Results: During the nasal step, the detailed endoscopic anatomy consisted of the inferior turbinate, the middle turbinate, superior turbinate, nasal septum, choana, speno-ethmoid recess and the sphenoidal ostium. During the sphenoidal and ethmoidal step, the detailed endoscopic anatomy was composed of the sella, tuberculum sellae, sphenoidal planum, anterior ethmoidal cell, posterior ethmoidal cell, the frontal recess, anterior ethmoidal artery, the third lamella, posterior ethmoidal artery and cribriform plate. The maximum of lateral extension was obtained between the two medial orbital walls, separately at the base of the crista galli (mean distance 34.1±4.2mm) and at the middle of the cribriform plate (mean distance 24.7±3.1mm). The distance between the bilateral anterior ethmoidal arteries was 26.8±3.4mm, and the distance between the bilateral posterior ethmoidal arteries was 24.3±4.1mm, while the mean distance between the anterior and posterior ethmoidal arteries at the level of the lamina papyracea was 17.9±2.7mm. The area of the anterior skull base was 430.6±53.4mm2 under the endoscopic view by the approach. The posterior portion of the third lamella was the most important anatomic landmarks for an approach to the orbital retrobulbar space. Once the dura was opened, the recognizable structure were the olfactory nerves, the gyri recti of the frontal lobes and the anterior interhemispheric fissure.Conclusions: The extended endoscopic endonasal approach guided with neuronavigation could provide wide operative field and also be considered a minimally invasive technique to approach the anterior skull base. The third lamella was the most important anatomic landmarks for an endoscopic endonasal approach to the orbital retrobulbar space. Adequate endoscopic skill, ample endoscopic anatomy and reliable reconstruction techniques were required for clinical application of the approach.PartⅡExtended Endoscopic Endonasal Approach to the Middle Skull Base: Anatomic StudyObjective: The endoscopic endonasal transsphenoidal approach is a minimally invasive surgical technique for the removal of sellar lesions. The aim of the present study based on the previous experience was to identify the important anatomic landmarks by extended endoscopic endonasal approach to the middle skull base. The endoscopic surgical anatomy of the sellar region, the suprasellar region and the cavernous sinus was studied to establish an anatomic basis, and to discuss the various anatomic conditions affecting clinical application and operative characteristic.Methods: Ten formalin-fixed adult cadaver heads whose arterial system was injected with red latex were dissected for the anatomical studies. Endoscopic dissections were performed with the adjunct of neuronavigation using a rigid endoscope (Karl Storz and Co.) that was 4 mm in diameter, 18 cm in length, and equipped with 0°, 30°and 45°lenses. An extended endoscopic endonasal approach to the middle skull base was made through two nostrils in all cases to measure the distance between main anatomical landmarks and area of exposure.Results: The posterior bony wall of the sphenoidal sinus was subdivided into five compartments: sellar region, suprasellar region, bilateral cavernous sinus region and clival region. The sellar region consisted of the bottom of the sella and the clival recess. The suprasellar region was composed of the posterior ethmodal cells, the sphenoidal planum, the tuberculum sellae and the optic protuberance. The cavernous sinus region contains the optocarotid recess, the parasellar internal carotid artery, four bony protuberances (orbital apex, maxillary, mandibular and vidian canal) and three anatomic triangles (the optic strut triangle, the V1-V2triangle and the V2-V3 triangle)The width of the pituitary was 12.2±2.1 mm anteriorly, 21.5±2.5 mm medially, and 17.6±3.4 mm posteriorly. The distance of bilateral medial optic-carotid recess was measured as 11.3±1.2mm, and the distance of pituitary between anterior and posterior margin was 9.1±2.9mm. The intradural suprasellar neurovascular structure areas included suprachiasmatic, subchiasmatic, retrosellar and ventricular region. Some anatomic conditions might influence the application of the extended endoscopic endonasal approach, such as the degree of pneumatization of the sphenoid sinus, the size of the sella, the position of chiasm, the height of the dorsum sellae and the size of the posterior clinoids. The venous compartment of the cavernous sinus can be divided into four spaces (ventral space, dorsal space, lateral space and medial space) based on the relationship to the internal carotid artery. The internal carotid artery of the cavernous sinus on endoscopic view is defined as trigeminal portion, posterior bend portion, inferior horizontal portion, anterior bend portion and superior horizontal portion.Conclusions: The extended endoscopic endonasal approach could provide a multiangled and clearly close-up view of the sellae region, the suprasellar region and the cavernous sinus and also be an effective, minimally invasive approach for lesions located in middle skull base. The optic-carotid recess was the key point anatomic landmark for the extended endoscopic endonasal approach to middle skull base. Adequate endoscopic skill, ample endoscopic anatomy and reliable haemostasis techniques were required for clinical application of the approach. PartⅢExtended Endoscopic Endonasal Approach to the Clivus and the Cranio-Vertebral Junction: Anatomic StudyObjective: The aim of study was to describe the endoscopic anatomical landmarks and extent of exposure to the clivus and the cranio-vertebral junction by extended endoscopic endonasal approach guided by neuronavigation system, and then to discuss the possibility of an extended endoscopic endonasal approach to the clivus and the cranio-vertebral junction. Further more attentions were focused on the effect of the vidian canal and the relationship to the division of the clivus.Methods: Ten formalin-fixed adult cadaver heads whose arterial system was injected with red latex were dissected for the anatomical studies. Endoscopic dissections were performed to simulate the operation with the adjunct of neuronavigation using a rigid endoscope (Karl Storz and Co.) that was 4 mm in diameter, 18 cm in length, and equipped with 0°, 30°and 45°lenses. An extended endoscopic endonasal approach to the clivus and the cranio-vertebral junction was made through two nostrils in all cases to measure the distance between main anatomical landmarks.Results: The extent of the surgical exposure by the extended endoscopic endonasal approach extended from the retrosellar region superiorly to the anterior foramen magnum inferiorly and bilaterally bordered on the parasellar internal carotid artery, the paraclival internal carotid artery, the Eustachian tube and the occipital condyle. The main anatomic landmarks on the clivus included the clivus recess, the vidian canal, the Eustachian tube and the occipital condyle. Several anatomic data were measured in cadaver heads: the distance from the columella to the anterior margin of foramen magnum was 92.1±7.2mm, the distance between both medial occipital condyles was 27.8±3.5mm, the distance between both the ostiums of Eustachian tube was 20.1±4.5mm, and the extent of removal of anterior arch of the atlas during exposure of the odontoid process was 1.4±0.8mm. The ventral clivus was divided into three areas in accordance with the clival recess and the bilateral vidian canal from the endoscopic endonasal view. The three areas included the retrosellar part extending from the superior margin of the sellar dorsum to the clival recess, the sphenoidal part from the clival recess to the plane of both vidian canal and the nasopharyngeal part from the the plane of both vidian canal to the anterior foramen magnum. After opening the dural mater, from rostrally to caudally, the intracranial structures included the mammillary bodies, posterior communicating artery, oculomotor nerve, superior cerebellar artery, basilar artery, abducent nerve, the pons, medulla oblongata, the lateral facial nerve, the vestibulocochlear nerve, the upper spinal cord, bilateral vertebral arteries, the posterior inferior cerebellar artery, the anterior ventral spinal artery, the hypoglossal nerve, the accessory nerve and the ventral surface of the pons were visible. The ventral and dorsal rootlets of C1 and C2 and the dentate ligament between them were identified in low portion of the surgical field.Conclusions: The extended endoscopic endonasal approach could not provide the clear endoscopic anatomy around the clivus and the cranio-vertebral junction but also be an appropriate approach to the clival and the cranio-vertebral junction region of the skull base. The vidian canal was an importantly consistent landmark to the petrous internal carotid artery. The endoscopic division of the ventral clivus based on the vidian canal and the clival recess would benefit the choice of the approach. With good knowledge of the endoscopic anatomic region and the adjunct of the neuronavigation system, endoscopic surgical procedures could be performed safely with more minimal invasiveness.