الفهرس 
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Abstract
Endonasal endoscopic cranial base surgery is a minimally invasive alternative to open transcranial cranial base approaches for specific indications. These minimally invasive approaches access the cranial base using the natural apertures in the face, namely the nostrils. Visualization is provided with rigid straight and angled endoscopes that can illuminate areas of the cranial base that were previously unreachable with standard microscope-based transsphenoidal or transoral approaches. Because the lens sits at the tip of the endoscope and travels to the pathology, magnification is unnecessary and the panoramic 360-degree view facilitates visualization, even around corners. A variety of approaches have been described; however, there is little consensus or codification of the available approaches and their indications.
Advances in technology have complemented the advances in endoscopic skull base surgery and stimulated the creation of dedicated endoscopic equipment and microinstruments specifically designed to fulfill the unique requirements of endoscopic skull base surgery. These instruments include rigid endoscopes, lens irrigation systems, pneumatically powered robotic holding arms, bipolars, light sources, high definition digital cameras, digital processors, digital monitors, digital versatile disc (DVD) recorders, Polaroid digital photo printers, nerve monitoring devices (electroencephalographs, electromyographs, and those for somatosensory, brainstem auditory, motor, and visual evoked potentials), microdrills, micro-Cavitron ultrasonic aspirators (microCUSAs), and specialized endoscopic microinstruments.
Endoscopic skull base surgery represents a major advance in patient outcome and recovery. It also presents a unique challenge to the neuroanesthesiologist. Highly specialized endoscopic techniques and equipment, together with the use of sophisticated intraoperative monitoring, all mandate skillful anesthetic management that is tailored to the needs of minimally invasive, fully endoscopic skull base surgery. The neuroanesthesiology team plays a vital role in ensuring a safe outcome to this delicate surgery.
Although cranial base anatomy has been well described, its ventral appearance is not commonly appreciated during standard surgeries. Thus, the most important step in developing endoscopic cranial base surgery skills is familiarization with endoscopic ventral cranial base anatomy. The modular approach to learning the various expanded endonasal approaches is based entirely on a thorough understanding of this anatomy.
Endoscopic surgical techniques have transformed all of the surgical specialties. In otolaryngology, endoscop¬ic sinus surgery is well established for the treatment of inflammatory sinus disease as well as benign and select¬ed malignant sinonasal tumors. Endoscopic techniques have also been applied to the treatment of cranial base pathology, most commonly cerebrospinal fluid leaks and pituitary tumors. By the time, it has been demon¬strated that the entire ventral skull base is accessible us¬ing an endonasal approach. This is termed the “expanded endonasal approach (EEA)” and provides access to the anterior, middle, and posterior cranial fossae.2-4. Endoscopic cranial base approaches are combination of three factors: 1) a target, 2) a cranial base approach, and 3) a nasal corridor. The first aspect of the surgical plan is the target. There are12 separate targets. They are: 1) anterior fossa, 2) olfactory groove, 3) orbital apex, 4) sella, 5) suprasellar cistern, 6) cavernous sinus, 7) pterygopalatine fossa, 8) infratemporal fossa, 9) Meckel’s cave, 10) petrous apex, 11) upper third of the clivus, 12) lower two-thirds of the clivus, and 13) odontoid-cervicomedullary junction. Some targets have one possible approach, whereas other targets have multiple approaches. The second aspect of the approach involves an understanding of the possible corridors though which one passes on the way to the target. There are four corridors that define the endonasal endoscopic approaches: 1) transnasal, 2) transsphenoidal, 3) transethmoidal, and 4) transmaxillary.
All approaches are initiated with a wide sphenoid sinus exposure, which permits the surgeons to maneuver the endoscope and instruments. For all endonasal cranial base procedures, the sphenoid sinus represents a vestibule that serves as an entryway providing access for all expanded approaches.
There are many pathologies of skull base could be managed endoscopically thorough the transnasal approach. Example for this; Pituitary adenoma is considered the commonest pathology that is managed by the endoscopic transsphenoidal procedure. Lesions that involve the cribriform plate are considered another example for skull base lesions could be managed endoscopically. These tumors include olfactory groove meningioma, esthesioneuroblastoma, adenocarcinoma, squamous cell carcinoma, sinonasal undifferentiated carcinoma, mucosal melanoma and many others. Of these rare lesions, the most published data on endoscopic resection is on esthesioneuroblastomas. Parasellar and suprasellar lesions could be managed by this way, these lesions include meningiomas, craniopharyngiomas, epidermoid cysts, and pituitary macroadenomas; could be managed endoscopically also. These tumors are accessed by triansgressing the planum sphenoidale, tuberculum sphenoidale and/or the sella turcica.
Clival lesions and the major lesions of the clivus are chordomas and chondrosarcomas. Chordomas are a rare tumor of the skull base representing less than 1% of intracranial tumors. Also, spinomedullary lesions could be managed by endonasal endoscopic approaches and the most common surgical lesion of this region is odontoid pannus usually secondary to rheumatoid arthritis. Traditionally, this is approached via a transoral route, but recently endoscopic approaches replace the transoral route.
For petrous apex the classic lesion of this area is the cholesterol granuloma however chordomas, chondrosarcomas and meningiomas are also among the lesions found here. This region represents the lateral extent of endoscopic approaches.
According to our study, patients with midline skull base tumors like pituitary adenoma, tuberculum sellae meningioma and clival chordoma; pure endoscopic surgery is considered safe and effective way for these tumors management. Also, using bi-nostril endoscopic procedure with removing the posterior bony part of nasal septum is considered an effective way to make a roomy space for instruments and make the surgeon working with ease. Performing the transseptal approach and preparing a vascularized septal mucosa graft allows perfect reconstruction of the sellar floor and sphenoid sinus; decreasing the possibility of C.S.F.
The incidence of intraoperative and postoperative complications is low when compared with results of microscopic transsphenoidal surgery. Also it offers shorter operative times, less intraoperative blood loss, superior differentiation between normal glandular tissue and tumor, better images of intrasellar and parasellar structures, reduced hospital stay, improved patient satisfaction, and decreased need for nasal packing. The presence of E.N.T. surgeon as an assistant to perform the nasal step is helpful; because of his experience with nasal cavity and save neurosurgeon power for the intracranial work. Preparing a vascularized graft from septal mucosa is important and helpful in decreasing the incidence of postoperative C.S.F. leake.