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Open Access Austin Journal of Otolaryngology Review Article Endoscopic Endonasal Approaches to the Skull Base - A Review Muto J1,3, Carrau RL1,2, Prevedello DM1,2*, Ditzel Filho LFS1, de Lara D1, Kasemsiri P2, Otto BA1,2 and Yoshida K3 1 Departments of Neurosurgical Surgery, Ohio State University, USA 2 Otolaryngology- Head and Neck Surgery, Ohio State University, USA 3 Department of Neurosurgery, Keio University School of Medicine, Japan *Corresponding author: Daniel M Prevedello, Department of Neurosurgery, Ohio State University, N-1011 Doan Hall, 410 W. 10th Avenue, Columbus, OH, 43210, USA Received: November 20, 2014; Accepted: September 01, 2015; Published: September 05, 2015 Abstract In the past decade, endoscopic endonasal approaches (EEAs) have progressed greatly, becoming an alternative to conventional transcranial approaches. EEAs to the ventral skull base may be categorized anatomically into five sagittal plane modules (transcribriform, transplanum, transsellar, transclival, transodontoid) and eight coronal plane modules (orbit, petrous apex, infrapetrous, suprapetrous, cavernous sinus, infratemporal fossa, condyle, jugular foramen). A safe and effective use of these techniques requires a deep understanding of pertinent anatomical landmarks and technical nuances to minimize patient morbidity. EEAs are useful approaches to the ventral skull base and craniocervical junction and hold great potential for evolutionary progress when coupled with careful patient selection, adequate training and experience. This manuscript describes and discusses important anatomical landmarks and critical aspects of the surgical technique used in each module, complementing their review with case illustrations. Keywords: Endonasal endoscopic approach; Coronal module; Sagittal module; Indications and limitations; Skull base; Reconstruction Abbreviations Sagittal Plane Approaches CT: Computed Tomography; MR Imaging: Magnetic Resonance Imaging; CS: Cavernous Sinus; GG: Gasserian Ganglion; EEA: Endonasal Endoscopic Approach; ICA: Internal Carotid Artery; MPP: Medial Pterygoid Plate; LPP: Lateral Pterygoid Palate; MPW: Medial Pterygoid Wedge; VA: Vertebral Artery; BA: Basilar Artery; ACA: Anterior Cerebral Arterie; MOCR: Medial Optic-carotid Recess; VBJ: Vertebrobasilar Junction; V2: Maxillary Division of the Trigeminal Nerve; SOF: Supraorbital Fissure Endonasal endoscopic approaches in the sagittal plane include five modules, namely the transcribiform, transplanum, transsellar, transclival, and transodontoid approaches. These modules can be combined according to the complexity of the lesion at hand. Essential key points are summarized in. Introduction Transcribiform approach (Figure 1) This module exposes the area between the posterior ethmoidal arteries and the frontal sinus; thus, it is defined by the removal of the cribriform plate. Its limits are bounded by the lamina A first attempt to perform endonasal endoscopic skull base surgery dates back a century. Initially these efforts were restricted to the pituitary fossa via transsphenoidal approaches [1]; however, with the parallel evolution of instruments and visualization technology, coupled with the ever increasing anatomical knowledge and surgical experience, these techniques gradually have progressed to encompass other areas of the cranial base [2,3]. Most EEAs include a trans-sphenoidal approach as the first step to access the ventral skull base with the subsequent extension of the approach relying on well-defined anatomy-based surgical modules along the sagittal and coronal planes. Therefore, EEAs may be divided into five modules in the sagittal plane (extending from the cribiform to the odontoid) [4-6]; and eight modules in the coronal plane (from paramedian internal carotid artery (ICA) to the jugular foramen) [7,8]. This review describes the anatomical landmarks; indications and limitations to these approaches to heightened awareness of their efficacy and the understanding of their caveats. Austin J Otolaryngol - Volume 2 Issue 7 - 2015 ISSN : 2473-0645 | www.austinpublishinggroup.com Prevedello et al. © All rights are reserved Figure 1: Transcribriform approach: A: Axial T1gadolinium enhanced MRI showing the frontal base meningioma before surgery. B: Coronal MRI showing the tumor originated from falx was attached to the frontal base. C: Axial MRI showing subtotal resection of the tumor. D: Coronal MRI showing partial resection of the tumor. E: operative image showing the left olfactory nerve was preserved. The tumor underneath the frontal lobe was resected completely. The residual tumor was located in the interhemispheric cistern. Citation: Muto J, Carrau RL, Prevedello DM, Ditzel Filho LFS, de Lara D, et al. Endoscopic Endonasal Approaches to the Skull Base - A Review. Austin J Otolaryngol. 2015; 2(7): 1055. Prevedello DM Figure 2: Transplanum approach: A: a preoperative axial T1 weighted gadolinium enhanced MRI showing craniopharyngioma extended to suprasellar lesion. B: Coronal MRI showing the tumor pushed up the floor of third ventricle and contained the cystic lesion. C: Sagittal postoperative MRI showing the complete tumor removal. D: Coronal MRI showing stalk and the third ventricle was intact. E: operative image showing the tumor behind the pituitary gland. F: operative image showing the tumor removed totally. The lamina terminalis was open and the arachnoid over the chiasm and optic nerve was preserved intact. papyracea laterally; the frontal sinuses anteriorly and the posterior ethmoidal arteries posteriorly. Therefore; the approach requires an extended posterior septectomy; complete anterior and posterior ethmoidectomies and a bilateral frontal sinusotomy (Draf III or endoscopic Lothrop sinusotomy). Its most critical anatomical landmarks are the anterior and posterior ethmoidal arteries. Suitable indications for this approach include olfactory groove meningiomas, esthesioneuroblastomas, certain craniopharyngiomas, and pituitary adenomas that extend into the anterior cranial fossa. Lesions that cross the mid-orbital roof (i.e. meridian of the orbit) laterally are not amenable to a complete resection by this approach. Transplanum/Transtuberculum approach (Figure 2) This module is defined by the removal of the planum sphenoidale and tuberculum sellae. Its lateral limits are the optic canals and paraclinoid ICAs, its anterior limit is the posterior ethmoid arteries and the posterior limit is the most antero-superior aspect of the sella turcica. A resection that extends further anteriorly incurs the risk of injuring the olfactory nerve and epithelium. Therefore, these approaches require a posterior septectomy, wide bilateral sphenoidotomies, posterior ethmoidectomies and removal of the planum sphenoidale with or without a sellotomy. The most critical anatomical landmark in this module is the medial optic-carotid recess (MOCR) [4]. In suprasellar lesions, the anterior cerebral arteries (ACAs) with its perforators, the superior hypophyseal artery, the pituitary stalk and optic chiasm are both critical structures and important landmarks. Suitable indications for this approach are planum sphenoidale or tuberculum sellae meningiomas, craniopharyngiomas, pituitary adenomas, chordomas and chondrosarcomas with suprasellar extension. Relative limitations of this approach include tumors that extend above the ICA or roof of optic canal, across the midline of the orbital meridian, or into the middle cranial fossa. Submit your Manuscript | www.austinpublishinggroup.com Austin Publishing Group Figure 3: Transsellar approach: A: a preoperative axial T1gadolinium enhanced sagittal MRI showing the pituitary tumor extended in the suprasellar, attached the optic nerve. B: Coronal MRI showing the tumor extended to cranial side. C: Sagittal postoperative MRI showing the complete tumor removal. D: a Coronal MRI showing stalk spared completely. E: epicapsular dissection was performed. The pituitary stalk was located behind the tumor. F: The view after the tumor removal completely showing pituitary stalk was intact and pituitary gland was preserved intact. Trans-sellar approach (Figure 3) This module may be considered the most basic EEA. It requires a posterior septectomy and wide bilateral sphenoidotomies, as well as partial posterior ethmoidectomies to obtain a panoramic view of the sellar face and floor. These steps are followed by a wide sellotomy, exposing the superior and inferior intercavernous sinuses and the bilateral cavernous sinuses. This broad exposure facilitates intrasellar dissection and tumor removal. The removal of the sellar floor facilitates maneuverability of instruments in the sella; thus, it is routinely performed. The most important key anatomical structures are the “four blues”, which comprise the superior and inferior intercavernous sinuses rostrocaudally and the cavernous sinuses laterally. Suitable indications for this approach are pituitary adenomas, Rathke’s cleft cysts and craniopharyngiomas. According to the location of tumor, this approach can be combined with transplanum and transclival approaches to access intradural lesions [4]. Its limitations include tumors that extend laterally beyond the ICA and cavernous sinuses. Transclival approaches (Figure 4) This module allows a partial (upper, middle or lower clivus) or complete removal of the clivus. It includes a posterior septectomy and bilateral removal of the rostrum and floor of sphenoid sinus. Approaches to the lower clivus requires a posterior and superior nasopharyngectomy (i.e. removal of mucosa, paraspinal muscles and pharyngobasilar fascia to expose the clival bone); whereas, approaches to the upper clivus may require a pituitary transposition. Besides the segments of the ICA (parapharyngeal, petrous, paraclival, parasellar), other relevant extradural anatomic structures in this module include the cavernous sinus and basilar plexus in the upper-third, Dorello’s canal in the middle-third, and the in the condyles and hypoglossal canals in the inferior third. Intradurally, at the level of the superior clivus, all significant anatomic structures Austin J Otolaryngol 2(7): id1055 (2015) - Page - 02 Prevedello DM Austin Publishing Group choana without the need for sphenoid sinus exposure or clival drilling. Critical anatomical landmarks include the tori tubari (Eustachian tubes), the odontoid ligaments and the occipital condyles. Its inferior limit is the body of C2 and laterally the lateral masses of C1. Most often it is an extradural approach; therefore, the dura is the posterior limit. Figure 4: Transclival approach: A: a preoperative axial T1 gadolinium enhanced MRI showing clivus chordoma extended into sphenoid sinus, ethmoid sinus, cavernous sinus, right orbital cavity. B: Coronal MRI showing the tumor pushed up the optic nerve and contains the cyst. C: postoperative axial MRI and D: coronal (D) MRI showing the tumor removed completely. E: operative image, showing the epidural tumor and clivus dura was intact to protect the tumor extension to prepontine cistern. F: operative image showing the tumor removed totally and tumor penetrate into the periosteum dura partially. The basilar venous plexus between the two layers of the dura was already occluded. are related to the interpeduncular fossa, and are limited laterally by the third cranial nerves and posteriorly by the mesencephalum (mammillary bodies) and the vascular structures (basilar tip, posterior cerebral arteries and superior cerebellar arteries). Lateral limits of the approach include the parasellar ICAs for the upper clivus; Dorello’s canal and the paraclival ICAs for the middle clivus; and the hypoglossal canal and parapharyngeal ICA for the lower clivus. The medial pterygoid wedge (MPW), defined as the most medial projection of the base of the pterygoid plate as it meets the floor of sphenoid sinus, is a critical anatomical landmark that heralds the transition from petrous to the paraclival segments of the ICA [8]. In the middle-third, the approach reaches the prepontine cistern containing the basilar artery and it is limited posteriorly by the pons and laterally by the six cranial nerves, ascending to reach the dura in the direction to Dorello’s canal. The inferior corridor reaches the pre-medullary cistern comprising the vertebral arteries and is limited laterally by the hypoglossal nerves and posteriorly by the medulla. Key extradural landmarks include the medial pterygoid wedge and tori tubari (Eustachian tubes). Suitable indications include clival meningiomas, chordomas, chondrosarcomas and craniovertebral invagination. Limitations of the approach include tumors extending beyond the lateral limits defined above as the parasellar and parapharyngeal ICA. Transodontoid approach This module facilitates the removal of the odontoid process of C2. Therefore, the approach requires a posterior septectomy, bilateral removal of the rostrum and floor of the sphenoid sinus and a posterior and superior nasopharyngectomy, similar to the access to the lower clivus with a caudal extension (nasopharyngectomy). The lower third of the clivus and anterior arch of C1 are removed after dissection of the nasopharyngeal mucosa and the longus capiti muscles [6]. This approach generally can be performed directly through the posterior Submit your Manuscript | www.austinpublishinggroup.com Suitable indications for this approach include degenerative/ inflammatory disease such as compressive pannus from rheumatoid arthritis, basilar invagination, and tumors such as chordomas, and chondrosarcomas. One limitation of the approach includes tumors extending laterally beyond the condyles or vertebral arteries. As this approach can potentially generate instability, the need for craniocervical fixation needs to be considered on every case. Foramen magnum meningiomas positioned posterior to the odontoid process represent a relative contraindication, as the exposure could potentially generate instability and the need for craniocervical fusion. A posterolateral approach seems more appropriate under these circumstances. Coronal Plane Modules Endonasal endoscopic approaches in the coronal plane are further divided by depth into anterior, middle, and posterior [7]. The anterior coronal plane is related to the anterior cranial fossa and the orbit, the middle coronal plane to the middle cranial fossa, and the posterior coronal plane to the posterior cranial fossa. Essential points are summarized in. Anterior Coronal Plane Transorbital approach Transorbital approaches require an uncinectomy, wide antrostomy, and anterior and posterior ethmoidectomies. These steps facilitate the removal of the lamina papyracea and the medial wall of the optic canals. Transorbital approaches can be divided into extraconal and intraconal. Extraconal approaches require the removal of the medial wall of orbit. A latero-inferior displacement of the orbital soft tissues enhances the visualization the orbital roof. This approach may be combined with a transcribiform or transplanum approach to obtain margins that extend laterally to include the medial half of the orbital roof. Additionally, an orbital and/or optic nerve decompression are included in this category. An intraconal approach is indicated for lesions that are inferior and medial to the optic nerve. A corridor between the inferior and medial rectus muscles is created that provides adequate access to the lesion, and preserves extraocular muscle function. Crossing the optic nerve should be avoided; therefore, lesions localized to the superior/lateral orbit are contraindications for this technique. Critical anatomical landmarks for this module include the optic nerve and ophthalmic artery, as well as the anterior and posterior ethmoidal arteries. The lateral limits are the optic nerve and ophthalmic artery. Suitable indications for this approach include inflammatory or autoimmune diseases (i.e. Grave’s exophtalmopathy) and tumors such as orbital meningiomas, cavernous hemangiomas, and osteomas. Austin J Otolaryngol 2(7): id1055 (2015) - Page - 03 Prevedello DM Middle Coronal Plane Modules Austin Publishing Group Modules of the middle coronal plane include seven different approaches to distinct anatomical areas: petrous apex, infrapetrous area, suprapetrous area, cavernous sinus, infratemporal fossa, occipital condyle and jugular foramen. The initial corridor for these modules requires a transpterygoid approach. However, lesions located medial to the petrous apex region may be approached through a simpler trans-sphenoidal corridor. the lateral pterygoid plate (LPP) is followed laterally to the foramen ovale. Foramen ovale and V3 are situated superficial (i.e. anterior) to the petrosal ICA. The medial limit is the vidian nerve, while the superior limit is the petrosal ICA. The most critical anatomical landmarks in this module are the facial, cochlear and vestibular nerves and Eustachian tube laterally, the petrosal ICA superiorly and the hypoglossal nerve inferolaterally. Suitable indications for this approach include cholesterol granulomas, chordomas, and chondrosarcomas. Transpterygoid corridor Suprapetrous approach This is a basic step to most of the modules in the middle coronal plane. Its basic format can be extended to accommodate the extent of the tumor resection. The sinonasal component includes passing through the natural space of the maxillary sinus after removing the middle turbinate and completing an uncinectomy, anterior and posterior ethmoidectomies, and a large mid-meatal nasomaxillary window. Extensive lesions may require a medial maxillectomy or even an endoscopic Denker’s approach to expose the entire posterior wall of the antrum and extend the line of sight laterally. This module is represented by the quadrangular space approach, which provides access to Meckel’s cave. The quadrangular space is a potential space limited medially and inferiorly by the ICA, laterally by maxillary nerve, and superiorly by the abducens nerve running inside the cavernous sinus [9]. This corridor demands removal of the medial and posterior walls of maxillary sinus. The soft tissues in the sphenopalatine fossa are mobilized laterally facilitating the identification of the vidian nerve and V2. The vidian canal (and its neurovascular bundle) and V2 are followed posteriorly to identify the petrous ICA, and to reach the Gasserian ganglion (GG) [8,10]. By drilling the lateral bone over the ICA, the periosteum of the middle fossa is exposed. The periosteum and dura are opened over the quadrangular space to access Meckel’s cave. The abducens nerve runs within the cavernous sinus as it travels toward the supraorbital fissure at the level of V1 [11-13]. Once this corridor is opened, the sphenopalatine and posterior nasal arteries are transected at the level of the sphenopalatine foramen. The posterior wall of the maxillary sinus and the ascending process of the palatine bone are removed; and the soft tissues of the pterygopalatine fossa are mobilized laterally, exposing the vidian canal, vidian nerve and the foramen rotundum and V2 over the anterior and superior aspect of the pterygoid process. Proper identification and preservation of these landmarks are followed by the opening of the lateral recess of the sphenoid sinus and drilling of the base of the pterygoid process; thus, allowing a direct access to the medial aspect of the infratemporal fossa and middle cranial fossa. Approach to the petrous apex This approach is basically a lateral extension of a mid-clivus approach [7], it is particularly useful when the tumor has protruded into the sphenoid sinus and therefore created a “corridor”. Exposure will mandate the isolation of the anterior genu of the ICA to access the petrous bone). Bilateral sphenoidectomies are required (the sphenoid floor is drilled until the clival recess is exposed. Key anatomical landmarks include the medial pterygoid plate (MPP) and the paraclival ICA. Removing the bone surrounding the ICA allows lateralization of the vessel to grant access to the petrous apex. Suitable indications for this approach include cholesterol granulomas, chordomas, and chondrosarcomas. The most critical anatomical landmarks in this module are the vidian nerve, the abducens nerve at Dorello’s canal and the carotid canal. All subsequent approaches in the middle and coronal planes employ a transpterygoid approach using the maxillary sinus as a working corridor. Infrapetrous approach The working corridor for this approach comprises the fossa of Rosenmüller, the lateral sphenoid recess and medial maxilla. Bilateral sphenoidectomies and a posterior maxillectomy are required; the sphenoid floor is drilled until the clival recess is exposed. The medial pterygoid plate is followed laterally to the foramen rotundum and Submit your Manuscript | www.austinpublishinggroup.com This module is used to access lesions located in the anteromedial segment of Meckel’s cave [9]. The most critical anatomical landmark are V2 laterally, the ascending ICA medially, the abducens nerve in the cavernous sinus superiorly, and the petrous ICA inferiorly. Suitable indications for this approach include invasive pituitary adenomas, meningiomas, trigeminal schwannomas, and adenoid cystic carcinomas. Cavernous sinus approach This area, located lateral to the sella, contains the oculomotor, trochlear and abducens nerves. This approach requires a posterior ethmoidectomy and sphenoidectomy. Removal of the overlying bone may decompress the nerves in the cavernous sinus; however, aggressive surgical maneuvering may cause neurological deficits. To enter the cavernous sinus, the dural opening is made just above the quadrangular space. Suitable indications for this approach include patients with tumors in this region presenting with oculomotor, trochlear, optic or abducens nerve palsies. The most critical anatomical landmarks in this module are the oculomotor, trochlear, ophthalmic and abducens nerves and the cavernous ICA with its accompanying sympathetic fibers. Infratemporal approach This module requires a medial maxillectomy-transmaxillary approach (with or without an endoscopic Denker’s maxillotomy) [7]. Angled endoscopes are especially useful in this approach. After completing a medial maxillectomy, the dissection continues laterally identifying and ligating the internal maxillary artery and its branches. The soft tissues in the sphenopalatine fossa are mobilized laterally. The medial pterygoid plate and the foramen rotundum (canal) are drilled Austin J Otolaryngol 2(7): id1055 (2015) - Page - 04 Prevedello DM until the pterygoid process is flush with the middle cranial fossa. The dissection is continued laterally identifying the lateral pterygoid plate, which can be followed posterolaterally to the foramen ovale. Austin Publishing Group Posterior Coronal Plane of key landmarks: the canal of the internal carotid artery, medial pterygoid plate, and vidian canal. The removal of infrapetrous bone, tracing the petroclival synchondrosis, posterolateral to the Eustachian tube, allows identification of the jugular foramen. Positioning of the endoscope at the fossa of Rosenmüller provides a panoramic view that includes the soft palate caudally, the Eustachian tube laterally, the pharyngobasilar fascia and floor of the sphenoid rostrally and the nasopharyngeal mucosa in the depth. The most critical anatomical landmarks are the sheath of the parapharyngeal ICA, its contents (jugular vein and lower cranial nerve IX, X, XI) and the hypoglossal nerve. Suitable indications for this approach include schwannomas, meningiomas, and certain paragangliomas. Condylar approach Discussion The most critical anatomical landmarks for this module are the ICA (pharyngeal and petrous segments), the medial pterygoid plate, the lateral pterygoid plate and Eustachian tube. Suitable indications for this approach include schwannomas, meningiomas and invasive carcinomas. In these cases the surgical-imaging correlation provided by a surgical navigation system is particularly useful, as the osseous landmarks can be destroyed by invasive tumors. As in the previous module, this approach requires a medial maxillectomy-transmaxillary approach (with or without an endoscopic Denker’s maxillotomy). Resection of the medial aspect of the Eustachian tube is also necessary to extend the lateral exposure. This module grants access to lesions posterior to the Eustachian tube and medial to the parapharyngeal ICA. This corridor contains the fossa of Rosenmüller, the occipital condyle and hypoglossal canal. The most critical anatomical landmark is the Eustachian tube, which can help to determine the position of the ascending parapharyngeal segment of ICA. Suitable indications for this approach include schwannomas, meningiomas, paragangliomas, chordomas and chondrosarcomas. Certain tumors, especially chordomas and chondrosarcomas can invade the hypoglossal canal and further extend laterally to jugular foramen. Jugular foramen approach (Figure 5) This module requires wide bilateral sphenoidotomies and a posterior and medial maxillectomy-transmaxillary approach (with or without an endoscopic Denker’s maxillotomy) as well as transecting or removing the pharyngobasilar fascia. This allows the identification Endoscopic endonasal approaches represent an additional tool for the management of lesions of the ventral skull base. Among the advantages of EEAs is that due to its ventral pathway and the fact that vital structures are typically displaced laterally by the tumor, there is less need to dissect cranial nerves or retract the brain. Furthermore, it allows direct devascularization in early stages of the procedure, especially in meningiomas attached to the dura of the ventral skull base. In extradural tumors, such as many chordomas and chondrosarcomas, there is no need to open the dura mater via EEA. Endoscopes provide high magnification and visualization. Thus, structures may be inspected closely and the arachnoid plane could be preserved while reducing vascular injury. In addition, angled scopes offer visualization “around corners”, which results in decreasing residual tumor and risk of neurovascular injury. Surgeons’ experience is a key factor to obtain optimal outcomes. The learning curve is steep and requires that the entire surgical team, including otolaryngologists and neurosurgeons, become proficient in the endoscopic technique and instrumentation. Lack of experience and poor understanding of the anatomy could lead to catastrophic complications. CSF leakage is the most common major complication for both endoscopic and open techniques. Its incidence varies widely from a low range for transsphenoidal approach (2% [14,15] to 3.5%) [16] to significantly higher incidence after conventional approaches to the anterior skull base tumor (13% [17], 20.3% [18] 29%) [19]. For endoscopic expanded approaches, the pedicled mucosal flaps provide vascularized tissue that have led to primary healing significantly improving the rates of postoperative CSF leaks. The proper surgical techniques based on the anatomical understandings can lead to the best surgical results. Conclusion Figure 5: Jugular foramen approach: A: preoperative axial section of T2weighted MRI showing a clival chordoma extending to the jugular foramen. B: a preoperative coronal T1-weighted gadolinium enhanced MRI showing the tumor homogenously enhanced and compress the pons. C: postoperative axial MRI showing the flap well bolstered against the defect by balloon packing. D: coronal T1-weighted gadolinium enhanced MRI showing the complete resection of the tumor. E, F: Endoscopic view during the surgery. The clivus dura was exposed and the tumor penetrated into the subdural space. (E) The tumor extended to the jugular foramen was resected with preservation of Eustachian tube (F). Submit your Manuscript | www.austinpublishinggroup.com EEA to the ventral skull base are divided into five modules in “sagittal plane” from the cribriform to the odontoid and eight modules in “coronal plane” from paramedian to jugular foramen. Each module is limited by tumor pathology, location of the lesion, relationships with surrounding vital structures, surgical skills and experience, and institutional resources. Understanding the limitations can help selecting the appropriate approaches, occasionally combining two or multiple approaches in order to avoid crossing the plan of cranial nerves and important arteries. Austin J Otolaryngol 2(7): id1055 (2015) - Page - 05 Prevedello DM Austin Publishing Group In well-selected patients, an EEA provides maximum effectiveness, superior outcomes with minimal deficits and morbidities. Despite improvements in instrumentation, techniques and anatomical understanding, EEAs are not the solution to every skull base lesion. Endoscopic approaches are not a substitute to conventional approaches, but a complement. Therefore it is inevitable that skull base surgeons should be familiar with all techniques to offer the best surgical strategy for their patients. References 1. Rosegay H. 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Kassam A, Snyderman CH, Mintz A, Gardner P, Carrau RL. Expanded endonasal approach: the rostrocaudal axis. Part I. Crista galli to the sella turcica. Neurosurg Focus. 2005; 19: E3. 15.Fatemi N, Dusick JR, de Paiva Neto MA, Kelly DF. The endonasal microscopic approach for pituitary adenomas and other parasellar tumors: a 10-year experience. Neurosurgery. 2008; 63: 244-256. 5. Kassam A, Snyderman CH, Mintz A, Gardner P, Carrau RL. Expanded endonasal approach: the rostrocaudal axis. Part II. Posterior clinoids to the foramen magnum. Neurosurg Focus. 2005; 19: E4. 16.Sudhakar N, Ray A, Vafidis JA. Complications after trans-sphenoidal surgery: our experience and a review of the literature. Br J Neurosurg. 2004; 18: 507512. 6. Kassam AB, Snyderman C, Gardner P, Carrau R, Spiro R. The expanded endonasal approach: a fully endoscopic transnasal approach and resection of the odontoid process: technical case report. Neurosurgery. 2005; 57: E213. 17.Deschler DG, Gutin PH, Mamelak AN, McDermott MW, Kaplan MJ. Complications of anterior skull base surgery. Skull Base Surg. 1996; 6: 113118. 7. Kassam AB, Gardner P, Snyderman C, Mintz A, Carrau R. Expanded endonasal approach: fully endoscopic, completely transnasal approach to the middle third of the clivus, petrous bone, middle cranial fossa, and infratemporal fossa. Neurosurg Focus. 2005; 19: E6. 18.Sekhar LN, Pranatartiharan R, Chanda A, Wright DC. Chordomas and chondrosarcomas of the skull base: results and complications of surgical management. Neurosurg Focus. 2001; 10: E2. 8. Kassam AB, Vescan AD, Carrau RL, Prevedello DM, Gardner P, Mintz AH, et al. Expanded endonasal approach: vidian canal as a landmark to the petrous internal carotid artery. J Neurosurg. 2008; 108: 177-183. Austin J Otolaryngol - Volume 2 Issue 7 - 2015 ISSN : 2473-0645 | www.austinpublishinggroup.com Prevedello et al. © All rights are reserved Submit your Manuscript | www.austinpublishinggroup.com 19.Feiz-Erfan I, Han PP, Spetzler RF, Horn EM, Klopfenstein JD, Porter RW, et al. The radical transbasal approach for resection of anterior and midline skull base lesions. J Neurosurg. 2005; 103: 485-490. Citation: Muto J, Carrau RL, Prevedello DM, Ditzel Filho LFS, de Lara D, et al. Endoscopic Endonasal Approaches to the Skull Base - A Review. Austin J Otolaryngol. 2015; 2(7): 1055. Austin J Otolaryngol 2(7): id1055 (2015) - Page - 06