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The Laryngoscope C 2012 The American Laryngological, V Rhinological and Otological Society, Inc. Endonasal Endoscopic Exposure of the Internal Carotid Artery: An Anatomical Study Felipe S. G. Fortes, MD, PhD; Carlos D. Pinheiro-Neto, MD, PhD; Ricardo L. Carrau, MD; Rubens V. Brito, MD, PhD; Daniel M. Prevedello, MD; Luiz U. Sennes, MD, PhD Objectives/Hypothesis: The aim of this work was to define the anatomical landmarks, limitations, and difficulties of obtaining internal carotid artery (ICA) exposure via endonasal endoscopic approaches (EEA). Study Design: Cadaveric descriptive study. Methods: The ICA was dissected via EEA in 10 cadaveric specimens (20 sides) prepared with intravascular injections of colored silicone. We carried the ICA dissection from the cavernous to the distal parapharyngeal segments through a transpterygoid corridor. Results: The transpterygoid approach provided adequate exposure of the lacerum and horizontal petrous ICA. Additional exposure of the ICA and the infrapetrous area required resection of the eustachian tube (ET) and the fibrocartilaginous tissue of the foramen lacerum after a medial maxillectomy and resection of the pterygoid plates. The main anatomical landmarks to the corresponding ICA segment include: the vidian nerve that points to the lacerum and horizontal segments, the mandibular nerve (V3) that heralds the petrous segment, the foramen ovale and the ET that signal toward the carotid canal, and the posterior trunk of the mandibular nerve (V3) and the ET that mark the parapharyngeal segment. Conclusions: EEAs provide access to the ICA from its cavernous to the distal parapharyngeal segments. A stepwise approach is critical to its exposure and control. Surgeons must be aware of its frequently tortuous three-dimensional course and the intimate relation of the vessel to the carotid canal and the cartilage of the foramen lacerum. Key Words: Endoscopy, skull base surgery, internal carotid artery, anatomy, infratemporal fossa, eustachian tube, transpterygoid approach. Level of Evidence: 2b. Laryngoscope, 122:445–451, 2012 INTRODUCTION Advances in endoscopic endonasal techniques, customization of endonasal instruments, and improved image-guided systems, coupled with the increased familiarity of surgeons with the skull base anatomy from the endoscopic perspective1,2 and the recent development of various vascularized flaps for skull base reconstruction,3–6 have propelled the use of expanded endonasal approaches (EEAs) for the management of select skull base lesions.7–13 EEAs can be classified in anatomical modules that access specific areas of the skull base as defined by the sagittal7,8 and coronal planes.14 Coronal plane EEAs allow access to the middle cranial and posterior fossae and their respective skull base.14,15 These include approaches to the petrous apex, suprapetrous From the Department of Otolaryngology (F.S.G.F., C.D.P.-N., R.V.B., University of São Paulo, São Paulo, Brazil; and the Department of Otolaryngology–Head and Neck Surgery (R.L.C.), and Department of Neurological Surgery (D.M.P.), The Ohio State University, Columbus, Ohio, U.S.A. Editor’s Note: This Manuscript was accepted for publication August 2, 2011. This work was supported by FAPESP (Fundação de Amparo a Pesquisa do Estado de São Paulo). The authors have no other funding, financial relationships, or conflicts of interest to disclose. Send correspondence to Felipe S. G. Fortes, MD, PhD, Departamento de Otorrinolaringologia, Universidade de São Paulo, Rua Prudente Meireles de Morais 847, 12243-750 SJC, São Paulo, Brazil. E-mail: [email protected] L.U.S.), DOI: 10.1002/lary.22395 Laryngoscope 122: February 2012 area (i.e., above the petrous internal carotid artery [ICA]), infrapetrous area (i.e., below the petrous ICA), and infratemporal fossa. In addition, the posterior coronal approach includes the area extending from the foramen magnum, across the occipital condyle and hypoglossal canal, to the jugular foramen.14 Control of the ICA is the keystone of all the coronal anatomical modules. A fundamental difference in exposing the ICA during an EEA, as opposed to a conventional open approach, is the dimensions of the surgical corridor. An EEA, although providing superior visualization, involves working through a narrow surgical corridor that imposes limitations on the movements of the dissecting instruments. In properly selected cases the risk of a major vascular or cranial nerve injury may be less than that associated with open approaches. However, the management of catastrophic bleeding through the EEA requires a two-team approach, and the instrumentation may be more complex. A comprehensive transpterygoid approach involves the identification and exposure of the cavernous, paraclival, horizontal segments of the ICA (lacerum and petrous).16 However, when performing a infrapetrous approach or a posterior coronal approach, a more proximal control of the ICA at the carotid canal and its distal parapharyngeal segment may be necessary.14,17,18 Surgical exposure of these segments—the parapharyngeal ICA, the carotid canal, and the petrous Fortes et al.: Endoscopic Exposure of the ICA 445 Fig. 1. Endoscopic exposure of the left pterygopalatine fossa (PPF) after medial maxillectomy. The fat content of the PPF have been removed. (A) The third portion of the maxillary artery with the terminal branches can be identified anteriorly to the neural content of the PPF. (B) Neural compartment of the PPF after lateral displacement of the vascular structures. At the level of the foramen rotundum, V2 continues as the infraorbital nerve. The pterygopalatine ganglion lies anteriorly to the vidian canal. Cav. ¼ cavernous; Post. ¼ posterior; A. ¼ artery; Seg. ¼ segment; Sphenopal. ¼ sphenopalatine; Max. ¼ maxillary; Desc. ¼ descending; Pteryg. ¼ pterygoid; Proc. ¼ process; Palat. ¼ ???; N. ¼ nerve; Gr. ¼ greater; Eust. ¼ eustachian; For. ¼ foramen; Infraorb. ¼ infraorbital; Pal. ¼ palatine; Les. ¼ lesser. portion of the ICA—represents a significant surgical challenge imposed by their deep and protected location in the skull base.19–21 In previous studies, we described surgical models and provided detailed descriptions of the anatomy related to endoscopic transpterygoid and infratemporal fossa approaches.16,17 The objectives of this study were to better define the anatomical landmarks, the limitations, and the difficulties of obtaining exposure of the ICA via EEAs using a previously developed anatomical model. MATERIALS AND METHODS This study, approved by our local institutional research committee, was completed at the Otolaryngology Surgical Skills Lab of the University of São Paulo Medical School. Ten fresh cadaveric specimens (20 sides) were prepared with intravascular injection of colored silicone using a previously described technique.22 The surgical dissection was performed using paranasal sinus and skull base/neurosurgical endoscopic instruments (Karl Storz, Tuttlingen, Germany), and a highspeed drill with angled handpiece and diamond cutting burrs (Karl Storz). All dissections were performed via a pure endonasal endoscopic approach with a two-surgeon/four-hand technique and using a 0 , 30 , and 45 rod-lens endoscope coupled to a high-definition camera and monitor (Karl Storz Endoscopy–America, El Segundo, CA). Photographs were taken during the endonasal endoscopic dissections with a digital single-lens reflex Nikon D70 with a resolution of 6.5 MP (Nikon, Tokyo, Japan), coupled to the rod-lens endoscopes. Dissection Technique Unilateral anterior and posterior ethmoidectomies, wide maxillary antrostomy, and sphenoidotomy were the initial steps of the dissection. After isolating the sphenopalatine and posterior septal arteries, we completed a medial maxillectomy (inferior turbinectomy and removal of the lateral nasal wall down to the level of the nasal floor). Next, we removed the posterior maxillary sinus wall and the orbital process of the palatine bone. After removing the periosteum of the posterior Laryngoscope 122: February 2012 446 maxillary sinus wall and fat from the pterygopalatine fossa, we identified the third and most distal segment of the maxillary artery and its major terminal branches: descending palatine artery, sphenopalatine artery, posterior septal artery, vidian artery, pharyngeal artery, and superior alveolar artery. This was best accomplished via retrograde dissection of the sphenopalatine artery (Fig. 1A). After displacing the vascular compartment of the pterygopalatine fossa laterally, we exposed the neural structures of the pterygopalatine fossa including the pterygopalatine ganglion, vidian nerve, greater palatine nerve, lesser palatine nerve, infraorbital nerve, and maxillary nerve (V2) at the foramen rotundum and its anastomotic branch to the pterygopalatine ganglion (Fig. 1B). A posterior septectomy and bilateral sphenoidectomies, removing the intrasinus septa and part of the floor of the sphenoid sinuses, facilitated a fourhand dissection. We then proceeded with the transpterygoid approach, drilling the base of the pterygoid process around the vidian canal in an anterior to posterior direction to expose the anterior genu and lacerum segment of the ICA (Fig. 2A). At this point we could access the medial aspect of the infratemporal fossa and identify the foramen rotundum, the infraorbital artery and infraorbital nerve entering the infraorbital canal, the inferior orbital fissure, the medial insertion of the upper and inferior heads of the lateral pterygoid muscle inserting on the lateral pterygoid plate, the deep aspect of the temporalis muscle (sphenomandibular muscle), and the temporal branches of the maxillary artery (Fig. 3). Removal of the bone around the foramen ovale facilitated the visualization of the horizontal petrous segment of the ICA just posterior to the foramen. On completion of the transpterygoid approach we had exposed V2, V3, the Gasserian ganglion, the dura mater of the middle cranial fossa, the cavernous sinus, and the ICA extending from the paraclival segment to the horizontal aspect of the petrous segment (Fig. 2B). Next, we removed the inferior remnants of the pterygoid plates to expose the eustachian tube. Muscles related to the eustachian tube, namely the tensor veli palatini and the levator veli palatini muscles, could be visualized at this point (Fig. 4A). Transection of the tensor veli palatini improves the visualization of the levator veli palatini muscle, the cartilaginous portion of the eustachian tube, and the fibrocartilaginous tissue of the foramen lacerum (Fig. 4B). Next, we removed the cartilaginous eustachian tube, exposing its proximal bony canal and the carotid canal, which lies just posterior. Drilling of the Fortes et al.: Endoscopic Exposure of the ICA Fig. 2. Endoscopic exposure after the transpterygoid approach. (A) The vidian nerve leads to the anterolateral aspect of the lacerum segment and the anterior genu of the internal carotid artery (ICA). V2 lies in a lateral and superior position to the vidian nerve and runs over the dura mater of the middle cranial fossa. A sympathetic bundle nerve on the cavernous sinus and a muscular branch of V3 are also visualized. (B) The bone of the floor of the middle cranial fossa, between V2 and V3, together with the anterior wall of the ovale foramen, has been removed. The cavernous, anterior genu, lacerum, and part of the horizontal petrous segment of the ICA are visualized. One can see the Gasserian ganglion, the branches of the V cranial nerve, and the VI cranial nerve in the cavernous sinus and their relation to the suprapetrous area. Cav. ¼ cavernous; Paracl. ¼ paraclival; Seg. ¼ segment; Sympat. ¼ sympathetic. Bund. ¼ bundle; Ant. ¼ anterior; MCF ¼ middle cranial fossa; For. ¼ foramen; N. ¼ nerve; M. ¼ muscular; Max. ¼ maxillary; A. ¼ artery; Pteryg. ¼ pterygoid; Proc. ¼ process; Lat. ¼ lateral., Opht. ¼ ophthalmic; G. ¼ ganglion; Fibr. ¼ fibro; Lac. ¼ lacerum. bony eustachian tube and the anteromedial carotid canal helped to expose the most proximal aspect of the petrous segment and the distal parapharyngeal ICA. Finally, we opened the carotid sheath exposing the parapharyngeal carotid artery down to the level of the nasal floor (Figs. 5 and 6). RESULTS We were able to expose the ICA, from the parapharyngeal to the cavernous sinus space, in all specimens Fig. 3. Endoscopic view of the medial infratemporal fossa. The infraorbital nerve arises from V2 and passes through the inferior orbital fissure before reaching the orbit. The infraorbital arterial branch of the maxillary artery can be seen entering the fissure. The temporal muscle and temporal arterial branches of the muscular division of the maxillary artery running and the lateral pterygoid muscle medial insertion are demonstrated. Infraorb. ¼ infraorbital; A. ¼ artery; MCF ¼ middle cranial fossa; N. ¼ nerve; ICA ¼ internal carotid artery; Temp. ¼ temporal; Pteryg. ¼ pterygoid; P. ¼ process; M. ¼ muscle; Lat. ¼ lateral; Max. ¼ maxillary; M = middle. Laryngoscope 122: February 2012 (Fig. 5). Access to the cavernous segment of the ICA was possible after widely opening the sphenoid sinus and removing the bone from its lateral and superior walls. The difficulty of this step was proportional to the degree of sphenoid sinus pneumatization. Access to the more proximal paraclival segment was facilitated by a prior exposure of the anterior genu. This step was followed by a superior (distal) dissection, thinning, and removing the bony canal around the paraclival ICA. A transpterygoid approach allowed us to expose the lacerum segment (including the anterior genu) and part of the horizontal petrous segment. The pterygoid canal and nerve (i.e., vidian canal and nerve) were constant landmarks to help identify the ICA anterior genu and lacerum segment, as the nerve runs on the anterolateral aspect of the ICA (Fig. 2). We found that drilling inferior and medial to the vidian nerve provided the safest access to the anterior genu of the ICA. After completing the transpterygoid approach, we also exposed the foramen rotundum and V2 (following the infraorbital nerve posteriorly) at a level that was superior and lateral to the vidian nerve (Fig. 3). Drilling and removing the bone inferior to V2 exposed the foramen ovale and V3. In turn, following V2 and V3 proximally exposed the Gasserian ganglion (Meckel’s cave) and the floor of the middle cranial fossa. The foramen ovale and the short segment of V3 proximal to the foramen are always anterior and superior to the petrous ICA. Therefore, they are reliable landmarks that help to control the petrous ICA (horizontal segment) (Fig. 2B). From the endoscopic standpoint, V3 partially blocks the view of the proximal petrous segment of the ICA (Fig. 5). A transpterygoid route provided a corridor that allowed access to the suprapetrous area (mid-coronal plane), which is bounded by the paraclival and lacerum segments of the ICA (Fig. 6). The medial infratemporal Fortes et al.: Endoscopic Exposure of the ICA 447 Fig. 4. The entire pterygoid process has been removed to expose the eustachian tube. (A) The tensor veli palatini runs in a vertical orientation laterally to the levator veli palatini muscles. The relation between lateral pterygoid muscle, V3, and tensor veli palatini is demonstrated. (B) The tensor veli palatini has been removed to expose the levator veli palatini muscles and the eustachian tube. The posterior opening of the vidian canal in the lacerum foramen can be seen as well as the relation of the vidian nerve to the horizontal internal carotid artery. Mid. ¼ middle; Cr. ¼ cranial; F. ¼ fossa; Paracl. ¼ paraclival; Seg. ¼ segment; N.¼ nerve; Ant. ¼ anterior; P. ¼ posterior; Max. ¼ maxillary; A. ¼ artery; Lat., lateral; M., muscle; Pteryg. ¼ pterygoid; Lev. ¼ levator; V. ¼ veli; Pal.¼ palatine; Tens. ¼ tensor; G. ¼ ganglion; Horiz. ¼ horizontal; For. ¼ foramen; Lac. ¼ lacerum; Fibrocart. ¼ fibrocartilaginous. fossa was adequately exposed, and the second portion of the maxillary artery was identified between the heads of the lateral pterygoid muscle. Temporal branches of the maxillary artery, running in the anterior surface of the temporalis muscle, were also well visualized (Fig. 3). At this point, the eustachian tube and the fibrocartilaginous tissue of the foramen lacerum represented the boundaries of the infrapetrous approach. To proceed with the proximal dissection of the ICA we found that it is important to expose the entire height of the pterygoid plate. In turn, this required partial removal of the lat- Fig. 5. Endoscopic access to the internal carotid artery (ICA) after resection of the eustachian tube and the foramen lacerum fibrous tissue. The relation of the V cranial nerve and the ICA is demonstrated: V1 and cavernous segment, Gasserian ganglion and suprapetrous area, foramen ovale and the posterior genu, V3 and the carotid canal, the posterior trunk of V3 and the cervical segment. Note the tortuous course of the horizontal ICA. Seg. ¼ segment; Mid. ¼ middle; Cr.¼ cranial; F. ¼ fossa; For. ¼ foramen; Ant. ¼ anterior; Post. ¼ posterior; N. ¼ nerve; P. ¼ posterior; Rosenm. ¼ Rosenmüller; Fos. ¼ fosseta. Laryngoscope 122: February 2012 448 eral nasal wall. After dissecting off the insertion of the lateral pterygoid muscle and elevating the mucosa of the lateral nasal wall anterior to the eustachian tube, we were able to remove the pterygoid plates and identify the muscles related to eustachian tube in all cases (Fig. 4A). The fibers of the tensor veli palatini are lateral to the eustachian tube and can be identified arising from its origin at the skull base (superiorly). The tensor veli palatini loops around the pterygoid hamulus to insert in the soft palate. Its insertion, however, is at a level that is inferior to the nasal floor; therefore, it was not visualized. Fibers from the levator veli palatini muscles are medial and follow the eustachian tube orientation to insert at the soft palate. Thus, they could be visualized after transecting the tensor veli palatini (Fig. 4B). The Fig. 6. The middle coronal plane modules areas and their relation to the internal carotid artery (ICA) are demonstrated. The neural landmarks (vidian nerve, Gasserian ganglion, ovale foramen, V3) and their relationship to the different segments of the ICA can be seen. Cav. ¼ cavernous; Seg. ¼ segment. MF. ¼ middle fossa. Fortes et al.: Endoscopic Exposure of the ICA TABLE I. Anatomically Based Classification of the Internal Carotid Artery*. Segment Proximal Limit Distal Limit Cervical (C1) Carotid artery bifurcation Carotid canal Petrous (C2) Carotid canal Posterior edge of the foramen lacerum Lacerum (C3) Cavernous (C4) Posterior edge of the Foramen lacerum Superior border of the petrolingual ligament Superior border of the petrolingual ligament Proximal dural ring Clinoid (C5) Proximal dural ring Distal dural ring Ophthalmic (C6) Communicating (C7) Distal dural ring Posterior communicating artery Posterior communicating artery ICA bifurcation *Proposed by Bhoutillier et al.23 ICA ¼ internal carotid artery. eustachian tube is anterior and medial to the ICA (carotid canal and parapharyngeal segments). Thus, we had to resect the eustachian tube to fully expose the ICA in these areas (Fig. 5). Anteriorly, we followed the cartilaginous eustachian tube to the level of its isthmus and bony canal. We were able to disarticulate the cartilaginous from the bony component of the eustachian tube, which was then carefully removed to expose the ICA foramen and petrous segment. We found that grasping the eustachian tube with angled forceps stabilized the cartilaginous canal to subsequently disarticulate it from its bony component. A posterior cut followed a medial to lateral diagonal orientation and was limited posteriorly by the mucosa of the fossa of Rosenmüller, which provided a safe plane for dissection. Exposure of the petrous ICA was relatively difficult to accomplish, as the vessel is firmly adherent to the bone canal and the lateral petrous bone. In the carotid canal, V3 lies anterior to the petrous ICA and lateral to its anterior genu and paraclival segments (Figs. 4B and 5). To have a better visualization of the posterior genu of the ICA during an EEA, V3 should be retracted laterally. Removing the eustachian tube and the fibrocartilaginous tissue of the foramen lacerum improved the working corridor of the infrapetrous EEA (Fig. 6). Complete exposure of the parapharyngeal ICA down to the level of the nasal fossa floor was accomplished in all specimens after opening the carotid sheath. The posterior trunk of V3 also serves as a landmark to this segment of the ICA, located laterally and anteriorly to the ICA as it runs in a course, which is relatively parallel to the parapharyngeal ICA (Fig. 5). DISCUSSION Multiple clinical situations may require exposure and control of the ICA, including the management of advanced sinonasal or nasopharyngeal malignancies, paragangliomas, and other skull base lesions originating in the middle or posterior cranial fossa, such as meningiomas, schwannomas, chordomas, and chondrosarcomas. In addition, primary lesions from the pterygopalatine fossa and infratemporal fossa can extend around the ICA. Traditionally, surgical approaches to this region Laryngoscope 122: February 2012 include a lateral corridor via an infratemporal approach (Fisch B and C), subtemporal-preauricular with orbitozygomatic osteotomies or Fisch D, and/or an anterior approach, such as the degloving technique or the Lefort I osteotomy. These approaches, although providing adequate exposure, may require retraction or resection of the glenoid fossa, mandibular condyle, facial nerve manipulation, and/or a craniotomy.19–21 Regardless of the approach, exposure of the ICA is a surgical challenge. This is more evident when dissecting the petrous, lacerum, and distal parapharyngeal segments. Thus, a detailed knowledge of the ICA is mandatory.19–21 The anatomy of the ICA from the perspective of the open skull base approaches is well established. However, despite recent advances in EEAs, the understanding of the endoscopic anatomy of the ICA remains insufficient. Various anatomical classifications of the ICA exist in the literature. Bouthillier et al.23 proposed a classification that seems most useful from our standpoint, as it is based on structures that are exposed during an EEA (Table I). In this article, we refer to the vertical segment of the cavernous segment as the paraclival segment and the distal cervical segment as parapharyngeal. During an endoscopic transpterygoid approach, which is a common step in the exposure of the suprapetrous and infrapetrous areas, one should recognize critical anatomical landmarks to the different segments of the ICA. The vidian canal and nerve are reliable landmarks to determine the height (vertical axis position) of the anterior genu and lacerum segment of the ICA as it emerges from the petrous bone (Fig. 2). In fact, the vidian canal connects the pterygopalatine fossa to the foramen lacerum. It is important to note that the canal has a slight posterolateral orientation, with the posterior opening located inferolateral to the anterior end of the carotid petrous canal and anterior genu of the ICA. Its anterior opening is at the upper medial surface of the pterygoid process of the sphenoid bone and can only be identified after exposing the medial pterygopalatine fossa. The union of the greater superficial and deep petrosal nerves forms the vidian nerve. It travels through the vidian canal to end in the pterygopalatine ganglion, which is positioned in front of the anterior opening of the canal (Fig. 1B).24–26 When present, a Fortes et al.: Endoscopic Exposure of the ICA 449 vidian artery runs in the vidian canal along with the vidian nerve. In the pterygopalatine fossa, the artery will be anterior to the nerve and ganglion. Therefore, it needs to be mobilized laterally to better expose the neural structures (Fig. 1A). Thus, the vidian nerve should be used as a landmark to determine the vertical position of the petrous ICA and lacerum foramen and not to injure the most medial aspect of the ICA as it turns into the paraclival ICA. After exposing the anterior genu, we can safely follow the ICA distally to the paraclival segment by removing its bony canal at the lateral wall of the sphenoid sinus. This exposure allows access to the petrous apex, located between the clival recess (mid-clivus) and paraclival ICA (Figs. 2 and 6). Constant landmarks to the ICA during the suprapetrous transpterygoid approach include the Gasserian ganglion and V3, both located lateral to the paraclival segment and superior to the lacerum segment of the ICA (Figs. 2B and 4B). An infrapetrous approach implies a working corridor inferior to the petrous and lacerum segments of the ICA (Fig. 6).15–17 The foramen lacerum is located at the confluence of the petrous portion of the temporal bone, basi-occipital, and basi-sphenoid bones, and in vivo is filled with fibrocartilage. The ICA courses across the endocranial surface of the foramen lacerum, and climbs upward at its rostral end to enter the posterior cavernous sinus (Fig. 4B).27 Inferior retraction of this fibrocartilage and the cartilage of the eustachian tube provides only limited access to the inferior aspect of horizontal petrous carotid. Therefore, to approach the proximal petrous carotid, carotid canal, and distal parapharyngeal segment it is necessary to remove the medial eustachian tube and fibrocartilaginous tissue of the foramen lacerum. The bony canal of the eustachian tube begins at the superior aspect of the anterior wall of the tympanic cavity and narrows progressively until it ends at the isthmus. The isthmus is located immediately anterior and superior to the bend of the petrous segment. The cartilaginous eustachian tube, which forms its inferior and medial aspect, is shaped as a concave gutter.3 The posterior wall of the cartilaginous eustachian tube interdigitates with the bony canal at the level of the isthmus. The eustachian tube guards the ICA, as it is medial and anterior to the parapharyngeal segment and lateral and anterior to its petrous segment. At this level, V3 is located anterolateral to the eustachian tube (Fig. 4). When resecting the eustachian tube, it is safe to develop a posterior plane of dissection between the eustachian tube and the mucosa of the nasopharynx, as this mucosa extends posteriorly and laterally into the Rosenmüller fossa. The petrous segment can be divided in a vertical, a bend (posterior loop), and a horizontal portion. The transition of the petrous segment of the ICA to the lacerum segment is inferomedial to the Gasserian ganglion within Meckel’s cave (Fig. 5). In this segment, the ICA runs within the periosteum of the carotid canal and is surrounded by areolar tissue, a venous plexus extension from the cavernous sinus and postganglionic sympaLaryngoscope 122: February 2012 450 thetic nerves. Endoscopic endonasal exposure of the horizontal petrous ICA is compounded by its orientation, as it runs in an anterior, inferior, and medial orientation (Fig. 2B).11 The cochlea lies posterior to the bend of the petrous carotid. The eustachian tube lies lateral and anterior to this horizontal portion. The petrous bone bounds the horizontal ICA (petrous segment) anteriorly, medially, and posteriorly. Therefore, after removing the cartilaginous eustachian tube, we have to drill petrous bone to expose the ICA.23,24,27 After drilling the petrous bone around the foramen ovale, the posterior bend of the petrous ICA can be visualized just posterior to V3 (Figs. 5 and 6). At the level of the carotid canal, the carotid sheath divides into two layers; the inner layer continues as the periosteum of the carotid canal and the outer layer continues as periosteum of the extracranial surface of the skull base.23 Removal of the anterior wall of the carotid canal requires utmost care, because the artery lies in intimate relation to the bone. Immediately posterior to the carotid canal lies the jugular fossa.28,29 The cervical segment of the ICA begins at the level of the carotid bifurcation usually at the level of C4.21 This segment runs inside the carotid sheath with the internal jugular vein laterally and the vagus nerve posterolaterally. Inside the carotid sheath, as in the carotid canal, the artery is surrounded by areolar tissue containing fat, a venous plexus, and postganglionic sympathetic nerves.23 However, in this segment, opening of the sheath is relatively easier and safer than in the carotid canal. We could approach this segment through an EEA only to the level of the nasal floor. In our dissections, we observed that this cervical segment usually makes a slight posterior and lateral curvature as it enters the carotid canal vertically before bending anteriorly toward the lacerum segment. We strongly advocate a stepwise approach identifying the lacerum and petrous segments of the ICA. V3 (posterior trunk) is a useful endoscopic anatomic landmark to the parapharyngeal segment, as it is located anterior and lateral and with a relative parallel orientation (Fig. 5). In this anatomical study, an EEA provided adequate exposure of ICA, from the cavernous to the parapharyngeal segments. It should be noted, however, that this surgical exposure is complex and requires ample experience and training before it is applied clinically, where injury to the vessel may produce catastrophic complications. In addition, we strongly advocate the use of an image-guided system (preferably using computed tomography angiography) and intraoperative acoustic Doppler sonography to further aid the identification of the ICA. Institutional intensive care support and the availability of an interventional angiographer are also important safeguards. CONCLUSION Endoscopic endonasal approaches provide access that extends from the cavernous to the parapharyngeal segments of the ICA. A stepwise approach is critical to the endonasal endoscopic exposure and control of the Fortes et al.: Endoscopic Exposure of the ICA ICA. The vidian nerve is an important landmark to the lacerum segment of the ICA in the transpterygoid approach. Our study suggests that resection of the fibrocartilaginous tissue of the foramen lacerum and the eustachian tube is critical to access the petrous and parapharyngeal segments of the ICA during the infrapetrous and posterior coronal approaches. V3 and its foramen (foramen ovale) are other useful landmarks to identify and control these segments of the ICA. When approaching the petrous and parapharyngeal segments the surgeon must be aware of the tortuous three-dimensional course of the ICA and the intimate relation of the ICA to the carotid canal. BIBLIOGRAPHY 1. Cappabianca P, Alfieri A, Thermes S, et al. Instruments for endoscopic endonasal transsphenoidal surgery. Neurosurgery 1999;45:392–396. 2. Prevedello DM, Doglietto F, Jane JA Jr, et al. History of endoscopic skull base surgery: its evolution and current reality. J Neurosurg 2007;107: 206–213. 3. Hadad G, Bassagasteguy L, Carrau RL, et al. A novel reconstructive technique after endoscopic expanded endonasal approaches: vascular pedicle nasoseptal flap. Laryngoscope 2006;116:1882–1886. 4. Fortes FS, Carrau RL, Snyderman CH, et al. Transpterygoid transposition of a temporoparietal fascia flap: a new method for skull base reconstruction after endoscopic expanded endonasal approaches. Laryngoscope 2007;117:970–976. 5. Fortes FS, Carrau RL, Snyderman CH, et al. The posterior pedicle inferior turbinate flap: a new vascularized flap for skull base reconstruction. Laryngoscope 2007;117:1329–1332. 6. Zanation AM, Carrau RL, Snyderman CH, et al. Nasoseptal flap reconstruction of high flow intraoperative cerebral spinal fluid leaks during endoscopic skull base surgery. Am J Rhinol Allergy 2009;23:518–521. 7. Kassam A, Snyderman CH, Mintz A, et al. Expanded endonasal approach: the rostrocaudal axis. Part I. Crista galli to the sella turcica. Neurosurg Focus 2005;19:E3. 8. Kassam A, Snyderman CH, Mintz A, et al. Expanded endonasal approach: the rostrocaudal axis. Part II. Posterior clinoids to the foramen magnum. Neurosurg Focus 2005;19:E4. 9. Kassam AB, Prevedello DM, Carrau RL, et al. The front door to Meckel’s cave: an antero medialcorridor via expanded endoscopic endonasal approach- technical considerations and clinicalseries. Neurosurgery 2009;64:71–83. 10. Prevedello DM, Thomas A, Gardner P, et al. Endoscopic endonasal resection of a synchronouspituitary adenoma and a tuberculum sellae meningioma: technical case report. Neurosurgery 2007;60:E401; discussion: E401. Laryngoscope 122: February 2012 11. Stippler M, Gardner PA, Snyderman CH, et al. Endoscopic endonasal approach for clival chordomas. Neurosurgery 2009;64:268–78. 12. Gardner PA, Kassam AB, Thomas A, et al. Endoscopic endonasal resection of anterior cranial base meningiomas. Neurosurgery 2008;63:36–52. 13. Jane JA Jr, Han J, Prevedello DM, et al. Perspectives on endoscopic transsphenoidal surgery. Neurosurg Focus 2005;19:E2. 14. Kassam AB, Gardner P, Snyderman CH, Mintz A, Carrau RL. 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. 15. Prevedello DM, Ditzel Filho LF, Solari D, Carrau RL, Kassam AB. Expanded endonasal approaches to the middle cranial fossa and posterior fossa tumors. Neurosurg Clin N Am 2010;21:621–635. 16. Fortes FS, Sennes LU, Carrau RL, et al. Endoscopic anatomy of the pterygopalatine fossa and the transpterygoid approach: development of a surgical instruction model. Laryngoscope 2008;118:44–49. 17. Falcon RT, Rivera-Serrano CM, Miranda JF, et al. Endoscopic endonasal dissection of the infratemporal fossa: anatomic relationships and importance of eustachian tube in the endoscopic skull base surgery. Laryngoscope 2011;121:31–41. 18. Theodosopoulos PV, Guthikonda B, Brescia A, Keller JT, Zimmer LA. Endoscopic approach to the infratemporal fossa: anatomic study. Neurosurgery 2010;66:196–203; discussion 202–203. 19. Liu JK, Fukushima T, Sameshima T, Al-Mefty O, Couldwell WT. Increasing exposure of the petrous internal carotid artery for revascularization using the transzygomatic extended middle fossa approach: a cadaveric morphometric study. Neurosurgery 2006;59:309–319. 20. Froelich SC, Aziz KMA, Levine NB, Pensak ML, Theodosopoulos PV, Keller JT. Exposure of the distal cervical segment of the internal carotid artery using the trans-spinosum corridor: cadaveric study of surgical anatomy. Neurosurgery 2008;62:354–362. 21. Fortes FSG, Silva ES, Sennes LU. Mandibular subluxation for distal internal carotid artery access. Laryngoscope 2007;117:890–893. 22. Brito RV, Bento RF, Yasuda A, et al. Anatomy of the lateral base of the skull: development of a method of study. Rev Bras Otorrinolaringol 2005;9:11–17. 23. Bouthillier A, van Loveren HR, Keller JT. Segments of the internal carotid artery: a new classification. Neurosurgery 1996;38:425–433. 24. Kassam AB, Vescan AD, Carrau RL, et al. Expanded endonasal approach: vidian canal as a landmark to the petrous internal carotid artery. J Neurosurg 2008;108:177–183. 25. Osawa S, Rhoton AL, Seker A, Shimizu S, Fugii K, Kassam AB. Microsurgical and endoscopic anatomy of the vidian canal. Neurosurgery 2009; 64:385–412. 26. Vescan AD, Snyderman CH, Carrau RL, et al. Vidian canal: analysis and relationship to the internal carotid artery. Laryngoscope 2007;117: 1338–1342. 27. Tauber M, van Loveren HR, Jallo G, Romano A, Keller JT. The enigmatic foramen lacerum. Neurosurgery 1999;44:386–93. 28. Zimmer LA, Hirsch BE, Kassam AB, Horowitz M, Snyderman CH. Resection of a recurrent paraganglioma via an endoscopic transnasal approach to the jugular fossa. Otol Neurotol 2006;27:398–402. 29. Dallan I, Bignami M, Battaglia P, Castelnouovo P, Tschabitscher M. Fully endoscopic transnasal approach to the jugular foramen: anatomic study and clinical considerations. Neurosurgery 2010;67:1–8. Fortes et al.: Endoscopic Exposure of the ICA 451