Endoscopic surgery has revolutionized thetreatment of skull base disorders and is routinelyused in some centers for the treatment ofneoplastic and non-neoplastic cranial basepathology. The group of minimally invasiveendoscopic techniques used to approach thecranial base are also known as expandedendoscopic approaches (EEA), which areclassified in a modular fashion under two maincategories: sagittal (or cranio-caudal) and coronal(or medio-lateral). Figure 1

The goals of this project are to develop ananatomical model to facilitate the study of theanatomy of the infratemporal fossa (ITF),pterygopalatine fossa (PPF), and post-styloidspace from the endoscopic endonasalperspective, and to determine the mostimportant anatomical landmarks in the endonasalendoscopic approach to these areas.

Endoscopic EndoEndoscopic Endonasalnasal Dissection of the Dissection of the Pterygopalatine fossa, Infratemporal fossa Pterygopalatine fossa, Infratemporal fossa,, and Post- and Post-styloid compartment.styloid compartment. Anatomical Relationships and Importance of Eustachian Tube in theAnatomical Relationships and Importance of Eustachian Tube in the

Endoscopic Skull Base SurgeryEndoscopic Skull Base SurgeryCarlos M Rivera-Serrano, MD1; Ramon Terre-Falcon1; Juan Fernandez-Miranda MD2; Daniel Prevedello MD2; Carl H Snyderman MD1,2; Paul

Gardner MD2; Amin Kassam MD1,2; Ricardo L Carrau MD1,2

University of Pittsburgh, Department of Otolarngology1 and Department of Neurosurgery2

Figure 3. A, view of the right pterygopalatine fossa. The subjacent periosteum and fatpad were dissected, discovering the internal maxillary artery (IMa) and its branches.Identification of each branch was ocassionally difficult due to the high anatomicalvariability of the distal third of the IMa. However, it was possible to identify all IMadivisions after dissecting one or more of its major branches, such as the infraorbital,descending palatine or sphenopalatine arteries. Despite the high anatomical variability,other minor branches (posterior superior alveolar and pharyngeal arteries) were alsoidentified. B, view of the distal third of the internal maxillary artery after resection ofsurrounding bone and fat. (IMa: internal maxillary artery, IOa: infraorbital artery, DPa:descending palatine artery, Spa: sphenopalatine artery, PSAa: posterosuperior alveolarartery, Pha: pharyngeal artery, Septal Post. art.: Posterior Septal artery, DTa: deep temporalartery, IOn: infraorbital nerve. Pictures were taken with a 0 degree rod lens endoscope).

Figure 8. A, endoscopic view of pre-styloid space after lateral displacement of thelateral pterygoid muscle and resection of the tensor veli palatini muscle. Thejunction of the cartilaginous and bony eustachian tube was the most importantlandmark in the location of the ICA (covered by the stylopharyngeal aponeurosis(SPHA)). B, View of the internal carotid artery after lateral displacement of theSPHA. (LPTm: lateral pterygoid muscle, MPTm: medial pterygoid muscle, TVPm: tensorveli palatini muscle, ET: eustachian tube, TT: torus tubarius, LVPm: levator veli palatinimuscle, TT: torus tubarius, SPHA: stylopharyngeal aponeurosis, PPv: pterygoid plexusvein, APhv: ascending pharyngeal vein, APha: ascending pharyngeal artery, ICA: internalcarotid artery).

Along with more traditional surgical approaches to the ITF, PPF and post-styloidspace, the endoscopic technique is a feasible surgical option. Precise anatomicalknowledge from a endonasal endoscopic perspective should further increase safetyand efficacy.

The most important landmarks in the transnasal endoscopic approach to the ITF andpost-styloid space are the pterygoid plates, V3, the Eustachian tubre and the styloidprocess.

The most important landmark for the location of post-styloid structures is thecartilaginous portion of the Eustachian tube. The Eustachian tube is always anteriorand medial to the parapharyngeal internal carotid artery.

The principal obstacles to locate the parapharyngeal internal carotid artery and theglosopharyngeal nerve are the stylopharyngeal fascia and the tensor veli palatinimuscle.  Dissection in this area is difficult due to their fibrousmuscular nature andattachments to the surrounding structures.

Via an endoscopic endonasal approach, the cranial nerve X nerve is located behindthe parapharyngeal carotid.  Cranial nerves XI and XII are not easily manipulated dueto the posterior location to cranial nerve X and to limitation of access by thenasal/maxillary floor. The IX cranial nerve is located in between internal carotid arteryand internal jugular vein, enclosed by the stylopharyngeal aponeurosis, and ispotentially the most susceptible nerve for injury during an endonasal endoscopicapproach to the post-styloid space.

Figure 1.  Bilateral transmaxillary approach to the cranial base.  On the right side,modular trans-pterygoid approaches in numbered boxes:   Area 1 or medialpetrous apex.  Area 2 or petroclival union.  Area 3 or cuadrangular space.  Area4 or superior cavernous sinus.  Area 5 or medial cranial fossa/infratemporal fossa. On the left side: main anatomic structures of these areas. (IMa: Internal maxillaryartery, APha: ascending pharyngeal artery, CICa: cavernous internal carotid artery, 2nd

genu of ICA: second genu of internal carotid artery, IPICa: petrosal internal carotidartery (dotted line), PPICa: parapharyngeal internal carotid artery, CS: cavernous sinus,V1: ophthalmic branch of trigeminal nerve, V2: maxillary division of trigeminal nerve, V3:mandibular division of trigeminal nerve, IOn: infraorbital nerve, GPn: greater palatinenerve, VI CN: VI cranial nerve, Hypophysis: hypophysis, ET: cartilaginous portion of theeustachian tube (partially resected and replaced by a plastic translucent tube), Sync:synchondrosis, SPHA: stylopharyngeal aponeurosis (partially resected), LCm: longuscapitis muscle, ITF: infratemporal fossa, Clivus: clivus, MCF floor: floor of the middelcranial fossa, MCF dura mater: dura mater of the middle cranial fossa, NF: nasalfloor).

1.Kassam, A.B., et al., Expanded endonasal approach: fully endoscopic,completely transnasal approach to the middle third of the clivus, petrousbone, middle cranial fossa, and infratemporal fossa. Neurosurg Focus,2005. 19(1): p. E6.

2.Kassam, A., et al., Expanded endonasal approach: the rostrocaudal axis.Part II. Posterior clinoids to the foramen magnum. Neurosurg Focus, 2005.19(1): p. E4.

3.Kassam, A., et al., Expanded endonasal approach: the rostrocaudal axis.Part I. Crista galli to the sella turcica. Neurosurg Focus, 2005. 19(1): p. E3.

4.Snyderman, C.H., et al., Endoscopic skull base surgery: principles ofendonasal oncological surgery. J Surg Oncol, 2008. 97(8): p. 658-64.

5.Fortes, F.S., et al., Endoscopic anatomy of the pterygopalatine fossa andthe transpterygoid approach: development of a surgical instruction model.Laryngoscope, 2008. 118(1): p. 44-9.

6.Rhoton, A.L., Jr., The temporal bone and transtemporal approaches.Neurosurgery, 2000. 47(3 Suppl): p. S211-65.

7.Alfieri, A., et al., Endoscopic endonasal approach to the pterygopalatinefossa: anatomic study. Neurosurgery, 2003. 52(2): p. 374-78; discussion378-80.

CONCLUSIONSCONCLUSIONS

INTRODUCTION

Department of

Otolaryngology

CONTACTCONTACTCarlos M. Rivera-Serrano, MDRicardo L Carraucarraurl@gmail.com

Eight pterygopalatine and infratemporal fossaswere dissected in four adult heads injected withcolored latex. Rod-lens endoscopes with 0, 30and 45 degrees lenses, a neurosurgicalmicroscope, and microsurgical endoscopicinstruments were used for dissection. A trans-antral approach was performed to access thepterygopalatine fossa, and a transpterygoidapproach was used to access the infratemporalfossa and post-styloid space.

MATERALS AND METHODSMATERALS AND METHODS

Transantral and transpterygoid approachesallowed dissection of pterygopalatine andinfratemporal structures. Dissection andresection of the sphenopalatine artery, anddettachment of the medial and lateralpterygoid muscles were essential to gain accessto deeper structures. The lateral pterygoid platewas the most useful landmark for location ofthe foramen ovale and the mandibular branchof the trigeminal nerve. The Eustachian tube,medial pterygoid plate, and styloid processwere the most useful landmarks used to locatepost-styloid anatomic structures (internalparapharyngeal carotid artery, internal jugularvein, cranial nerves IX and X).

RESULTSRESULTS

Figure 2. A, view of the right maxillary sinus after medial endoscopic antrostomy.B, access to PPF was obtained by performing an endoscopic trans-antralapproach using Kerrison rongeurs. (Vomer: vomer bone resected, Eth. Crest:ethmoidal crest of the palatine bone, Sp. Sinus: sphenoid sinus, Spa: sphenopalatineartery, SpF: sphenopalatine foramen, Post. Wall of Max. Sinus: posterior wall ofmaxillary sinus, Inf. Turbinate: inferior turbinate, DPa: descending palatine artery,Surrounding fat tissue of ITF and PPF: Surrounding fat tissue of infratemporal fossaand pterygopalatine fossa, Periosteum of Post. Wall of Max. Sinus: periosteum of theposterior wall of the maxillary sinus. Pictures were taken with a 0 degree rod lensendoscope).

Figure 4. A, view of the right infratemporal and pterygopalatine fossae after resectionof the internal maxillary artery and its branches. Neural structures were identifiedposterior to the vascular structures. The origin and number of the lesser palatinenerves were variable. B, closer view of the right pterygoid “wedge” (dotted blacktriangle). Vidian nerve and sphenopalatine ganglia were easily identified. (LPn: lesserpalatine nerves, IOn: infraorbital nerve, GPn: greater palatine nerve, SPg: sphenopalatineganglion, V2: maxillary division of the trigeminal nerve, Vn: vidian nerve, Va: vidian artery.Tm: temporalis muscle, FR: foramen rotundum, PvC: palatovaginal canal, VC: vidian canal,ICA: internal carotid artery. A and B pictures were taken with 0 degree rod lensendoscope).

Figure 5. A, view of right infratemporal and pterygopalatine fossas after resection ofinternal maxillary artery and dettachment of lateral pterygoid muscle from the lateralpterygoid plate. In this specimen, the vidian and palatovaginal canals had a commonentrance orifice. B, view of the right drilled pterygoid “wedge” (dotted black triangle).The vidian nerve was resected and followed until the second genu of internal carotidartery. (Zn: zygomatic nerve, V2: maxillary division of the trigeminal nerve, SPg:sphenopalatine ganglion, GPn: greater palatine nerve, LPn: lesser palatine nerves, IOn:infraorbital nerve, LPm: lateral pterygoid muscle, Tm: temporalis muscle, 2nd genu of ICA:second genu of internal carotid artery, ICA: internal carotid artery, VC / PV: vidian andpalatovaginal canals common entrance. Pictures were taken with 0 degree rigid endoscope).

Figure 6. A, view of the right infratemporal fossa after resection of the surrounding fat.The buccal and pterygoid nerves were observed traveling in between the superior andinferior heads of the lateral pterygoid muscle. B. View of the mandibular division of thetrigeminal nerve (V3) and branches through the right foramen ovale. The V3 divisiondivided itself in two minor trunks: anteromedial and the posterolateral. The buccal nerveis the first and only sensitive branch of the anteromedial trunk, and innervates the skin ofthe cheek. The other branches of the anteromedial trunk (deep temporal nerves, lateraland medial pterygoid nerves, and masseteric nerve) are motor in nature. Theposterolateral trunk is sensitive and is divided in: lingual nerve, inferior alveolar nerve andauriculotemporal nerve. The V3 division was the first important landmark in the locationof the post-styloid space, as it was always anterior and in very close proximity. (Zn:zygomatic nerve, Bn: buccal nerve, Ptn: medial and lateral pterygoid nerves, GPn: greaterpalatine nerve, LPn: lesser palatine nerve, IOn: infraorbital nerve, Ln: lingual nerve, IAn: inferioralveolar nerve, Vn: vidian nerve, SPg: sphenopalatine ganglion, LPm: lateral pterygoid muscle,FO: foramen ovale, VC: vidian canal, IMa: internal maxillary artery. B picture was taken with 0degree rod lens endoscope).

Figure 7. A, view of ITF before and after resection of the pterygoid plates. After thelateral pterygoid muscle was displaced laterally, it was necessary to perform twoosteotomies at the inferior insertion of the pterygoid plates. This step permitted the gainof important working space (once the muscles that insert in the pterygoid fossa werelateralized). B, view of the muscular insertions in the pterygoid fossa after the remainingpterygoid plates were drilled from medial to lateral and from rostral to caudal. Forlocation of deeper structures, the medial pterygoid muscle and the tensor veli palatinimuscle were dissected and laterally displaced. (Bn: buccal nerve, Zn: zygomatic nerve, IOn:infraorbital nerve, Ln: lingual nerve, GPn: greater palatine nerve, LPn: lesser palatine nerve, Vn:vidian nerve, SPg: sphenopalatine ganglion, MCF floor: medial craneal fossa floor, FO: foramenovale, MPm: medial pterygoid muscle, LPm: lateral pterygoid muscle, TVPm: tensor veli palatinimuscle, Tm: temporalis muscle, IMa: internal maxillary . A and B pictures were taken with a 0degree rod lens endoscope)

Figure 9. A, endoscopic view of the right post-styloid space after resection ofthe stylopharyngeal aponeurosis (SPHA). The cranial nerve IX was located inbetween the internal jugular vein and the internal carotid artery (ICA), literallyencased in the SPHA. A1, Magnified view of the post-styloid space (of figure 9A) reveals the intimal relationship of the ICA and the eustachian tube (ET).The IJV was posterior to ICA and styloid process. B, view of the right cranialnerve X after ICA reflection. B1, Magnified view (of figure 9 B) of posteriorstructures to the ICA. The cranial nerves XI and XII were identified posteriorto cranial nerve X, but they could not be dissected at this level due to itsposterior, lateral and inferior location to the ICA. (ET: eustachian tube, TT: torustubaris, LVPm: levator veli palatini muscle, IMa: internal maxillary artery, MMa:medial meningeal artery, APhv: ascending pharyngeal vein, APha: ascendingpharyngeal artery, PPv: pterygoid plexus vein, ICA: internal carotid artery, IJV:internal jugular vein, XI-XII: XI and XII cranial nerves, IX: IX cranial nerve, X: Xcranial nerve, Ln: lingual nerve, IAn: inferoalveolar nerve, ChTn: chorda tympaninerve, V3: mandibular division of the trigeminal nerve, SP: styloid process. A and Bpictures were taken with a 30 degree rigid endoscope.

REFERENCESREFERENCES

Figure 10. A, anterior view of the right Eustachian tube (ET) after lateraldisplacement of the medial pterygoid muscle and resection the tensor velipalatini muscle. The ET had a posterosuperior direction of approximately 40-45 degrees towards the cranial base and 30-35 degrees towards the bonypalate. The torus tubaris relates to the posterior border of the medialpterygoid plate anteriorly and the nasopharyngeal mucosa and longus capitismuscle posteriorly. The levator palatini muscle has a very close relationshipwith the stylopharyngeal aponeurosis (SPHA) and internal carotid artery. B,view of the post-styloid space after resection of the SPHA. The ET relateswith the post-styloid space and the internal carotid artery (ICA)posterolaterally.   The ET relates anterolaterally with V3 and the medialmeningeal artery, at the level of the foramen ovale and spinosum respectively.The most lateral aspect of the cartilaginous portion of the ET limits with theICA. C, superolateral view of the ET once the vidian canal is drilled. Themedial and postero-superior aspect of the torus tubaris is in intimalrelationship with the foramen lacerum and the second genu of the ICA(through the synchondrosis). D, view of the infratemporal fossa afterresection of the ET (ET has been replaced by a plastic translucent tube). Theascending pharyngeal artery and vein are located at the level of the posterioraspect of the cartilaginous ET, in between the ICA and the ET. All extracranialportions of the ICA are represented. Dotted black line = petrous internalcarotid artery and a portion of the parapharyngeal internal carotid artery (ET:eustachian tube, LVPm: levator veli palatini muscle, MPm: medial pterygoidmuscle, Clivus: clivus, IMa: internal maxillary artery, MMa: medial meningealartery, APhv: ascending pharyngeal vein, PPv: pterygoid plexus vein, APha:ascending pharyngeal artery, Sync: synchondrosis, Ln: lingual nerve, IAn: inferioralveolar nerve, ChTn: chorda tympani nerve, GPn: greater palatine nerve, DTn:deep temporal nerve, IOn: infraorbital nerve, VI CN: VI cranial nerve, CS: cavernoussinus, MCF dura mater: middle cranial fosa duramater, FL: foramen lacerum, 2nd

genu of ICA: second genu of internal carotid artery, NF: nasal floor, SPHA:stylopharyngeal aponeurosis, PPICa: parapharyngeal internal carotid artery, IPICa:intrapetrosal internal carotid artery, CICa: cavernous internal carotid artery, ICA:internal carotid artery, TT: torus tubarius, V3: mandibular division of the trigeminalnerve, V2: maxillary division of the trigeminal nerve, V1: ophthalmic division of thetrigeminal nerve. B and C pictures were taken with 30 and 45 degree rod lensendoscopes respectively).