doi: 10.1055/s-0042-1759874.
eCollection 2024 Feb.
Anatomical Step-by-Step Dissection of Complex Skull Base Approaches for Trainees: Surgical Anatomy of the Endoscopic Endonasal and Endoscopic-Assisted Transmaxillary Transpterygoid Approaches
Affiliations
- PMID: 38274480
- PMCID: PMC10807960
- DOI: 10.1055/s-0042-1759874
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Anatomical Step-by-Step Dissection of Complex Skull Base Approaches for Trainees: Surgical Anatomy of the Endoscopic Endonasal and Endoscopic-Assisted Transmaxillary Transpterygoid Approaches
J Neurol Surg B Skull Base.
.
Abstract
Introduction The endoscopic endonasal transpterygoid approach (EETPA) with or without the addition of the endoscopic-assisted sublabial anterior transmaxillary approach (ESTA) has become increasingly utilized for lesions posterior to the pterygopalatine fossa (PPF), including infratemporal fossa (ITF), lateral recess of the sphenoid sinus, Meckel's cave, petrous apex, and parapharyngeal space. The main goal of this study is to develop an educational resource to learn the steps of the EETPA for trainees. Methods EETPA and ESTA were performed in 12 specimens by neurosurgery trainees, under supervision from the senior authors. One EETPA and one ESTA were performed on each specimen on opposite sides. Dissections were supplemented with representative cases. Results After a wide unilateral sphenoidotomy, ethmoidectomy, and partial medial maxillectomy, the anteromedial bone limits of the PPF were identified and drilled out. The pterygoid progress was modularly removed. By enlarging the opening of the posterior and lateral walls of the maxillary sinus through EETPA and ESTA, respectively, the neurovascular and muscular compartments of the PPF and ITF were better identified. The EETPA opens direct corridors to the PPF, medial ITF, middle cranial fossa, cavernous sinus, Meckel's cave, petrous apex, and internal carotid artery. If a more lateral exposure of the ITF is needed, the ESTA is an appropriate addition. Conclusion Despite the steep learning curve of the EETPA, granular knowledge of its surgical anatomy and basic surgical steps are vital for those advancing their learning in complex endoscopic approaches to the ventral skull base when expanding the approach laterally in the coronal plane.
Keywords: Meckel's cave; endonasal endoscopy; infratemporal fossa; pterygopalatine fossa; skull base surgery; step-by-step anatomical dissections; sublabial; transmaxillary; transpterygoid.
Thieme. All rights reserved.
Conflict of interest statement
Conflict of Interest None declared.
Figures
Stepwise dissection of the endoscopic endonasal right complete ethmoidectomy, maxillary antrostomy, and sphenoidotomy. The 0-degree endoscope is used in all pictures except B. (
A
) The endoscope is inserted in the nasal cavities along the inferior nasal corridor. The inferior nasal corridor is bounded by inferior turbinate laterally and the nasal septum medially. (
B
) Moving upward along the middle nasal corridor, a 30-degree endoscope is faced to the right showing the lateral nasal wall. (
C
) The middle turbinate is gently medialized, and the middle meatus is accessed. (
D
) The intermediate portion of the uncinated process is removed. (
E
) A complete uncinectomy is then performed. This allows to better expose the anterior limit of the bulla ethmoidalis. An accessory maxillary sinus ostium is identified below the inferior limit of the bulla ethmoidalis. (
F
) Anterior and posterior fontanelles and (
G
) bulla ethmoidalis are modularly removed. A wide maxillary antrostomy is completed. The bone limits of the maxillary antrostomy are the nasolacrimal duct anteriorly, the posterior wall of the maxillary sinus posteriorly, the orbital floor superiorly, and the attachment of the inferior turbinate inferiorly. (
H
) A posterior ethmoidectomy and sphenoidotomy are then performed, exposing the bony anatomical landmarks for the EETPA, including vertical plate of the palatine bone, sphenoid and orbital processes of the palatine bone, and the posterior wall of the maxillary sinus. EETPA, endoscopic endonasal transpterygoid approach; horiz., horizontal; interm., intermediate; IT, inferior turbinate; med., medial; MS, maxillary sinus; MT, middle turbinate; orb., orbital; PB, palatine bone; post., posterior; pr., process; sphen., sphenoidal; UP, uncinate process; vert., vertical.
Stepwise dissection of the EETPA. Pictures obtained with a 0-degree endoscope. (
A
) The vertical plate, sphenoid process, and orbital process of the palatine bone are localized. The anterior margin of the torus tubarius of the Eustachian tube is identified posteromedially to the medial pterygoid plate of the pterygoid process. The sphenopalatine artery is divided, the submucosal dissection is continued posteriorly, and the lateral portion of the anterior margin of the sphenoid floor is exposed. (
B
) By drilling the sphenoid floor and the sphenoid process of the palatine bone, proceeding in a medial to lateral direction, the pharyngeal artery within its canal, the vidian canal with its contents, and the PPF contents protected by its periosteum are progressively exposed. (
C
) The palatovaginal canal (or palatosphenoidal canal) communicates the PPF with the roof of the nasopharynx and contains the pharyngeal artery and neural branches from the pterygopalatine ganglion. The pharyngeal artery is identified within the palatovaginal canal along its course from the PPF to the roof of the nasopharynx. (
D
) The pharyngeal artery is divided and the palatovaginal canal is drilled out, better defining the medial and inferior limits of the vidian canal. The vidian canal travels within the base of the pterygoid, with a medial to lateral direction, and it connects the PPF with the middle cranial fossa. It contains the vidian artery and nerve. In all cadaveric dissections of this study, the vidian artery has been consistently identified. (
E
) Using a 90-degree dissector, the vidian is completely isolated from the vidian canal. The entry point of the vidian canal on the PPF and the proximal portion of the vidian nerve are better defined. (
F
) The orbital process of the palatine bone, the perpendicular plate of the palatine bone, and the posterior wall of the maxillary sinus are progressively drilled out, better exposing the periosteum of the PPF in its anterior, medial, and superior limits. (
G
) The PPF, still protected by its periosteum, is lateralized. (
H
) The anteromedial portion of the base of the pterygoid is drilled out. (
I
) The vidian artery is divided. (
J
) Subsequently, the vidian nerve is divided. This maneuver allows easier lateralization of the PPF contents and the exposure of the medial margin of the foramen rotundum at the superoposterior limit of the PPF. (
K
) The pterygoid base is completely removed, exposing the floor of the middle cranial fossa. (
L
) The medial and lateral pterygoid plates are drilled out (excluding the distal portion of the lateral pterygoid plate), and the passage of V3 through the foramen ovale and its anterior and posterior division with the respective main branches are identified. (
M
) The PPF contents are carefully dissected. V2 and the muscular and pterygopalatine MAX with their main branches are identified. Starting from a standard transpterygoid access, different surgical corridors can be followed from medial to lateral: the midclivus, lacerum and cavernous ICA, lateral compartment of the cavernous sinus, the floor of the middle cranial fossa, Meckel's cave, petrous apex and petrous bone, PPF, and medial portion of the ITF. (
N
) The neurovascular contents of the PPF are transposed inferolaterally better showing the relation between the PPF and ITF neurovascular structures. (
O
) Closer view on V3 along its intracranial passage through the foramen ovale. The relation between the lingual process, V3, and vidian nerve are highlighted. (
P
) The medial portion of the greater sphenoid wing between V2 and V3 is removed, up to the level of the foramen spinosum. The MMA is isolated along its extra- to intracranial segments. (
Q
) Access to the middle cranial fossa is gained in an extradural fashion. The superolateral surface of the Meckel's cave is exposed. The greater superficial petrosal nerve is isolated from the anterior surface of the petrosal process of the sphenoid bone to its entry point into the vidian canal. (
R
) The temporal dura is incised and the inferomesial portion of the right temporal lobe is exposed. AAA, alveolar antral artery; B., bone; br., branch; DPA, descending palatine artery; DPB, descending palatine bundle; EETPA, endoscopic endonasal transpterygoid approach; FL, foramen lacerum; GSPN, greater superficial petrosal nerve; ICA, internal carotid artery; MAX, maxillary artery; inf., inferior; IOA, infraorbital artery; ION, infraorbital nerve; IT, inferior turbinate; lat., lateral; LPM, lateral pterygoid muscle; MMA, middle meningeal artery; MS, maxillary sinus; N., nerve; orb., orbital; PB, palatine bone; PN, palatine nerve; post., posterior; PPF, pterygopalatine fossa; pr., process; PSAA, posterior superior alveolar artery; PVC, palatovaginal canal; SPA, sphenopalatine artery; sphen., sphenoidal; sphenopal., sphenopalatine; temp., temporal; tens., tensor; V2, maxillary nerve; V3, mandibular nerve; VA, vidian artery; VC, vidian canal; vert., vertical; VN, vidian nerve.
Anatomical overview of the anatomical relationships of the areas accessed through the EETPA. Pictures obtained with a 0-degree endoscope (
A
) The PPF is a pyramidal space located between the pterygoid process of sphenoid bone posteriorly, the perpendicular plate of the palatine bone medially, and the superomedial portion of the posterior wall of the maxillary sinus anteriorly, the body of the sphenoid superiorly. The PPF communicates laterally through the pterygomaxillary fissure with the ITF. Its main neurovascular structures are the pterygopalatine segment of the MAX and its branches, V2, and vidian nerve. Following the corridor medial to the medial pterygoid plate, the anterior attachment of the Eustachian tube (green dotted line) is exposed. Superomedially, the EETPA give the access to the inferolateral recess of the sphenoid sinus (yellow dotted line). (
B
) The vidian nerve is formed by the junction of the greater superficial petrosal nerve and deep petrosal nerve and run through the vidian canal. The greater superficial petrosal nerve brings sensory fibers and pre-parasympathetic fibers (belonging to the pre-parasympathetic neurons of the geniculate ganglion) from the facial nerve, while the deep petrosal nerve brings post-sympathetic fibers from the carotid plexus (belonging to the post-sympathetic neurons of the superior cervical ganglion). The vidian nerve runs within the vidian canal anteriorly and medially from the lateral margin of the lacerum ICA. Just posterior to the posteromedial margin of the lacerum ICA, the most medial point of the petrous apex (white dotted line) is identified at its point of articulation with the petrosal process of the sphenoid bone in correspondence (i.e., petroclival junction). (
C
) The maxillary nerve arises from the trigeminal ganglion between ophthalmic and mandibular divisions of the trigeminal nerve, it courses in the lateral wall of the cavernous sinus, and it leaves the middle cranial fossa through the foramen rotundum, entering the superoposterior compartment of the PPF. By drilling the pterygoid plates, the access to the peri-Eustachian tube musculature (light-blue dotted line) is gained. (
D
) The EETPA opens several intra- and extracranial surgical corridors by the modular drilling of the base of the pterygoid, medial pterygoid plate and lateral pterygoid plate. EETPA: one approach, many surgical corridors to different extra- and intracranial regions (both medial and posterior cranial fossae), including ITF, middle cranial fossa, Meckel's cave, inferolateral recess of the sphenoid sinus, lacerum and cavernous ICA, petrous apex, and Eustachian tube. BA, basilar artery; br., branch; DPA, descending palatine artery; EETPA, endoscopic endonasal transpterygoid approach; ICA, internal carotid artery; MAX, maxillary artery; inf., inferior; lat., lateral; M., muscle; med., medial; lev., levator; lig., ligament; LPM, lateral pterygoid muscle; OA, ophthalmic artery; ON, ophthalmic nerve; PB, palatine bone; PG, pituitary gland; PPF, pterygopalatine fossa; pr., process; SPA, sphenopalatine artery; sphen., sphenoidal; temp., temporal; V1, ophthalmic nerve; V2, maxillary nerve; VA, vidian artery; vert., vertical; VI, abducens nerve.
Stepwise dissection of the PPF and ITF through the ESTA. (Macroscopic view
A
–
D
) (
A
) A right superior sublabial incision is performed between the right upper canine and right upper second molar, about 5 mm above the gingival sulcus. (
B
) The periosteum is progressively elevated from the anterior wall of the maxilla. The canine fossa, canine eminence, and infraorbital foramen are progressively exposed. The infraorbital nerve and artery are identified at their exit point from the infraorbital canal. (
C
) A window of 3 cm diameter in the anterior wall of the maxillary sinus is opened, visualizing the underlying mucosa. (
D
) The maxillary sinus mucosa is removed, and the maxillary sinus cavity is entered. (Endoscopic view with a 0-degree endoscope
E
–
N
) (
E
) The mucosa of the maxillary sinus is removed exposing its posterior wall, the perpendicular plate of the palatine bone posteromedially, the orbital floor superiorly, the infraorbital canal superolaterally, the zygomatic recess laterally, and the alveolar recess inferiorly. Then, the posterior wall of the maxillary sinus is removed exposing the underlying periosteum of the PPF and medial ITF. The periosteum and superficial fat are modularly removed and the neurovascular structures of the PPF and medial ITF come into view. (
F
) The collateral branches of the pterygopalatine MAX, namely the vidian artery, pharyngeal artery, infraorbital artery, deep temporal arteries, posterior superior alveolar artery, and alveolar-antral artery, are progressively identified. The two terminal branches of the pterygopalatine MAX (i.e., the sphenopalatine artery and descending palatine artery) are visualized. The sphenopalatine artery goes medially, entering the sphenopalatine foramen, while the descending palatine artery, alongside the greater palatine nerve, runs inferiorly toward the greater palatine canal. The vidian nerve and V2 come out of the distal foramen of vidian canal and the foramen rotundum, respectively. While the V2 courses from medial-to-lateral, the vidian nerve travels from lateral-to-medial. The pterygopalatine ganglion contains pre-parasympathetic neurons and post-sympathetic fibers along with sensory fibers of the V2. A lacrimal branch runs from the pterygopalatine ganglion into the zygomatic nerve, carrying the post-parasympathetic fibers for the parasympathetic innervation of the lacrimal gland. The two terminal branches of the V2, namely the greater palatine nerve and infraorbital nerve, are isolated. The greater palatine nerve divides into the lesser and greater palatine nerves, while the infraorbital nerve reaches the infraorbital artery before to enter the homonym canal. (
G
) The content of the infraorbital canal is exposed, including the infraorbital nerve and artery. (
H
) The opening of the maxillary sinus wall is extended laterally, gaining access to the lateral ITF. (
I
) Once the musculature of the ITF is exposed, three different corridors are identified and modularly dissected in between the three parts of the temporalis muscle (i.e., superficial, deep, and zygomatic part), the two heads of the lateral pterygoid muscle (i.e., superior and inferior head), and the body of the sphenoid. (
J
) The entry point of the first corridor through the ITF is identified between the superficial and deep parts of the temporalis muscle. The first corridor is progressively dissected. (
K
) The medial surface of the coronoid process of the mandible comes into view by detaching the attachments of the superficial and deep parts of the temporalis muscle to the coronoid process. (
L
) Moving posteriorly, the second corridor is progressively opened between the deep and the zygomatic part of the temporalis muscle. As the dissection proceeds, the anterior and posterior deep temporal arteries are identified. The temporomandibular joint, composed by the mandibular fossa of the temporal bone, articular cartilage, and the condylar process of the mandible, is finally exposed. (
M
) The third corridor is between the lateral pterygoid muscle and the body of the sphenoid. The upper head of the lateral pterygoid muscle is removed, and the foramen ovale and V3 with its anterior and posterior divisions come into view. (
N
) The main branches of the anterior division of V3 are the deep temporal nerve, buccal nerve, masseteric nerve, and lateral and medial pterygoid nerves. The posterior division of V3 and its branches (i.e., lingual, auriculotemporal, meningeal, and inferior alveolar nerves) are progressively dissected and identified. A., artery; AAA, alveolar antral artery; alv., alveolar; ant., anterior; art., articular; auriculotemp., auriculotemporal; b., bone; br., branch; div., division; DPA, descending palatine artery; DPB, descending palatine bundle; ESTA, endoscopic-assisted sublabial anterior transmaxillary approach; GPN, greater palatine nerve; inf., inferior; IOA, infraorbital artery; IOC, infraorbital canal; ION, infraorbital nerve; IT, inferior turbinate; ITF, infratemporal fossa; lev., levator; lat., lateral; LPM, lateral pterygoid muscle; med., medial; mid., middle; M., muscle; MAX, maxillary artery; MS, maxillary sinus; N., nerve; orb., orbital; post., posterior; PN, palatine nerve; post., posterior; PPF, pterygopalatine fossa; PPG, pterygopalatine ganglion; pr., process; PSAA, posterior superior alveolar artery; PSAN, posterior superior alveolar nerve; SPA, sphenopalatine artery; sup., superior; superf., superficial; temp., temporal; TM, temporalis muscle; tub., tubercle; V2, maxillary nerve; V3, mandibular nerve; vert., vertical; VN, vidian nerve; zyg., zygomatic.
Illustrative cases. (Case 1
A
–
C
) (
A
) Preoperative T1-weighted magnetic resonance imaging (MRI) in the coronal plane demonstrates a large right temporal meningoencephalocele extending into the right inferolateral recess of the sphenoid sinus (yellow star). (
B
) Intraoperative view of the EETPA. The pharyngeal artery and the vidian nerve have been divided, allowing better lateralization of the PPF contents and opening a wider corridor to the lesion (yellow star). (
C
) Postoperative contrast-enhanced T1-weighted MRI in the coronal plane confirms the effective reconstruction of the skull base. (Case 2
D
–
F
) (
D
) Preoperative contrast-enhanced T1-weighted MRI in the axial plane shows a right large homogeneously enhancing ITF mass extending superiorly to foramen ovale, most likely representing a V3 schwannoma. (
E
) Intraoperative view of the combined EETPA and ESTA. Through the sublabial anterior transmaxillary route, the masticatory musculature of the ITF is carefully displaced laterally. In this way, the central and lateral portions of tumor and its origin from the anterior division of V3 are widely exposed (tumor-yellow shadowed area). (
F
) Postoperative contrast-enhanced T1-weighted MRI in the axial plane confirms gross total resection of the tumor. DPB, descending palatine bundle; EETPA, endoscopic endonasal transpterygoid approach; ESTA, endoscopic-assisted sublabial anterior transmaxillary approach; PPF, pterygopalatine fossa.
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