5 Corridor to Lateral Spaces



10.1055/b-0039-172567

5 Corridor to Lateral Spaces

Alberto Schreiber, Vittorio Rampinelli, Marco Ferrari, Marco Ravanelli

Lateral exposure is exceedingly important when approaching skull base pathologies with extension along the medial–lateral axis. Some coronal approaches basically consist of the lateral extension of midline corridors across neighboring cranial base areas. Conversely, several pathways along the coronal plane require a complex and specific preparatory phase. In particular, six bony doors can be schematically considered to access lateral portions of the skull base and adjacent areas: the maxillary walls, orbital walls (Chapter 14), pterygoid process (Chapters 21, 23, and 24), lateral sphenoidal wall (Chapters 18 and 21), petrous bone (Chapters 19 and 20), and occipital condyle (Chapter 22). The maxillary sinus, besides being the target in functional procedures and selected sinonasal neoplasms (i.e., schneiderian papillomas), represents a natural corridor toward several infracranial areas (i.e., pterygopalatine fossa, infratemporal fossa, and upper parapharyngeal space). The present chapter focuses on modular types of removal of the medial and anterior walls of the maxillary sinus, referred to as “modular endoscopic medial maxillectomies.” 1 Moreover, a brief description of the lacrimal sac anatomy as seen through an endoscopic dacryocystorhinostomy is reported.


The medial wall of the maxillary sinus is a complex and heterogeneous structure, composed by the horizontal portion of the uncinate process, inferior turbinate, bony nasolacrimal duct, and a vertical bony lamina going from the nasal floor to the inferomedial orbital corner. 1 , 2 The maxillary ostium lies in the superior and anterior portion of the medial maxillary wall. It is oriented anteriorly, superiorly, and medially, facing the intermediate third of the uncinate process, between its vertical and horizontal portions. Not infrequently, one or more defects of the medial maxillary wall (called accessory maxillary ostia or fontanelles) can be found along the inferior insertion of the uncinate process. This complex wall can be disassembled in a modular fashion to tailor the entity of bone removal in relation to the need for lateral and inferior exposure. 1 The anterior wall of the maxillary sinus can be divided into two halves with respect to the sagittal plane passing through the infraorbital foramen. The medial half of the anterior wall can be removed to enhance the working space toward maxillary and retromaxillary areas, as formerly described by Denker, Sturmann, and Canfield in the early 20th century. 3 – 5 The lateral half of the anterior maxillary wall can be partially removed when far-lateral exposure is required. 2 – 7

Fig. 5.1 Diagonal view of transnasal routes toward the lateral spaces. This illustration shows anatomy of the maxillary sinus and neighboring spaces.
Fig. 5.2 Sagittal view of the lateral nasal wall and medial maxillary wall. This cadaver cut shows anatomy of the medial maxillary wall. AE, anterior ethmoidal compartment; AgN, agger nasi; AMOs, accessory maxillary ostium; EB, ethmoid bulla; hUP, horizontal segment of the uncinate process; IT, inferior turbinate; MMW, medial maxillary wall; MT, middle turbinate; vUP, vertical segment of the uncinate process. (Black dashed line, position of the lacrimal sac and nasolacrimal duct; white dotted line, position of the maxillary ostium).

Aiming to standardize the nomenclature and facilitate teaching and learning the surgical technique of endoscopic medial maxillectomies, a modular classification was recently proposed by our group. 1 The distinction among four different types of maxillectomies is based on preclinical evidence of gain in terms of working volume and exposure. Type A endoscopic medial maxillectomy includes an inferior uncinectomy and removal of the medial maxillary wall to the inferior turbinate insertion (inferiorly), orbital floor (superiorly), descending palatine canal (posteriorly), and nasolacrimal duct (anteriorly). Type B maxillectomy corresponds to a type A plus inferior turbinectomy and removal of the maxillary sinus medial wall posterior to the nasolacrimal duct. Type C procedure also includes the resection of the nasolacrimal duct and removal of the residual anterior portion of the medial maxillary wall. Type D endoscopic maxillectomy involves the removal of the anterior wall of the maxillary sinus medial to the infraorbital foramen. The modularity of the classification allows easy extension from a less to a more invasive removal of the maxillary walls, according to intraoperative findings and need for exposure. In terms of medial–lateral exposure, types A to D maxillectomies allow reaching the foramen rotundum, foramen spinosum, mandibular condyle, and coronoid process, respectively. In terms of cranial–caudal exposure, a type A procedure reaches the vidian nerve, types B and C maxillectomies reach the axial plane passing through the root of the styloid process, and type D resection also provides the exposure of the inferior border of the lateral pterygoid plate. 1


With the intent to minimize surgical morbidity related to endoscopic maxillectomies, some authors have designed variants of traditional approaches. For instance, the prelacrimal approach consists of a surgical corridor that passes lateral to the nasolacrimal duct with the intent to prevent lacrimal stenosis. 8 – 13 In terms of exposure, this approach is similar to types C and D endoscopic maxillectomies, depending on whether the bony edge of the piriform aperture is spared or removed, respectively. As an alternative, transseptal approaches through the contralateral nostril were developed to optimize lateral exposure while minimizing disassembling of maxillary walls. 1 , 14 , 15

Fig. 5.3 (a–d) Coronal CT anatomy of the maxillary sinus and adjacent structures. The panel includes four coronal CT scans passing through the maxillary sinus (MS) disposed from anterior (a) to posterior (d). The maxillary sinus can be described according to its six walls. On a coronal plane, the medial, inferior, lateral, and superior walls can be analyzed. The medial maxillary wall (MMW) separates the maxillary sinus from the inferior nasal meatus and ethmoidal compartment. The maxillary ostium (white dotted line) connects the maxillary sinus with the ethmoidal infundibulum (EIn) and is located in the superior and anterior portion of the medial maxillary wall. Anteriorly, the medial maxillary wall enlarges to house the nasolacrimal duct (NLD). The passage between the medial and anterior walls of the maxillary sinus corresponds to the frontal process of the maxillary bone, where the anterior superior alveolar nerve (ASAN) is located. Of note, the posterior ethmoid (PE), horizontal portion of the uncinate process (hUP), and inferior (IT) and middle turbinate (MT) insert onto the medial maxillary wall. The inferior wall is formed by the alveolar process of the maxilla, which can be variably pneumatized by the alveolar recess (AR). The latter can also extend into the hard palate in highly pneumatized maxillary sinuses. The lateral wall of the maxillary sinus (LWMS) is variably deep in the anterior portion, where it forms the zygomatic recess (ZR), and flat in the posterior portion, where it smoothly continues into the posterior wall. The lateral wall houses the posterior superior alveolar nerve (PSAN). The superior wall of the maxillary sinus is the orbital floor (OrF), where the infraorbital canal (IOCa) is located. GPF, greater palatine foramen; InF, infraorbital foramen; IOF, infraorbital fissure; IOR, infraorbital rim; LF, lacrimal fossa; MaC, maxillary crest; NaF, nasal floor; NS, nasal septum; PEA, posterior ethmoidal artery; ST, superior turbinate.
Fig. 5.4 (a–d) Axial CT anatomy of the maxillary sinus and adjacent areas. The panel includes four axial CT scans passing through the maxillary sinus (MS) disposed from cranial (a) to caudal (d). The anterior maxillary wall (AMW) separates the maxillary sinus from the premaxillary tissue and houses the anterior superior alveolar nerve (ASAN). The posterior (PWMS) and lateral walls of the maxillary sinus (LWMS) neighbor the pterygopalatine (PPF) and infratemporal fossa, respectively. The lateral wall houses the posterior superior alveolar nerve (PSAN). The angle between the posterior and medial maxillary wall (MMW) represents the pterygomaxillary junction, where the descending, greater (GPC), and lesser palatine canals (LPC) run toward the caudal face of the hard palate. AR, alveolar recess; CoP, coronoid process; FRo, foramen rotundum; IOCa, infraorbital canal; IOF, inferior orbital fissure; LF, lacrimal fossa; LPP, lateral pterygoid plate; MPP, medial pterygoid plate; MT, middle turbinate; NLD, nasolacrimal duct; NS, nasal septum; PE, posterior ethmoidal compartment; PMF, pterygomaxillary fissure; PVC, palatovaginal canal; SPF, sphenopalatine foramen; SpS, sphenoid sinus; ST, superior turbinate; vUP, vertical portion of the uncinate process; ZR, zygomatic recess.
Fig. 5.5 Coronal and parasagittal CT anatomy of the infraorbital canal and adjacent structures. The panel includes one coronal (a) and one parasagittal CT scans (b) passing through the infraorbital canal (IOCa). The infraorbital canal runs along the orbital floor (OrF). In the most anterior portion, the course of the canal turns anteroinferiorly to reach the anterior maxillary wall and form the infraorbital foramen (InF). At this level, the canal gives off a small secondary canal inferolaterally that houses the anterior superior alveolar nerve (ASAN). The latter canal runs inferiorly to the infraorbital foramen with a lateral-to-medial direction to reach the lateral bony edge of the pyriform aperture, where it turns caudally. As seen in a coronal plane, the most anterior and medial portion of the maxillary sinus (MS) form a niche between the nasolacrimal duct (NLD) and infraorbital foramen. This niche is also called the retrolacrimal recess and can be tricky to expose from a transnasal perspective. HV, Hasner’s valve; IT, inferior turbinate.


Endoscopic Dissection


Steps




  • Step 1: Horizontal uncinectomy.



  • Step 2: Type A endoscopic medial maxillectomy.



  • Step 3: Inferior turbinectomy.



  • Step 4: Type B endoscopic medial maxillectomy.



  • Step 5: Nasolacrimal duct resection.



  • Step 6: Type C endoscopic medial maxillectomy.



  • Step 7: Exposure of the bone of the piriform aperture.



  • Step 8: Premaxillary dissection.



  • Step 9: Type D endoscopic medial maxillectomy.



  • Step 10: Transposition of the infraorbital nerve.



  • Step 11: Prelacrimal type D endoscopic medial maxillectomy.



  • Step 12: Transseptal approach.



  • Step 13: Dacryocystorhinostomy.

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1 Classification of Endoscopic Transnasal Approaches to the Skull Base and Adjacent Areas 8 Transplanum–Transtuberculum Approach 17 Medial Transcavernous Approach 15 Transpterygomaxillary Approach 18 Lateral Transcavernous Approach 21 The Suprapetrous (Meckel’s Cave) Approach

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May 10, 2020 | Posted by in NEUROSURGERY | Comments Off on 5 Corridor to Lateral Spaces

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