4 Corridor to Sella Turcica, Surrounding Areas, Posterior Skull Base, and Cervical Spine

The corridors illustrated in this chapter pass through the sphenoid sinuses, ethmoidal complex, and nasopharynx, providing a direct trajectory toward the posterior portion of the anteri- or skull base (i.e., planum sphenoidale and tuberculum sellae), the median/paramedian portions of the middle and posterior skull base, the craniocervical junction, and part of the cervical spine. ¹ – ¹¹ Similarly to the corridor toward the anterior skull base and orbit, the amount of structures to be removed can be modulated according to the need of exposure. ¹² – ¹⁵

Being located at the center of the skull, the sphenoid sinus and nasopharynx serve as crossroads toward several subunits of the cranial base. A large number of bony landmarks (discussed in depth in the following chapters) can be identified on the walls of the sphenoid sinus. The roof of the sphenoid sinus is a thick and flat lamina called planum sphenoidale, which further thickens posteriorly forming the tuberculum sellae. The latter corresponds to the cranial limit of the posterior wall of the sphenoid sinus, which ends inferiorly merging with the sphenoidal floor. The midline portion of the posterior wall is formed by the sellar prominence superiorly and clival recess (when present) inferiorly, while the lateral portions are formed by the carotid prominences superiorly and carotid sulci inferiorly, corresponding to the parasellar and paraclival tracts of the internal carotid artery, respectively. The intersphenoid sinus septum is rarely located on the midline; rather, it attaches onto the carotid prominence and/or sulcus of one side. In addition, a number of incomplete septa, frequently inserting on the bony canal of neighboring neurovascular structures, can be found in the sphenoid sinuses. As a consequence, drilling is favored over fracturing bony septa and sepimentations due to the risk to injure the internal carotid artery by creating sharp bony edges along fracture rims. The lateral sphenoidal wall lies anteriorly and laterally to the carotid bony landmarks (i.e., carotid prominence and sulcus). The dihedral angle where the lateral sphenoidal wall joins the planum sphenoidale houses the optic canal, which follows posterior-to-anterior and medial-to-lateral directions to connect the suprasellar area to the orbital cavity.

The possibility to identify sphenoid bony landmarks depends on the degree of pneumatization of the sphenoid sinus, which is variable on both the anterior-to-posterior and medial-to-lateral axes. ¹⁶ On the anterior-to-posterior axis, the sphenoid sinus can be classified according to where the air space ends posteriorly: a conchal (agenesis/hypoplasia of the sphenoid sinus), presellar (air space anterior to the plane passing through the anterior sellar wall), sellar (air space below the sella turcica, between the planes passing through anterior sellar wall, anteriorly, and dorsum sellae, posteriorly), or retrosellar/clival type (air space posterior to the plane passing through the dorsum sellae) can be distinguished. On the medial-to-lateral axis, the sphenoid sinus can be classified as body (when pneumatization does not overcome the lateral wall), lesser wing (when an optic-carotid recess takes shape; this variant will be discussed in the following chapters), and lateral type (when the pneumatization overcomes the line connecting the vidian canal to foramen rotundum, forming a space called lateral recess). The lateral recess is, in turn, classified as greater wing, pterygoid, or full type, according to the extent of pneumatization.

The sphenoid sinus is usually opened via the nasal cavity (i.e., paraseptal sphenoidotomy) proceeding centrifugally from the sphenoid ostium, which is found medial to the superior turbinate. Lateralization or partial removal of the superior turbinate can be necessary to gain enough space to handle instruments. The same procedure can be done through the ethmoid after completing a total ethmoidectomy (i.e., functional transethmoidal sphenoidotomy); in such a scenario, it is advantageous to remove the inferior part of the superior turbinate in order to identify the sphenoid ostium rather than blindly pierce the anterior sphenoidal wall. An additional way to open the sphenoid sinus is by harvesting a submucosal corridor along the nasal septum (i.e., subseptal sphenoidotomy).

Differently from functional sinus surgery, the opening of the sphenoid sinus should be enlarged as much as possible in order to provide an adequate working volume toward the skull base. As a consequence, the anterior sphenoidal wall between the nasal septum medially, superior turbinate laterally, sphenoidal floor inferiorly, and planum sphenoidale superiorly is completely removed. When further exposure and/or a binostril approach are needed, a posterosuperior septectomy with transrostral sphenoidotomy can be performed. Increasing working volume and skull base exposure can be obtained with expanded transrostral and modular transethmoidal sphenoidotomy: the former consists of removing the superior turbinate and part of the orbital process of the palatine bone, the latter is accomplished adding a posterior or total ethmoidectomy.

The nasopharynx is delimited by the vault (which corresponds to the sphenoidal floor), lateral walls with tori tubarii (that are the footprint of eustachian tubes on the nasopharyngeal mucosa), and posterior wall. The limit between the posterior and lateral wall corresponds to the lateral recess of the nasopharynx, which is also called Rosenmüller fossa. As a result of the natural communication with the nasal cavities via the choanae, the nasopharynx is easily accessed through the inferior nasal corridors, which can be merged via a posteroinferior septectomy. When needing a wide corridor, including the transsphenoidal pathway as well, the sphenoidal floor/nasopharyngeal vault is removed to connect the nasopharynx with the sphenoidal lumen. The lateral landmarks used to entirely remove the sphenoidal floor are the vidian canals. The lateral portion of the sphenoidal floor houses several neurovascular structures (palatovaginal and vomerovaginal bundles). ¹⁷

Related posts:

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

Stay updated, free articles. Join our Telegram channel

Join