19.2.1 Sinonasal Cavity Preparation

Cranial fixation pins are applied, the patient is positioned supine, and the head is translated upward slightly to facilitate the access. Because the sellar and retrosellar regions are located relatively in-line with the angle created by the sinonasal access corridor, neither flexion nor extension of the neck is recommended, as the neutral position is the most ergonomically favorable for working toward these regions. If both surgeons are right-handed, which is the most common case, the neck may be slightly tilted toward the left (away from the surgeons in the coronal plane of the patient′s body) and then slightly rotated toward the right (toward the surgeons) to further improve operative ergonomics. The patient is then registered to the stereotactic navigation device using preoperative magnetic resonance imaging (MRI) to delineate the lesion of interest as well as a computed tomography angiogram to highlight the intracranial vasculature.

The nasal cavity is decongested with either 0.05% oxymetazoline spray or 1:100,000 epinephrine injected into the axilla of the middle turbinate, anterior nasoseptal mucosa, and the region of the sphenopalatine artery. A bilateral inferior and middle turbinates are infiltrated with epinephrine-containing anesthetic to further promote hemostasis. Both inferior turbinates and the left middle turbine are lateralized bluntly, taking care not to lacerate their mucosa. The right middle turbinate is medialized to expose its attachment and then removed to permit adequate room for both the nasal endoscope and a suction tip throughout the case. This is done in an anterior-to-posterior fashion with scissors using multiple cuts at the attachment, with the scissors oriented parallel with the nasal floor (spreading laterally when opened) with downward pressure on the turbinate in between cuts to facilitate hemostasis and to avoid creating an inadvertent skull base defect. Next, the uncinate process is removed, revealing the natural ostium of the maxillary sinus and maximizing the view of the prominent ethmoid bulla, which is resected with a microdebrider, revealing the lamina papyracea laterally. The microdebrider is then used to remove as much of the anterior and posterior ethmoid air cells as is necessary to gain unimpeded access to the sphenoid sinus. The lamina papyracea serves as the lateral limit for resection of the ethmoid air cells to maximize the space available in the sinonasal corridor. In anticipation of working in the posterior fossa subdural space, a nasoseptal mucosal flap pedicled on the posterior nasoseptal artery (a branch of the sphenopalatine artery) is harvested at this point using needle-tip electrocautery along the superior and inferior borders of the sphenoid face, extending anteriorly along the nasal septum 1 to 2 cm below the anterior skull base superiorly (to preserve olfaction) and roughly at the junction of the nasal septum and nasal floor.1 Although it is possible to extend the lateral border of the inferior incision to include the inferior turbinate mucosa, it is rarely necessary or advantageous to do so. Anteriorly, the inferior and superior incisions are joined with an incision parallel to the columella just proximal to the mucosal–epidermal junction. The flap is elevated from the nasal septum using a ball-tip probe in an anterior-to-posterior fashion, taking care not to perforate the flap or compromise its proximal blood supply, and then it is stored in the choana for the duration of the case to prevent accidental blunt injury or entanglement with a spinning drill. The synostosis of the vomer and the sphenoid rostrum is identified and bluntly disarticulated, and 1 to 2 cm of the bony septum is removed using a back-biting rongeur to facilitate bimanual surgery through both nares as well as to permit a mucosal “reverse” flap to cover the denuded nasal septum to avoid postoperative crusting on it. To create the reverse flap, a vertical incision in the coronal plane of the rostrum is made in the contralateral mucosa, and horizontal incisions are made 1 cm caudal to the skull base and at the level of the nasal floor. This randomly vascularized flap is then pulled forward to cover the contralateral (typically right-sided) denuded donor septum, fixed in place with absorbable suture, and protected with a silicone splint to prevent inadvertent injury from subsequent instrument passage.

19.2.2 Sphenoid Preparation

The sphenoid ostia are visible posterolaterally to the rostrum. These can be substantially widened bluntly with a Cottle dissector and then expanded using a Kerrison rongeur once the surgeon has visualized the roof and lateral walls of the sinus. The rostrum is then resected entirely, completing a wide anterior sphenoidotomy, which provides the essential freedom of movement for subsequent bimanual dissection as well as placement of an angled endoscope, if necessary, along the sphenoid sinus floor. The intrasinus septae are visualized ( Fig. 19.1 ) and carefully drilled (not cracked, as they nearly always terminate on an internal carotid artery [ICA])2 until flush with the posterior aspect of the sinus. At this point, the critical anatomic landmarks of the posterior sphenoid sinus are identified: the clivus, the paraclival carotid arteries, the anterior sellar face, the medial and lateral opticocarotid recesses, the tuberculum sellae, and the parasellar carotid protuberances ( Fig. 19.2 ).

The anterior sellar bone is thinned with a 3- or 4-mm-diameter coarse diamond drill and extended outward over the tuberculum sellae to include the planum anterosuperiorly, the medial cavernous sinuses laterally, and the inferior intercavernous sinus (IIS) and sellar floor inferiorly. The thinned bone is then flaked off bluntly from the sellar face and smoothed with a Kerrison rongeur laterally, ensuring the parasellar dura and ICAs are not injured in doing so. With adequate thinning, the sellar floor can usually be fractured off with gentle downward pressure applied with a Cottle dissector below the sellar dura. Superiorly, an adequately thinned tuberculum can also be removed bluntly. After bone removal, one should see the four blues around the sella: bilateral cavernous sinuses, the superior intercavernous sinus (SIS), and the IIS confirming an adequate exposure.

19.2.3 Intradural Preparation and Pituitary Transposition

The anterior sellar dura is incised carefully with a feather blade knife, ensuring the underlying pituitary gland is not injured. It is especially important to maintain the integrity of the gland′s capsule, as inadvertent injury greatly increases the difficulty of defining the plane between the gland and the sellar dura, leading to glandular injury ( Fig. 19.3 ). Next, the dura of the tuberculum sellae is incised, ensuring that the underlying prechiasmatic cistern arachnoid is not initially violated ( Fig. 19.4 ). Between the sellar dura and the tuberculum dura, the SIS is now isolated and ligated after coagulation with bipolar electrocautery or thrombosis induced by hemostatic agents ( Fig. 19.5 ). The incision is carried laterally just below the SIS and at the level of the IIS as well, to view the entire anterior aspect of the pituitary gland from the diaphragma to the sellar floor. Laterally, small fibrous attachments tether the pituitary gland to the medial cavernous sinus dural walls ( Fig. 19.6 ). These “pituitary ligaments” must be released, usually by sharp dissection, to significantly reposition the gland.3 Although the gland is detached from the medial cavernous sinus wall, it should still be left attached to the posterior sellar dura to maintain venous drainage. The IIS is transected laterally in the transition between the floor of the sella and the medial cavernous sinus wall. As the gland is detached laterally, it “rolls” superiorly even with the posterior attachment preserved. Additionally, the incision in the inferolateral aspect of the sellar floor should stop posteriorly at the entry point of the inferior hypophyseal arteries, which arise from the intracavernous meningohypophyseal trunk and traverse the dura of the medial cavernous sinus wall ( Fig. 19.7 ). At the same level of the entrance of the inferior hypophyseal artery, there is a significant point of glandular venous drainage, which is conserved once the artery is preserved. Preserving the artery and venous drainage seems to correlate with less incidence of diabetes insipidus. The final preparatory step involves identifying the anterior fold of dura mater that forms the sellar roof, termed the diaphragma sellae or central aperture. Having incised the dura above and below this structure, it is possible to incise it from anteriorly to posteriorly up to the pituitary stalk, taking care not to violate the prechiasmatic cistern arachnoid superiorly and the pituitary stalk or superior hypophyseal arteries. Once complete, the pituitary gland is entirely free to transpose superiorly into the suprasellar space. It is important to understand that this description is a variation to the technique previously described.3 Specifically, the preservation of the posterior dura still attached to the gland and the respective posterior intercavernous sinus allows for a physiologic preservation of the gland with appropriate venous drainage. The drawback of this technique is the fact that the gland may be pulled down by the posterior dural attachment, and glue or constant superior retraction may be necessary.