Chapter 12 Endoscopic Sellar Approach
Introduction
The transsphenoidal route has been used for a century for the resection of pituitary and other sellar tumors.1,2 For the past two decades,3 the advent of the purely endoscopic endonasal approach introduced the advantages of a more direct, minimally invasive modality in performing surgery for lesions within this area.4–6 This technique is rapidly becoming the standard of care for pituitary tumors. Indeed, surgery of the sellar region has always been a challenge due to the complex anatomy of this area, the important neurovascular structures around the sella, that is, the optic chiasm and nerves, the pituitary stalk, the superior and inferior hypophyseal arteries, the parasellar segment of internal carotid artery, and the ophthalmic artery.
The nasal cavities can be considered the natural corridor toward different regions of the skull base and the use of endoscopes allows for an effective and safe visualization of the operative field ( Fig. 12.1 ).
From a practical perspective, the anatomic knowledge of the sellar region is essential for the safe conduct of surgical procedures in this area. The aim of this chapter is to describe the anatomy of the endonasal approach to the sellar area, highlighting the key points of the surgical approach and the main anatomic landmarks.
12.1 Indications
The purely endoscopic endonasal approach provides minimally invasive access to sellar region. A soft consistency of the lesions is also an important consideration in the surgical strategy to remove tumors in this area. The main contraindications are lesions with prevalent lateral, posterior, and superior localization to the sella.
It is indicated for the surgical management of the following:
Pituitary tumors:
Macroadenomas.
Microadenomas.
Secreting.
Nonsecreting.
Rathke′s cleft cysts.
Selected sellar meningiomas.
Arachnoid cysts.
Metastatic tumors.
Cerebrospinal fluid (CSF) leaks within the sellar area.
12.2 General Anatomic Considerations
The sellar region lies within the center of middle cranial fossa and is occupied by major neurovascular and endocrinological structures: internal carotid artery, cavernous sinuses, optic nerves and optic chiasm, and pituitary gland and stalk. More detailed description of the anatomy is presented elsewhere in the book. For a minimally invasive approach, it is important to obtain an anatomic orientation with optimal knowledge of the mucosal, bony, and neurovascular landmarks.7 In the nasal cavity, these landmarks are nasal septum, choana, inferior turbinate, middle turbinate, sphenoethmoid recess, sphenoid ostium, and sphenopalatine foramen ( Figs. 12.2–12.4 ). The sphenoid sinus offers a wide range of pneumatization models and septations.8 Important landmarks within the sphenoid sinus are sellar floor, bony prominences of the intracavernous carotid artery (ICA), the optic nerve, and opticocarotid recess (OCR) ( Figs. 12.5 and 12.6 ).
12.3 Surgical Steps
12.3.1 Patient Positioning
The patients is operated on general anesthesia and orotracheal intubation, in supine position with the head fixed in a standard Mayfield three-pin holder, slightly flexed and turned 10 degrees toward the surgeon. Flexion or extension of the head is really important for the approach trajectory, as a minimal change of the head position could lead to an important modification of trajectory and thus disorientation.
12.3.2 Ergonomics
Most important thing to consider is comfortable position with direct sight to the video screen for the surgeon, the assistant, and the scrub nurse. Depending on the technique used, surgeons can stand on one side or both side of patients’ head, with the main surgeon on the right side (if right-handed) and a scrub nurse opposite.
12.3.3 Instrumentation
Visualization is achieved by 0-, 30-, and 45-degree rigid endoscope (18 cm in length, 4 mm in diameter) and a high-definition video equipment.9 The 0-degree lens reduces the risk of disorientation, but the instruments remain in the periphery of the field of vision. With 30-degree endoscopes, there is better control of the instruments and a wider angle of view.10 Using an irrigation provides a clear image without the constant need of removal and cleaning the tip of the lens. High-speed drill, various dissectors, forceps, scissors, and suctions are available. Bipolar and hemostatic materials (such as the thrombin hemostatic matrixes and thrombin-soaked gelatin sponges) need to be available. In cases with complex tumors invading the para-, supra-, and retrosellar regions, a neuronavigation system is recommended. The micro-Doppler probe is crucial for localizing the carotid arteries in selected cases.
12.3.4 Preparation
Cottonoids soaked in a special antiseptic preparation with 50% diluted povidone-iodine solution are applied within the nasal cavity. The mucosa is prepared with adrenaline (1:10,000)/lidocaine (1:20) or xylometazoline hydrochloride–soaked Cottonoids, placed for at least 5 minutes in the space between the septum and the turbinates, to gain maximum vasoconstrictor effect and control the mucosal bleeding.
12.4 Neuroimaging Techniques for Planning
The advent of 3D computer-generated models provides accurate patient-specific 3D reconstructions from neuroimaging data and virtual reality devices, improving training in endoscopic neurosurgery. Our group has developed computational models for educational purposes applied to the transsphenoidal perspective, guiding the acquisition of specific visual information for endoscopic approaches to the skull base.11–13
Preoperative neuroimaging studies were mainly developed using the Dextroscope (Volume Interactions Pte. Ltd) and Osirix, (OsiriX open-source imaging software; Version 5.8.1; free download from http://www.osirix-viewer.com/) ( Fig. 12.7 ).
12.5 General Surgical Principles for Endoscopic Endonasal Transsphenoidal Approach
Midline is safe. Check on the preoperative images for reliability of midline structures, such as nasal septum and intersphenoidal septum, that could have anatomic variations and deviate from midline; intraoperatively, the floor of each choana can be very useful to check the midline orientation.
The surgeon should have the optimal surgical freedom required for the approach.14,15 To gain comfortable working space, sufficient bone (i.e., the sphenoid prow) should be removed, providing optimal movement for the endoscope and instrument within the nasal cavities.
Movements should be gentle and under constant endoscopic control. Minimal surgical trauma to the mucosa decreases bleeding and the need for nasal packing, shortening the wound healing time and decreasing postoperative adhesions, crusting, and postsurgical septal perforations.16
Bipolar is used for small arterial bleeding (i.e., the sphenopalatine artery and its branches). Alternative hemostatic materials should always be available, particularly for venous bleeding.
12.6 Surgical Steps
Approach could be roughly divided into the following phases: nasal, sphenoidal, and sellar
12.6.1 The Nasal Phase
A better exposure is gained using the binostril approach (being more comfortable two-surgeon with the four-handed technique).16–18 Introducing the endoscope in the nasal cavity, the first structure at sight is the inferior turbinate followed superiorly by the middle turbinate ( Figs. 12.2 and 12.3 ). The approach is followed by mobilization of the middle turbinate laterally to widen the surgical space and gain access to posterior portion of nasal cavity ( Fig. 12.4 ). The next step is the identification of the sphenoid ostium. The sphenoethmoid recess is an important landmark to localize the sphenoid ostium located approximately 1.5 cm above the choana ( Fig. 12.4a ). Bleeding during this part of the approach is usually from the mucosa.
More space for the approach can be obtained by a gentle out-fracture of the middle turbinate. Concerning the binostril approach, some authors describe removal of right middle turbinate and lateralization of the left.19 However, this is unnecessary in the majority of cases. The next step is debriding the mucosa around the sphenoid ostium, starting the incision in the posterior part of nasal septum. In doing this, one should always take care not to go cranially to the superior turbinate and injure olfaction.
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