9 Expanded Endoscopic Endonasal Approaches to the Sellar and Parasellar Regions
Abstract
The sellar and parasellar regions are anatomical areas that include critical neurovascular structures that reside in close relationships with each other such as the internal carotid artery (ICA), the anterior communicating artery complex, the cavernous sinus (CS), the pituitary gland, and the optic nerves. The nasal cavity offers straightforward surgical access to these structures located near the anterior, middle, and posterior cranial fossa. This corridor had been thoroughly studied since its first use in the last century, until the endoscopic endonasal approach as we know it nowadays. Here we describe the endoscopic anatomical features followed by the surgical approaches to the sellar and parasellar regions, which are divided into three modules: the anterior, middle, and posterior. The anterior module includes the planum sphenoidale and the tuberculum sellae (TS); the middle is formed by the sellar and parasellar regions; and the posterior is formed by the clival region on its middle and superior third, lying immediately inferior and behind the sella turcica (ST), respectively. Surgical pearls, key anatomical landmarks, surgical instrumentation, positioning, and most frequent surgical morbidity and complications of each module are discussed. Finally, we describe two clinical cases to further illustrate the contents of this chapter.
Keywords: Keywords: endoscopic anatomy, expanded endoscopic endonasal approach, parasellar region, sellar region, skull base
9.1 Introduction
The sellar and parasellar regions are anatomical areas that include bony, vascular, nervous, brain tissue, and glandular structures that reside in close relationships with each other. The nasal cavity offers straightforward surgical access to anatomical structures located at the anterior, middle, and posterior cranial fossa. This surgical corridor was first described by Schloffer in 19071 as the “transsphenoidal approach” and has been studied and used since the second half of the past century through the appearance of microscopic surgery and later through the endoscopic endonasal techniques.2 The current technology (preoperative neuroimaging, transoperative image guidance, surgical equipment, etc.) and detailed understanding of this area not only make the endoscopic endonasal approach (EEA) a possibility to treat multiple lesions and tumors located within these regions, but also a challenge for even the most experienced surgeons due to its complex nature.3 Multiple techniques have been developed to preserve the pituitary gland function during the neurovascular dissection and tumor resection, to safely expose the cavernous sinus (CS) and the internal carotid artery (ICA), and to reconstruct large skull base defects, etc., therefore redefining the EEA as we know it nowadays.1 , 4 , 5 , 6 , 7
9.2 Endoscopic Anatomy of the Sellar and Parasellar Regions
9.2.1 Anterior Skull Base
Visualization of the anterior skull base structures located at the roof of the nasal cavity requires resection of the superior portion of the nasal septum (perpendicular plate of ethmoid), the anterior and posterior ethmoidal cells, and middle turbinates to expose the medial wall of the orbits (lamina papyracea) from both sides, leaving in between the frontal recess and the cribriform plate.8 , 9 After the surgical corridor is expanded, the anterior skull base ends up resembling a rectangular structure with the medial wall of both orbits as the lateral limits, the planum sphenoidale as the posterior limit, and the frontal recesses as the anterior limit.10
The midline portion of the anterior skull base is formed by the vertical portion of the ethmoid bone, which continues intracranially as the crista galli and constitutes the base of the perpendicular lamina toward the nasal cavity. Lateral to the midline we find the cribriform plates, where the olfactory fibers enter the nasal cavity, and further lateral the frontoethmoidal sutures.3 , 10
The vascular supply of most portions of bone and dura of the anterior skull base is provided by the anterior and posterior ethmoidal arteries, which arise from the internal carotid circulation (ophthalmic artery). The posterior ethmoidal artery is located 10 to 17 mm posterior to the anterior ethmoidal artery and 8 to 16 mm anterior to the optic canal and is the anterior limit of the planum sphenoidale.8
9.2.2 Sellar and Parasellar Regions
The sellar and parasellar regions, which are contained inside the sphenoid sinus (SS), within and adjacent to the sella turcica (ST), are in close relationship to critical neurovascular structures such as the ICA, the CS, the pituitary gland, and the optic nerves. The EEA through the SS provides wide exposure to all these structures (Fig. 9.1).9
Fig. 9.1 Anatomic cadaveric dissections of the expanded endonasal endoscopic approach (EEEA). (a) Nasal phase. Relationships between the sphenoid ostium, the sphenoid rostrum, and the vascular pedicle of the septal mucosa are illustrated. In this specimen, a right nasoseptal flap was harvested. (b) Sphenoid phase. Wide removal of the sphenoid rostrum exposes the sellar and parasellar regions, including the planum sphenoidale, tuberculum sellae (TS), sella turcica (ST), and clival recess as midline landmarks. Medial opticocarotid recess (OCR) (*) lies underneath, medial and lateral to the optic nerve prominence, internal carotid artery (ICA) prominence, and ST, respectively. Lateral OCR (**) lies beneath the optic nerve prominence but lateral to the ICA. In this specimen, a left nasoseptal flap was harvested. (c) After bone drilling, complete exposure of the dura of the sellar and parasellar regions is achieved. Intercavernous sinus lies under the TS and above the pituitary gland, and the anterior wall of the cavernous sinus (CS), paraclinoid, and parasellar ICA lies under the ICA prominence. Medial OCR (*), lateral OCR (**), and the middle clinoid process dural indentation (***) are shown. Clival recess is located superficially to the middle third of the clivus dura. (d) After opening the anterior wall of the CS, the inferior, superior, posterior, and lateral compartments (blue latex) can be identified in close relationship with the parasellar and paraclival ICA. Basilar plexus is identified in between both layers of the clivus dura.
Once the SS is exposed after removing the rostrum sphenoidale, the extracranial aspect of the floor of the ST forms the most prominent landmark in the midline. This landmark is limited superiorly by the tuberculum sellae (TS), laterally by the ICA prominences, and inferiorly by the clival recess ( Fig. 9.1b).3 , 10 Depending on the pneumatization of the sinus, the planum sphenoidale can be easily identified anterior to the TS in the roof of the SS.11 The middle clinoid processes are located lateral to the ST. These bony prominences arise from the anterior third of the floor of the ST and are found in roughly 50% of cadaveric specimens. They project upward and laterally toward the anterior clinoid processes on each side ( Fig. 9.1c).12 , 13 Their identification relies on the degree of pneumatization of the SS.3
At each side of the TS, the extracranial impression of the optic canals can be identified. Medial and inferior to the optic nerve prominences, medial to the paraclinoid ICA, and superior to the ST, the medial opticocarotid recess (OCR) can be seen as small bone excavations that resemble a drop-like shape.13 The lateral OCR, which corresponds with the optic strut intracranially, is located lateral to the medial OCR and the paraclinoid ICA prominence, and inferior to the optic canal, and is often pneumatized ( Fig. 9.1b, c).8 , 11 In the lateral portion of the SS a flat osseous lamina constitutes the anterior wall of the CS and below it the anterior genu of the cavernous ICA (parasellar ICA).14
From an endoscopic perspective, the clinoid segment of the ICA (paraclinoid ICA) can also be exposed. This segment is limited superiorly by the distal dural ring (DDR) and inferiorly by the proximal dural ring (PDR). The PDR is formed by the carotidoculomotor membrane in the lateral aspect of the ICA and by the carotidoclinoid ligament on its medial aspect. The latter attaches to the middle clinoid process. Similarly, the DDR serves as a division between the intradural and extradural ICA. The PDR has continuity with the CS roof on its lateral aspect and with the TS dura on its posteromedial aspect.15
Due to the clinical relevance during endoscopic procedures, and the differences in the surgical view of the CS between the endoscopic perspective and the traditional microscopic descriptions, the CS can be divided into compartments depending on their relationship with the ICA: superior, posterior, inferior, and lateral compartments ( Fig. 9.1d)14:
●Posterior compartment: It is limited posteriorly by the petroclival dura and anteriorly by the short vertical subsegment and the posterior genu of the cavernous ICA. This compartment contains the meningohypophyseal trunk and the intradural segment of the abducens nerve.
●Superior compartment: It is enclosed inferiorly by the horizontal subsegment of the cavernous ICA, anteriorly by the anterior genu of the ICA, superiorly by the roof and posterolateral wall of the CS, and anterolaterally by the ventral surface of the paraclinoid ICA. It contains the oculomotor nerve as it enters the roof of the CS.
●Inferior compartment: It is bounded superiorly by the horizontal subsegment of cavernous ICA and its anterior genu, posteriorly by the vertical subsegment of the ICA, and anteriorly by the anterior wall of the CS. In this compartment, we find the sympathetic plexus and the distal cavernous segment of the abducens nerve.
●Lateral compartment: It is enclosed medially by the horizontal subsegment of the cavernous ICA and its anterior genu, superiorly by the PDR, and inferiorly by the maxillary strut. This compartment contains the oculomotor and trochlear nerves and the first branch of the trigeminal nerve.
9.2.3 Clival Region and Posterior Skull Base
Immediately inferior to the ST, depending on the degree of pneumatization of the SS, a bony excavation called the clival recess can be identified. This is related intracranially to the upper third of the clivus, which includes the dorsum sellae located superiorly and the posterior clinoid processes superolaterally.16 , 17 This recess can be delimited by the two paraclival ICAs, which are normally separated by 20 mm, measured at the level of the foramen lacerum ( Fig. 9.1c, d).16 , 18 On the contrary, the lower third of the clivus, located at the posterior wall of the nasopharynx, is located outside the SS cavity. An osseous prominence called the pharyngeal tubercle is located at the midline and serves as a consistent landmark with important proximity to the foramen magnum and hypoglossal canal.18
Fig. 9.2 Transoperative photographs of an endoscopic endonasal approach (EEA) to the sellar region. (a) In the nasal phase the endoscope is inserted into the nasal cavity and the inferior, middle, and superior turbinates laterally, the nasal septum medially, and the choana posteroinferiorly are identified. (b) The sphenoid ostium is used as the landmark to identify the superolateral limits of the sphenoid rostrum. Then the mucosa is dissected avoiding damage to the vascular pedicle and the sphenoid rostrum is removed using Kerrison rongeurs and high-speed drills to access the sphenoid sinus (SS). (c) In the sphenoidal phase, the osseous landmarks are identified—the sella turcica (ST) in the central part, the optic nerve prominence is superolateral, and below are the internal carotid artery (ICA) prominence bilaterally. Medial and lateral between those structures are the medial and lateral opticocarotid recess (OCR), respectively. Careful drilling of the sellar region exposes the outer (periosteal) dura, sometimes enlarged for tumoral lesion (*). (d) Once the tumor is removed, the pituitary fossa limits are exposed—laterally is the medial wall of the cavernous sinus (CS), superolaterally are the sellar diaphragm and the arachnoid of the suprasellar cistern, and the deeper part is the dorsum sellae. (e) In some cases, after the tumor resection, the arachnoid of the suprasellar cistern descends and protrudes through the dural defect and is in contact with the sellar floor.
9.3 Surgical Technique, Technical Nuances, and Complications
9.3.1 Trans-sellar Approach
Surgical Technique
In the operative room, the patient is positioned supine with the head tilted toward the surgeon with the trunk elevated by approximately 20 degrees to aid venous return. The position of the patient’s head is usually in a neutral position when our target is located within the pituitary fossa, but it can be slightly extended (10–30 degrees) for the pathology of the anterior skull base or slightly flexed (20–40 degrees) for that of the clival region and below. It is recommended to administer perioperative steroids depending on hormonal function (100 mg hydrocortisone) and a single dose of broad-spectrum antibiotics (e.g., cefuroxime or ceftriaxone). The patient is sedated under general anesthesia and the next step is the nasal preparation. Usually, a topical nasal decongestant is employed (e.g., oxymetazoline). It is important to consider preparing the abdominal wall and outer thigh in an antiseptic manner since abdominal fat and fascial graft may be used for reconstruction.19 , 20 The scrub nurse is positioned on the patient’s left side, the surgeon stands on the patient’s right side, and the anesthesiologist remains at the patient’s feet. An assistant stands on the left of the surgeon to direct the endoscope, allowing the primary operator to use a bimanual technique for tumor resection.
The EEA to the sellar and parasellar regions is divided into four phases: nasal, sphenoidal, sellar/parasellar, and closure.
●Nasal phase: The goal of this phase is to reach the SS via the sphenoid ostia and a posterior nasal septectomy. The technique begins with the insertion of a 0-degree endoscope into one nostril to identify the inferior turbinate laterally, the nasal septum medially, and the choana posteroinferiorly ( Fig. 9.2a).21 The middle and superior turbinates, which are landmarks to the sphenoid ostium, are lateralized with blunt pressure, avoiding excessive mucosal injury, or can be removed unilaterally to increase the width of the exposure in case more lateral access in the CS is needed. The sphenoid ostium is identified 1.5 cm above the choana ( Fig. 9.1a). The mucosa at the rostrum is incised and dissected away, preserving the irrigation the nasoseptal flap in the case it is needed.22 The placement of the remaining mucosal incisions depends on anticipated closure needs and whether a nasoseptal flap will be required for skull base closure. The flap can be harvested at the beginning of the procedure, or after tumor resection in case a cerebrospinal fluid (CSF) leak is identified as described elsewhere,23 and should be tucked into the nasopharynx for protection during the operation.24 Once the bony rostrum is exposed, the nasal septum and vomer are detached from the rostrum with a dissector.19 About 1.0 to 1.5 cm of the posterior nasal septum is removed for simultaneous access to the SS through both nasal nostrils. A Kerrison rongeur or a reverse cutting forceps is used to this end.25 The anterior septum incision can be made until the junction of the bony and cartilaginous septum and carried inferiorly and posteriorly according to the surgeon’s needs.
●Sphenoidal phase: The whole anterior wall of the sphenoidal sinus is enlarged circumferentially, taking care not to enlarge the sphenoidotomy too much in the inferolateral direction, where the sphenopalatine artery and its major branches lie.12 In case inferolateral access within the SS is intended, the flap should be harvested in the contralateral side to prevent injury to its vascular supply. The sphenoid rostrum is removed using Kerrison rongeurs and high-speed drills ( Fig. 9.2b). The key factor determining the difficulty in exposing the pituitary fossa within the SS is the configuration of the sinus cavity in terms of “sellar,” “pre-sellar,” and “conchal” variants. In a pre-sellar or conchal SS, bone is removed through careful drilling; neuronavigation can be helpful in these cases. Mucosa within the SS is removed to reduce the risk of postoperative mucocele.26 The septations are removed always being aware that 20% of septations lead to a cavernous carotid protuberance.21 It is important to identify all the anatomical landmarks described above to orient the surgical procedure.20
●Sellar phase: As the sellar floor can be thin and partially dehiscent because of chronic remodeling by a large intrasellar mass, a 4-mm diamond burr is preferred to make an initial opening of the pituitary fossa dura to verify the midline. The bony window is widened with a Kerrison punch or further drilling to expose the planum above, the clival recess below, and the anterior wall of the CS laterally ( Fig. 9.2c).21 The durotomy is usually carried out with a sickle or retractable knife in a cruciate fashion, starting in the middle and cautiously extending it with angled microscissors. Care should be taken to avoid CSF leak from an inadvertent opening of the arachnoid folding in the anterior recess.20
After the dura is opened and hemostasis achieved, exploration of the intrasellar mass depends on the nature of the pathologic process. For a large mass, such as macroadenomas, resection proceeds in a sequential manner. The inferior and lateral portions are removed first to allow the superior aspect to descend into the surgical field. If the superior portion is delivered first, diaphragmatic descent will obscure the operative field ( Fig. 9.2d, e). The sellar diaphragm can be sharply dissected and incised to access suprasellar tumors such as a craniopharyngioma, after coagulation and cutting of the superior intercavernous sinus (SIS) in case it is needed.21 Given that most adenomas are soft in consistency, tumor removal is usually performed with a variety of microdissectors, ring curettes (preferably blunt types), and suction cannulas. On the contrary, a tumor with a harder consistency may be removed with the aid of an ultrasonic aspirator. Careful exploration of the ST with the 0- or 30-degree endoscope to look for any residual tumor or small perforators of the sellar diaphragm that could result in CSF leaks is done after removal of the tumor.25
●Closure: A variety of reconstruction methods and graft materials are available for the surgeon. In case of a CSF leak, the gasket seal method can be used by placing a piece of harvested fascia lata or allograft dural substitute over the bony defect so that its dimensions exceed that of the defect by at least 1 cm circumferentially. A rigid implant cut to fit the opening is then placed over the fascia lata and counter-sunk within the bony defect. An alternative approach involves a multilayer reconstruction placing layers in apposition to one another, the first being an inlay dural substitute, followed by an onlay fascia lata graft, thereby potentially obviating the need for a rigid buttress.27 The nasoseptal flap is then placed over the preferred method of initial closure so that the flap is in direct contact with the surrounding bony skull base and is subsequently held in place with fibrin glue or an inflated Foley catheter balloon for 3 to 5 days (Fig. 9.3).20 After surgery, the patient is taken to the intensive care unit, where stress-dose steroids are continued for 24 hours. The use of subarachnoid lumbar drainage is controversial. Although some surgeons delay initiation of lumbar drainage for 4 to 6 hours following the procedure so as to avoid overdrainage of CSF, others keep the drain open right away during extubation and transport so that increases in intra-abdominal pressure are less likely to dislodge the closure construct.26 A prospective, randomized controlled trial showed that a lumbar drainage after an EEA reduces postoperative CSF leaks in approaches with large dural defects associated with anterior and posterior fossa pathologies.28 In cases with no evident CSF leak, a free mucosal graft from the middle turbinate or nasal floor, or the harvested nasoseptal flap, can be placed alone over the surgical cavity and held in place with absorbable nasal packing.29
