Summary
Sellar region tumors, though diverse in pathology, most frequently present as tumors of adenohypophyseal origin. Detailed history, physical examination, and biochemical and radiographic work-up are necessary to confirm diagnosis. Although various surgical approaches can be used to access the sella, the endoscopic endonasal transsphenoidal approach has gained significant popularity within the past two decades, starting in the 1990s. Here we detail the technical nuances and anatomical knowledge necessary for complication avoidance and successful surgery.
22 The Evaluation and Management of Sellar Tumors
22.1 Introduction
The sella turcica is a small saddle-shaped indentation in the posterior aspect of the sphenoid bone that houses the pituitary gland. Sellar tumors of both pituitary and nonpituitary origin may cause endocrinopathy and/or neurologic deficit secondary to mass effect. Although initial attempts at sellar tumor surgery in the late 1800s were via transcranial approaches, luminaries in neurosurgery such as Cushing1 and Hardy2 adopted the transsphenoidal approach at the beginning of the 20th century. After being abandoned in the 1920s, the approach became popular again in the 1970s and again recently in the 1990s with the introduction of endoscopic endonasal transsphenoidal (EETS) approaches.3
22.2 Surgical Anatomy
Sellar tumors are most often accessed via a transsphenoidal approach. Accordingly, knowledge of extracranial structures such as the nasal cavity and sphenoid sinus, as well as of the sellar and parasellar regions, is essential for successful surgery.
22.2.1 Nasal Cavity
In the sagittal orientation, the nasal septum, which comprises the perpendicular plate of the ethmoid along with the vomer, divides the nasal cavity in half. From the lateral walls of the nasal cavity arise the superior, middle, and inferior turbinates. At the posterior end of the nasal cavity, the inferior turbinate marks the location of the choana, an aperture that demarcates the transition from nasal cavity to nasopharynx. Approximately 1.5 cm superior to the choana, at the level of the inferior third of the superior turbinate within the sphenoethmoidal recess, is the sphenoid os, the passageway from the nasal cavity to the sphenoid sinus.
22.2.2 Sphenoid Sinus
The sphenoid sinus can be classified into one of three classes based on the degree of pneumatization: conchal, presellar, and sellar. Conchal sphenoid sinuses, though rare in the adult population, are the most common type in the pediatric population and are characterized by lack of pneumatization—that is, a solid block of bone. Approximately 25% of adult sphenoid sinuses are presellar, the other 75% sellar. Presellar sphenoid sinuses denote a sinus in which the air cavity does not extend beyond the anterior border of the sellar wall. Sellar sphenoid sinuses have air that extends below the sella and as far back as the clivus.4
Knowledge of the sphenoid type allows the surgeon to anticipate what degree of bony removal is necessary for the anterior sphenoidotomy. After this, the sphenoid septae should be visible. Although the major sphenoid septum may occasionally mark midline, studies have shown that it more often does not and can be up to 8 mm off midline.4 A more consistent marker of midline is the sphenoidal rostrum. Other bony landmarks that can orient the surgeon to midline include the carotid protuberances and the opticocarotid recesses. The lateral opticocarotid recesses represents the space between the carotid and optic protuberances. These protuberances mark the location of the cavernous internal carotid artery (ICA) and optic nerves. The midpoint between either the carotid protuberances or opticocarotid recesses will also serve as a marker of midline. Structures inferior to the sella include the clivus and clival recess; superior to the anterior wall of the sella are the tuberculum sellae and planum sphenoidale (Fig. 22.1).
22.2.3 Sellar and Parasellar Regions
Anterior to the sella are the tuberculum sella and the chiasmatic groove. The posterior limits of the sella are demarcated by the dorsum sellae, which transitions laterally into the posterior clinoid processes and posteriorly as the clivus. The sella itself contains the pituitary gland, whose anterior and posterior lobe correspond to the adenohypophysis and neurohypophysis, respectively. The pituitary stalk descends from the hypothalamus to the pituitary through a small opening in the diaphragma, a small dural fold that serves as the roof of the sella. Lateral to the sella is the cavernous sinus, within which runs the cavernous ICA. Here the ICA gives off the meningohypophyseal trunk and capsular artery of McConnell, which supply the neurohypophysis (via a branch off the meningohypophyseal trunk, the inferior hypophyseal artery) along with the capsule of the pituitary and dura of the anterior wall and floor of the sella. The adenohypophysis derives its blood supply from the hypophyseal portal system, a plexus of capillaries that ultimately derives its origin from the superior hypophyseal artery, a branch off the ICA after it leaves the cavernous sinus. The cavernous sinus also contains the oculomotor nerve, the trochlear nerve, the ophthalmic and maxillary divisions of the trigeminal nerve, and the abducens nerve. The abducens nerve, unlike the other nerves, is not within the lateral wall but rather is in close association with the cavernous ICA.
Superior to the sella are the suprasellar cistern. The suprasellar cistern contains the optic chiasm along with additional structures which we list. Superior to the optic chiasm lie the anterior cerebral arteries, anterior communicating artery, lamina terminalis, and third ventricle. Sellar tumors that have significant suprasellar extension, in addition to causing visual disturbances secondary to optic chiasm compression, may encase the anterior cerebral arteries or cause hydrocephalus if sufficient tumor invades the third ventricle.
22.3 Regional Pathology and Differential Diagnosis
22.3.1 Tumors of Pituitary Origin
Pituitary adenomas comprise an estimated 14% of all brain tumors and trail only meningioma and glioma in prevalence5; they can be classified as either nonfunctioning or functioning adenomas. Nonfunctioning adenomas are the most common, comprising just over a third of pituitary adenomas.6 Although not themselves hormonally active, nonfunctional adenomas, particularly large macroadenomas, can compress normal pituitary tissue, leading to hormonal hyposecretion and hypopituitarism. Compressive effects on the pituitary stalk may also cause endocrinopathy in the form of hyperprolactinemia. Hormonally active adenomas, in order of prevalence, include prolactinoma, growth hormone (GH) adenoma, adrenocorticotropic hormone (ACTH) adenoma, postadrenalectomy ACTH adenoma, and thyroid stimulating hormone (TSH) adenoma. Gonadotropin adenomas, conversely, are typically hormonally silent, albeit very rarely hormonally active7; nonfunctioning adenomas frequently arise from gonadotrophs.
Pituitary carcinoma, unlike nonfunctional and functional adenomas, is a malignant process having a poor prognosis. Fortunately, pituitary carcinoma is rare, accounting for 0.1 to 0.2% of all pituitary tumors.8 Hallmarks of pituitary carcinoma include spread throughout the central nervous system (CNS) as well as sites external to the CNS, such as the liver, ovaries, and bone. Most pituitary carcinomas are hormonally active, producing either ACTH or prolactin.
Neurohypophyseal tumors are also quite rare and can include granular cell tumors or gliomas. Granular cell tumors typically afflict women in the fourth or fifth decade of life but are neurochemically silent and rarely grow large enough to exert mass effect.9 Interspersed among the axons of the neurohypophysis are glial cells, referred to as pituicytes. Tumors of the pituicytes, known as pituicytomas, typically present with mass effect.10
22.3.2 Tumors of Nonpituitary Origin
Craniopharyngioma is a frequently cystic and locally aggressive lesion thought to arise from the rests of squamous epithelium from the embryological remnant of the craniopharyngeal duct.11 Among children who have sellar masses, craniopharyngioma is the most common diagnosis, accounting for 1.2 to 4% of all brain tumors.12 Although craniopharyngiomas may present at any age, they classically have a bimodal distribution, with a predilection for pediatric patients aged 5 to 14 years and adults aged 50 to 74 years.13 Among the two histological types of craniopharyngioma, the adamantinomatous type follows a bimodal distribution, whereas the papillary type is almost exclusively found in adults.14 Craniopharyngiomas have a propensity for suprasellar extension, with a majority of tumors (75%) having suprasellar origin alone with invasion of the third ventricle.15 Additional sellar tumors of nonpituitary origin can include germ cell tumors, gliomas of the optic apparatus or hypothalamus with inferior extension, meningioma, and chordoma.
22.3.3 Cyst, Hamartomas, and Malformations of the Sellar Region
Rathke’s cleft cysts are thought to arise from the embryologic remnant of Rathke’s pouch11 and classically have been thought to represent a separate entity from craniopharyngioma. Some have challenged this distinction, as multiple accounts of cystic tumors of indeterminate radiographic and histological features have been reported. These practitioners have advocated that Rathke’s cleft cyst and craniopharyngioma represent two spectrums of the same disease process.11 Nevertheless, recent studies have identified genetic mutations that are specific to papillary (BRAF V600E) and adamantinomatous (CTNNB1 encoding beta-catenin) craniopharyngiomas, supporting an immunohistochemical distinction between craniopharyngiomas and Rathke’s cleft cysts.16 Other cystic sellar lesions include arachnoid, epidermoid, and dermoid cysts. Epidermoid and dermoid cysts are composed of abnormal rests of surface ectoderm, with epidermoid cysts comprising epithelial cell debris, keratin and dermoid cysts of dermal elements such as hair follicles, and glands.
22.4 Clinical Assessment
Patients who have sellar tumors can present with endocrinopathy secondary to pituitary hypersecretion, hypopituitarism, or neurologic symptoms secondary to mass effect. Careful history and physical examination often strongly suggests a diagnosis, particularly in cases of endocrinopathy, in which many syndromes have classic clinical features. Nevertheless, laboratory and radiographic work-up help further establish diagnosis.
22.4.1 Pituitary Hypersecretion
Functioning adenomas include prolactinoma, GH adenoma, ACTH adenoma, and TSH adenoma. Each of these conditions will present with their own respective clinical symptoms—namely, galactorrhea/amenorrhea, acromegaly, or gigantism; Cushing’s disease; or secondary hyperthyroidism. Initial laboratory work-up for any of these conditions includes baseline measures of prolactin, GH, ACTH, luteinizing hormone, follicle stimulating hormone, TSH, free-T4, α-subunit, cortisol, IGF-1, testosterone, and estradiol. Aberrations in any of these tests may subsequently trigger provocative tests that stress the hypothalamic–pituitary–end organ axes.6
Prolactinoma
Classic manifestations of prolactinoma include galactorrhea and hypogonadism. Women, who present three times more often than men,17 typically present earlier in life with endocrinopathy. Men generally present later in life with symptoms attributable to mass effect.18 Prolactin levels > 200 ng/mL coupled with a pituitary adenoma confirmed on MRI establish a diagnosis of prolactinoma.18 Patients who have signs and symptoms of prolactinemia and who display lower-than-expected prolactin levels may suffer from the hook effect, in which excessively elevated levels of prolactin oversaturate the antibodies used in prolactin assays, leading to an artificially low result. For suspected cases of hook effect, a 1:100 sample dilution will lead to accurate results.19 Hyperprolactinemia is not exclusive to cases of prolactinoma, however. Sellar masses, regardless of hormonal function, can compress the pituitary stalk and release lactotrophs from tonic dopaminergic inhibition in what is termed the stalk effect. Hyperprolactinemia secondary to stalk effect, however, is generally mild to moderate, with levels < 94 ng/mL.20
GH Adenoma
Symptoms of GH adenoma depend on age of presentation. Prior to closure of the epiphyseal plate, GH adenomas present with gigantism, whereas after the closure of the epiphyseal plate, acromegaly prevails. Although signs of gigantism are often obvious at ultimate presentation, the progression of acromegaly is insidious, with an average time from symptom onset to diagnosis of 7 years.21 Symptoms can include coarsening of facial features, acral enlargement, headaches, carpal tunnel syndrome, hypertension, sleep apnea, cardiovascular disease, and diabetes.21 Although historical diagnostic metrics have relied on GH levels for diagnosis, recent guidelines do not support this. Rather, diagnosis of acromegaly rests on elevated levels of IGF-1 along with lack of GH suppression to < 0.4 μg/L after an oral glucose tolerance test.22
ACTH Adenoma
Hypersecretion from an ACTH adenoma leads to overproduction of cortisol from the adrenal glands and a clinical diagnosis of Cushing’s disease. Signs of Cushing’s disease can include central obesity, diabetes, hypertension, plethora, abdominal striae, osteoporosis, myopathy, and neuropsychiatric disturbances. Diagnosis of Cushing’s disease must first exclude hypercortisolemic states such as iatrogenic causes, ectopic ACTH lesions, and ACTH-independent lesions. First hypercortisolemia must be established, which can be done by measuring free cortisol in a 24-hour urine sample. With hypercortisolemia confirmed, serum ACTH level should be analyzed to distinguish between ACTH-dependent and ACTH-independent cases of hypercortisolemia. ACTH-dependent cases display elevated levels of ACTH, whereas ACTH-independent cases (e.g., an adrenal adenoma) in which cortisol is directly secreted would be expected to have low levels of ACTH secondary to feedback inhibition. The final step in diagnosis, distinguishing Cushing’s disease from ectopic ACTH conditions, remains perhaps the most challenging step. Provocative tests such as high-dose dexamethasone and corticotropin-releasing hormone stimulation tests can be performed to aid diagnosis. If testing remains inconclusive or conflicting, inferior petrosal sinus sampling (IPSS)23 can be pursued.
22.4.2 Hypopituitarism
Hypopituitarism may occur when a sellar mass compresses the anterior pituitary, leading to its impairment. The hormones of the anterior pituitary have differing susceptibilities to hyposecretion, with gonadotropins being the most sensitive, followed by TSH, GH, and ACTH.15 Consequently, hypopituitarism may present with diminished libido, infertility, fatigue, and/or hypothyroidism. Pituitary apoplexy due to hemorrhagic necrosis of a pituitary adenoma may present with acute features of hypopituitarism along with sudden-onset headache, meningismus, visual decline, and ophthalmoplegia.
22.4.3 Neurologic Symptoms Secondary to Mass Effect
Bitemporal hemianopsia may occur secondary to suprasellar extension of a sellar mass, leading to optic chiasm compression. Moreover, patients may also experience declines in acuity and, more rarely, ptosis and ophthalmoplegia secondary to lateral extension into the cavernous sinus. Baseline ophthalmologic evaluation, including assessment of acuity and fields, is recommended for patients who have preoperative visual complaints and/or chiasmal compression, as they may portend prognostic recovery of visual complaints after surgery while documenting any postoperative change.24 Beyond visual symptoms, suprasellar extension of sellar masses, particularly craniopharyngioma, may encroach on the hypothalamus and third ventricle, causing neurologic disturbance and hydrocephalus. Giant pituitary adenomas with lateral extension into the temporal lobes may additionally present with seizures.6
22.5 Diagnostic Imaging
Imaging of suspected sellar pathology begins with MRI unless contraindicated. Attention should be paid to the coronal and sagittal images, because the sella is best delineated in these planes. Basic work-up includes T1 pre- and postcontrast images along with T2 images. Further sequences can be performed, depending on the suspected pathology.
Pituitary adenomas are often slightly hypointense compared with the normal pituitary, which is isointense. Moreover, adenomas have delayed enhancement relative to the normal gland, which avidly enhances in a homogenous manner.25 Special consideration should be given to cases of suspected Cushing’s disease. Spoiled gradient recalled acquisition in the steady state sequences should be obtained in the work-up of Cushing’s disease due to its superior characterization of soft tissue contrasting and improved sensitivity compared with standard T1 postcontrast spin echo images, which may miss up to 40% of cases (Fig. 22.2).26 For macroadenomas, the cavernous sinuses should also be examined, because these tumors are frequently locally invasive. In such cases, the Knosp score, which is determined based on the macroadenoma’s relationship to the cavernous and supracavernous ICA, can be highly predictive of cavernous sinus invasion (Fig. 22.3).27
Other sellar tumors may have common imaging characteristics that can help narrow the differential diagnoses. Examples include sellar/parasellar meningioma (homogenous enhancement, dural tail, possible calcification), craniopharyngioma (solid/cystic components with calcification), Rathke’s cleft cyst (cystic structure with possible fluid/debris level), and arachnoid cyst (cystic mass with signal comparable to CSF without fluid restriction on diffusion weighted imaging).25
22.6 Preoperative Preparation
Any comorbid conditions, such as diabetes, hypertension, and cardiovascular disease, should be optimized prior to surgery. Attention should be paid to cases of Cushing’s disease and acromegaly, as the aforementioned conditions are frequently present. In patients who have hypopituitarism, proper hormonal replacement should be instituted prior to surgery. This is of utmost importance for hypocortisolemia, which if left untreated could result in an Addisonian crisis brought on by surgery.
22.7 Surgical Technique
Because our experience and expertise lie with the EETS approach, our discussion focuses on this approach (Video 22.1). Details regarding microscopic sublabial, microscopic endonasal, and transcranial approaches can be found elsewhere.28
22.7.1 Positioning
Patients are placed in a semirecumbent position with their right shoulder at the right upper corner of the operating table with the right arm tucked. A horseshoe headrest supports the head; we do not routinely use rigid fixation. The horseshoe headrest is then shifted left, moving the patient’s left ear toward the left shoulder. The operating table is then turned until the patient’s ears are parallel to the operating room walls. This moves the patient’s body and allows the surgeon to be positioned directly in front of the surgical field. The head of bed is then elevated to approximately 20° so that the nose bridge is parallel to the floor. Positioning the head in such a manner improves venous outflow and thereby decreases cavernous sinus bleeding. The bed height should be appropriately lowered to allow the surgeon to comfortably operate with elbows at 90° (Fig. 22.4).29
22.7.2 Nasal Preparation
We administer nasal oxymetazoline prior to induction and then again following induction and prior to positioning. After the patient is prepped, each nare is packed with three half-by-three patties soaked with oxymetazoline and left in place for 5 to 10 minutes. During this period, the patient is draped in the usual sterile manner. We customarily additionally prep and drape the abdomen for possible abdominal fat graft for sellar floor reconstruction. Patties are then removed from the nares, and the middle turbinates, nasal septum, and rostrum are instilled with 0.2% ropivacaine with 1:200,000 epinephrine, under direct visualization.
22.7.3 Soft Tissue Dissection
The 0° endoscope is used to inspect each nare; we prefer to pick the nare with more space for initial approach. If each nare is approximately equal, the right side is selected by convention. The inferior and middle turbinates are identified and then lateralized in succession with a Cottle instrument. With the turbinates lateralized, the inferior third to half of the superior turbinate is removed using a straight Thru-Cut sinus forceps. This maneuver should then allow identification of the sphenoid os. Once identified, the sphenoid os is enlarged superiorly and laterally. At the level of the sphenoid os, a rectangular incision is then made on the septal mucosa and using a soft tissue shaver the posterior 1.0 to 1.5 cm of the nasal septum is removed to complete the posterior septectomy. The same procedure is then performed in the other nare. Up until the posterior septectomy, the procedure is performed in a two-handed mononarial fashion. The posterior septectomy allows additional instruments to pass into the sphenoid sinus, transitioning the procedure to a three-handed binarial technique.
22.7.4 Sphenoidotomy and Sellar Entry
The sphenoidotomy is enlarged lateral to the sphenoid ostia to ensure adequate exposure. This can be accomplished using Kerrison punches, a soft-tissue shaver, or a drill. While drilling down the sphenoid rostrum, care must be taken to not injure the sphenopalatine artery, which is typically found in the mucosa of the inferolateral rostrum. Accordingly, mucosa from the inferior portion of the rostrum is carefully separated from the bone prior to its removal, after which the mucosa—along with the sphenopalatine artery—is preserved. Damage to the sphenopalatine artery may result in postoperative epistaxis. The sphenoidotomy should continue until certain structures become visible: the optic protuberances, opticocarotid recesses, the sellar floor, clival recess, and planum sphenoidale. Identification of these structures, and particularly of the optic protuberances and opticocarotid recesses, will help establish the midline. Image guidance may also be used to establish midline, but we reserve its use for repeat surgeries in which anatomical landmarks may not be easily identifiable as well as cases involving presellar or conchal sphenoid sinuses. Some sellar tumors may erode through the floor of the sella itself or leave the floor thin enough to flake off with a blunt hook. In other cases, a small chisel or a high-speed drill may be used to open the sellar floor. With the floor opened, a Kerrison punch is used to widen the opening to the medial border of the cavernous sinuses. A small lip of bone is left in place to help facilitate sellar floor reconstruction at the conclusion of the case.
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