Endoscopic Approach to the Sella
Summary
The endoscopic endonasal approach is currently the approach of choice for most sellar tumors, including pituitary adenomas, craniopharyngiomas, meningiomas, and Rathke cysts. Improved visualization, avoidance of brain retraction, faster recovery, lack of external scars, and the ability to directly access tumors with minimal damage to critical neurosurgical structures are among its obvious benefits. This is reflected in improved outcomes in terms of higher rates of gross macroscopic tumor removal and normalization of hormones (in secreting adenomas) and reduced hospitalization requirements. However, it presents surgeons with several challenges, including a steep learning curve, complicated reconstruction requirements, and the need for a true team approach.1
Introduction
Anatomically, it is obvious that the route via the sphenoid sinus is the more direct way to access the sellar region. The transsphenoidal approach to the sella evolved from a sublabial transseptal to a transnasal approach with the use of the operating microscope. Although otolaryngologists were the first to use the endoscope in the nasal cavity, Gerard Guiot2 was the first neurosurgeon to perform an endoscopic trans sphenoidal approach to the skull base in 1963; however, he had to abandon the procedure because of poor visualization. Subsequently it was felt that the endoscope was to be used as a visual aid, in addition to the microscope, rather than as the primary means of visualization. Jankowski and coworkers from the Central Hospital of the University of Nancy reported in 1992 the first removal of hypophysial tumors in three patients using a purely endoscopic transnasal, transsphenoidal approach to the sella.3 Several pioneers in transnasal endoscopic skull base surgery subsequently emerged, including Jho,4 Cappabianca et al,5 and Frank and Pasquini,6 who extended the limits of what can be achieved via a transnasal endoscopic approach.
The endoscopic endonasal, transsphenoidal approach provides an excellent panoramic view of the sphenoid sinus and of the sellar and parasellar regions, with intraand extracapsular visualization using straight and angled endoscopes, preservation of sinonasal function, reduced hospital stay, and increased patient comfort. More importantly, there is increasing evidence that the endoscopic transsphenoidal approach is associated with improved patient outcomes compared with the traditional microscopic approach.7–10
However, operating with the use of an endoscope has a definite learning curve,11 while the improved rates of complete tumor removal are associated with larger skull base defects and the potential for cerebrospinal fluid (CSF) leaks.10
Indications/Patient Selection
The differential diagnosis of sellar lesions is presented in Table 38.1 and consists of primary and metastatic tumors, cysts, and inflammatory and vascular lesions. The most common are pituitary adenomas, craniopharyngiomas, meningiomas, Rathke cleft cysts, and pituitary apoplexies. The main aims of surgery for pituitary adenomas are
Normalization of excess hormone secretion
Elimination of mass effect
Preservation or restoration of normal neurologic function, including visual acuity and fields
Preservation or restoration of normal pituitary function
Prevention of tumor recurrence
Achievement of a complete pathologic diagnosis
Craniopharyngiomas
Craniopharyngiomas are slow-growing tumors originating from remnants of the Rathke pouch (see Video 62, Endoscopic Removal of Retrochiasmatic Craniopharyngioma, Pituitary Transposition ). They usually occur in children and young adults. Depending on their location and size, they may present with headaches, visual loss, pituitary insufficiency, failure to thrive, or (rarely) signs and symptoms of increased intracranial pressure. Despite their benign nature, they tend to infiltrate and adhere to adjacent structures, making their complete removal difficult.
Tumor | Pituitary adenoma Craniopharyngioma Meningioma Glioma (hypothalamic, optic nerve) Metastasis Chordoma Lymphoma |
Cyst | Rathke cleft cyst Dermoid cyst |
Inflammatory and granulomatous disorders | Bacterial abscess Langerhans cell histiocytosis Sarcoidosis Tuberculosis Granulomatous hypophysitis |
Hamartoma | Hypothalamic hamartoma |
Vascular lesions | Carotid aneurysm |
Pituitary apoplexy |
Meningiomas
Meningiomas usually arise from the tuberculum sellae or diaphragma sellae and may cause headaches or visual disturbances due to the close relationship to the optic nerves and chiasm (for a more extensive discussion of anterior skull base tumors and approaches, see Chapter 40).
Rathke Cleft Cysts
Rathke cleft cysts are usually small cystic lesions derived from Rathke pouch remnants, causing headaches.
Pituitary Adenomas
Pituitary adenomas are by far the most common tumors of the sellar region, comprising 90 to 95% of all such tumors. Pituitary adenomas are benign epithelial tumors derived from secretory cells of the anterior pituitary gland (adenohypophysis), which are classified according to the immunohistochemical expression patterns of hormones. They are divided into microadenomas (tumors < 10 mm in size) and macroadenomas (> 10 mm).
The vast majority of pituitary adenomas are asymptomatic and occur in ~10% of the general population (incidentalomas), as shown by autopsy and magnetic resonance imaging (MRI) studies.12,13 If clinical symptoms are present, they are due to cranial nerve compression, hormonal hyper- or hyposecretion, or a combination of these.
Nonfunctioning/Inactive Adenomas
Pituitary adenomas without hormonal overproduction are referred to as nonfunctioning or inactive. Treatment is determined by their size and clinical manifestations. Mechanical compression of the normal pituitary can cause pituitary dysfunction, and pressure on the surrounding structures may be associated with a variety of symptoms: pressure on the optic chiasm, for example, often produces the classic bitemporal hemianopsia. Adenomas with lateral extension and invasion of the cavernous sinus may cause symptoms from cranial nerve [CN] III (oculomotor), CN IV (trochlear), and CN VI (abducens), or a combination, leading to ophthalmoplegia. Extensive suprasellar extension can lead to obstruction of the foramen of Monro, resulting in obstructive hydrocephalus. Headaches occur frequently and may be caused by compression or stretching of the sellar diaphragm or dura.14
Hypersecreting Adenomas
Prolactinoma
Prolactin-secreting adenomas (prolactinomas) are the most common type of hypersecreting adenomas. The majority of such patients are women presenting with secondary oligoamenorrhea, infertility, and (less often) galactorrhea. Men present with galactorrhea, headache, impotence, and visual abnormalities. The size of pituitary adenomas is usually proportional to the degree of prolactin elevation. Prolactin is under inhibitory control by dopamine from the hypothalamus; therefore, any mass effect in this area may produce increased prolactin levels, called the stalk effect (due to disruption of dopamine transport down the pituitary stalk). However, in such cases, prolactin levels tend to be < 100 µg/L, while the majority of macroprolactinomas present with levels > 200 µg/L.
The treatment of prolactinomas is primarily medical (dopamine agonists), with good results (> 90% response rates). Dopamine agonists (bromocriptine, cabergoline) normalize prolactin levels and reduce tumor size, thereby restoring vision even in the case of large tumors with severe visual loss.15,16 Surgery is indicated only
If visual fields fail to improve, and there is ongoing chiasmal compression despite medical treatment
In cases of intolerance to dopamine agonists17
Acromegaly
Overproduction of growth hormone (GH) in adults results in deformity and thickening of the bones and soft tissues; the most striking feature is the enlargement of the nose and chin and of the hands and feet. This syndrome is called acromegaly and frequently presents in combination with several endocrine disorders (hypermetabolism, diabetes mellitus). The diagnosis of acromegaly, which is often long delayed, is made on the basis of the characteristic clinical changes, the finding of elevated serum GH and insulinlike growth factor (IGF)–1 values, and the failure of the serum GH concentration to rise in response to the administration of glucose (oral glucose tolerance test). Surgical removal is the treatment of choice for GH-producing tumors and results in biochemical cure in 75 to 95% of patients, although this is markedly lower in tumors > 2 cm or with cavernous sinus invasion.18
The medical treatment of acromegaly includes somatostatin receptor ligands (SRLs), GH receptor antagonists, and dopamine agonists. SRLs can be used before and after surgery and have been shown to be moderately effective in tumor control and controlling GH/IGF-1 hypersecretion. Radiation therapy is usually given only as a last resort and consists of conventional or stereotactic radiotherapy. The main disadvantage is loss of pituitary function in > 50% of patients, which compares unfavorably with the rates of hypopituitarism (10–20%) after surgery.
Cushing Disease
Adrenocorticotropic hormone (ACTH)–producing pituitary adenomas causing the clinical picture of Cushing disease are relatively rare, occur mostly in women, and have a poor prognosis if left untreated. Note that Cushing disease refers exclusively to excess ACTH of a pituitary origin, usually a (micro)adenoma, whereas all other causes of nonphysiologic hypercortisolism are grouped under the term Cushing syndrome. The clinical effects of hypercortisolism are the same: truncal obesity, hypertension, muscle weakness, amenorrhea, hirsutism, abdominal striae, glycosuria, osteoporosis, and in some cases psychosis. Sellar enlargement, visual symptoms, and cavernous sinus extension are rare. Demonstrating increased concentration of plasma and urinary cortisol makes the diagnosis. Plasma cortisol levels are not suppressed by the administration of small doses of dexamethasone.
The first line of treatment is transsphenoidal removal of the adenoma. Radiotherapy can be an alternative in patients who failed surgery or if surgery is not possible. Another option is bilateral adrenalectomy with steroid replacement.19
Gonadotropin-secreting Adenoma
Gonadotropin-secreting (luteinizing hormone [LH], follicle-stimulating hormone [FSH]) adenomas are usually clinically silent. Symptoms may arise in cases of large tumors with chiasmal compression or hormonal deficiency of one or more hormones due to compression of the normal pituitary gland.
Thyrotropin-producing Adenoma
Thyrotropin-secreting adenomas are the rarest type of adenomas. Patients usually present with hyperthyroidism (palpitations, tremor, weight loss, and sweating) and goiter in combination with compression symptoms. Patients can be treated with somatostatin analogues, while surgery is reserved in cases of chiasmal compression.
Pituitary Apoplexy
Pituitary apoplexy is caused by a pituitary hemorrhage or a hemorrhage in an adenoma causing sudden visual loss with headache and vomiting.
Goals of Surgery
A management algorithm based on the “European Position Paper on the Endoscopic Management of Tumours of the Nose, Paranasal Sinuses, and Skull Base” is presented in Fig. 38.1 .19 The goal of surgery is always complete tumor removal (and subsequent normalization of the hormone levels) in hormone-secreting adenomas. The same goal is mostly true for nonsecreting adenomas and meningiomas, although patients with pressure symptoms can be improved by tumor debulking (decompression of the chiasm in patients with hemianopsia; cavernous sinus decompression in patients with occulomotor dysfunction and headaches). Rarely, a biopsy may be performed in case of uncertain diagnosis to plan further management. There is controversy regarding the management of Rathke cleft cysts. However, simple drainage and subtotal cyst removal are usually effective with minimal risk of recurrence; the opposite is true for craniopharyngiomas, where complete resection is normally the goal of surgery except in circumstances where adherences to critical neurovascular structures preclude complete resection.
Note
Surgery is the mainstay of management for nonsecreting adenomas with compressive symptoms, as well as ACTH- and GH-producing adenomas. Patients with prolactinomas should be treated primarily medically.
Note
Complete surgical resection should be the aim with all hormone-secreting tumors. Simple drainage is usually sufficient for Rathke cleft cysts and apoplexy; in nonsecreting adenomas, craniopharyngiomas, and meningiomas, complete resection should be balanced against the expected associated morbidity.
Preoperative Planning
Every patient with a sellar lesion should have a preoperative radiological, endocrinological, and (when indicated) ophthalmological work-up.
Ophthalmological Assessment
In patients with chiasmal compression, ophthalmological assessment should include a measurement of visual acuity and fields with the Goldman perimeter, as visual compromise necessitates rapid treatment.
Endocrinological Assessment
Patients with sellar nonhypersecreting lesions have potentially varying degrees of hypopituitarism, occasionally requiring substitution therapy. The decision to use perioperative glucocorticoids in patients undergoing pituitary surgery can be based on the results of the preoperative screening tests.20 If preoperative cortisol is subnormal, the patient should start with hydrocortisone replacement (15–30 mg daily) with an increase to cover surgery and the first 48 hours postoperatively. Our standard perioperative regimen includes 50 mg hydrocortisone at induction of anesthesia, 50 mg 4 dose dense (DD) for the first day, 20 mg 4 DD for the second day, then return to regular replacement. Patients with normal cortisol levels preoperatively do not require perioperative replacement provided that basal cortisol levels are tested immediately after surgery.
Imaging
MRI using a pituitary protocol with delayed postcontrast images is the imaging modality of choice for patients with sellar lesions. Important anatomical structures of the sellar region that are visualized on MRI include the pituitary gland, optic chiasm, cavernous sinus, and intracavernous internal carotid artery (ICA). The pituitary gland has an anterior (adenohypophysis) and posterior (neurohypophysis) part showing signal intensity differences. The neurohypophysis usually has a high signal intensity on noncontrast T1-weighted MRI. The cavernous sinus lies lateral to the pituitary gland and is essentially a venous space containing the ICA and cranial nerves. The dominant structure within the cavernous sinus is the ICA, which, when patent, appears as a signal void on a T2-weighted coronal MRI. High-resolution MRI can demonstrate CN III (oculomotor) and CN IV (trochlear) above and lateral to the ICA. The ophthalmic division of CN V1 (trigeminal) and CN VI (abducens) is below and lateral to the ICA. CN V2 (maxillary) is in the inferior part of the cavernous sinus ( Figs. 38.2a and 38.10a,b ). High-resolution (three-dimensional) MRI can also be incorporated into the navigation system and be used for surgical planning, particularly with respect to tumor invasion in the cavernous sinus ( Fig. 38.3 ).21 Localization of the pituitary gland is best done by following the pituitary stalk from superior to inferior on a T1-weighted axial MRI with 1-mm slices. With macroadenomas, it can be remarkably difficult to see the gland on contrast-enhanced T1-weighted MRI, although usually a brighter enhancing rim will provide a clue to its location. The posterior lobe of the pituitary gland can be best seen as a hyperintense signal on sagittal T1-weighted MRI without contrast. Sometimes following the enhancing pituitary stalk from the third ventricle down can help in identifying the gland. Failure to identify the gland prior to tumor removal can result in damage, or even resection, of the pituitary gland.
Identifying the optic nerves on contrast-enhanced T1-weighted MRI can be difficult. The contrast reduces resolution somewhat; therefore, sometimes optic nerves can be best seen on a thin-slice coronal T1-weighted MRI, without intravenous (IV) contrast ( Fig. 38.2a ).
Large adenomas or macroadenomas (> 1 cm) are usually hypo- or isointense to gray matter on noncontrast T1-weighted images and exhibit homogeneous contrast enhancement, whereas microadenomas (< 1 cm) appear as hypointense areas compared with the normal pituitary gland and enhance only on delayed images. Macroadenomas frequently extend superiorly with compression of the optic chiasm. Some tumors pass through the diaphragma sellae (“dumbbell” adenomas) ( Figs. 38.2 and 38.3 ). Lateral growth into or beyond the cavernous sinus can occur ( Fig. 38.4 ), while erosion of the sellar floor causes anteroinferior extension into the sphenoid sinus.
Craniopharyngiomas present as heterogeneous masses on MRI, but the presence of calcifications on computed tomography (CT) makes the diagnosis more likely ( Fig. 38.5 ). Meningiomas mostly have diffuse contrast enhancement and a characteristic dural tail (contrast enhancement along the dura) on MRI ( Fig. 38.6 ).
We perform a standard CT scan of the paranasal sinuses and the skull base for the assessment of calcifying lesions such as craniopharyngiomas, as well as for CT/MRI fusion during intraoperative navigation. A thin-slice CT scan provides information on paranasal bony structures, including the presence of concha bullosa, and the size and septations of the sphenoid sinus.22 Three types of sphenoid sinus have been described, depending on the degree of pneumatization.23,24 First, the conchal type, in which the area below the sella is bony without any air cavity, is common in children before puberty. Second, the sellar type, is the most common type of sphenoid sinus and is present in 98% of adults.23 In this type, the air cavity extends into the body of the sphenoid below the sella and as far posteriorly as the clivus ( Fig. 38.7a ). Third, the presellar type, in which pneumatization is limited to the anterior sellar wall ( Fig. 38.7b ), occurs in ~2% of adults.
Note
We strongly feel that the preoperative assessment, the surgical indication, the choice of approach, and postoperative care should be done jointly by the neurosurgeon and the otolaryngologist in a multidisciplinary setting, including an endocrinologist and neuroradiologist.
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