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The transsphenoidal approach to the pituitary is used for the excision of tumors that lie within the sella or that have extension to the immediate suprasellar area. The most common lesions are prolactin-secreting microadenomas. These patients are usually women with secondary amenorrhea. Three other less common pituitary tumors are growth hormone-secreting lesions, which result in acromegaly; adrenocorticotropin hormone (ACTH)-secreting tumors, which cause Cushing's disease; and a very rare thyroid-stimulating hormone (TSH)-secreting lesion that results in hyperthroidism ( Table 53-13 ).
The important preoperative considerations relate to the patient's
endocrine status. In general, as a pituitary lesion expands and compresses the pituitary
tissue, the sequence in which hormonal function is lost is first gonadotrophins;
second, growth hormone; third, ACTH; and fourth and last, TSH. The precise definition
of the adrenal status of these patients is often not critical because the patients
will commonly receive adrenal hormone supplementation at least temporarily. However,
profound hypocortisolism with associated hyponatremia should be corrected preoperatively.
It is, in fact, uncommon for thyroid
| Location | Hormone Secreted | Clinical Findings | Comment |
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| Anterior pituitary | Prolactin | Galactorrhea, amenorrhea, hypogonadism, infertility | Bromocriptine sensitive |
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Adrenocorticotropin | Cushing's disease (hypercortisolism) | Basophilic adenoma |
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Centripetal obesity |
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Diabetes mellitus |
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Friable tissues |
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Growth hormone | Acromegaly/gigantism, glucose intolerance | Eosinophilic adenoma |
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Difficult airway |
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Thick skin (difficult cannulation) |
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Nonsecretory | Mass effect, panhypopituitarism | Chromophobe adenoma |
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Preoperative hormones? |
| Suprasellar | Nonsecretory | Panhypopituitarism, SIADH, visual (optic chiasm) symptoms | Craniopharyngioma or suprasellar extension of pituitary lesion |
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Hydrocephalus |
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| SIADH, syndrome of inappropriate antidiuretic hormone secretion. | |||
Many practitioners place an arterial catheter, but it is not absolutely necessary. Access for blood sampling is a valuable adjunct to postoperative care if diabetes insipidus develops. Blood loss is usually modest. However, the cavernous sinus is in an immediate lateral relationship to the pituitary and may be entered during the resection of large tumors. In addition, some patients have a venous sinusoid that lies in front of the pituitary gland and connects the two cavernous sinuses. This sinusoid can be the origin of substantial blood loss. It has, on occasion, actually precluded this approach to the pituitary gland.
Latitudes are broad with respect to the choice of anesthetics, although tumors with suprasellar extension can cause hydrocephalus and thereby add increased ICP constraints to the anesthetic technique. The procedure is performed in a supine position, usually with some degree of head-up posture to avoid venous engorgement. A pharyngeal pack will prevent an accumulation of blood in the stomach (which causes vomiting) or in the glottis (which contributes to coughing at extubation). A RAE-type tube secured to the lower jaw at the corner of the mouth opposite the surgeon's dominant hand (e.g., the left corner of the mouth for a right-handed surgeon) is suitable. A small esophageal stethoscope and temperature probe can lie with the endotracheal tube. Covering the entire bundle with a towel drape (a plastic sheet with an adhesive edge) placed just below the lower lip so that it hangs from the lower jaw like a veil will protect it from the preparation solutions.
The procedure requires a C-arm image intensifier (lateral views), and the head and arms are relatively inaccessible once the patient is draped. It is appropriate to establish the nerve stimulator at a lower extremity site. The surgical approach is through the nasal cavity by means of an incision made under the upper lip. During the approach, the mucosal surfaces within the nose are infiltrated with a local anesthetic and epinephrine solution, and the patient should be observed for the occurrence of dysrhythmias.
Surgical preferences for CO2 management will vary. In some instances, hypocapania will be requested to reduce brain volume and thereby minimize the degree to which the arachnoid bulges into the sella. One of the important surgical considerations is the avoidance, when possible, of opening the arachnoid membrane. Postoperative CSF leaks can be persistent and are associated with a considerable risk of meningitis. By contrast, in tumors with suprasellar extension, normal or increased CO2 will help deliver the lesion into the sella for excision. [314] As an alternative method, some surgeons have resorted to "pumping" saline or air into the lumbar CSF space.[315] [316]
Diabetes insipidus (DI) is a potential complication of this procedure. Antidiuretic hormone (ADH) is synthesized in the supraoptic nuclei of the hypothalamus and is transported down the supraoptic-hypophyseal tract to the posterior lobe of the pituitary. This portion of the pituitary gland is frequently spared. Even when it is excised, water homeostasis commonly normalizes, presumably because ADH is released from the cut end of the tract. However, even when the posterior lobe of the pituitary is left intact, transient DI may occur. DI usually develops 4 to 12 hours postoperatively and very rarely arises intraoperatively. The clinical picture is one of polyuria in association with a rising serum osmolality. The diagnosis is made by comparison of the osmolality of urine and serum. Hypo-osmolar urine in the face of an elevated and rising serum osmolality strongly supports the diagnosis. Urine specific gravity is a useful bedside test. In the presence of bona fide DI, specific gravity will be low, less than 1.002.
When the diagnosis of DI is established, an appropriate fluid management regimen is hourly maintenance fluids plus two thirds of the previous hour's urine output. (An acceptable alternative is the previous hour's urine output minus 50 mL plus maintenance.) The choice of fluid will be dictated by the patient's electrolyte picture. In general, the patient is losing fluid that is hypoosmolar and relatively low in sodium. Half-normal saline and 5% dextrose in water (D5 W) are commonly used as replacement fluids. Beware of hyperglycemia when large volumes of D5 W are used. An unacceptable fluid regimen that has been used calls for maintenance fluids plus the previous hour's urine output. This regimen has the potential to put you and the patient in a "chase your tail" situation. Should the patient become iatrogenically fluid overloaded, this regimen precludes a return to isovolemia, and in fact, when the maintenance fluid allowance is generous, it guarantees that the patient will become increasingly hypervolemic. If the hourly requirement exceeds 350 to 400 mL, desmopressin (DDAVP) is usually administered.
A smooth emergence (see the section "Emergence from Anesthesia") is desirable, especially if the CSF space has been opened (and resealed with fibrin glue or by packing the sphenoid sinus with fat or muscle). Repeated, intense Valsalva maneuvers, as with coughing or vomiting, may contribute to reopening of a CSF leak and worsen the risk for subsequent meningitis. The airway should be cleared of debris, including formed clot. Some clinicians routinely inspect the pharynx with a laryngoscope. Such inspection also permits assessment of whether active bleeding is still present, and this allows one to more confidently extubate promptly at the first signs of reactivity to the endotracheal tube.
In situations in which one is concerned that a persistent CSF leak may occur, some surgeons will place a lumbar CSF drain to maintain CSF decompression in the early postoperative period.
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