Hypophysectomy, the removal of the pituitary gland, can be performed through a number of surgical approaches. For large tumors that have extended beyond the pituitary fossa, a bifrontal craniotomy is often necessary. Most pituitary tumors lie within the sella (or immediate suprasellar area) and are therefore amenable to excision via the transsphenoidal technique. Transsphenoidal hypophysectomy requires the use of a microscope or endoscope to enter the sella through the nose and sphenoid sinus. Advantages include rapid midline access to the sella with minimal risk of brain injury or bleeding. The incision may be made in the back wall of the noise, along the front of the nasal septum, or under the upper lip. Endoscopy enables excellent tumor visualization, opening of the diaphragmatic sellae, and decompression of the optic nerve.
About 25% of pituitary tumors are considered nonfunctioning. Depending upon the specific type of lesion, some tumors of the anterior pituitary have endocrine manifestations related to hormonal hypersecretion. Sometimes hyposecretion of hormones can occur due to compression of adjacent normal tissue, prior radiation therapy, hemorrhage (apoplexy), or postpartum infarction of the pituitary gland (Sheehan syndrome). In either situation, these conditions carry significant implications for anesthetic management:
Prolactinomas—Nearly half of all pituitary tumors are prolactinomas. Their mass effect on the optic chiasm is usually more clinically significant than the prolactin hypersecretion. Women present with secondary amenorrhea and galactorrhea, while men show signs of secondary hypogonadism, erectile dysfunction, and decreased libido. These patients are typically on bromocriptine therapy, an agonist at dopamine D2 and various serotonin receptors.
Acromegaly—The excess of growth hormone (GH) from a pituitary tumor leads to acromegaly. These patients may have problems with airway management during general anesthesia due to macroglossia, prognathism, hypertrophic oropharyngeal tissues and laryngeal structures, and recurrent laryngeal nerve palsy. Most patients have a history suggestive of obstructive sleep apnea. Cardiac manifestations include left ventricular hypertrophy, interstitial myocardial fibrosis, coronary artery disease, and supraventricular dysrhythmias. Acromegalics may also have impaired glucose tolerance and diabetes mellitus.
Cushing’s disease—Hypersecretion of the adrenocorticotropin (ACTH) hormone from a pituitary tumor can lead to Cushing’s disease (see Chapter 110).
Hyperthyroidism—Tumors which release an excess of thyroid-stimulating hormone (TSH) produce symptoms of hyperthyroidism (see Chapter 105). These rare tumors are often more locally invasive and carry the risk of extensive blood loss. Management of hyperthyroidism is necessary prior to hypophysectomy.
An enlarged pituitary gland may eventually produce a mass effect on nearby structures. Usually these problems occur when the tumor is a large nonfunctioning macroadenoma (> 1 cm diameter) with suprasellar extension. Neurologic examination may reveal signs and symptoms of elevated intracranial pressure such as headache, nausea, and papilledema. Obstruction of cerebrospinal fluid outflow can lead to hydrocephalus. In the absence of intracranial hypertension, compression of the optic chiasm can also cause visual field defects such as bitemporal hemianopia. Palsy of the oculomotor ...