In addition to the tests performed to assess tumor anatomy, it is important that patients with pituitary tumors be evaluated for pituitary hormone status by an experienced endocrinologist, to overcome the difficulties in diagnosis discussed. The biochemical evaluation should to some extent depend on the patient's complaints, but the patient may have minimal symptoms even with significant hormone loss. For that reason, all patients with large tumors should have at least a basic evaluation for each of the pituitary hormones (11,12). Preoperative evaluation should include the following (see Table 1):
1. PRL level. All patients with pituitary tumors in whom an operation is considered must have a preoperative PRL level. PRL deficiency is not an issue, because it is not treated, but elevated PRL levels are important to document. Markedly elevated PRL levels indicate the presence of a prolactinoma, which is important because in most cases it obviates the need for surgery.
Suggested Preoperative Endocrine Evaluation of Pituitary Tumors
Not routinely tested if no suggestive clinical findings and surgery planned
FSH, LH, a-subunit, testosterone (men) or estradiol (women)
Low-dose ACTH stimulation test
Testosterone (men); FSH, LH, a-subunit levels if preoperative levels elevated GH stimulation testing if indicated
Antidiuretic Not routinely tested Not routinely tested hormone if no symptoms if no symptoms
Rule out prolactinoma; PRL deficiency not routinely evaluated TSH levels are not useful
Can cover with empiric low-dose glucocorticoids until surgery if clinically indicated; further evaluation occurs postoperatively Rule out gonadotropin secreting tumor; gonadal deficiency not routinely evaluated preoperatively
Rule out silent GH-secreting tumor; GH deficiency not routinely evaluated preoperatively Glucocorticoid deficiency can mask symptoms of diabetes insipidus
Prolactinomas are usually easily diagnosed with a basal PRL measurement. As discussed, mild hyperprolactinemia in the context of a large tumor does not indicate a prolactinoma. There is a rough direct correlation between tumor size and PRL level in prolactinomas, so the PRL level must be interpreted in relation to the tumor size.
2. Thyroid hormone levels. Each patient with a clinically nonfunctioning pituitary tumor should have a free-T4 level measured. A low free-T4 level indicates the need for l-thyroxine replacement therapy. The goal of therapy is a midnormal free-T4 level. As mentioned, it is not helpful to follow TSH levels. Free T4 should be measured before surgery to provide necessary l-thyroxine replacement before the induction of general anesthesia, because hypothyroid patients may have problems with clearance of anesthetic agents and other postoperative complications. If possible, surgery should be delayed for at least 1 wk. In dire emergency, rapid thyroid replacement can be achieved with triiodothyronine, but this can involve cardiac dangers.
3. Adrenal axis evaluation. In general, if the patient does not have symptoms of hypoadrenalism, and surgery is planned in the near future, there is no need to routinely evaluate the adrenal axis preoperatively, because evaluation of the adrenal axis is more complicated than the other pituitary axes.
In addition, it is our practice that all patients receive perioperative coverage with glucocorticoids, and the adrenal axis is evaluated after surgery in any case. This, however, is not the case in all centers (see Chapter 11). If patients have suggestive symptoms or a low cortisol level, it is appropriate to place them on a replacement dose of hydrocortisone until surgery. This low dose protects them from adrenal insufficiency without causing side effects related to overtreatment.
We do not routinely evaluate patients with large clinically nonfunctioning tumors for ACTH excess. Although there are reports of "silent" ACTH-secret-ing tumors, macroadenomas making ACTH are quite rare. This is a histologic diagnosis, and such patients need surgery and postoperative reevaluation regardless of the presence of ACTH secretion.
4. Gonadal hormones. We measure FSH, LH, a-subunit, and testosterone (in men) or estradiol (in women) routinely, although this is not the rule in all centers. Our goal is not to evaluate the patient for hypogonadism, because this will need to be addressed postoperatively. However, based on the discussion under "Pathophysiology" earlier, many nonfunctioning tumors make one or more of the gonadotropins, and preoperative elevated levels can provide a tumor marker for postoperative monitoring.
5. Growth hormone. Adults do not need an evaluation for GH deficiency before surgery. However, it is sensible to routinely measure the insulin-like growth factor 1 (IGF-1) level in all patients with large nonfunctioning pituitary tumors. IGF-1 is a good screening test for GH excess, and there are a few reports of silent GH-secreting tumors (13). Such tumors make GH but do not present clinically as acromegaly. They still require surgery for the tumor mass, but it is helpful to know that the tumor is making GH, because medical therapies are available postoperatively for GH-secreting tumors. Children with large pituitary tumors are often evaluated for growth failure as their presenting symptom of the pituitary tumor.
6. ADH. Patients are not routinely evaluated preoperatively for ADH deficiency, because it is rare in patients with nonfunctioning tumors and should present with polyuria, polydipsia, and nocturia. Therefore, if a patient does not have those symptoms, one can wait until after the surgery to evaluate the patient's ADH status. If a patient does have symptoms, treatment is not needed unless the polyuria and nocturia are severe or unless the patient has trouble with access to water. Note that ADH deficiency symptoms may be masked by adrenal insufficiency, and treatment of such patients with glucocorticoids may lead to the first appearance of symptomatic diabetes insipidus.
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