26-05: Nonfunctioning Pituitary Adenomas

ESSENTIALS OF DIAGNOSIS

GENERAL CONSIDERATIONS

Nonfunctioning pituitary adenomas are benign neuroendocrine neoplasms that do not produce symptoms from hormone oversecretion. Pituitary nonfunctioning adenomas occur more frequently in men than women and are more common with age. Nonfunctioning pituitary microadenomas (smaller than 1 cm) are common, detected as an incidental finding in 4–37% of brain CT or MR imaging. Although they are clinically nonfunctioning, immunohistochemistry has found that 58% stain for gonadotrophs; 10% stain for ACTH; and 9% stain for GH, PRL, or TSH, while 23% show no hormonal staining and are truly nonfunctioning “null cell” pituitary adenomas.

CLINICAL FINDINGS

A. Symptoms and Signs

Nonfunctioning pituitary macroadenomas (1 cm or larger) tend to be more aggressive than functioning pituitary adenomas. Those with nonfunctioning macroadenomas are much more likely to be symptomatic from mass effect with visual field compromise, headache, cranial nerve palsies affecting extraocular muscles, and pituitary apoplexy. Larger macroadenomas frequently cause some hypopituitarism, particularly hypogonadotropic hypogonadism. Nonfunctioning pituitary microadenomas are asymptomatic.

B. Laboratory Findings

1. Pituitary hormone hypersecretion

All patients with a pituitary adenoma require testing for pituitary hormone hypersecretion. Obtain a serum PRL to screen for prolactin hypersecretion; women with hyperprolactinemia are tested for pregnancy with a serum hCG. Testing for Cushing disease or acromegaly should be obtained, if clinically indicated.

2. Anterior hypopituitarism

Men should have following tests: serum free T₄, TSH, morning serum testosterone and free testosterone. Serum LH and FSH should be obtained in men with low serum testosterone, women who are postmenopausal, and younger women with amenorrhea. Serum sodium and glucose should also be obtained in all patients. A serum IGF-1 is drawn to screen for GH deficiency. Younger patients with short stature who have not fused their epiphyses should have a full evaluation for growth hormone deficiency.

3. Pituitary macroadenomas

Patients with a macroadenoma that impinges upon the optic chiasm require formal visual field testing. A cosyntropin stimulation test is performed for patients with hyponatremia or symptoms of possible hypoadrenalism.

C. Imaging

Pituitary dynamic contrast-enhanced MRI (3T) is the imaging modality of choice for the evaluation and follow-up of pituitary adenomas. About 10% of nonfunctioning pituitary microadenomas enlarge over several years, whereas 23% of pituitary nonfunctioning macroadenomas enlarge significantly. Nonfunctioning pituitary microadenomas that are smaller than 0.5 cm require no further MRI follow-up. For nonfunctioning pituitary adenomas 0.5 ...