You review the magnetic resonance imaging (MRI) scan of a patient who presented with headaches after head trauma. No brain injury is present, but a mass is visible in the pituitary gland — a pituitary incidentaloma, or asymptomatic mass in the pituitary gland found on imaging done for an unrelated reason. What tests, if any, should you obtain? Does the pituitary mass need treatment, or may it be monitored rather than treated?
Todd B. Nippoldt, M.D., of the Division of Endocrinology, Diabetes, Metabolism, and Nutrition at Mayo Clinic in Minnesota says that to answer these questions and to develop rational recommendations for the testing and follow-up of a patient with a pituitary incidentaloma, the physician needs to:
Autopsy and head MRI studies indicate that the prevalence of incidentally discovered pituitary masses is approximately 10%. Most pituitary incidentalomas are less than 1 cm in largest diameter and prove to be pituitary adenomas or Rathke cleft cysts.
Dr. Nippoldt explains, "Prolactin-producing pituitary adenomas are common (12% to 28%) in patients with pituitary incidentalomas. Prolactinomas have potential for morbidity, testing is easy, and treatment is safe and effective."
The incidence of growth hormone (GH) production by an incidentally found pituitary mass is between 2% and 8%. Patients whose pituitary incidentaloma is detected early in the course of disease may have GH-related symptoms and physical findings that are subtle. There is potential for serious morbidity and increased risk of death, however, when GH excess goes undiagnosed. In addition, the likelihood of surgical cure for a GH-secreting pituitary adenoma is increased when the tumor is small.
Dr. Nippoldt notes that although 1% of the pituitary adenomas detected at autopsy are corticotroph adenomas, no instances of corticotropin excess have been reported in clinical studies of pituitary incidentaloma.
Cushing disease is a serious disorder, but testing for corticotropin excess in asymptomatic patients with pituitary incidentaloma is not recommended because of the low prevalence of disease and the high false-positive rates associated with the case detection tests used for this disorder.
Gonadotroph cell adenomas represent approximately 4% of pituitary adenomas discovered at autopsy. Most gonadotroph cell adenomas do not hypersecrete luteinizing hormone or follicle-stimulating hormone. Thus, there is no reliable preoperative biochemical test to detect gonadotroph adenomas.
Thyrotropin (TSH)-secreting pituitary adenomas are exceedingly rare, and none have been reported in clinical or autopsy series of incidentally found masses. Patients with TSH-secreting pituitary tumors usually present with signs and symptoms of hyperthyroidism.
Pituitary microadenomas (d10 mm in largest diameter) have a very low probability of being associated with hormonal hypofunction of the neighboring pituitary gland. Most studies report an incidence of 0%. Macroadenomas (>10 mm in largest diameter), however, are frequently (15% to 57%) associated with varying degrees of pituitary hypofunction.
Both microadenomas and macroadenomas have the potential to increase in size over time. Growth may occur after several years of apparent stability. Growth of a macroadenoma is more likely to be detected (up to 50% enlarge) during imaging follow-up than growth of a microadenoma (up to 22% enlarge). Any increase in the size of a macroadenoma is associated with an increased probability of clinically important mass effects such as hypopituitarism and vision loss.
Dr. Nippoldt advises, "To exclude excess hormone production, measurement of prolactin and insulinlike growth factor 1 (IGF-1) should be obtained for all patients with pituitary incidentalomas." See recommended laboratory studies table.
Laboratory testing to exclude pituitary hormone deficiencies is not needed for patients with microadenomas. The following blood tests, however, should be obtained for patients with macroadenomas:
With regard to gonadal function, a menstrual history should be obtained for women and serum testosterone concentration should be measured for men. The physician should keep in mind that baseline blood levels of cortisol and IGF-1 may not be sufficient to indicate normalcy or deficiency and that dynamic studies may be necessary. Quantitative perimetry to assess visual fields should be obtained when a macroadenoma is near or in contact with the optic chiasm.
According to Dr. Nippoldt, observation is appropriate when there is no evidence of pituitary hormone hyperfunction or hypofunction and when the pituitary mass is not causing or threatening vision loss. Reevaluation with pituitary-directed MRI should be completed 6 to 12 months after the initial scan, annually for 2 to 4 years, and periodically thereafter.
All follow-up scans should be compared with the baseline scan in addition to the prior scan, since slow changes in size may not be appreciated from one year to the next. The follow-up for pituitary macroadenomas should also include formal visual field assessment, since the decision to remove a nonfunctioning macroadenoma rests primarily on the development or risk of vision loss.