A 35-year-old woman is seen in the outpatient clinic for evaluation of an incidental pituitary macroadenoma. Her medical history is significant for hypertension, diabetes, hyperlipidemia, polycystic ovary syndrome, and obesity. She initially presented to the emergency department (ED) a week ago after an episode of right visual field changes that she described as waviness in her right eye and right hemibody sensory changes without motor deficits. While in the ED, she underwent a full workup for possible stroke, which was negative. Magnetic resonance imaging (MRI) of her brain without contrast revealed a 12-mm pituitary lesion; a repeat MRI with contrast was then ordered (Figure). No serum hormonal panel was available for review from ED records.
Upon further questioning of her medical history during the clinic visit, the patient notes that a few years ago she was attempting to become pregnant and was evaluated by her gynecologist for amenorrhea. At that time, she reportedly completed an endocrine laboratory workup that showed a slightly elevated prolactin level between 30 and 40 ng/mL (normal level in nonpregnant women, <30 ng/mL). Per the patient, the minimal elevation was not enough to concern the gynecologist and no MRI was ordered at that time. Her gynecologist recommended that she lose weight. Her menses returned to normal with weight loss. With a history of disrupted menstrual cycles, infertility, and patient reported elevated prolactin level, there is high suspicion for endocrine disruption. A complete pituitary panel is ordered again to examine the current hormone function considering the recent MRI findings. This revealed a prolactin of 33.7 ng/ml, and all other hormonal levels were within normal limits.
Because the patient reports multiple episodes of visual disturbances and the size of the pituitary adenoma on MRI, a neuro-ophthalmology referral is initiated for visual field testing and to determine if the pituitary macroadenoma is causing mass effect and compressing the optic nerve. The neuro-ophthalmologist found she had no visual field defect from her adenoma on visual field testing and believed that her visual disturbances were probably migraine in nature.
Incidental pituitary adenomas are usually found on imaging studies obtained for other reasons or in workup of patients with abnormal endocrine hormone levels (both decreased and increased levels) or with symptoms of mass effect from the lesions.1 These tumors are typically benign in nature; cases with malignancy are extremely rare.1 The exact pathophysiology of pituitary adenomas remains unknown but is thought to be linked to heredity, hormonal influences, and genetic mutations.1
Pituitary tumors are commonly found in adults between the ages of 35 and 60 years of age.2,3 The estimated prevalence of pituitary adenomas varies widely by study and findings are typically based on autopsy and radiology data. Surveillance, Epidemiology, and End Results (SEER) Program data from 2004 to 2018 show an incidence rate of pituitary adenomas and pituitary incidentalomas of 4.28 ± 0.04 and 1.53 ± 0.02 per 100,000 population.4 Pituitary tumors have been found in 14.4% of unselected autopsy cases and 22.5% of radiology tests.1
The SEER data suggest that incidence rates are similar among women and men but are higher among women in early life and higher among males in later life.5 Rates of prolactinomas (prolactin-secreting tumors) and corticotropinomas (adrenocorticotropic hormone-secreting tumors; Cushing disease) are higher in women than men.6
Earlier SEER data showed a significantly higher incidence of pituitary adenomas in Black individuals compared with other racial/ethnic groups; several factors may account for this discrepancy such as the higher stroke rate in this population, which leads to a greater likelihood for brain imaging that detects incident pituitary tumors.5
Incidental pituitary adenomas may be found during workup related to hormonal dysfunction (amenorrhea, galactorrhea, fertility disorders, sexual dysfunction), noticeable vision change, new-onset headaches, or imaging performed for other diagnostic purposes.7
Pituitary Adenoma Types
Pituitary tumor types are differentiated by location, size, and functional status. Pituitary tumors commonly arise from the anterior portion of the gland (adenohypophysis) and rarely from the posterior portion (neurohypophysis).2 Both adenohypophyseal and neurohypophyseal tumors are commonly benign and slow-growing.1 Malignant pituitary tumors account for less than 1% of pituitary lesions and are usually metastases from breast and lung cancers.3 Adenohypophyseal carcinoma is rare, with less than 140 reported cases.2
Pituitary tumors are categorized by the size1,2:
- Microadenomas (<10 mm)
- Macroadenomas (>10 mm to 40 mm)
- Giant adenomas (>40 mm)
Pituitary adenomas are further classified as functioning (hormone-secreting) or nonfunctioning (nonsecreting).1,6 If the adenoma is functioning, hormone levels will be found in excess. If the levels are within normal limits, a nonfunctioning pituitary adenoma is suspected.
Approximately 65% of all pituitary adenomas are functioning tumors.2 Functioning pituitary adenomas present in various ways depending on which hormone is involved and the level of hormone secretion. Prolactinomas are the most common type of functioning adenomas followed by growth hormone-secreting and adrenocorticotropic hormone-secreting pituitary tumors. Adenomas secreting thyrotropin and follicle-stimulating hormone are less commonly found.2 Clinical features of functional pituitary adenomas are outlined in Table 1.2.8
Table 1. Clinical Features and Laboratory Findings of Functioning Pituitary Adenomas
Approximately 20% to 30% of pituitary adenomas are nonfunctional.3 These tumors may go undiagnosed for years until the mass of the tumor starts to effect surrounding structures and causing secondary symptoms such as compression of the optic chiasm causing vision impairments.
Nonfunctioning pituitary adenomas and prolactinomas (functioning) are the 2 most common types of pituitary adenomas.2,3 The consulting clinician must understand the difference in pathology of these 2 types of lesions, what diagnostic test to order, how to interpret the test results, and which specialty to refer the patient to best on the initial workup findings.