A prolactinoma is a benign tumor (adenoma) of the pituitary gland that produces the hormone prolactin. It is the most common type of functioning pituitary tumor. Symptoms of prolactinoma are due to abnormally high levels of prolactin in the blood (hyperprolactinemia), or due to pressure of the tumor on surrounding tissues. Based on size, a prolactinoma can be classified as a microprolactinoma (<10 mm diameter) or a macroprolactinoma (>10 mm diameter). Signs and symptoms
The symptoms due to a prolactinoma are broadly divided into those that are caused by increased prolactin levels or mass effect. Those that are caused by increased prolactin levels are:
Amenorrhea (disappearance of ovulation periods)
Galactorrhea (Milk production; infrequent in men)
Loss of axillary and pubic hair
Hypogonadism (Reduced function of the gonads.) Gynecomastia (an increase in male breast size)
Erectile dysfunction (in males)Those that are caused by mass effect are:

Headaches
Vision Changes-visual field deficits, blurred vision, decreased visual acuity
Cranial nerve palsies-especially with invasive tumors or with pituitary apoplexy
Seizures, Hydrocephalus, Unilateral exophthalmos are rare presentations
Hypopituitarism
Pituitary apoplexy is a medical emergency because of spontaneous hemorrhage into the pituitary tumor and presents with severe headaches, vision changes, and acute panhypopituitarism. Causes
The cause of pituitary tumors remains unknown. Though most pituitary tumors are sporadic, some genetic syndromes include increased risk for pituitary adenomas including Multiple endocrine neoplasia type 1 (caused by a mutation in the MEN1 gene) and Familial isolated pituitary adenoma (FIPA). The majority of moderately raised prolactin levels (up to 5000 mIU/L) are not due to microprolactinomas but other causes.
However, people with low blood pressure should use caution when starting cabergoline treatment, as the long half-life of the drug (4–7 days) may inadvertently affect their ability to keep their blood pressure within normal limits, creating intense discomfort, dizziness, and even fainting upon standing and walking until the single first dose clears from their system. As with bromocriptine therapy, side effects may be avoided or minimized if treatment is started slowly. If a patients prolactin level remains normal for 6 months, a doctor may consider stopping treatment. Cabergoline should not be interrupted without consulting a qualified endocrinologist.Other dopamine agonists that have been used less commonly to suppress prolactin include dihydroergocryptine, ergoloid, lisuride, metergoline, pergolide, quinagolide, and terguride. Surgery
Surgery should be considered if medical therapy cannot be tolerated or if it fails to reduce prolactin levels, restore normal reproduction and pituitary function, and reduce tumor size. If medical therapy is only partially successful, this therapy should continue, possibly combined with surgery or radiation treatment.The results of surgery depend a great deal on tumor size and prolactin level. The higher the prolactin level the lower the chance of normalizing serum prolactin. In the best medical centers, surgery corrects prolactin levels in 80% of patients with a serum prolactin less than 250 ng/ml. Even in patients with large tumors that cannot be completely removed, drug therapy may be able to return serum prolactin to the normal range after surgery.