prolactinoma prolactinoma a prolactinoma is a 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). prolactinomaspecialtyoncology, endocrinology, neurology, neurosurgery signs and symptoms