Answer is A (Pituitary adenoma): Pituitary adenomas produce excess prolactin which causes hypogonadism, decreased levels of testosterone and explains loss of erection. Pituitary adenomas (Prolactinomas) lead to an excess of prolactin. This inhibits hypothalamic release of LHRII resulting in defective LH & FSH secretion. Defective LH & FSH secretion in turn result in decreased levels of estrogen in females & testosterone in males. This is how prolactin excess can cause hypogaonadism In men prolactin excess can cause In females prolactin excess can cause Decreased Libido, impotence Irregular mensus (amenorrhea) Infeility. Infeility despite regular mensus. This explains this 30 year old male's complaints of loss of erection & his low testosterone & high prolactin levels. Testicular failure explains both loss of erection and low testosterone levels but not the high prolactin levels