The anterior pituitary gland is under predominantly stimulatory control by the hypothalamus. The function of the normal pituitary gland depends on the integrity of the hypothalamus, the portal circulation, and the pituitary stalk. Portal vessels originate in a capillary bed in the median eminence and extend through long portal vessels into the pituitary stalk and to the adenohypophysis. The pituitary hormones adrenocorticotropic hormone (ACTH), growth hormone (GH), prolactin, thyroid-stimulating hormone (TSH), luteinizing hormone (LH), and follicle-stimulating hormone (FSH) are controlled by the hypothalamic hormones corticotropin-releasing factor (CRF), dopamine (aka prolactin inhibitory factor [PIF]), thyroid-releasing hormone (TRH), and gonadotropin-releasing hormone (Gn-RH), respectively. This is efficiently accomplished via a portal vascular system connecting the hypothalamus with the anterior pituitary gland. These hypothalamic releasing factors are then under negative feedback control from the end-organ products, i.e., adrenal gland products, thyroid hormone, etc., thereby completing the axis loop [1]. The predominant net hypothalamic regulatory influence is stimulatory for all pituitary hormones except prolactin, which is under dominant inhibitory control [2]. Any interruption or compression of the network of portal vessels as a result of pressure or invasion by any perisellar mass can alter the delivery of these hypothalamic factors to the anterior pituitary and cause impairment in its function.