Page:Tumors of the pituitary gland.djvu/18



Figure 1-8 EMPTY SELLA SYNDROME: RADIOLOGIC FINDINGS

Magnetic resonance imaging (MRI) identifies an en- larged sella turcica in which the pituitary parenchyma is compressed at the bottom; the space is filled with cerebro- spinal fluid. (Courtesy of Dr. 8. Ezzat, Toronto, Canada.)

has been attributed to distortion of the infundib- ular stalk and reduction in hypothalamic tonic inhibition (10).

Other minor anatomic variations in the size and shape of the hypophysis and its relation to surrounding structures appear to have no endo- crine significance (6).

Blood is supplied to the human hypophysis by a complex portal system that originates in the hypothalamus (fig. 1-11). This hypophysial por- tal circulation carries hypothalamic stimulatory and inhibitory hormones from the infundibulum to adenohypophysial cells, thereby playing a major role in the regulation of adenohypophysial hormone secretion (4,5,7,15-17).

The arterial supply of the median eminence and posterior pituitary is derived from two or, in some individuals, three paired arteries which arise from the intracranial portions of the inter- nal carotid arteries: the superior, middle, and inferior hypophysial arteries. The superior hypo- physial arteries branch into an external and an internal plexus. The external plexus is composed

of small arteries that surround the upper half of the stalk and give rise to a mesh of capillaries. The internal plexus forms the gomitoli, unique vascular structures which measure 1 to 2mm in length and 0.1 mm in width. They are composed of a central muscular artery surrounded by a spiral of capillaries; the arteriole feeds the capi laries through small orifices surrounded by mus- cular sphincters. Flow through these complex

The Normal Pituitary

Figure 1-9 EMPTY SELLA SYNDROME A widely opened sellar diaphragm allows increased pres- sure from cerebrospinal fluid to compress the pituitary. (Plate 1B from Fascicle 21, 2nd Series.)

Figure 1-10 EMPTY SELLA SYNDROME

In the “empty sella syndrome,” the pituitary gland is attenuated along the bottom of the enlarged sella. (Plate 1C from Fascicle 21, 2nd Series.)