Page:Tumors of the pituitary gland.djvu/17

Tumors of the Pituitary Gland

Figure 1-6 ANATOMIC COMPONENTS OF THE PITUITARY GLAND (Figure 3 from Fascicle 21, 2nd Series.)

Figure 1-7 NORMAL DIAPHRAGMA SELLAE

Gross view of a normal sella as viewed from above shows an intact diaphragm and pituitary gland. (Plate IA from Fascicle 21, 2nd Series.)

The adenohypophysis comprises about 80 per- cent of the pituitary. It is composed of three parts: the pars distalis, the pars intermedia, and the pars tuberalis (fig. 1-6). The pars distalis constitutes the largest portion of the gland; it is generally known as the anterior lobe or the pars glandularis. The pars intermedia or intermedi- ate lobe is rudimentary in the human pituitary; it is the vestigial posterior limb of Rathke’s pouch (see Embryology) and is found in an underdevel- oped form adjacent to the residual cleft of the gland. The pars tuberalis is an upward extension of adenohypophysial cells that surround the lower hypophysial stalk; it is also known as the pars infundibularis.

The hypophysis is enveloped by dura mater, a layer of dense connective tissue that lines the sella turcica. The diaphragma sellae, a reflection of the dura which constitutes the roof of the sella turcica, has a small central opening for the hypo- physial stalk, the connection to the hypothala- mus (fig. 1-7). The sellar diaphragm protects the pituitary from the pressure of cerebrospinal fluid (CSF). Defective development or absence of this structure causes the empty sella syndrome in which increased CSF pressure results in enlarge- ment of the sella turcica and compression of the pituitary (figs. 1-8-1-10); in severe cases, the entire gland may be found as only a thin layer of tissue at the bottom of the sella turcica. This lesion is usually unassociated with functional hypophysial abnormalities (3,12), however, 5 per- cent of patients have hyperprolactinemia, which may be caused by a coexistent prolactin-produc- ing pituitary adenoma but is often idiopathic and