Mitchell E. Geffner, MD

Disclosures

Cancer Control. 2002;9(3) 

In This Article

Anatomy

The adult pituitary gland is a pea-sized midline structure located below the optic chiasm. It hangs down on a pedicle (the hypothalamic-pituitary stalk) from the inferior portion of the hypothalamus. The pituitary gland contains two anatomical components. The anterior portion, also known as the adenohypophysis, receives its signals through the portal system of blood vessels that arise in the hypothalamus and traverse the stalk. The posterior section, also known as the neurohypophysis, receives its signals through axons that arise in neural bodies within the hypothalamus and also traverse down the stalk. Embryologically, the anterior pituitary gland is derived from Rathke's pouch, an evagination of the stomodeal ectoderm. In contrast, the posterior pituitary arises in the infundibulum, a part of the diencephalon.[1]

Most cases of childhood hypopituitarism, especially those that develop after birth, result from diseases of the hypothalamus and the stalk that result in a failure of the normal hypothalamic signals to reach the pituitary gland. In other words, the pituitary gland is usually fully functional but is unable to produce normal levels of its stimulating hormones because it does not receive the proper stimulation by the hypothalamic-releasing hormones or factors.[2] Therefore, if patients with hypopituitarism could be treated with the appropriate types and doses of hypothalamic-stimulating hormones, normal hormonal production by the pituitary gland could be restored. Thus, the term hypopituitarism, while convenient, is technically incorrect. Children with congenital hypopituitarism and adults with hypopituitarism are more likely to have primary diseases of the pituitary gland compared to children with acquired hypopituitarism, in whom hypothalamic and stalk disease is much more common.

As can be seen on a normal head magnetic resonance imaging (MRI) scan, the anterior pituitary, on T1-weighted imaging, appears dark and equal in intensity to gray matter, while the posterior pituitary gland appears white and is referred to, radiologically, as the posterior "bright spot" (Fig 1A).[3] This difference may reflect a layer of fat within or around the posterior pituitary. In some cases of congenital hypopituitarism, this "bright spot" is completely absent and correlates well with the clinical presence of diabetes insipidus (DI). In other cases of congenital hypopituitarism, the "bright spot" is found ectopically in an anatomical location in the normal pathway of posterior pituitary embryologic development (either at the base of the hypothalamus or in the stalk), in which case DI is usually absent (Fig 1B). Such radiological findings are sometimes helpful in securing the congenital nature of hypopituitarism. In acquired forms of hypopituitarism in which DI develops either spontaneously or postoperatively, the "bright spot" is typically absent.

Figure 1.

(A) Normal head MRI showing a sagittal view through the pituitary gland. The large arrow indicates the anterior portion of the pituitary gland, whereas the small arrow indicates the posterior (normally whiter) portion of the pituitary gland. (B) Coronal head MRI with posterior pituitary bright spot noted ectopically at the base of the hypothalamus (arrow). (C) Sagittal MRI view of an infant pituitary gland showing a transected hypothalamic-pituitary stalk (arrow).

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