aberrant formation or incomplete differentiation of the anterior lobe of the pituitary gland which arises as a pouch-like outgrowth of ectoderm known as the hypophyseal (Rathke's) pouch from the dorsal midline roof of the stomodeum (primitive oral cavity); the hypophyseal pouch grows toward the brain and the neurohypophyseal bud; as the hypophyseal pouch and the infundibulum make contact, the hypophyseal pouch loses its connection with the pharynx, creating a hollow ball of cells that lies inferior to the floor of the diencephalon posterior to the optic chiasm; these cells undergo division, the central chamber gradually disappears, and this endocrine mass becomes the anterior pituitary gland; the fully developed adenohypophysis consists of a glandular pars distalis, a thin proximal extension called the pars tuberalis, and a narrow pars intermedia