Immunohistochemical survey of migration of human anterior pituitary cells in developmental, pathological, and clinical aspects: A review

Developmentally pathological conditions of the anterior pituitary cells inc lude failed separation of the primary pituitary gland into sellar and phary ngeal ones, ectopic migration into the subarachnoid space, and basophil inv asion into the posterior lobe although the last is a physiological phenomen on with pathological potentiality in certain circumstances. Pituitary primo rdium appears at about 4 weeks of gestation. One of the causes of the pitui tary gland agenesis may be a formation of the primary hypothalamic ganglion ic hamartoma just at the time of occurrence of the pituitary primordium, as analyzed in cases of Pallister-Hall syndrome. A double pituitary in a sing le individual is a rare malformation. Its pathogenesis is considered as a r esult of notochordal anomaly. In the 8th gestational week, the primary pitu itary gland separates into sellar and pharyngeal parts. The disturbance of this histogenesis results in a rare pituitary malformation, a "pharyngosell ar pituitary." Despite the failed separation in this case, differentiation of the pituitary cells proceeds and the hormone production of this malforme d pituitary gland can be displayed immunohistochemically. In this case, the distribution of the different hormone producing cells was atypical, partic ularly in those of gonadotropic hormones and ACTH. Life-long existence of t he pharyngeal pituitary is a normal anatomical state in humans. Cell differ entiation (hormone production) in the pharyngeal pituitary occurs about 4-1 0 weeks later than in the sellar pituitary. In pharyngeal pituitary, all ki nds of adenohypophyseal hormones are produced. Extracranial pituitary adeno mas (with intact sellar pituitary), exclusively found in the nasopharynx, s phenoid sinus, and clivus, may occur from the pharyngeal pituitary while an other tumorigenesis can develop from the residual tissue fragment in the cr aniopharyngeal canal. The "overshoot" of the adenohypophyseal cell migratio n in the distal part of the sellar pituitary is frequently observed in the leptomeninges of the peri-infundibular or peri-hypothalamic region as ectop ic pituitary cell clusters that are apparently independent of the pars tube ralis. It is suggested that these cells, frequently found in "normal" indiv iduals, may be one of the possible origins of the intracranial ectopic pitu itary adenomas. However, the reason why a majority of the reported intracra nial ectopic pituitary tumors are ACTH-adenomas remains unexplained, since the ectopic cells, found in "normal" individuals, consist of fairly differe nt hormone-producing cells. A further enigmatic phenomenon is a "basophil i nvasion." ACTH-positive cells invade from the pars intermedia into the post erior lobe of the pituitary. This invasion increases in intensity and frequ ency according to increase in age. However, the invasion of ACTH cells is o bserved as early as in the fetal life. The invasive cells display occasiona lly cell atypia as well as mitotic activity. The origin of extremely rare p ituitary adenomas inside the posterior lobe can be explained by the existen ce and proliferative activity of basophil invasion. Microsc. Res. Tech. 46: 59-68, 1999. (C) 1999 Wiley-Liss, Inc.