An apparent cluster of congenital hypopituitarism in central Massachusetts: magnetic resonance imaging and hormonal studies.

Between 1980 and 1989, five infants (four males and one female) with congenital hypopituitarism were born within a relatively sparsely populated area of central Massachusetts, an incidence 25-fold greater than expected. In all infants the pituitary stalk was undetectable on magnetic resonance imaging, and a bright spot on T-1 weighted imaging, probably representing posterior pituitary tissue, was found ectopically located inferior to the median eminence. The height of the anterior pituitary remnant on magnetic resonance imaging varied from undetectable to 4 mm, and similarly, on hormonal testing a spectrum of deficiencies of GH, TSH, ACTH, and gonadotropin was observed. The magnitude of the hypopituitarism was less in the three patients whose anterior pituitary remnant was greater than 2 mm, and in them, TRH testing resulted in exaggerated TSH and PRL responses, suggestive of hypothalamic disease. In contrast, in the other two patients in whom the anterior pituitary remnant was less than 2 mm in height, hypopituitarism was more severe, and TRH administration resulted in little if any TSH or PRL response, characteristic of pituitary disease. The size of the anterior pituitary remnant correlated significantly with that of the ectopic posterior pituitary bright spot (P less than 0.005). We conclude that patients with congenital hypopituitarism may exhibit a spectrum of hormonal responses, varying from findings typical of hypothalamic to those characteristic of primary pituitary disease. The pattern of hormonal responsiveness is dependent on the quantity of residual anterior pituitary tissue and probably results from abnormal transport of the hypothalamic hypophyseal releasing hormones rather than to any putative hypothalamic abnormality. The significant correlation between the size and function of the anterior pituitary gland and the size of the ectopic posterior pituitary remnant suggests that the fetal pituitary gland may secrete a factor necessary for the growth and descent of the neuroepithelium to form the infundibulum and posterior pituitary gland.