0021-972X/91/7201-0010$02.00/0 Journal of Clinical Endocrinology and Metabolism Copyright© 1991 by The Endocrine Society

Vol. 72, No. 1 Printed in U.S.A.

EDITORIAL: Magnetic Resonance Imaging in Hypopituitarism anatomical abnormality may occur as a consequence of an insult to the pituitary stalk and/or vasculature occurring in utero (7), hypoxia and trauma at birth (8), or pituitary tumors in older subjects (9). In an adult patient with pituitary apoplexy documented by MRI, the ectopic high intensity signal developed 1 yr after the primary insult (9). The nature of the intrauterine injury that interfered with the normal development of the anterior and posterior pituitaries in the infants with congenital hypopituitarism described by Brown et al. (7) in the current issue is unknown. Since four of five infants were born within a confined geographic area and within 2 yr of one another, one wonders if there may have been a toxic environmental factor to which the pregnant women were exposed in the first trimester. Further epidemiological studies concerning family occupations, exposure to chemicals or hazardous wastes, or common water source would be of interest. It is clear that the primary site of injury to the hypothalamic-pituitary unit in patients with hypopituitarism cannot be identified by functional evaluation. As documented by Brown et al. (7) and others (8, 10), patients with transection of the pituitary stalk may have an isolated hormone deficiency (often GH) or multiple, but unpredictable, hormone deficits; the anterior pituitary hormonal secretory response to hypothalamic releasing factors probably reflects the amount of residual anterior pituitary tissue rather than the site of insult and may vary over time. The suggestion that a trophic factor from the anterior pituitary is necessary for neurohypophyseal development is of interest (7). However, development of an ectopic posterior pituitary in adults after hypophysectomy or other insult to the pituitary suggests that it is the site of injury to the axons of the neurohypophysis that influences their ability to regenerate. Lesions above the median eminence prevent this process. The MRI has delineated a common anatomical abnormality in patients with hypopituitarism which may be the result of developmental, toxic, hypoxic, or traumatic insults and has contributed greatly to our understanding of the pathophysiology of this disorder. Allen W. Root Department of Pediatrics University of South Florida College of Medicine

Magnetic resonance imaging (MRI) has disclosed a consistent abnormality in many patients with idiopathic anterior hypopituitarism characterized by an adenohypophysis of varying volume (and sella turcica of varying configuration), attenuation or transection of the pituitary stalk, absence of the usual intrasellar location of the high intensity signal of the posterior pituitary, and the presence of such an image at or below the median eminence of the hypothalamus, considered an "ectopic" neurohypophysis. The posterior pituitary is composed of nonmyelinated axon terminals whose cell bodies are located in the supraoptic and paraventricular nuclei. Neurosecretory granules within the axons contain antidiuretic hormone (ADH), oxytocin, and their respective neurophysin carrier proteins. Also within the posterior pituitary are astrocytic glial cells termed pituicytes interspersed among and abutting the axon terminals. In dogs and cats pituicytes contain lipid droplets. The source of the high intensity signal of the posterior pituitary seen on Tl weighted MRI is uncertain. In dogs and cats an increase in signal intensity as ADH is secreted has been attributed to increase in the lipid content of the pituicytes as membrane lipids of the axons released during ADH secretion are engulfed by the pituicytes (1). However, in rabbits (and in man) the high intensity signal appears to emanate from the neurosecretory granules themselves, as its intensity diminishes with ADH secretion, and lipids are not present in the pituicytes of these species (2). There is a decrease in the frequency of the high intensity signal with age (3). Rarely is there anatomical variation in the location of this signal; in only 1 of 1500 MRI scans was a high intensity signal present in the median eminence in a patient without hypopituitarism (3). This intrasellar signal is absent in patients with central diabetes insipidus (4). Transection of the pituitary stalk in experimental animals and humans is followed by hypertrophy of the axons above the point of transection and reorganization into an ectopic posterior pituitary capable of secreting ADH (5, 6), a process now visualized by MRI. This Received July 5, 1990. Address requests for reprints to: Dr. Allen Root, Department of Pediatrics, All Children's Hospital, 801 6th Street S, St. Petersburg, Florida 33701.


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Tampa, Florida 33612 All Children's Hospital St. Petersburg, Florida 33701

References 1. Kucharczyk J, et al. Histochemical characterization and functional significance of the hyperintense signal on MR images of the posterior pituitary. Am J Nucl Roentgenol. 1988;9:1079-83. 2. Fujisawa I, et al. Hyperintense signal of the posterior pituitary on Tl-weighted MR images: an experimental study. J Comp Asst Tomogr. 1989;13:371-7. 3. Brooks BS, et al. Frequency and variation of the posterior pituitary bright signal on MR images. Am J Nucl Roentgenol. 1989;10:9438. 4. Gudinchet F, et al. MR imaging of the posterior hypophysis in children. Am J Nucl Roentgenol. 1989;10:511-4.


5. Fujisawa I, et al. Transection of the pituitary stalk: development of an ectopic posterior lobe assessed with MR imaging. Radiology. 1987;165:487-9. 6. Ehrlich RM. Ectopic and hypoplastic pituitary with adrenal hypoplasia; case report. J Pediatr. 1957;51:377-84. 7. Brown RS, Bhatia V, Hayes E. An apparent cluster of congenital hypopituitarism in central Massachusetts: magnetic resonance imaging and hormonal studies. J Clin Endocrinol Metab. 1991;72:1218. 8. Kikuchi K, et al. Hypothalamic-pituitary function in growth hormone-deficient patients with pituitary stalk section. J Clin Endocrinol Metab. 1988;67:817-23. 9. El Gammal T, Brooks BS, Hoffman WH. MR imaging of the ectopic bright spot signal of posterior pituitary regeneration. Am J Nucl Roentgenol. 1989; 10:323-8. 10. Root AW, Martinez CR, Muroff LR. Subhypothalamic high-intensity signals identified by magnetic resonance imaging in children with idiopathic anterior hypopituitarism. Am J Dis Child. 1989;143:366-7.

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Magnetic resonance imaging in hypopituitarism.

0021-972X/91/7201-0010$02.00/0 Journal of Clinical Endocrinology and Metabolism Copyright© 1991 by The Endocrine Society Vol. 72, No. 1 Printed in U...
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