Clinical diagnosis
Case 80
【Progress】She was given growth hormone (Genotropin 0.25 mg) periodically for approximately five years. She received MRI to check the change of her pituitary gland.
【Discussion】
Pituitary gland sits on sella tunica (hypophyseal fossa) and is covered by a dura matter fold. Pressure from arachnoid space sometimes compress pituitary gland, causing empty sellae. Pituitary gland weighs approximately 0.5 g and composes of anterior, intermediate, and posterior lobes (1-3). Anterior lobe generates originally from oral ectoderm and intermediate lobe, originally from hypophyseal ectoderm (Rathke pouch), while posterior lobe originally from neural ectoderm, belonging to a part of hypothalamus. Then, anterior lobe is called adenohypophysis and posterior lobe is called neurohypophysis. Posterior lobe directly connects to hypothalamus via pituitary stalk. Although anterior lobe and intermediate lobe do not directly connect to hypothalamus, they are deeply involved with hypothalamus through hypothalamus-hypophyseal portal system.
There exist at least 5 different cells in anterior lobe which synthesis and secret growth (somatotropin) hormone (GH, 30-40%), adrenocorticotropin hormone (ACTH, 20%), thyroid stimulating hormone (TSH, 20%), Gonadotropic hormone (follicle stimulating hormone FSH, luteinizing hormone LH 3-5%) and prolactin (PRL 3-5%) (1-3). These cells are regulated and stimulated by hypothalamus via hypothalamus-hypophyseal portal system. In intermediate lobe, there exist cells synthesizing and secreting melanocyte-stimulating hormone (MSH). In posterior lobe, there exist cells secreting (but not synthesizing) antidiuretic hormone (ADH, also known as vasopressin) and oxytocin. These hormones are synthesized in neuro-secretary cells in hypothalamus whose axon down the pituitary stalk to terminates in the posterior lobe.
In our case, T1WI of MRI showed no visualization of pituitary stalk and a tiny nodule at the bottom of hypothalamus which was the same high signal intensity as posterior lobe, which might indicate retention of ADH and oxytocin. It is considered that because ADH and oxytocin are secreted in hypothalamus, the presence of the retention nodule implies that the supply of these hormones is not disorganized but retained. Our patient had no disorder of diabetes insipidus.
Pituitary stalk interruption syndrome (PSIS) is associated with either GH deficiency or multiple anterior pituitary hormone deficiencies with normal function of posterior lobe (4-8). There are two unknown points for pituitary stalk interruption syndrome (PSIS). One is that occurrence of this disorder is genetic, diplomatic or ischemic. Another is small stature due to growth hormone deficiency is usually found in PSIS and other hormone deficiencies are not always.
Stature with selective GH deficiency was only associated with pituitary stalk interruption. Anterior lobe is divided into pars tuberalis, pars intermedia and pars distalis. Pars tuberalis and pituitary stalk form pituitary infundibulum. Recent studies (9, 10) revealed that neural secretary cells at pars tuberalis are related with releasing growth hormone as an effector role of secreting growth hormone at para tuberalis. On MRI, the differentiation of pars tuberalis from pituitary stalk is difficult, so that pituitary stalk interruption means the infundibulum interruption of both pituitary stalk and pars tuberalis.
【Summary】
We present a two years and five months-old infant suffering from small stature and low level of growth hormone. MRI on T1WI showed absence of pituitary stalk and presence of small nodule with the high signal intensity at the bottom of hypothalamus. The degree of high signal intensity is the same as posterior lobe found in other patients. Based on the symptoms and MRI findings, she was diagnosed as pituitary stalk interruption syndrome. We should keep in mind that anterior pituitary lobe is composed of pars tuberalis, pars intermedia and pars distalis, and pars tuberalis which secrets growth hormone is one component of a pituitary stalk (infundibulum). Although a pure pituitary stalk anatomically connects to hypothalamus, ADH and oxytocin are synthesized in hypothalamus, no dysfunction of these hormones occurs in case of pituitary interruption syndrome but synthesizing dysfunction of growth hormone occurs because of interruption of pars tuberalis of anterior lobe.
【References】
1.Mancall, Elliott L.; Brock, David G., eds. (2011). "Cranial Fossae". Gray's Clinical Anatomy. Elsevier Health Sciences. p. 154. ISBN 9781437735802
2.Melmed, Shlomo (2011). The Pituitary - (Third Edition). San Diego, CA 92101-4495, USA: Academic Press is an imprint of Elsevier. pp. 23–25. ISBN 978-0-12-380926-1.
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4.Fujisawa I, et al.Transection of the pituitary stalk: development of an ectopic posterior lobe assessed with MR imaging. Radiology. 1987, 165: 487-489. 10.1148/radiology.165.2.3659371.
5.Vijayanand P, et al. Pituitary stalk interruption syndrome (PSIS). Indian J Pediatr. 2007, 74: 874-875. 10.1007/s12098-007-0161-4.
6.Guo Q, et al. Pituitary stalk interruption syndrome in Chinese people: clinical characteristic analysis of 55 cases. PLoS One. 2013, 8: e53579-10.1371/journal.pone.0053579.
7.Pinto G, et al. Pituitary stalk interruption syndrome: a clinical-biological-genetic assessment of its pathogenesis. J Clin Endocrinol Metab. 1997, 82: 3450-3454.
8.Reynaud R, et al. Pituitary stalk interruption syndrome in 83 patients: novel HESX1 mutation and severe hormonal prognosis in malformative forms. Eur J Endocrinol. 2011, 164: 457-465. 10.1530/EJE-10-0892.
9.Lee SS, et al. Growth without growth hormone in combined pituitary hormone deficiency caused by pituitary stalk interruption syndrome. Ann Pediatr Endocrinol Metab. 2017 Mar;22(1):55-59. doi: 10.6065/apem.2017.22.1.55. Epub 2017 Mar 31.
10.Lafarque MM, et al. Bovine pars tuberalis secretions release growth hormone from rat pars distalis of pituitary gland. Neuro Endocrinol Lett. 2004 Aug;25(4):273-7
2017.11.15