MR imaging in children with ectopic pituitary gland and anterior hypopituitarism.D Patkar, T Patankar, A Krishnan, S Prasad, J Shah, J Limdi
Department of Radiology, Dr Balabhai Nanavati Hospital, Mumbai, India., India
Correspondence Address: Source of Support: None, Conflict of Interest: None PMID: 0010734341
Source of Support: None, Conflict of Interest: None
Posterior pituitary ectopia refers to an absent normal posterior pituitary bright spot within the sella with ectopic bright signal at another site (such as the median eminence) on a weighted magnetic resonance. We describe two children with idiopathic anterior hypopituitarism who showed an ectopic posterior pituitary and absent pituitary stalk on imaging. We emphasize the association of the absent pituitary stalk in ectopic pituitary gland and low growth hormone levels.
Keywords: Case Report, Child, Choristoma, diagnosis,Female, Human, Hypopituitarism, etiology,Magnetic Resonance Imaging, Male, Median Eminence, Pituitary Gland,
Ectopic posterior pituitary tissue could result from defective neuronal migration during embryogenesis. We report two cases of children presenting with idiopathic anterior hypopituitarism, who on magnetic resonance imaging (MRI) demonstrated a bright signal at the median eminence and an absent pituitary stalk and correlated this with growth hormone levels.
An 8-year-old boy presented with short stature and growth retardation. Past records showed that he was a full term normal vaginal delivery. There was no evidence of any perinatal complication recorded. Clinical examination was unremarkable except for obvious growth retardation. Laboratory investigations revealed growth hormone levels of 3 (g/L after insulin induced (0.1 IU/Kg body weight) hypoglycaemia. The thyrotropin secretory response to thyrotropin releasing hormone was delayed and prolonged. She had an intact posterior pituitary function with a urinary specific gravity of 1.031. MRI revealed an hyperintense signal on T1WI at the median eminence. The pituitary stalk was however not visualized on the MR scans.
A 10-year-old girl in whom the diagnosis of hypopituitarism was established at 22 months of age after presentation with recurrent hypoglycaemic seizures and growth retardation. There was no history of any complications occurring during delivery. The growth hormone level after insulin induced hypoglycaemia was 5 (g/L. The thyrotropin secretory response to thyrotropin releasing hormone was prolonged. Gonadotropin secretion after administration of gonadotropin releasing hormone was low for the age of the patient. There was no clinical or laboratory evidence of posterior pituitary dysfunction. The specific gravity of urine was normal. MRI revealed a absent normal posterior bright signal with a ectopic signal at the median eminence. The pituitary was normal in size but no evidence of the stalk was seen on any of the MR images.
The anterior and the posterior pituitary are composed of tissues that differ from each other embryologically and histologically Normal development results in the fusion of the anterior lobe growing upward from the ectoderm of the stomadaeum (Rathkes pouch) and the posterior pituitary growing downward from the neuroectoderm of the diencephalon. The pituitary functions as an endocrine gland under control of the hypothalamus via the infundibular stalk. Nerve fibres of the supraoptic and paraventricular nuclei of the hypothalamus course into the infundibulum to reach the posterior pituitary gland.
Normally the anterior pituitary and the stalk are well defined and the posterior pituitary is easily identified as a hyperintense bright spot on MR. The source of this distinct signal has been attributed to lipid concentrations within the glial cell pituicytes, the arginine vasopressin neurophysin complex, and most recently, phospholipids within the walls of the secretory vesicles containing the arginine vasopressin neurophysin complex. Kucharezyk et al showed that the magnetic resonance characteristics of phospholipids and not antidiuretic hormone is responsible for the magnetic resonance properties of the posterior pituitary gland. Ectopic posterior pituitary tissue could result from defective neuronal migration during embryogenesis. Another possible pathophysiologic mechanism for ectopic posterior pituitary tissue is transection of the pituitary stalk followed by hypertrophy of the proximal axons with subsequent reorganization. Trauma of the pituitary stalk due to vascular accidents, anoxia or compression injuries may act through similar mechanisms leading to reorganization of the proximal neurons of the neurohypophysis. Breech deliveries and perinatal anoxia have been implicated as causes of hypopituitarism secondary to transection of the pituitary stalk, with ensuing neuronal reorganisation of the proximal stump of the infundihulum. However, many patients with hypopituitarism with ectopic posterior pituitary hyperintense signal have been reported to have uncomplicated perinatal courses. In both our patients there was no history of breech delivery or perinatal anoxia to suggest any such possible cause for the ectopic pituitary gland.
Growth hormone deficiency (GHD) is a common endocrine cause of short stature. The rate of occurrence has been estimated at one per 4000 persons. It may be idiopathic or associated with organic causes such as tumour, surgery, or irradiation of the sellar area. Idiopathic GHD may occur in isolation or in association with multiple anterior pituitary hormone deficiencies. Hamilton et al reported an association between the severity of GHD and the likelihood of finding ectopic posterior pituitary on MR images He showed that patients with growth hormone peak levels less than 3 (g/L are more likely to have ectopic posterior pituitary than those whose peak level was 3 (g/L or greater. In both our patients G1-1 levels were below 3 (g/L.
Non-visualisation of the stalk is associated with lack of anterior pituitary function while visualization of the stalk is associated with preservation of some anterior function. A posterior pituitary hormone deficiency in the presence of posterior pituitary ectopia appears to be uncommon suggesting that this ectopic tissue functions normally to produce antidiuretic hormone. In both our patients the pituitary stalk was not visualized. This was presumed to indicate absence of the pituitary stalk, but the possibility of an extremely attenuated stalk that might not be visualized by the current MR scanners cannot be completely excluded. Absence of the pituitary stalk by enhanced MR imaging associated with hypopituitarism is also known with an earlier age of onset. Both our patients were children and showed a very low growth hormone levels and a normal posterior pituitary function.
MR imaging can show characteristic anatomic pituitary abnormalities in patients with idiopathic GHD, including a small to absent anterior pituitary gland, a small or truncated stalk and an ectopic posterior pituitary (EPP) hyperintensity located at the base of the hypothalamus or at the inferior end of the truncated pituitary stalk. A higher frequency of MR abnormalities has been seen in children with multiple pituitary hormone deficiencies (MPHD) than in those with isolated GHD has been seen.
In summary an ectopic hyperintense T1 signal or bright spot on NM imaging is associated with anterior pituitary hormone deficiencies. Attenuation of the stalk is associated with anterior pituitary hormone deficiencies limited to GH and thyrotropin and an inconstant age of onset. Absence of the pituitary stalk shown by enhanced MR imaging is associated with hypopituitarism and an earlier age of onset and low GH levels. Hence we emphasize the benefits of a careful examination of the pituitary stalk in patients with ectopic pituitary seen as a focus of hyperintense T1 signal in the suprasellar cistern.
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