Dynamic contrast – enhanced MR imaging of the stimulated pituitary gland

Apoplexy due to infarction and/or hemorrhage is a frequent complication of pituitary adenoma, occurring either spontaneously or precipitated by several factors, among them combined pituitary stimulation test with the four hypothalamic releasing hormones CRH, TRH, GHRH and GnRH. The mechanism by which releasing hormones cause pituitary apoplexy is unclear. It has been proposed that increase in pituitary size and/or alterations in blood flow could be responsible. The aim of this study was to explore the effects of intravenous administration of hypothalamic releasing hormones on pituitary size and hemodynamics in healthy subjects. Gadolinium-enhanced dynamic magnetic resonance imaging (MRI) was performed under basal conditions and 20 minutes after injection of the 4 hypothalamic releasing hormones. 2 out of 10 apparently healthy subjects had pituitary abnormalities in the basal MRI scan and were excluded from further analysis. In the remaining 8 subjects pituitary height, width and length were determined on corresponding MRI slices from basal and stimulated conditions. None of the measured parameters of pituitary size nor their product (as an additional surrogate of pituitary volume) differed significantly between basal and stimulated conditions. In contrast, mean upslopes of gadolinium enhancement curves were significantly steeper after stimulation (p=0.017). In conclusion, the pituitary does not swell in healthy subjects in response to stimulation with hypothalamic releasing hormones, whereas transfer of contrast agent to tissue (blood flow and/or vessel permeability) is enhanced.