Aim: The absence of the hyperintense signal of the posterior pituitary in magnetic resonance imaging (MRI) is considered by some authors to be evidence of neurohypophyseal dysfunction. To evaluate the utility of MRI as a complementary diagnostic aid in patients with central diabetes insipidus (CDI), we studied the MR images of pediatric patients at diagnosis and during follow-up.
Methods: MR images from 14 patients (4 females, 10 males; mean age 8.5 years) who were referred for polyuria and polydipsia and whose diagnosis was central diabetes insipidus (CDI) were analyzed. Mean time of evolution from onset of polyuria until the first MRI was 1.5 years. In 11 patients more than one MR image was obtained during follow-up. Mean time of follow-up was 2.8 years.
Results: In 10 patients CDI was idiopathic, in 3 it was secondary to a hypothalamic tumor and in 1 it was secondary to histiocytosis. In one patient with idiopathic CDI, the hyperintense signal was present at diagnosis but disappeared during the following 15 months. Four of the patients with idiopathic CDI developed thickening of the pituitary stalk, some at their diagnosis and others during follow-up. Of the three patients in whom CDI was secondary to a germinoma, the hyperintense signal was absent in two of them, while in one the signal was ectopic and associated with a thickened pituitary stalk. In the patient with histiocytosis, the hyperintense signal was absent at diagnosis.
Conclusions: 1. In most of the patients with CDI the hyperintense signal of the posterior pituitary was absent at diagnosis; however in one patient this signal disappeared during follow-up and consequently its presence does not rule out a diagnosis of CDI. 2. Although a thickened pituitary stalk could reflect only a non-specific, transient inflammatory process, its presence makes ruling out tumoral or infiltrative disease obligatory.