Diabetes insipidus in pediatric germinomas of the suprasellar region: characteristic features and significance of the pituitary bright spot

The pituitary bright spot is acknowledged to indicate functional integrity of the posterior pituitary gland, whilst its absence supports a diagnosis of central diabetes insipidus (DI). This feature was evaluated, together with the incidence and clinical characteristics of DI in children with suprasellar/neurohypophyseal germinomas. We performed a review of all suprasellar (SS) or bifocal (BF) germinoma pediatric patients treated in Toronto since 2000. Demographics, symptomatology, treatment outcome and imaging were evaluated. Nineteen patients fulfilled inclusion criteria (10 SS, 9 BF; median age 12.5 years (6.2-16.8 years)). All remained alive at 6.4 years median follow-up (1.2-13.7 years) after receiving chemotherapy and radiotherapy (13 focal/ventricular, four whole brain, two neuraxis), with only one progression. All had symptoms of DI at presentation with a symptom interval above one year in eight cases (42 %). Desmopressin was commenced and maintained in 16 patients (84 %). The pituitary bright spot was lost in most diagnostic interpretable cases, but was appreciated in three patients (18 %) who had normal serum sodium values compared to 'absent' cases (p = 0.013). For two such cases, spots remained visible until last follow-up (range 0.4-3.3 years), with one still receiving desmopressin. No case of bright spot recovery was observed following therapy. Protracted symptom intervals for germinoma-induced central DI may reflect poor clinical awareness. Explanations for persistence of the pituitary bright spot in symptomatic patients remain elusive. Desmopressin seldom reverses the clinical features of germinoma-induced DI to allow discontinuation, nor does treatment cause bright spot recovery.