Occult neurohypophyseal germinoma discovered during the course of long-term diabetes insipidus: illustrative case

BACKGROUND: The authors report a case of occult neurohypophyseal germinoma detected in a patient with long-term diabetes insipidus. Central diabetes insipidus is the initial symptom in 95% of cases of neurohypophyseal germinoma. In occult neurohypophyseal germinomas, no abnormalities are seen on magnetic resonance imaging (MRI) at the onset of symptoms. It can take several months or even years for these changes to be detected on MRI. OBSERVATIONS: A 20-year-old male was diagnosed with central diabetes insipidus at the age of 17 years, and gonadal and adrenal corticosteroid insufficiency was noted at the age of 19 years. Head MRI showed an enlarged and enhanced pituitary stalk. He was referred to our department for a suspected neoplastic lesion. Endoscopic transsphenoidal biopsy indicated a pure germinoma. He was treated with chemotherapy and radiotherapy and then was discharged. LESSONS: In this case, new imaging findings appeared 19 months after the onset of diabetes insipidus, and the pathological diagnosis was made after almost 24 months. Because the patient had a history of growth hormone deficiency and had a positive test result for diabetes insipidus, occult neurohypophyseal germinoma was suspected, and periodic contrast-enhanced MRI monitoring was deemed essential.