Neurohypophysis Cyst: Not Always Straightforward

Incidentaloma, a term frequently used in endocrinology to refer to the adrenal glands and thyroid, also applies to the pituitary gland. The management of pituitary incidentalomas is controversial. The incidental discovery of a pituitary cyst is relatively common and often warrants an endocrinological consultation. Some lesions can increase in size and lead to pituitary insufficiency or compression of the optic chiasm, while others remain stable and cause no tumor-like or hormonal symptoms. Our case concerns a 48-year-old woman followed in our department for a simple neurohypophysis cyst discovered incidentally. After two years of biological and radiological monitoring, her condition progressed with the gradual onset of asthenia, bradycardia, and hypotension, with a tendency toward hypoglycemia and the biological assessment revealed hyperprolactinemia with borderline low cortisol levels and a tendency towards hyperkalemia. A brain MRI revealed that the neurohypophysis cyst had doubled in size, increasing from 3.5 × 4 mm to 7 × 7.5 mm, while remaining well-defined, prompting the initiation of hormone replacement therapy with complete resolution of symptoms. When a cyst in the sellar region is discovered incidentally during a CT or MRI scan, the first challenge is to differentiate it from various pituitary cystic lesions: Rathke’s pouch cyst, cystic craniopharyngioma, cystic adenoma, or simple neurohypophysis cyst, as this diagnosis significantly influences the treatment decision. Clinical and radiological monitoring can be considered when the lesion is small and non-secreting, thus relegating surgery to other indications.