[Reversible blindness caused by an invasive prolactinoma]

A 40-year-old man presented with severe headache, nausea and acute blindness. A CT-scan of the skull revealed a huge tumor along the basis of the skull. The patient was referred to our clinic for diagnostic and therapeutic evaluation.

MRT showed a large right-sided paramedian tumour displacing the brain stem with signs of increased intracranial pressure. Routine laboratory tests were normal except a normochromic anaemia. Endocrine tests demonstrated partial hypopituitarism with alteration of the somatotropic, gonadotropic and corticotropic axis and moderate hyperprolactinaemia.

On the day of admission a transnasal biopsy was taken. The preliminary histopathological diagnosis was a low differentiated carcinoma. Because of this diagnosis and because of the infiltrative tumour growth an operation was not performed but emergency irradiation was begun and dopamine agonist therapy was started because of hyperprolactinaemia. Several days later the final microscopic diagnosis of the transnasal biopsy specimen was reported to be an invasive prolactinoma. Under dopamine agonist therapy prolactin levels rose to a maximum of 6460 ng/ml to decline thereafter to normal values, and the visual disturbances recovered. After 5 weeks of therapy considerable shrinkage of the tumor was demonstrated by MRT.

The differential diagnosis of acute visual deterioration caused by a large tumour along the basis of the skull includes an invasive prolactinoma. The diagnosis is made by demonstrating grossly elevated prolactin levels. To avoid falsely low prolactin measurements, caused by a hook-effect in the prolactin assay, serum dilution is mandatory in the diagnostic work-up. In the case of a prolactinoma medical treatment with dopamine receptor agonists is the therapy of choice because it causes rapid tumour shrinkage and symptomatic improvement in most patients, so that irradition of the tumour is not indicated. As dopamine agonist therapy is rapidly effective and well tolerated, it should be started even in case of doubt to lose no time until final diagnosis.