Visual recovery after acute blindness from an invasive prolactinoma

History: 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 thera peutic evaluation. Investigations: MRT showed a large right-sided paramedian tumour displacing the brain stem with signs of increased intracranial pressure. Routine labo ratory tests were normal except a normochromic anaemia. Endocrine tests dem onstrated partial hypopituitarism with alteration of the somatotropic, gona dotropic and corticotropic axis and moderate hyperprolactinaemia. Treatment and course: On the day of admission a transnasal biopsy was taken . The preliminary histopathological diagnosis was a low differentiated carc inoma. Because of this diagnosis and because of the infiltrative tumour gro wth an operation was not performed but emergency irradiation was begun and dopamine agonist therapy was started because of hyperprolactinaemia. Severa l days later the final microscopic diagnosis of the transnasal biopsy speci men was reported to be an invasive prolactinoma. Under dopamine agonist the rapy 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. Conclusion: The differential diagnosis of acute visual deterioration caused by a large tumour along the basis of the skull includes an invasive prolac tinoma. The diagnosis is made by demonstrating grossly elevated prolactin l evels. 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 tum our 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.