This report describes a patient with a cystic non-functioning neuroendocrine glucagon cell pancreatic tumor presenting with demyelination of the optical nerve that had initially provoked marked monolateral reduced vision and had led to a suspected diagnosis of multiple sclerosis. Cystic degeneration is uncommon in endocrine pancreatic tumors due to their abundant vascular supply. Very few cases of cystic neuroendocrine non-functioning pancreatic tumors have been reported in the international literature. The presence of atypical neurological symptoms, such as sudden visual impairment, should be taken into account in the differential diagnosis for such tumors. The prognosis is poor, because most of these tumors are malignant and diagnosed at an advanced stage. The three-year disease-free survival of our patient, however, encourages the use of aggressive surgical treatment.