RESUMO
Hyponatremia is the most common fluid electrolyte disorder in hospitalized patients. Syndrome of inappropriate antidiuretic hormone secretion (SIADH) is the main cause of normovolemic hyponatremia, it can be caused by diverse etiologies: malignant tumors are the most feared cause that clinician persists in finding. Exceptionally, SIADH can complicate Esthesioneuroblastoma (ENB) or olfactory neuroblastoma, a rare tumor of the nasal sinus cavities. We report the case of a 26-year-old female patient admitted for recurrent headaches and vomiting, with a profound normovolemic hyponatremia at the initial assessment. Biological explorations have concluded in a SIADH. Imaging showed a mass of the left nasal cavity with extensions to the ipsilateral paranasal sinuses. The biopsy of the lesion, under endoscopic control, was inconclusive. The anatomopathological study, after surgical removal, concluded in ENB. The postoperative evolution was marked by the normalization of the natremia.