RT Journal Article SR Electronic T1 Olfactory neurocytoma as a unique cause of chronic SIADH JF BMJ Case Reports JO BMJ Case Reports FD BMJ Publishing Group Ltd SP e235021 DO 10.1136/bcr-2020-235021 VO 14 IS 1 A1 Mohammad Farwana A1 Chrysostomos Tornari A1 Ann Sandison A1 Pavol Surda YR 2021 UL http://casereports.bmj.com/content/14/1/e235021.abstract AB A 32-year-old man was found to have a nasal mass on DOTATATE positron emission tomography (PET) scan to investigate the cause of his syndrome of inappropriate antidiuretic hormone secretion (SIADH). The patient presented 6 years earlier with malignant hypertension followed by a second emergency admission for hyponatraemia. Multiple scans and blood tests over 6 years yielded no cause for his SIADH. Nasendoscopy was unremarkable. A PET scan prompted endoscopic sinus surgery which resulted in the resection of a mass in the anterior hiatus semilunaris. The histological findings were fitting with a diagnosis of a neurocytic-type tumour favouring an olfactory neurocytoma. Following resection, the patient remains well and is cured of his SIADH. An olfactory neurocytoma although rare should be considered as a benign differential for a mass in the nasal space. This case demonstrates how an olfactory neurocytoma can present as a cause of SIADH.