Olfactory neurocytoma as a unique cause of chronic SIADH

Abstract

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.

Keywords: adrenal disorders; ear; endocrine cancer; head and neck cancer; neurooncology; nose and throat/otolaryngology.

Figure 1

Axial and coronal images from MRI of the head and neck demonstrating mild mucosal thickening of the right maxillary sinus and obstructed sinus drainage pathway, of doubtful clinical significance. No skull base or pituitary abnormality is evident.

Figure 2

Nuclear Medicine Ga-68 DOTATATE positron emission tomography CT scan highlighting focal uptake in the right nasal turbinate, low-grade activity in normal size bilateral level II nodes. Distribution elsewhere through the extracranial head, neck and chest is normal, low level hylan uptake likely inflammatory.

Figure 3

Axial and coronal images from CT scan of the sinus demonstrating mild sinonasal mucosal thickening as described. There is focal soft tissue thickening related to the right ethmoid infundibulum is longstanding (being seen on the MRI of 2015 when it was of increased T2 signal).