Endocrine Abstracts

Background: Extraventricular neurocytoma of the sellar region (EVNSR) is exceptionally rare, with ~30 cases reported. These tumours often mimic pituitary adenomas on imaging; but, differ in endocrine dysfunction, hyponatremia, and histopathological findings.

Cases: We describe two patients with EVNSR managed at a UK tertiary centre.

Case 1: An 82-year-old man with a history of headaches and progressive visual decline. MRI showed ~30 mm sellar/suprasellar mass invading the cavernous sinus and encasing the left ICA. Transsphenoidal debulking was performed (May 2025), but the tumour’s fibrous, adherent nature and intra-operative instability prevented full resection. Postoperatively, he developed SIADH (sodium nadir 125 mmol/l) managed with fluid restriction. Histology confirmed a neuronal tumour (synaptophysin/NeuN positive, Ki-67 3–4%) with non-matching methylation class. Residual tumour remains under clinic review. Case 2: A 33-year-old man presented in 2020 with headache, lethargy, constipation, and hyponatraemia. MRI revealed a 23 mm sellar/suprasellar lesion displacing the optic chiasm. Urgent transsphenoidal surgery was undertaken for visual field deterioration. Intra-operatively, tumour was soft/gelatinous with adherent areas; at redo surgery (Dec 2024) dense fibrosis allowed partial resection. Histology demonstrated a neuroendocrine/neurocytoma-like tumour (synaptophysin/NeuN/ChromograninA positive, Ki-67 5–7%, no matching methylation class), with electron microscopy revealing dense secretory granules. He developed GH and cortisol deficiency and intermittent SIADH. Despite repeat surgery and somatostatin analogue therapy, the tumour progressed; radiotherapy planned.

Discussion: Both cases highlight the diagnostic challenge of EVNSR, which often masquerades as pituitary macroadenoma. Key issues include cavernous sinus invasion, non-diagnostic methylation profiles, and SIADH from AVP secretion. Gross total resection is rarely feasible, recurrence is common, and adjuvant options remain limited, with variable SSA response and a role for radiotherapy.

Conclusion: EVNSR is a rare but important differential diagnosis of atypical sellar lesions. Hyponatraemia, neuronal immunoprofile, and non-diagnostic methylation arrays should prompt suspicion.