Pituicytoma in the third ventricle suggesting a third ventricular floor origin: illustrative case.

backgroundPituicytoma is a rare thyroid transcription factor-1 (TTF-1)-positive glial neoplasm classified as a posterior pituitary tumor in the 2022 WHO classification. Most cases arise in the sellar or suprasellar region; intraventricular occurrence is exceedingly rare, with only 6 cases reported in the literature. OBSERVATIONS: A 72-year-old man presented with an incidentally detected suprasellar mass that gradually enlarged over 18 months, resulting in visual field disturbance. Preoperative imaging demonstrated a well-enhancing lesion without calcification and with intratumoral flow voids suggestive of hypervascularity. The patient underwent extended endoscopic transsphenoidal surgery (eTSS). Intraoperatively, the tumor was located in the third ventricle without continuity with the pituitary gland or stalk. Subtotal resection was performed. Histopathological and immunohistochemical analyses demonstrated positivity for TTF-1, S100, and glial fibrillary acidic protein, and DNA methylation profiling confirmed the diagnosis of pituicytoma. At 6 months postoperatively, the residual tumor showed progression and was treated with Gamma Knife radiosurgery. LESSONS: This case suggests that pituicytoma may rarely originate from the floor of the third ventricle. Extended eTSS may represent a safe and minimally invasive surgical approach for selected third ventricular lesions. https://thejns.org/doi/10.3171/CASE26414.