A third ventricular floor-associated TTF-1-positive posterior pituitary tumor: illustrative case.

backgroundTTF-1 (thyroid transcription factor 1)-positive posterior pituitary tumors are rare low-grade neoplasms and are difficult to diagnose preoperatively because they can mimic other sellar, suprasellar, or third ventricular lesions. OBSERVATIONS: A 30-year-old man presented with intermittent headaches, normal visual field testing, normal basal pituitary endocrine function, and normal serum alpha-fetoprotein and human chorionic gonadotropin levels. MRI showed a solid enhancing suprasellar mass closely related to the lamina terminalis and floor of the third ventricle. Gross-total resection (GTR) was achieved through a frontobasal interhemispheric approach with opening of the lamina terminalis under microscopic visualization. Histopathological analysis showed a bland spindle cell neoplasm with nuclear TTF-1 positivity and a low Ki-67 labeling index, supporting a TTF-1-positive posterior pituitary tumor in the pituicytoma/spindle cell oncocytoma spectrum. The patient had no postoperative diabetes insipidus or neurological deficit, and no recurrence was seen at 1 year. LESSONS: This entity should be considered for solid enhancing suprasellar or third ventricular floor-associated tumors. TTF-1 immunostaining is essential for diagnosis, and GTR can lead to a favorable outcome. https://thejns.org/doi/10.3171/CASE26664.