A rare tumor with unique features: polymorphous low-grade neuroepithelial tumor of the young with third ventricular location and TP53 mutation. Illustrative case.

backgroundPolymorphous low-grade neuroepithelial tumors of the young (PLNTYs) are rare, generally indolent brain tumors first described in 2017 and recently included as a recognized entity in the 5th edition of the World Health Organization Classification of Tumors of the Central Nervous System. PLNTYs occur most commonly in children and young adults and are often associated with epilepsy and favorable clinical outcomes. OBSERVATIONS: The authors present a case of PLNTY in the third ventricle, an unusual location for this tumor, with operative, histological, and molecular analysis. Notably, they identified a pathogenic TP53 mutation, which has been rarely reported in this tumor type. The operative video demonstrates anatomical and surgical considerations for this rare and newly recognized tumor type. LESSONS: The authors contribute a new case of PLNTY to the literature, highlighting the uncommon features of this case, including third ventricular localization and the presence of a TP53 mutation. They include a surgical case video for comprehensive visualization. These tumors typically exhibit indolent behavior and can be managed with resection alone. Comprehensive radiological, histological, and molecular evaluation is necessary to distinguish these tumors from other low-grade neoplasms. https://thejns.org/doi/10.3171/CASE25346.