Endolymphatic Sac Tumor

**Semantic type:** Neoplastic Process

**Definition:** A rare, low-grade malignant epithelial tumor arising from the endolymphatic sac in the temporal bone. Morphologically, it is characterized by the presence of papillary and cystic structures. As tumors grow, they may destroy petrous temporal bone and extend into the middle ear and the middle and posterior cranial fossae and into the cerebellopontine angle. (WHO 2017)

**Synonyms:** - ELST - Heffner Tumor - Low Grade Papillary Adenocarcinoma of Endolymphatic Sac Origin - Low-Grade Papillary Adenocarcinoma of Endolymphatic Sac Origin