Endolymphatic sac tumor Aggressive papillary middle ear tumor Endolymphatic sac tumour Endolymphatic sac tumors (ELSTs) may arise sporadically or in von Hippel-Lindau (VHL) disease. The symptoms (hearing loss with or without tinnitus, vertigo, impairment of cranial nerve function) and the physical and neuro-otologic examination and imaging findings (computed tomography, magnetic resonance imaging) are not specific for tumors of the cerebellopontine angle (CPA). The final diagnosis can often only be reached through histopathological and immunohistochemical evaluation of the tumor specimen. The differential diagnosis in tumors of the CPA includes paraganglioma, chondroid tumor, atypical schwannoma, meningioma, and also rare entities such as aneurysm, hemangioblastoma, craniopharyngioma, and choroid plexus papilloma. A low-grade papillary epithelial neoplasm (adenocarcinoma) with a slow growth pattern. The endolymphatic duct emerges from the posterior wall of the saccule (of the inner ear) and ends in a blind pouch, the endolymphatic sac. Endolymphatic sac tumors (ELSTs) are known under different names in the literature (Heffner tumor, aggressive papillary middle ear tumor, and low-grade adenocarcinoma of endolymphatic sac origin). Low-grade adenocarcinoma of endolymphatic sac origin Heffner tumor UMLS:C2348239 SNOMEDCT_US:699817008 Aggressive papillary middle ear tumour Heffner tumour Neoplasm of the inner ear