摘要Endolymphatic sac tumor (ELST) is an uncommon neoplasm which can be encountered in Von Hippel-Lindau (VHL) disease or sporadically. Herein, we report a sporadic case of ELST in 30-year-old women who was at first recognized with cerebellopontine angle (cp angle) tumor. Computed tomography (CT) imaging showed an expansile lytic lesion of the mastoid process of the left-sided petrous bone. Magnetic resonance imaging (MRI) showed a 4 cm × 4 cm × 3 cm mass with hyperintensity on T1- and T2-weighted images. Histologic sections showed an aggressive papillary. Although the mass was large, it was incredulously removed completely with the transaortic approach. After surgery, the patient underwent radiotherapy for the microscopic residual of the tumor. The findings indicate that ELST can easily be misdiagnosed with other tumors, like paraganglioma, adenocarcinoma, middle ear adenoma, thyroid papillary carcinoma or papilloma of choroid plexus, because of the rarity of this tumor. When it is large, it is difficult to extirpate surgically, owing to its locally aggressive nature.