Endolymphatic sac tumor of the left fossae termporalis and fossa cranii posterior: report of a rare case

Endolymphatic sac tumor (ELST) is a rare low-grade non-metastasizing adenocarcinoma of endolymphatic sac origin that arises in the petrous part of the temporal bone. Here we present a case of endolymphatic sac tumor of the head in a 53-year-old man who had symptoms in his left ear since 40 years ago after drowning and found a mass about 2 cm around his left ear 8 years ago, which grows slowly to about 10 cm in appearance. MRI detected a mass about 8.4 cm×6.2 cm, located in the left fossae termporalis and fossa cranii posterior, with the left petrous bone in the center of the tumor. Histologically, the tumor cells are low cuboidal cells without marked atypia and show papillary architecture and glandular formation. Immunohistochemical staining shows that the tumor cells were positive for CK (AE1/AE3), but negative for vimentin, Pax-8, TTF-1 and PSA. Ki67 index was lower than 5%.