OBJECTIVETo study the clinicopathologic features and immunophenotype of endolymphatic sac tumor (ELST) and normal endolymphatic sac.

METHODSThe clinical and histologic features were evaluated in 5 cases of ELST. Eight cases of choroid plexus papilloma at cerebellopontine angle and 2 cases of normal endolymphatic sac were used as controls. Immunohistochemical study for vimentin, AE1/AE3, CK8/18, CK5/6, EMA, GFAP, synaptophysin, S-100 protein, CEA, TTF-1, VEGF, D2-40, calponin, calretinin and Ki-67 was carried out.

RESULTSThe age of onset of ELST ranged from 23 to 35 years (median = 24 years). The male-to-female ratio was 2:3. The clinical presentation was tinnitus, otalgia, hearing loss, otorrhagia with effusion and headache. The duration of symptoms ranged from 6 months to 10 years. Local recurrences were noted in 3 cases. Radiologically, the tumors were located at cerebellopontine angle and demonstrated petrous bone destruction. Histologic examination showed that the tumors had a papillary-glandular pattern. The papillae were covered by a single layer of low cuboidal cells. The tumor cells had distinct cell borders and contained eosinophilic to clear cytoplasm. The nuclei were slightly atypical and sometimes apically located. Focal dilated glandular structures with colloid-like material were also identified. The surrounding stroma was vascularized. All of the 5 cases had dural or petrous bone infiltration. Immunohistochemical study showed that all of the 5 cases were positive for AE1/AE3, CK8/18, CK5/6 and VEGF, 4 cases for EMA, 3 cases for calponin (focal), 2 cases for vimentin, 2 cases for S-100 protein, 1 case for GFAP and 1 case for synaptophysin (focal and weak). The Ki-67 index measured less than 1%. The staining for D2-40, calretinin, CEA and TTF-1 was negative. The 2 cases of the normal endolymphatic sac were positive for AE1/AE3 and CK8/18, and negative for CK5/6, EMA, S-100 protein, GFAP and synaptophysin. The 8 cases of choroid plexus papilloma were positive for synaptophysin. Seven cases were also positive for S-100 protein, 2 cases for GFAP and 1 case for D2-40. All of the 8 cases were negative for EMA, CK5/6 and calponin.

CONCLUSIONSELST is a rare slow-growing and potentially malignant tumor with a tendency of bone invasion and local recurrence. Distant metastasis is not observed. It must be distinguished from choroid plexus papilloma occurring at cerebellopontine angle. Correlation with clinical, radiologic and immunohistochemical findings would also be helpful.