Cytology of endolymphatic sac tumor

A 77-year-old man presented with decreased mental status and an enhancing p artially cystic tumor along the left tentorium on magnetic resonance imagin g after mastoidectomy and petrosectomy for an "auditory canal tumor." Smear s of the aspirated cyst fluid revealed rare epithelial cell clusters, some with papillary features, foamy macrophages, and blood. The cells were order ly, with fairly bland nuclei and well-defined cell borders. The cell block contained similar epithelium, with cells containing eosinophilic and focall y vacuolated cytoplasm, some with pigmented granules resembling hemosiderin . Numerous foam cells were also present. Review of the patient's previous a nd concurrent resection material showed an endolymphatic sac tumor, a rare neoplasm that arises in the endolymphatic sac in the temporal bone. The pre viously undescribed cytologic features of this rare neoplasm are discussed.