The patient went on to have resection.

Histology

The sections show a moderately cellular tumor. It forms elongated nests and acinar-like structures. Some contain calcific deposits and psammoma bodies. The tumor cells have round nuclei, inconspicuous nucleoli and moderate amounts of 'oncocytic type' eosinophilic cytoplasm.

The tumor cells are CAM5.2, AE1/3, CK7, EMA, S-100 and SOX-10 positive. Progesterone receptor, melan-A, synaptophysin, TTF-1 and thyroglobulin are negative.

The PAS stain shows no fungi. The Ziehl-Neelsen stain shows no acid-fast bacilli. Though the architecture is not quite papillary but given the immunoprofile and the site, the features are consistent with papillary tumor of the endolymphatic sac.

FINAL DIAGNOSIS: Papillary tumor of the endolymphatic sac.