June 2000: 68 year old woman with clinical diagnosis of jugular paraganglioma - Diagnosis: Endolymphatic sac tumor (ELST) clinically mimicking jugular paraganglioma.

The June COM: A 68-year-old woman presented with an 8-year history of left- sided progressive hearing loss, tinnitus, vertigo and intermittent trigemin al neuralgia. Neuroradiology showed a highly vascularized tumor with destru ction of the left petrous bone and extension into the cerebellopontine angl e and the jugular foremen without compression or infiltration of the brain. Clinical diagnosis was jugular paraganglioma. Histologically, a papillary, cystic, highly vascularized adenoid epithelial tumor with some thyroid fol licle-like glandular structures and a variable stromal component was seen. Its epithelial lining consisted of a single row of cuboidal to low columnar or more flattened cells with eosinophilic or clear cytoplasm. These tumor cells were PAS-positive and showed strong cytokeratin- and EMA- and focal N SE-immunoreactivity as well as vimentin-positivity in their basal cell port ion. Stromal capillaries were often located directly subjacent the epitheli um. Nuclear pleomorphism, mitoses or necroses were absent. Diagnosis was en dolymphatic sac tumor (ELST) (low-grade adenocarcinoma of probable endolymp hatic sec origin). ELST is a rare locally invasive tumor of the petrous bon e and/or with extension into the cerebellopontine angle and the jugular for amen, often clinically misdiagnosed as jugular paraganglioma. It may arise in patients with von Hippel-Lindau disease. Metastases of ELST have never b een reported.