ENDOLYMPHATIC SAC TUMOR (ELST) CLINICALLY MIMICKING JUGULAR PARAGANGLIOMA.
ELST is a rare tumor with about 60 reported cases in the literature (5). Heffner (3) recorded the first large (20 cases) clinicopathologic study where an endolymphatic sac origin of these tumors was supposed under the heading of "low-grade adenocarcinoma of probable endolymphatic sac origin". Previous reports used designations such as "primary adenocarcinoma of the middle ear" (3), "primary adenocarcinoma of the temporal bone" (3) or "aggressive papillary tumor of middle ear/temporal bone (APMET)" (1, 2). Recent literature prefers ELST favoring an endolymphatic sac tumor origin (4, 5). Indeed, it is open to question, whether similar papillary adenocarcinomas actually can originate from middle ear (4).
ELST is a locally invasive papillary adenoid tumor which may extend into the cerebellopontine angle leading to neurosurgical intervention (3, 4, 5, 6). Metastases of ELST have never been reported (4, 5, 7).
Microscopically, ELST represents a highly vascularized, papillary adenoid epithelial tumor with cystic spaces and often thyroid follicle-like glandular structures. These formations are lined by a single row of cuboidal to low columnar or more flattened epithelial cells with eosinophilic or vacuolated (clear) cytoplasm. The content of clear cells, thyroid follicle-like structures and of tumor stroma is highly variable in individual cases (3, 4, 5). Siderophages, siderosis of tumor cells and cholesterol clefts are frequently found (3, 7). A capillary network immediately subjacent to the epithelium corresponds to findings in normal endolymphatic sac (3). (Diastase-sensitive) PAS-positivity of tumor cells is typical (3, 4, 5). Cytokeratin- and EMA-immunoreactivity are regularly found (3, 4, 5). Vimentin-positivity of the basal portions of cytoplasm has previously been reported (2). Immunohistochemical detection of GFAP, NSE, synaptophysin and S-100 protein may show focal positivity (3, 4, 5, 7). Mitoses are rare or lacking. Location of tumor origin determines tumor extension. If the neoplasm arises in the intraosseous, rugose part of the endolymphatic sac, there is extension into the petrous bone. Arising in the distal, intradural part of the endolymphatic sac, it extends into the cerebellopontine angle and the jugular foramen; large tumors show a combined extension (5).
History of long-standing hearing loss is often very typical of ELST (3, 4, 5). Careful early otological examination may lead to detection of an increasing number of small tumors possibly without massive destruction of petrous bone.
Typical clinical diagnosis of large ELST is jugular paraganglioma (3, 6, 7). Together with differential diagnosis of meningioma it can easily be excluded by microscopy. Possible metastasis of carcinoma of the thyroid should be tested by thyroglobulin-immunohistochemistry. ELST with numerous clear cells may be difficult to distinguish from metastasis of renal cell carcinoma, but it usually shows additional typical histological areas of ELST. Transthyretin-immunohistochemistry may help to separate choroid plexus tumors, but findings can be inconclusive. Exact clinical tumor localisation can resolve this problem. Reported cases of isolated (no contact with intraventricular choroid plexus) cerebellopontine angle choroid plexus tumors actually may represent examples of ELST (3, 5). ELST can - possibly in 15% of cases (1) - arise in patients with VHL disease (1, 4, 5). Bilateral ELST is probably exclusively found in VHL disease (4).
Contributed by Klaus Kuchelmeister MD, Michael Winking MD, Monika Hügens-Penzel MD, Dieter-Karsten Böker MD, Walter Schachenmayr MD