Predominant catecholaminergic differentiation in tympanic paragangliomas: report of three consecutive cases.

Middle ear paragangliomas (ME-PGLs) are rare non-epithelial neuroendocrine neoplasms and the most common neoplasms of the middle ear. Tympanic paragangliomas (Ty-PGLs), a subset of ME-PGLs, are often biochemically non-functional, although prior studies have reported expression of cholinergic and, less frequently, catecholaminergic markers. The expression of functional biomarkers and somatostatin receptor type 2 A (SSTR2A) remains poorly defined in Ty-PGLs. We analyzed three surgically resected Ty-PGLs from adult patients without hyperadrenergic symptoms using immunohistochemistry. All tumors exhibited strong, diffuse tyrosine hydroxylase expression; dopamine β-hydroxylase was negative in all cases, while choline acetyltransferase was focally positive in only one case. All Ty-PGLs showed moderate membranous SSTR2A expression. These findings indicate that a catecholaminergic immunophenotype may be relatively common in Ty-PGLs, challenging the traditional distinction between sympathetic and parasympathetic paragangliomas. Further studies are needed to clarify the clinical significance of these features and the physiological role of tympanic paraganglia.