Pleomorphic adenoma arising in salivary heterotopia-cyst complex of parathyroid: a rare origin for ectopic salivary gland neoplasia.

We report a case of an early pleomorphic adenoma arising in salivary heterotopia (SH) with an associated Kürsteiner cyst, all in the fat adjacent to a hypercellular parathyroid. The association of SH-cyst complexes with parathyroid is a recurring finding with suggested origin from Kürsteiner canals (KC), which are putative embryologic remnants of the developing thymus and inferior parathyroid glands in the third branchial pouches. We subsequently established the immunophenotype for KC (SOX-10 positive, parathyroid hormone negative, PAX-9 variable) and confirmed that the cysts of SH-cyst complexes do indeed have this phenotype and as expected, share SOX-10 positivity with the acinar and intercalated duct components of SH. Our case shows an intimate association with ductal elements, plasmacytoid myoepithelial cells, and HMGA2 reactivity, justifying designation as an incipient pleomorphic adenoma. Thus, this incidental finding provides another rare but plausible rationale for primary salivary gland tumors in the neck without a known primary.