Mucinous (secretory) myoepithelioma is a very uncommon variant of myoepithelioma characterized by the presence of intracellular mucin. We herein report the findings of a 51-year-old woman who presented with a mass in the right parotid region, which had been slowly growing over the previous year. Magnetic resonance imaging revealed a rounded mass with lobulated margins in the tail of the right parotid gland that showed heterogeneous uptake in the anterior margin of the mass. A clinical diagnosis of pleomorphic adenoma was made. Superficial parotidectomy revealed a 3.6 cm encapsulated, round-shaped, light brown, gelatinous, solid tumor. The neoplasm showed a reticular pattern forming pseudoglandular structures that were filled with abundant extracellular mucin secretion. Additionally, lakes of mucin of different sizes appeared to be scattered throughout the neoplasm. The epithelioid tumor cells were medium-sized with eosinophilic cytoplasm, centrally located, small, uniform nuclei, and inconspicuous nucleoli. Mitoses were not observed. Signet-ring or univacuolated cells, ductal, and glandular components were absent. The extracellular mucin was positive for mucicarmine and Alcian blue staining. Immunohistochemical staining revealed that the tumor cells were diffusely and strongly positive for S100 protein, cytokeratin AE1/AE3, SOX10, and DOG-1. Occasional compact solid clusters of epithelioid cells showed intense positivity for CK7 and high-molecular-weight CK. The diagnosis was pure extracellular mucin-producing (colloid) myoepithelioma. To our knowledge, this type of neoplasm has not been previously published. Knowledge of this new variant will avoid diagnostic difficulties.
Keywords: Colloid type; Mucinous type; Myoepithelioma; Salivary gland; Secretory type.
Copyright © 2022 Elsevier GmbH. All rights reserved.