Multicentric basal cell adenoma with intercalated Duct lesions

Intercalated duct lesions (IDLs) represent abnormal proliferations of the intercalated ducts that are occasionally associated with salivary gland neoplasms, such as epithelial-myoepithelial carcinoma and basal cell adenoma (BCA). The concomitant occurrence of these entities has led to speculation that IDLs may represent a precursor for certain salivary gland neoplasms. This is supported by recent studies that have demonstrated molecular similarities between IDLs and their associated tumors. Herein we describe a 65-year-old male who presented for evaluation of a left parotid mass present for 2 years. An MRI with contrast revealed 7 well-defined masses within the left parotid gland. The lesions demonstrated areas of heterogeneous enhancement with predominantly T2 hypointensity. The patient’s medical history was significant for an adenomatoid nodule of the left thyroid and a distant history of melanoma treated 40 years prior. Histologic examination of the left parotidectomy revealed multiple well-demarcated epithelial proliferations, in which tumor islands showed peripherally palisaded hyperchromatic nuclei and foci of ductal differentiation. Also noted within the peripheral parotid parenchyma were foci of intercalated ducts showing occasional serous acinar differentiation, consistent with IDLs. Immunohistochemical analysis revealed nuclear positivity for beta-catenin in both populations, and a Ki-67 showed a proliferative index of approximately 5%-10%. A diagnosis of multicentric basal cell adenoma with intercalated duct lesions was rendered. The patient is 1-month postexcision with no complications. The IDLs remain a poorly understood group of benign salivary gland proliferations that include hyperplasias, adenomas, and hybrid lesions displaying features of both. Their synchronous occurrence with benign salivary gland neoplasms can present diagnostic challenges and raise the possibility of malignancy if misinterpreted as infiltrative growth. A greater awareness of the histopathological and immunohistochemical spectrum of IDLs and their potential synchronous occurrence with salivary gland neoplasms can aid in avoiding such diagnostic pitfalls.