Bilateral Multifocal Nodular Oncocytic Hyperplasia of the Parotid Gland Mimicking Warthin Tumor and Acinic Cell Carcinoma: A Case Report and Literature Review.

内容摘要

Multifocal nodular oncocytic hyperplasia (MNOH) of the salivary glands is a rare benign condition that can mimic both benign and malignant neoplasms, posing significant diagnostic challenges. Its bilateral and multifocal presentation is exceptionally uncommon. We present a unique case initially interpreted as bilateral Warthin tumor, later redefined as bilateral acinic cell carcinoma and finally reclassified as MNOH after comprehensive histopathological and immunohistochemical evaluation, and review the literature. A 71-year-old woman presented with a long-standing mass in the left mandibular angle region. Fine-needle aspiration was compatible with Warthin tumor. MRI revealed a well-defined, partially cystic, enhancing lesion in the left parotid gland and a similar nodule in the contralateral gland. A left parotid tumorectomy with synchronous submandibular nodule excision was performed, both initially reported as acinic cell carcinoma (DOG1 positive). Subsequent left total parotidectomy showed multifocal acinic cell carcinoma, with negative FISH for CRTC1/MAML2, ruling out mucoacinar carcinoma. Contralateral MRI revealed multiple nodules with perfusion curves suggestive of Warthin tumor. Right parotidectomy revealed multifocal oncocytic hyperplasia with oncocytomas and extensive clear cell change. Immunohistochemistry demonstrated DOG1 apical positivity, but focal p63 expression and SOX10 negativity favored oncocytic hyperplasia/oncocytoma. Clinicopathologic correlation confirmed the diagnosis of bilateral MNOH. This case illustrates the pitfalls in diagnosing oncocytic lesions, where radiology, cytology, and even immunohistochemistry may mimic acinic cell carcinoma. The review of published cases confirms the rarity of bilateral MNOH and highlights the importance of correlating morphology, immunoprofiles, and clinical context. MNOH should be considered in the differential diagnosis of bilateral parotid lesions to avoid overtreatment. Recognition of its histological spectrum, including clear cell and oncocytoma-like features, is essential for accurate diagnosis.