Metastasizing pleomorphic adenoma of the parotid gland: A case report with multimodal imaging and histopathological...

Pleomorphic adenoma (PA) is the most common benign salivary gland tumor, predominantly arising in the parotid gland. Although usually indolent, it may rarely exhibit metastatic behavior without histological malignancy, a condition known as metastasizing pleomorphic adenoma (MPA). We report the case of a 43-year-old male with a history of right parotid pleomorphic adenoma (PA), initially treated by enucleation in 2010, followed by recurrence requiring total parotidectomy in 2019. The patient presented with a painless mass in the right parotid region associated with ipsilateral cervical swelling, a frontal scalp mass and lumbar pain. Magnetic resonance imaging (MRI) revealed a multilobulated lesion in the parotidectomy bed demonstrating low T1 signal intensity, high T2 signal intensity, elevated apparent diffusion coefficient (ADC ratio >1.3) and progressive contrast enhancement with a type A time-intensity curve, consistent with pleomorphic adenoma. Additional lesions with similar imaging features were identified in the right masticator space involving the lateral pterygoid muscle and along the right cervical level VIIb nodal chain. Whole-body computed tomography (CT) demonstrated an enhancing scalp mass and multiple osteolytic skeletal metastases. Histopathological analysis confirmed recurrent pleomorphic adenoma with metastatic deposits without malignant transformation. This case highlights the paradoxical behavior of MPA, the importance of complete surgical excision to reduce recurrence risk and the key role of MRI in lesion characterization and long-term surveillance. Prolonged follow-up is essential due to the potential for late metastatic spread.