Metastasizing pleomorphic adenoma in the multiple organs A case report on FDG-PET/CT imaging

Rationale: Pleomorphic adenoma, the most common tumor of the salivary glands, is usually benign. It is well known, however, that pleomorphic adenomas occasionally undergo malignant transformation to carcinoma ex pleomorphic adenoma and can metastasize. More rarely pleomorphic adenomas can metastasize without histological malignant transformation. We herein report an unusual case of pleomorphic adenoma with multiple metastases comprehensively demonstrated on F-18 fluorodeoxyglucose positron emission tomography/computed tomography (FDG-PET/CT). Patient concerns: A 63-year-old woman was referred to our hospital because of urine occult blood and lung nodules detected on a health checkup. She had a history of resection of a pleomorphic adenoma in the parotid gland at the age of 40 years and tumor recurrence at the age of 53 years. CT scan and magnetic resonance imaging revealed bilateral renal tumors, multiple pulmonary nodules, and an osteolytic lesion in the first lumbar vertebra. Diagnoses: Ultrasonography-guided percutaneous biopsy of the right renal tumor revealed a myxoid epithelial tumor that was consistent with metastasis of the pleomorphic adenoma from the parotid gland. Interventions: The patient was carefully observed with regular imaging examinations. Outcomes: The multiple lesions gradually progressed, and FDG-PET/CT subsequently revealed additional metastases in the liver and perineum. Lessons: Metastases of pleomorphic adenomas may occur years after the initial disease in association with local recurrences. Careful observation with whole-body imaging such as FDG-PET/CT is necessary.