LAUSR

Rationale: Metanephric adenoma (MA) is a rare and often benign tumor. Most MAs were misdiagnosed as renal cell carcinomas (RCCs) preoperatively. Diffusion weighted imaging (DWI) and apparent diffusion coefficient (ADC) mapping can help to differentiate benign and malignant tumors. However, there are still pitfalls in using DWI and ADC to discriminate benign and malignant lesions. Patient concerns: A 56-year-old woman had a right renal metanephric adenoma. The tumor showed very low ADC value preoperatively and was misdiagnosed as a renal cell carcinoma. Diagnosis: Intraoperative ultrasound-guided percutaneous biopsy of tumor was performed. Based on the histopathological findings and immunohistochemical stains, a diagnosis of metanephric adenoma was suggested. Interventions: The patient received percutaneous cryoablation of this tumor. Five years later, she underwent right partial nephrectomy because local recurrence was revealed on a follow-up computed tomography (CT). Outcomes: MA was confirmed again by histological examination. The patient was uneventful after surgery. Lessons: ADC mapping can be used for differentiating RCCs from other benign tumors by their lower ADC values. However, some benign and malignant lesions have overlapped low ADC values. This case illustrated that a benign lesion such as MA could mimic RCC on ADC, by its highly cellular component. Cryoablation is an optional treatment, which has an increased risk of local recurrence. Follow-up CT or MRI is useful and necessary for detection of local recurrence by depicting enhancing solid parts in a tumor over time.