Upper pole of a duplex kidney mimicking adrenal incidentaloma in 18F-fluoro-2-deoxy-D-glucose positron emission tomography: a pitfall in diagnosis.

18F-fluoro-2-deoxy-D-glucose positron emission tomography (FDG-PET) has proved to be valuable in the diagnosis and management of a variety of malignancies, but is still limited in providing detailed anatomical information. According to the literature, an adrenal incidentaloma with high FDG uptake usually indicates malignancy and requires further investigation. However, accurate localization of the adrenal gland in FDG-PET is difficult without the presence of surrounding well-visualized organs, such as the kidney or liver. If these organs have a congenital anomaly or are altered due to a previous operation, misdiagnosis can occur. We present a case with right partial duplex kidney accompanied by abnormal urine retention in the upper pole, which was misinterpreted as an adrenal incidentaloma in FDG-PET. A subsequent CT scan revealed a normal right adrenal gland, but a right partial duplex kidney. Fusion of the PET and CT images showed that the right adrenal lesion seen in the PET image corresponded to the upper pole of the duplex kidney.