The value of 18 F-FDG PET/CT in the distinction between retroperitoneal fibrosis and its malignant mimics.

OBJECTIVE: To discuss the utility of 18 F-fluorodeoxyglucose (FDG) positron emission tomography/computerized tomography (PET/CT) in the diagnosis of idiopathic retroperitoneal fibrosis (iRPF).

METHODS: IRPF patients diagnosed between September 2011 and June 2016 were included. Retroperitoneal malignancy patients were included as control. The morphological features and FDG uptake of retroperitoneal lesions were measured along with lymph node (LN) mapping.

RESULTS: Seventy-one iRPF patients were included. Fifteen lymphoma patients and 6 retroperitoneal metastatic malignancy patients were included as control. Significant differences in morphological features were observed between iRPF and lymphoma but not retroperitoneal metastatic carcinoma. Compared with malignancy, iRPF displayed a lower frequency of high-FDG-uptake retroperitoneal lesions (P = 0.017) and a lower mean maximum standardized uptake value (SUVmax ) (P < 0.001). LNs located at axillary, retroperitoneal, supraclavicular, inguinal or peritoneal sites were more frequently observed in retroperitoneal malignancy, therefore, were defined as specific LNs. The area under the curve (AUC) for SUVmax was 0.893 with a sensitivity of 85.7% and a specificity of 80.3%, when the cut-off value of the SUVmax was 6.23. The AUC for the logistic regression model combining the lesions above renal arteries, the SUVmax and the number of specific LNs was 0.987 with a sensitivity of 90.5% and a specificity of 98.6%. The risk stratification model analysis indicated that most of the retroperitoneal malignancy patients were at moderate or high level, while most of the iRPF patients were at low risk.

CONCLUSIONS: Retroperitoneal malignancy can mimic iRPF morphologically. 18 F-FDG PET/CT can help to distinguish iRPF from retroperitoneal lymphoma and metastatic malignancy.