18F-FDG PET-CT in the diagnosis of tumor thrombus: can it be differentiated from benign thrombus?

The correct diagnosis of tumor thrombosis and its differentiation from benign thrombus can change patient management and prevent unnecessary anticoagulation treatment. This study was aimed at evaluating the role of fluorodeoxyglucose (FDG) positron emission tomography-computed tomography (PET-CT) in the diagnosis of tumor thrombosis, and its differentiation from benign thromboembolism.

We conducted a retrospective review of FDG PET-CT scans of patients who underwent the study for staging/restaging of a known malignancy and had FDG-avid thrombosis. Maximum standardized uptake value (SUV max) of the thrombus, SUV max of tumor (if any), and SUV max of mediastinal blood pool were calculated. PET-CT results were confirmed with clinical follow-up, structural imaging, and histopathology when available.

A total of 24 patients (15 male and nine female) with a mean age of 43.8 years (range: 3-72 years; median: 47.5 years) were evaluated. On the basis of structural imaging and clinical follow-up, 10 patients had benign and 14 patients had tumor thrombosis. On FDG PET-CT, uptake in the thrombus was linear in 18 patients and focal in six patients. The most common site of thrombosis was the inferior vena cava. The mean SUV max was 3.2 (range: 2.3-4.6; median: 3.3) in the benign thrombosis group and was 6.0 (range: 2.3-13.8; median: 3.3) in the tumor thrombosis group. The difference in SUV max was significant (P=0.013). On receiver operating characteristic analysis, a cut-off SUV max of 3.63 (sensitivity: 71.4% and specificity: 90%) was obtained to differentiate tumor thrombus from benign thromboembolism. In six patients, FDG PET-CT detected occult vascular thrombosis.

FDG PET-CT can detect active tumor thrombosis and is helpful in differentiating it from benign thrombus.