18F- FDG-PET/CT for the Diagnosis of Tumor Thrombosis

Background: Venous thromboembolism is a well-recognized and relatively frequent complication of malignancy, whereas tumor thrombosis is a rare complication of solid cancers. The correct diagnosis of tumor thrombosis and its differentiation from VTE can alter patient management and prevent unnecessary long-term anticoagulation treatment.

Objectives: To evaluate the contribution of 18F-fluorodeoxyglucose positron emission tomography/computed tomography to the diagnosis of tumor thrombosis and its differentiation from VTE.

Methods: PET/CT scans from 11 patients with suspected tumor thrombosis were retrospectively evaluated. Suspicion arose from positive PET/CT in eight cases, or from findings on contrast-enhanced CT in three patients. Criteria for positivity of PET/CT included increased focal or linear uptake of 18F-FDG in the involved vessel. Findings were categorized as PET/CT positive, or PET/CT negative and compared to contrast-enhanced or ultrasound Doppler, pathology where available, and clinical follow-up.

Results: Eight occult tumor thromboses were identified by PET/CT-positive scans. Underlying pathologies included pancreatic, colorectal, renal cell, and head-neck squamous cell carcinoma, as well as lymphoma (4 patients). Three thrombotic lesions on contrast-enhanced CT were PET/ CT negative, due to VTE (2 patients) and leiomyomatosis. Accuracy of PET/CT to differentiate between tumor thrombosis and benign VTE was 100% in this small study.

Conclusions: Contrast-enhanced CT defines the extent of thrombotic lesions, while the functional information from PET/CT characterizes the lesions. It appears that PET/CT may be helpful in the diagnosis of occult tumor thrombosis and its differentiation from VTE.