Role of 18 F-FDG PET/CT in the diagnosis of benign vs. malignant tumor thrombus.

Purpose: Hypercoagulable state is a complication of various infections, and inflammatory processes and is a common scenario in cancer patients also. Timely diagnosis and treatment are essential to reduce further complications in such patients. The present study aimed to assess the role of FDG PET/CT in the diagnosis of benign vs. malignant tumor thrombus and to determine cut-off SUVmax to differentiate them.

Patients And Methods: We retrospectively reviewed all FDG PET/CT scans of patients done in our department from January 2017 to March 2022. All scans were reviewed by two experienced nuclear medicine physicians. A total of 135 patients who had venous or arterial thrombus in FDG PET/CT scans were included. All the FDG PET/CT scans of 135 patients were analyzed for primary tumor site and/or site of thrombus. Additional clinical data were collected for patients with benign conditions in the form of ESR and CRP if available and doubtful cases were followed up by HPE reports and/or CEMRI. The SUV max of the primary tumor(in cancer patients), thrombus, and background (aorta) were calculated.

Results: A total of 135 patients (108 cancer patients and 27 with benign thrombus) were included with an age range of 3 to 86 years (median 50 years). There were 91 males and 44 females. Of 108 cancer patients, the most common cancers were hepatocellular cancer - 38 (35.18%), renal cell cancer - 28(25.92%), and carcinoma of the thyroid - 6 (5.55%). Of 108 cancer patients, 36 (33.33%) had tumor thrombosis in inferior vena cava, 31 (28.70%) in the portal vein, and 41 (37.96%) in other vessels (renal vein, jugular vein, etc.). Of 27 patients with benign conditions,13 had venous thrombi, 11 had arterial thrombus and three had atrial thrombus and the most common thrombus sites were thoraco-abdominal aorta in seven (25.92%) and right atrium in three (11.11%) patients. In the subgroup of 108 oncological patients, the mean SUV max of the primary tumors was 17.67 (range 2.1-91.0; median 10.82), thrombi were 17.61 (range 2.14-90.11; median 14.56) and background was 5.29 (range 0.29-25.00; median 3.12). Of 27 patients with benign conditions, the mean SUV max of the thrombi was 11.09 (range 1.98-31; median 8.10) and the background was 9.80 (range 1.46-24.50; median 10.20) The ESR was raised in 13 of 26 patients (mean 35.84, range 10.98-62.00, median 35.00) and CRP was raised 22 of 26 patients (mean11.46, range 3.45-24.50, median 20.40). Upon plotting the receiver operating curve, a cutoff SUV max of 12.7 with a sensitivity of 62.96% and specificity of 77.77% was produced to demarcate tumor thrombus from benign thrombus.

Conclusion: FDG PET/CT plays a significant role in the detection of thrombo-embolic disease and can differentiate benign thrombus from tumor thrombus.