Characterization of tumor thrombosis of F-18 FDG PET/CT

Tumor thrombosis is important in cancer patients as it has adverse outcomes and surgical planning is more complex. Its incidence depends on types of malignancy with most common in primary renal and liver malignancies. Its identification is challenging as there are no specific clinical symptoms, nor it is restricted to any stage of malignancy. The current standard guidelines recommend Contrast Enhanced Computed Tomography (CECT) and Magnetic Resonance Imaging (CE-MRI) in distinguishing it from bland thrombus by presence of contrast enhancement and direct continuation of the primary tumor mass as characteristic of tumor thrombus. Studies suggest uptake of F-18 FDG on PET/CT as confirmation of tumor thrombus. With this retrospective analysis, we explore other metabolic parameters like SUVmax ratios of tumor thrombus, primary tumor and liver, and other imaging features that can further characterize tumor thrombus on F-18 FDG PET/CT especially on non contrast studies. We conducted a retrospective review of FDG PET/CT studies of patients done in our department or sent for review from February 2021 to September 2022, for known malignancy and had FDG avid tumor thrombosis irrespective of contrast status. The variables recorded were as follows, SUV max (tumor thrombus), SUV max (primary malignancy), SUV max (liver), volume of the thrombus on FDG, contiguity or non contiguity of the thrombus with primary malignancy, and presence or absence of distant metastases. Correlation between these parameters was calculated using SPSS ver 2. Out of 2277 patients reviewed, 12 patients had tumor thrombus with a prevalence of 0.52%. Median age of our study population was 56.5 years (8-74 years), and 50% were males. The most common primary malignancy was lung (25%), followed by bone, renal, liver and lymphoma (16% each). The mean SUV max of tumor thrombus was 6.3. The most common vessel involved was IVC (26%), and most of them were contiguous in nature (62%).10% thrombi reached up to right atrium. 83% patients had distant metastases evident of FDG- PET/CT with most common site was lung-pleura (60%). Significant correlation was found between SUVmax of tumor and thrombus, indicating similar biological origin. There was no significant correlation noted between the volume and metabolic activity of the tumor thrombus. Tumor thrombus is an aggressive feature of any malignancy, and is usually associated with distant metastases at the time of presentation. In cases where intravenous contrast cannot be administered, F-18 FDG PET/ CT can still detect tumor thrombosis with metabolic activity similar to the primary tumor. Further in any case of suspected malignancy where intravascular metabolic activity is more than liver, possibility of tumor thrombus should be considered. (author)