Background:

Splanchnic vein thrombosis (SVT) is one of the manifestations of unusual site venous thromboembolism (VTE). SVT includes portal vein thrombosis (PVT), mesenteric vein hrombosis (MVT), splenic vein thrombosis (SpVT) and the Budd-Chiairi syndrome (BCS).There is no validated clinical algorithm for the diagnosis of SVT and there are no specific laboratory tests available to confirm or rule out the disease. Particularly, D-dimer tests do not have a role in the diagnosis of SVT, due to its low specificity and the high percentage of false positive results, especially in patients with cancer, liver cirrhosis or underlying inflammatory conditions, present in more than half of the total SVT population. Thus the diagnosis of SVT relies on imaging tests alone. Whereas Doppler ultrasound is the imaging test of choice for most forms of SVT, its sensitivity is only 90%, as is the sensitivity of CT angiography (CTA). MR angiography (MRA) has been reported to have 90-100% sensitivity for SVT, but this technique is limited by the need to administer a contrast agent. Furthermore, in studies evaluating the accuracy of MRA for the diagnose of SVT, gold standard for SVT (surgical validation) was lacking. Importantly, many of SVT diagnoses in clinical practice (up to 30%) are incidental findings, i.e. findings on imaging tests of the abdomen performed for another reason than suspected SVT. Whereas the diagnosis of symptomatic SVT is often challenging, the correct diagnosis of acute versus chronic SVT is even more difficult, as neither of the current available imaging tests is helpful in determination of the age and clinical relevance of the thrombus, especially in non-symptomatic patients. Due to this impossibility to determine whether the incidentally observed thrombosis is acute, chronic or even an imaging artefact, the vast majority of patients with incidental SVT are treated with often lifelong anticoagulants. It is widely acknowledged that this practice likely results in overdiagnosis and unjust exposure to anticoagulant therapy with associated risk of bleeding. An alternative imaging technique for more accurate diagnosis of SVT is MR Direct hrombus Imaging (MRDTI). This technique is in an advanced stage of development (Theia study, NCT02262052, supported by TSN grant 2013-02) and is close to implementation in clinical practice. The method is based on the formation of methemoglobin in a fresh thrombus leading to shortening of the T1 signal. It does not require contrast dye. Both the diagnostic accuracy (sensitivity 97-100%, specificity 100%) as well as the inter-observer agreement of MRDTI for first and recurrent DVT of the leg were reported to be excellent (kappa 0.89-0.98). Moreover, it was shown to accurately differentiate acute from chronic thrombosis. There is an unquestionable need for improved diagnostic approaches for (incidental) SVT. The researchers plan to evaluate the MRDTI technique, that has been shown to be accurate in other settings of difficult-to-diagnosis venous thrombosis, for the notoriously challenging diagnosis of incidental SVT. This study targets an important unmet need and will provide the basis for precision medicine for patients with SVT in the near future, i.e. the possibility of assessment of the age of the thrombus in patients with incidental SVT, which is of utmost importance for determination of the indication for anticoagulant therapy.

Study design:

This study is a prospective diagnostic proof of concept study to explore the diagnostic accuracy of MRDTI in the diagnostic management of acute and chronic SVT. This will be achieved by performing MRDTI scans to adjust and optimize the DTI scan sequence in 3-5 patients with confirmed, acute SVT. If a reproducible clearly positive DTI signal is achieved in all patients, the study can proceed with the inclusion of cohort 1 and 2, i.e. 35 patients with confirmed acute SVT and in 35 patients with confirmed, chronic SVT. All scans will be evaluated post-hoc by expert readers blinded for the final diagnosis. It is predetermined that at least five patients of each SVT site (PVT, SpVT and BCS and at least five patients of each SVT risk factor (oncologic, post-surgical and inflammatory/infectious) will be included. To make sure that cohort 1 is generally similar to cohort 2 frequency matching will be performed, in which all controls will be selected to get the same distribution according to SVT site and risk factor as cases.