Is Deep-Vein Thrombosis Always the Origin of Pulmonary Embolism? Imaging of Veins with a Total-Body Direct Thrombus MRI Technique

Pulmonary embolism (PE) is thought to originate from embolisation of a deep-vein thrombosis (DVT), resulting in two clinical manifestations of one disease: venous thrombosis. However, in up to 50% of patients with PE, no DVT is found with ultrasound. A new technique in diagnosing DVT is ‘MR Direct Thrombus Imaging’ (MRDTI), using methaemoglobin in the thrombus as endogenous contrast. We performed total body MRIs to visualize thrombi from calf veins to subclavian veins, to assess the origin of PE.

Consecutive patients with a first PE diagnosed by Multi Detector CT scan are included. All patients undergo a 1.5 T MRDTI scan. In addition, blood is sampled for determination of genetic risk factors: the Factor V Leiden (FVL) and prothrombin G20210A (FII) mutations.

99 patients have been enrolled in the study. In 44/99 (44%) a thrombus was identified on MR images. Most thrombi originated from the left side of the body (27/44). The upper leg was involved most often (22/44), with thrombi extending into the calf in 16 of these patients. Other thrombi were present in the pelvic veins (4/44), and deep calf veins alone (12/44). 6 patients had merely thrombophlebitis. The FVL mutation was present in 14% (95% CI 6–27) of patients with a thrombus on MRI, and in 7% (95% CI 3–18) of patients without a thrombus. For FII, the prevalence in the group with a DVT on MRI was 2% (95% CI 0.4–12) and without a DVT 4% (95% CI 1–13).

In less than half of PE patients a thrombus can be found with total body MRI. When thrombi were present, they were mainly found in the upper leg, extending into the calf veins. Interestingly, 27% of PEs with a thrombus on MRI was related to isolated calf vein thrombosis and 14% to thrombophlebitis. In PE patients with no thrombus on MRI, a local origin of PE, a thrombus from cardiac origin or complete embolisation needs to be considered.

Supported by Netherlands Heart Foundation grant number 2009B050

No relevant conflicts of interest to declare.