Massive pulmonary embolism caused by internal iliac vein thrombosis with free-floating thrombus formation in the inferior vena cava.

Nowadays, compression ultrasonography (CUS) is the gold standard for the routine diagnosis of deep venous thrombosis (DVT). The drawback of CUS is the low sensitivity concerning the diagnosis of isolated pelvic vein thrombosis, especially referring to isolated internal iliac vein and ovarian vein thromboses. Therefore, magnetic resonance (MR) venography has become a valuable alternative. We present the case of a 45-year-old female patient with a massive pulmonary embolism with the indication for thrombolytic therapy due to severe right ventricular overload. We were not able to detect a DVT in the lower limbs of this patient with CUS. However, further DVT workup by MR venography showed a free-floating thrombus formation originating from the right internal iliac veins into the inferior vena cava. Owing to the fact that this thrombus was free floating, surgical removal of the thrombus was scheduled and performed successfully. In some patients it might be important to look for so-called rare causes of pulmonary embolism, even when CUS of the lower limbs does not reveal any DVTs. The diagnostic procedure of choice for these patients seems to be MR phlebography, as iliac and pelvic veins can be evaluated without radiation exposure with this procedure.