Inferior Vena Cava Filter Thrombus: a Possible Cause of an Unanticipated Finding of 99mTc-labeled Red Blood Cell Scintigraphy

Abstract

99m Tc-labeled red blood cell scintigraphy, a sensitive and specific diagnostic test, is useful for patients suspected of suffering from active gastrointestinal bleeding. This study follows a case of a patient who was suspected of gastrointestinal bleeding after an inferior vena cava filter was inserted due to a deep vein thrombosis of the femoral vein. To evaluate an exact focus of bleeding, 99m Tc-labeled red blood cell scintigraphy was executed. Herein, an unanticipated finding of 99m Tc-labeled red blood cell scintigraphy probably due to a thrombus on the inferior vena cava filter is reported.Keywords Deep vein thrombosis . Red blood cells . Scintigraphy . Gastrointestinal . BleedingIn November 2014, an inferior vena cava (IVC) filter was inserted in a 64-year-old male because of deep vein thrombosis of the right common femoral vein. He was prescribed 2 mg to 5 mg warfarin to prevent thrombosis from developing. After 2 weeks of taking warfarin, he complained of hematochezia. His hemoglobin levels were 70-90 g/l; gastrointestinal (GI) bleeding was suspected, and warfarin treatment was ceased. Computed tomography (CT) angiography, capsule endoscopy, gastroscopy and colonoscopy were performed, but the tests showed no specific areas of active bleeding. However, they did find ulcers in the cecal area. To identify the focus of the bleeding, 99m Tc-labeled red blood cell (RBC) scintigraphy was executed, and a modified in vitro method was used for RBC labeling. Focal radioactivity appeared in the mid-abdomen area on the 50-min image, remained with no interval change for 4 h, then disappeared on the 21-h image (Fig. 1a). Since this was not a typical pattern of GI bleeding (initial focal activity, increasing activity with time and focus moving in a pattern corresponding to the lumen), GI bleeding could be ruled out [1]. The CT angiography performed 3 days earlier was reviewed retrospectively. The CT angiography showed that an IVC filter existed at the same location as where focal radioactivity appeared in the 99m Tc-labeled RBC scintigraphy (Fig. 1b, c; empty arrows). The authors postulated that a thrombus developed after the injection of 99m Tc-labeled RBC and was caught by the IVC filter because of warfarin management, which had been withdrawn 1 week before, and RBCs were considered to be involved in venous thrombi via passive trapping [2]. It is supposed that the thrombus, located in a lower extremity, rose to the inferior vena cava area after the 40-min image. A possible cause of the disappeared radioactivity on the 21-h image is the thrombus dropping down from the IVC filter after the 4-h image [3]. Consequently, physicians could not find the focus of the bleeding and suspected ulcers of the cecal area. After conservative management, including RBC transfusion, the patient's hemoglobin levels returned to normal. 99m Tc-labeled RBC scintigraphy is a very useful method for detecting active GI bleeding; previous studies have reported the sensitivity and specificity of 99m Tc-labeled RBC scintigraphy as 78.6-...