British Journal of Radiology 75 (2002),692-694 © 2002 The British Institute of Radiology
Pseudothrombosis of the iliac vein in patients following combined kidney and pancreas transplantation
R Gupta, FRCS, FRCR1,
G Rottenberg, MRCP, FRCR1 and
J Taylor, MD, FRCS2
Department of 1 Radiology and 2 Transplant Surgery, Guy's and St Thomas's Hospital NHS Trust, 2nd Floor Guy's Tower, St Thomas's Street, London SE1 9RT, UK
Correspondence: Dr G Rottenberg
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Abstract
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Pseudothrombosis of the infrarenal inferior vena cava is a well recognized sign seen on helical CT of the abdomen. We report on pseudothrombosis of the iliac vein related to combined kidney and pancreas transplantation in the pelvis.
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Introduction
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Combined pancreatic and renal transplantation is performed for patients with insulin dependent diabetes and renal failure.
The renal transplant is placed in the left iliac fossa with end-to-side vascular anastomosis to theleft external iliac vessels. The pancreatic graft is taken from the donor en bloc with a loop of duodenum and is placed in the right iliac fossa. The pancreatic graft artery and vein are anastomosed to the right common iliac artery and vein,respectively, using an end-to-side technique. Pancreatic exocrine secretions are drained into the bladder via the duodenal loop. These patients may have complicated post-operative courses and may present with complications of surgery that require radiological investigation. We report on two patients shown to have filling defects seen in the iliac veins that mimicked thrombus on helical CT scanning and were shown to be artefactual.
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Case report
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Case 1
A 31-year-old Caucasian male with insulin dependent diabetes mellitus and end stage renal failure underwent a combined kidney and pancreas transplant; 7 days following surgery the patient complained of right thigh pain. Contrast enhanced CT of the abdomen and pelvis was performed on a Philips Tomoscan helical CT scanner (Philips Medical Systems International B.V., Eindhoven, The Netherlands). Images were acquired in a caudal direction following 100 ml iv contrast medium (Iopromide, 370 mg I ml-1) given at 3 ml s-1 via an antecubital fossa vein cannula and using a mechanical injector. Imaging commenced from the most cephalad section of the liver at 60 s following onset of contrast medium injection. This scan showed a collection around the graft pancreas that extended to involve the right psoas muscle. There was also a filling defect in the right external iliac vein with expansion of the vein (Figure 1a
). The filling defect commenced 5 cm below the insertion of the graft pancreatic vein and extended 3 cm superiorly. The contralateral iliac veins and inferior vena cava had opacified normally (Figure 1b). The patient had no leg swelling and, in view of the clinicoradiological discrepancy, a duplex ultrasound was performed that showed patent iliac and femoral veins. The patient is well, and is off dialysis and exogenous insulin injections.
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Figure 1. (a) Axial CT of the pelvis, following injection of iv contrast medium, showing an apparent filling defect in the right external iliac vein (arrow). The left external iliac vein is clearly opacified. (b) The inferior vena cava is well opacified from mixing of blood from both common iliac veins.
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Case 2
A 38-year-old caucasian male with insulin dependent diabetes mellitus and end stage renal failure underwent a combined kidney and pancreas transplant. 6 months following surgery the patient presented with right-sided abdominal pain. Contrast enhanced CT of the pelvis, performed as inCase 1 but with a 75 s delay from the onset of contrast medium injection, showed that there was afilling defect in the left external iliac vein with expansion of the vein. The filling defect commenced 5 cm below the insertion of the graft renal vein and extended 7 cm superiorly (Figures 2a,b). Once again there was contrast medium opacification in the inferior vena cava below the native kidneys (Figure 2c). owing to the lack of clinical signs, a duplex ultrasound scan was performed thatshowed patent iliac and femoral veins.
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Figure 2. (a) Axial CT of the pelvis, following injection of iv contrast medium, showing an apparent filling defect in the left external iliac vein (arrow) below the insertion of the renal vein. (b) CT showing the cranial extent of pseudothrombus in the left external iliac vein (arrow) above the insertion of the renal vein. (c) Scan demonstrating at a higher level than (b) that the inferior vena cava is opacified.
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Discussion
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Pseudothrombosis of the infrarenal inferior vena cava is a common artefact seen in helical CT and has been reported to occur in 21% of patients [1]. Recognition of this artefact is important to avoid an erroneous diagnosis of caval thrombosis. Studies have shown that it may take up to 2 min for the infrarenal cava to opacify in normal patients [2], however, this does not apply if there is a transplant connected to the iliac vessels. There is an arterial steal of blood in the transplant kidney with rapid excretion of contrast into the renal vein. This will prematurely opacify the iliac vein on the side of the transplant. Contrast medium may then reflux into the femoral veins if the patient performs a valsalva manoeuvre during the examination.
In Case 1 the apparent pseudothrombus sign onthe right side is due to slower flow of venous blood in the pancreatic graft vein failing to opacify the right external iliac vein, whereas the left side is opacified by the rapid blood flow from the graft renal vein, giving the false appearance ofthrombus on the right.
The cause for the pseudothrombus in Case 2 in the left external iliac vein is the more conventional explanation of rapidly flowing opacified blood in the transplant renal vein mixing with unopacified venous return from the left leg, producing the "filling defect" on the left side.
These cases are unusual in that both are related to the presence of two transplants. In both casesthe true native infrarenal inferior vena cava was opacified and appeared clear of thrombus. Neither patient had symptoms that could be attributed to thrombus in the iliac veins and in both cases the presence of thrombus was refuted on subsequent duplex ultrasound examination.
Pseudothrombosis of the infrarenal inferior vena cava in the absence of transplants is more common in men. This is thought to be due to the more rapid blood flow in the renal vein in men [3], resulting in a greater discrepancy in the enhancement of the cava above and below the insertion of the renal vein.
Hounsfield numbers of the thrombus, size of the cava and margination of the thrombus are signs that have been described to distinguish true thrombus from pseudothrombus, but none have been found to be particularly reliable [4, 5].
These two cases demonstrate that pseudothrombosis may occur in a segment of iliac vein with opacification of the rest of the infrarenal inferior vena cava. Recognition of this artefact is essential to avoid an incorrect diagnosis in these patients. We recommend that if pseudothrombosis is suspected either delayed CT through the area of abnormality or duplex ultrasound examination should be performed to confirm diagnosis.
Received for publication December 4, 2001.
Revision received April 16, 2002.
Accepted for publication May 9, 2002.
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References
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- Mcwilliams RG, Chalmers AG. Pseudothrombosis ofthe infra-renal inferior vena cava during helical CT. Clin Radiol 1995;50:751–5.[Medline]
- Foley WD, Oneson SR. Helical CT: clinical performance and imaging strategies. Radiographics 1994;14:894–904.[Abstract]
- Dworkin LD, Sun AM, Brenner BM. The renal circulation. In: Brenner BM, Rector FC. The kidney (6th edn). Philadelphia, PA: WB Saunders Co, 2001:277–318.
- Glazer GM, Callen PW, Parker JJ. CT diagnosis of tumor thrombus in the inferior vena cava avoiding the false-positive diagnosis. AJR 1981;137:1265–7.[Free Full Text]
- Vogelzang RL, Gore RM, Neiman HL, et al. Inferior vena cava CT pseudothrombus produced by rapid arm-vein contrast infusion. AJR 1985;144:843–6.[Abstract/Free Full Text]
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Abstract
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