Imaging description

Multidetector computed tomographic angiography (CTA) is a fast non-invasive imaging technique with a sensitivity of 95% and a specificity of 99% for detection of arterial injuries in the extremities. CTA is usually performed with 100–120ml of contrast material injected at a rate of 4ml/sec and images acquired at the time of maximal arterial enhancement (around 40 seconds). Bolus tracking may be used but is usually not necessary as most of the patients in the trauma setting are young adults. Evaluation is performed with axial images along with sagittal and coronal reconstructions and three-dimensional post-processing techniques such as volume rendering and MIP. In the presence of an arteriovenous fistula (AVF) there is early filling of the involved vein on arterial phase imaging and lack of contrast opacification of the veins on the contralateral side (Figures 88.1 and 88.2).

Importance

AVFs are due to abnormal connections between the arterial and venous system bypassing the normal capillary beds. Acquired AVF usually occurs as a consequence of percutaneous vascular access but can also be secondary to penetrating injury to the lower extremity from stab wounds and gunshot injuries. Accurate diagnosis is important as long-standing AVFs can cause edema, arterial aneurysm, ischemia, and even high-output cardiac failure. There is excellent prognosis of AVFs after surgical or endovascular repair.

Typical clinical scenario

Typically presentation would be a young person with history of lower extremity penetrating trauma presenting with limb edema. On examination machine-like murmur, bruit, or a pulsatile mass may be found.

Differential diagnosis

Inaccurate or mistiming of the bolus may cause opacification of the veins interfering with the evaluation of AVF. Absence of opacification of the contralateral veins helps differentiate mistiming of contrast bolus from an AVF. Intravenous contrast injection from the lower extremity causes opacification of the ipsilateral venous system; however, the contrast is usually denser than within the arteries (Figure 88.2). In the presence of central venous obstruction, early opacification of a peripheral vein can also occur due to the presence of collateral vessels (Figure 88.3).