Endovascular abdominal aortic aneurysm repair (EVAR) has revolutionised the management abdominal aortic aneurysm (AAA) and is well recognised as a primary treatment modality. Despite EVAR demonstrating an initial survival advantage over AAA repair, it is associated with more frequent complications and late re-intervention. As such lifelong post-treatment imaging surveillance is paramount to the identification of endoleaks and the prevention of aortic ruptures. Traditionally, duplex ultrasonography and computed tomography angiography have been utilised for imaging surveillance, however, their ability to distinguish between the types of endoleaks can be suboptimal. As such the introduction of 4D CTA provides a dynamic imaging adjunct to characterise an enlarging aneurysm sac with an undetermined source of endoleak, thus determine the necessity for intervention as well as assisting with procedural planning.

At the Princess Alexandra Hospital, 4D CTA been utilised in the EVAR surveillance algorithm for patients with enlarging aneurysm sac size following standard imaging follow up, where localisation of an endoleak has not been observed. Between December 2017 and April 2021, a total of 19 4D CTAs have been performed on 17 different patients.

A total number of 15 endoleaks were demonstrated with 65% correlation between between radiologist and the Vascular MDT. 6 patients proceeded to intervention. 1 patient was awaiting intervention when they presented with a rupture prior to their procedure. Procedures performed included 4 angiographic embolisation, 1 cuff and anchors, glue embolisation through direct puncture. 1 type 1a, and 4 type 2 endoleaks were treated. Of the 6 that underwent intervention, 5 patients had intraoperative findings that correlated to the imaging and Vascular MDT findings (4 type 2 and 1 type 1a), and 1 patient quoted to have a type 2 endoleak, with MDT correlation was found to have no leak on the subsequent angiogram. 13 patients didn't undergo intervention. 4 patients with positive triple phase CTA findings, underwent a subsequent 4D CTA which showed no endoleak. 9 patients had positive 4D CTA findings but didn't proceed to intervention. 2 of these patients were considered not fit for intervention. The remainder 7 patients had their 4D CTAs discussed at the Vascular MDT. thought to be inaccurately described as an endoleak. All these patients went back on to surveillance imaging. All 7 patients were reported to have type 2 endoleaks and 1 patient was quoted to have a type 2 and type 3 endoleak.

Our department intended to utilise the 4D CTA as an imaging modality to ascertain the cause of an endoleak where standard imaging fails to and as a means of operative planning. However, the experience from this unit is that it doesn't add to the overall care of the patient. The discrepancy between a radiologist's interpretation and that of the Vascular MDT, is not insignificant. The 4D CTA confirmed the findings of the triple phase CTA in 16 patients and only 6 patients eventually went on to need intervention. The positive predictive value for a 4D CTA is therefore low. Its place in the algorithm of assessing endoleaks may therefore need to be rationalised to specific cases.