Abdominal aortic aneurysm: Treatment options, image visualizations and follow-up procedures

Abstract

Abdominal aortic aneurysm is a common vascular disease that affects elderly population. Open surgical repair is regarded as the gold standard technique for treatment of abdominal aortic aneurysm, however, endovascular aneurysm repair has rapidly expanded since its first introduction in 1990s. As a less invasive technique, endovascular aneurysm repair has been confirmed to be an effective alternative to open surgical repair, especially in patients with co-morbid conditions. Computed tomography (CT) angiography is currently the preferred imaging modality for both preoperative planning and post-operative follow-up. 2D CT images are complemented by a number of 3D reconstructions which enhance the diagnostic applications of CT angiography in both planning and follow-up of endovascular repair. CT has the disadvantage of high cummulative radiation dose, of particular concern in younger patients, since patients require regular imaging follow-ups after endovascular repair, thus, exposing patients to repeated radiation exposure for life. There is a trend to change from CT to ultrasound surveillance of endovascular aneurysm repair. Medical image visualizations demonstrate excellent morphological assessment of aneurysm and stent-grafts, but fail to provide hemodynamic changes caused by the complex stent-graft device that is implanted into the aorta. This article reviews the treatment options of abdominal aortic aneurysm, various image visualization tools, and follow-up procedures with use of different modalities including both imaging and computational fluid dynamics methods. Future directions to improve treatment outcomes in the follow-up of endovascular aneurysm repair are outlined.

Keywords: Abdominal aortic aneurysm; Computed tomography; Follow-up; Stent graft; Treatment; Visualization..

Figure 1.. An axial CT image shows a large aortic aneurysm with extensive artery wall calcification. The black line refers to measurement of the aneurysm diameter at transverse dimension, while arrows indicate the calcification in the aortic wall.

Figure 2.. 3D volume rendering shows an infrarenal aortic aneurysm with near total occlusion of the abdominal aorta extending to the common iliac arteries (long arrows in A). Left renal artery is also occluded with no enhancement of the left kidney. Coronal and sagittal maximum-intensity projection images (B and C) demonstrate similar findings with extensive calcifications in the common iliac arteries (long arrows in B). Short arrows refer to the collateral arteries, while arrowhead indicates the patent right renal artery.

Figure 3.. Diagram shows preoperative planning of endovascular aneurysm repair with detailed measurements of the relevant parameters and design of the stent-graft to be implanted in a patient with an infrarenal aortic aneurysm. (A). Viewing from the top to the bottom, scallop fenestration, large fenestration and small fenestrations are recommended for the celiac axis, superior mesenteric artery and bilateral renal arteries, respectively (B).

Figure 4.. Extensive calcifications are noticed in a large infrarenal aortic aneurysm with angulation in the proximal and distal aneurysm necks.

Figure 5.. A type 1 endoleak is present in the proximal and distal segments of aortic stent graft, as demonstrated on the axial CT images (long arrows in A and B). A type II endoleak (short arrow in B) is also noticed within the aneurysm sac at the level of common iliac artery due to patent inferior mesenteric artery (arrowhead in B).

Figure 6.. A type 2 endoleak (short arrows) is present in the anterior aspect of an aortic aneurysm following endovascular repair due to backfilling from the patent inferior mesenteric artery (long arrows).

Figure 7.. 3D volume rendering (A) in a patient treated with fenestrated stent-graft shows different colours, such as red and white, are coded to blood vessels and bones and stent wires, respectively. Coronal maximum-intensity projection (MIP) (B) shows that fenestrated renal stents are placed inside the renal arteries with successful exclusion of the aneurysm, while thin-slab MIP image (C) clearly demonstrates the intra-aortic fenestrated stents.

Figure 8.. Virtual intravascular endoscopy demonstrates intraluminal appearances of the celiac axis and superior mesenteric artery (SMA) ostia (A), left renal ostium (arrows in B) and right renal ostium (arrows in C).

Figure 9.. 2D axial images show that suprarenal stent graft is placed above the left renal artery (arrows in A) and superior mesenteric artery (SMA) (arrows in B) in a patient treated with aortic stent-graft. Corresponding virtual intravascular endoscopy confirms that the left renal and SMA ostia are crossed by a single and multiple stent wires, respectively. Short arrows in C and D indicate the renal and SMA ostia, while long arrows refer to the suprarenal stent wires.

Figure 10.. Coronal reformatted images (A,B) reveal the fenestrated renal stents that were implanted in a patient treated with fenestrated stent-graft. Corresponding virtual intravascular endoscopy images show the fenestrated renal stents (C and D) with normal circular appearance. Arrows indicate the intra-aortic protrusion of bilateral renal stents (arrows in A and B) with a large intra-aortic extension from the left renal stents (arrows in B).

Figure 11.. Virtual intravascular endoscopy shows the flaring effect at the inferior component of right renal stent (A) due to balloon inflation during fenestrated stent grafting procedure, and deformed right renal stent (B). Arrows indicate the intraluminal appearances of fenestrated renal stents.

Figure 12.. A computer modelling of aortic aneurysm pre-and post-stent grafting is based on a realistic patient CT data. Turbulent flow pattern with low flow velocity is noticed inside the aneurysm (A) prior to stent grafting, but the flow becomes laminar and flow rate increases after stent graft placement (B). Low wall shear is observed inside the aneurysm (C), with the shear stress increasing following stent graft placement (D).

Figure 13.. Computer modelling of abdominal aorta with a focus on blood flow to the renal artery prior to stent graft placement (A). After simulation of suprarenal stent wires crossing the renal arteries, flow pattern and flow velocity are not affected (B). With simulation of fenestrated renal stents with a 5 mm intra-aortic protrusion (C), flow recirculation is seen in the proximal parts of renal arteries due to stent protrusion.