Understanding vascular pathoanatomy: Cinematic rendering of an abdominal aortic aneurysm treated with chimney endovascular aortic repair

We present a case with an infrarenal AAA, treated with chimney endovascular aortic repair (CHEVAR) due to a strong inferior mesenteric artery (IMA). To enhance understanding of anatomy and pathoanatomy, pre- and postoperative cinematic rendered (CR) images were obtained from the patients’ multidetector computed tomography (MDCT) datasets. We want to discuss possible applications for CR images to facilitate understanding of complex vascular pathologies and postprocedural conditions for medical professionals, students and the general public.


Background
CHEVAR has been established as a suitable option for the treatment of AAAs with involvement of the mesenteric or renal arteries. In this procedure, the perfusion of the target vessels is maintained through stent grafts laying alongside with a main graft tube. There are two main techniques in CHEVAR: the snorkel technique, where the blood flow is maintained antegrade from the proximal end of the main body stent graft to the target vessel, and the periscope technique, where the blood flow is secured in a retrograde fashion from the distal end of the main body stent graft to the target vessel. An alternative to CHEVAR is the fenestrated endovascular aortic repair (FEVAR), where the blood flow to the involved visceral and/or renal vessels is maintained through the implantation of stent grafts in individually designed and manufactured fenestrations in the main body stent graft [1][2][3].
An advantage of CHEVAR over FEVAR is, that there is no need for individually designed stent grafts. Thus, CHEVAR can also be used in emergency settings and in situations with challenging vascular pathoanatomy, where FEVAR is not possible. CHEVAR may also result in lower procedural costs. On the other hand, FEVAR delivers better long-term results and is associated with a lower rate of reinterventions [1,2,4,5].

Case report
We present a case of a 81 year old male patient, who was diagnosed with a saccular infrarenal AAA. As a complicating anatomic feature, a strong IMA was present. An additional finding was a significant soft plaque stenosis of the left renal artery. Due to the eccentric saccular configuration of the aneurysm and the strong IMA, indication for CHEVAR with snorkel technique was made.
For the procedure, decision for a biinguinal retrograde access and an open retrograde trans brachial access from the left arm was made.
After cannulation of the left renal artery via the right inguinal access, the soft plaque stenosis of the left renal artery was treated with a covered stent (Advanta, Getinge, Sweden). To facilitate optimal placement of the main body stent graft and the chimney stent grafts, a 5F pigtail diagnostic catheter was placed in the infrarenal aorta from the right inguinal access. Next, the IMA was cannulated over the brachial access with a 5F Berenstein (Cordis Inc., USA) catheter and a 0,035'' hydrophilic guidewire (Terumo Corp., Japan), which was then exchanged for a stiff 0,      was inserted from the brachial access. During partial detachment of the main body stent graft the second chimney stent graft was carefully inflated at a low-pressure level. Then the main body stent graft was then fully deployed from the delivery system, which was then exchanged for a compliant balloon (Reliant, Medtronic Inc., USA). As a final step, the main body stent graft was molded to the aortic wall with full inflation of the chimney stent graft to facilitate sealing of the treated aortic section.
Final angiogram showed good placing of the stent grafts, preserved blood flow to the left kidney and IMA as well as to the iliac arteries, and no relevant endoleak. Postoperative course was uneventful. The first follow-up MDCT scan on the seventh postoperative day showed no early complications and good stent graft placement.

Discussion
Several authors have proposed a more aggressive therapeutic approach towards saccular aortic aneurysms, since the rupture risk is higher than in fusiform aneurysm sac, as they become acute earlier at smaller diameters. This might be associated with their etiology, which includes penetrating atherosclerotic ulcer, infection or trauma of the aorta, and previous aortic surgery [19,20]. In the presented case, penetrating atherosclerotic ulcer of the infrarenal abdominal aorta was suspected, which led to the indication of an EVAR. As colon ischemia is associated with an increased mortality rate, decision for preservation of the strong IMA through CHEVAR was made [19][20][21].
In aortic and vascular diseases, it can be challenging to understand pre-and post-therapeutic anatomical and pathoanatomical particularities. As shown in the images above, it is much easier to understand the main pathology and the postoperative condition with meaningful and often self-explaining CR images. In interdisciplinary discussions, in the planning phase of a procedure, during the informed consent discussion with the patient, when teaching medical and healthcare students and when educating the general public, it can be helpful to use photorealistic CR images to facilitate understanding of such complex pathologies and post-therapeutic conditions [6][7][8][9][10][11][12][13][14][15][16][17][18].

Conclusion
CHEVAR is an established procedure for endovascular repair of AAAs involving the visceral vessels, especially in emergency situations and when a challenging anatomy is present. CR can facilitate understanding of complex problems for medical professionals, medical and health-care students and medical lay persons.