Endovascular aortic aneurysm repair (EVAR) is an effective alternative to traditional open surgery for abdominal aortic aneurysm (AAA), with many advantages such as less trauma, faster recovery, and shorter operative and hospital stays. However, not all patients with AAA are suitable for EVAR, and the anatomical shape of the patient’s aneurysm is the main factor in determining whether EVAR can be performed. Preoperative imaging of AAA patients is crucial to determine whether a patient is suitable for EVAR. Contrast-enhanced CT is by far the most important imaging test for preoperative anatomic morphologic evaluation of AAA patients, which provides important information on AAA tumor neck diameter, angle, tumor diameter, length, visceral artery openings, and degree and diameter of tortuosity of the introducing artery, allowing determination of the patient’s suitability for EVAR; and what type of stenting is appropriate for the patient. The focus of the anatomic evaluation is to obtain information on the proximal aneurysmal neck, the aneurysmal lumen, the iliac artery and, to a lesser extent, the visceral artery. I. Proximal aneurysmal neck The proximal aneurysmal neck refers to this segment of the abdominal aorta between the inferior border of the renal artery and the superior border of the aneurysmal neck. A segment of the aneurysmal neck of sufficient length is required for adequate stenting of the rivet. Anatomic evaluation of the proximal aneurysmal neck includes diameter, length, angle, morphology, and the presence of calcification and appendage thrombus. Diameter The diameter of the tumor is measured by minimal cross-sectional CT. To obtain adequate riveting, the diameter of the stent-graft (SG) generally exceeds the diameter of the tumor neck by 10% to 20%, so the limitation of the tumor neck diameter depends on the maximum diameter of the SG available. At present, the maximum diameter of SG available in China is 34 mm, so the maximum diameter of the tumor should not exceed 30 mm, and the oversizing of the stent should not be too large, as oversizing will affect the long-term treatment effect. It has been pointed out in the literature that stent diameter exceeding 30% can lead to stent displacement and enlargement of the tumor, which may be related to the reduction of contact area with the tumor neck due to large SG folds after oversizing. Length The length of the tumor was measured by the shortest axial position of CT and 3-dimensional reconstructed images. In order to ensure adequate closure of the tumor cavity and to reduce stent displacement and type I endoleaks, the neck length should not be shorter than 15 mm, and the shortest proximal neck length can be 10 mm in the case of a good anatomic neck; in the case of a bare stent SG with transrenal release (a bare stent released below the level of the renal artery) or a barbed SG (cook Zenith). EVAR is not indicated for tumors less than 10 mm in length. The newer fenestrated SGs have the potential to solve the problem of short proximal neck. The fenestrated stent has an opening for the visceral artery, which allows the stent to be released proximally while maintaining the patency of the visceral artery, thus broadening the traditional concept of aneurysmal neck. However, open-window stents also have certain problems: 1. they are complicated to operate, and it is difficult to locate the visceral artery, and the opening of the visceral artery can be blocked if it is not positioned properly; 2. they take a long time to operate, use a large amount of contrast agent, and have a large amount of X-ray exposure. In China, there is no certified open-window type stent available. Angle The angle of the aneurysmal neck is defined as the angle between the first segment of the aneurysmal neck (the first 3 cm) and the suprarenal abdominal aorta and is usually measured on CTA 3-dimensional imaging. Severe distortion of the neck (angle of 60°) is associated with a high rate of complications, especially type I endoleaks. For larger angled AAAs, even if the SG morphology is good at intraoperative release, the stent is still susceptible to stent displacement, stent fracture or disintegration during follow-up because the stent continues to receive stress from blood flow. Patients with tumor angles greater than 60° are usually not candidates for EVAR. Recent studies have shown that when suprarenal release is used (one segment of bare stent located above the level of the renal artery), short- to medium-term follow-up results found no significant difference between those with a larger tumor neck angle (60°) and those with a smaller angle (60°). The Cook Zenith stent (with barb and one bare stent) was used for the treatment of large tumor necks, and the immediate and short- and medium-term follow-up results were also good, and further follow-up is ongoing. If EVAR is attempted in a large neck (60°), the neck length must be 15 mm and the first bare stent must be placed above the level of the renal artery. Large neck angles with insufficient neck length, calcification, and appendage thrombosis are absolute contraindications to EVAR. Morphology of the aneurysmal neck The morphology of the aneurysmal neck can be defined as straight (D1=D2), conical (D1D2), or inverted cone (D1D2) based on the comparison of the diameter of the inferior border of the renal artery (D1) and the diameter of the inferior border of the renal artery 10 mm away (D2). Enlarged tumor neck was defined as an increase of at least more than 3 mm within 15 mm of the proximal end of the tumor neck. Inverted tapered and distended necks are associated with a high incidence of proximal endoleaks and are a contraindication to EVAR surgery. Calcification and appendage thrombosis Calcification and appendage thrombosis can affect the effectiveness of SG riveting and closure of the tumor cavity. Wall thrombus affects the measurement of tumor neck diameter. Wall thrombus can be extruded during SG release, so the endothelium-to-endothelium distance should be used as the tumor neck diameter when measuring. The severity of calcification and appendage thrombus is defined by the circumference of the vessel lumen involved. A higher incidence of type I endoleaks and stent dislocation is associated with proximal neck calcifications and wall thrombi exceeding 90° circumference. The anatomical information of the tumor cavity that should be evaluated before EVAR includes the diameter of the tumor, the inner diameter of the tumor cavity (diameter of the blood flow channel), the inner diameter of the lower part of the tumor cavity (if the bifurcation is involved), and the inner diameter of the bifurcation. This is measured by CT of the vertical luminal cross-section and the minimum axial position. Maximum diameter of the tumor The purpose of measuring the maximum diameter of the tumor is to determine whether the patient needs to undergo EVAR. Consistent with conventional surgery, EVAR is indicated for aneurysms up to 5 cm in diameter or 5 cm in diameter with complications or an increase of more than 0.5 cm in size within 6 months. 6.5 cm is prone to type I endoleaks. The internal diameter of the tumor cavity/distal tumor cavity/bifurcation should be large enough to allow the passage and release of SG. The minimum diameter should exceed 18 mm (9 mm for a single limb at the bifurcation of the stent) to allow for implantation and opening of the contralateral limb. If the luminal ID/distal luminal ID/internal diameter at the bifurcation is 18 mm, this can be addressed with a single-limb type (Aortauniilac, AUI) stent, contralateral iliac artery occlusion, and femoro-femoral bypass. The success of iliac artery EVAR requires both a suitable introducer artery and iliac artery morphology. The morphology of the iliac artery determines the availability of the distal riveting zone, and the successful delivery of SG is related to the internal diameter of the introducer artery, the degree of tortuosity, and the presence of calcification and collateral thrombus. The internal diameter of the iliofemoral artery is measured in cross-sectional position by CTA, and 3-dimensional reconstruction allows observation of the degree of tortuosity, the presence of collateral thrombosis and calcification. Internal diameter of the iliac artery The distal end of the SG is usually riveted to the common iliac artery. In order to ensure good riveting and closure, the internal diameter of the common iliac artery at the SG rivet site must be at least 2 mm smaller than the external diameter of the distal SG limb. Previously, the internal diameter of the common iliac artery was considered unsuitable for EVAR due to stent size limitations, which exceeded 14 mm. In recent years, with the development of new generation stents, the internal diameter of the common iliac artery can be relaxed to 20 mm. About 20% of patients with AAA also have iliac artery aneurysms. The common iliac artery may not have a suitable riveting area, and the distal end of the SG can be riveted to the external iliac artery in this case. If the ipsilateral internal iliac artery is occluded, the SG can be released directly into the external iliac artery; 2. If the internal iliac artery is patent bilaterally, embolization of the ipsilateral internal iliac artery is recommended to prevent type II endoleaks; 3. Simultaneous closure of both internal iliacs is likely to result in ischemia of the colon, gluteus and pelvis. Length As with the proximal aneurysm neck, a normal segment of at least 10-15 mm is required for good riveting and closure of the iliac artery segment. The diameter of the external iliac artery must be large enough to accommodate the stent delivery system (18F-22F), therefore, the internal diameter of the external iliac artery must not be less than 7 mm. if the external iliac artery has calcified plaque and local stenosis that interferes with stent passage, the iliac artery can be balloon dilated before stent introduction; if the stenosis is not severe, an empty delivery system can be introduced first to try to pass the stent. The empty delivery system can also be used to dilate the iliac artery. Twisting The SG delivery system is large and stiff, and it is generally not easy to pass through twists that are too angular, especially in the presence of a combination of small iliac artery diameter, calcification, and stenosis. Forced passage can easily result in vessel wall damage. Currently, with the use of rigid and superrigid guidewires, it is generally possible to straighten the torsion of the iliac artery intraoperatively and to introduce and release the stent smoothly. However, after stent release, the iliac artery with the stented segment is usually no longer twisted. However, because the total length of the iliac artery is not shortened, the remaining iliac artery is twisted at a greater angle, especially at the end of the stent migration, and sometimes the larger twist can lead to complete loss of ipsilateral femoral blood flow. Solutions include open surgical truncation of the iliac artery with end-to-end anastomosis or correction by implantation of a bare stent in the iliac artery. Calcification and appendage thrombosis Calcification leads to reduced vessel wall compliance and can easily cause vascular injury during SG introduction. The coexistence of diffuse calcification and iliac artery tortuosity can make the introduction of SG delivery systems very difficult. The solution is to try to use an empty delivery system, and if this is not possible, to use a balloon for dilation and then try to introduce it. The evaluation of the visceral arteries includes the celiac artery, superior mesenteric artery, inferior mesenteric artery, lumbar artery, internal iliac artery, and collateral renal artery. When patients have occlusion of the celiac or superior mesenteric artery, closure of the internal iliac or inferior mesenteric artery predisposes to intestinal ischemia. In some patients, the paranephric artery is present, and when the diameter of the paranephric artery is thicker, the corresponding supply of renal parenchyma is also relatively large, so if EVAR is performed, it is necessary to consider whether the patient can tolerate partial loss of renal function in this vessel. Regurgitation of the lumbar and submesenteric arteries is the main cause of type II endoleaks. When a patient has a large artery as described above, it is important to monitor for reflux intraoperatively. If the regurgitation persists during follow-up, it can be embolized to eliminate the endoleak. EVAR is a safe and effective method of treating AAA. The anatomical morphology of the aneurysm is a determining factor in the success of the procedure and in the long-term outcome after surgery. The operator must be familiar with the assessment of the anatomical morphology of AAA in order to make a rational treatment plan, anticipate possible problems, and prepare appropriate countermeasures to reduce early and late complications of EVAR and improve the outcome of AAA treatment.