An Analysis of Variables Affecting Aortic Neck Length with Implications for Fenestrated Endovascular Repair of Abdominal Aortic Aneurysm

Abstract

A major factor in the selection of patients for endovascular aneurysm repair (EVAR) is the character of the aortic neck, and studies suggest that many patients are treated outside of the instructions for use (IFU) criteria. By analyzing aortic neck morphology, we hope to identify factors that may influence decision making about the use of fenestrated endografts as an alternative to extending the neck limitations of traditional endografts. A retrospective analysis was completed on 111 patients who underwent computed tomography angiography (CTA) scans between May 1, 2009 and January 3, 2011 for the evaluation of abdominal aortic aneurysm (AAA). Individual characteristics of neck and aneurysm morphology were analyzed to establish whether certain factors determined suitability for EVAR with traditional nonfenestrated endografts. In considering augmented neck lengths (ANL), anatomic measurements of distance from the start of aortic dilatation to the lowest renal artery (LRA) and highest renal artery (HRA) were analyzed. Measurements were analyzed using Stata software (version 11.2; StataCorp, College Station, TX). There were 86 men and 25 women in the patient population, with an average age of 72.9 years. In 46 patients, the proximal neck length was <15 mm, with 26 patients having neck lengths <10 mm. There was a negative relationship between AAA maximum diameter and proximal neck length (rs = -0.2237; P = 0.018), indicating that as aneurysm size increases, proximal neck length decreases. There was a significant correlation between proximal neck length and proximal neck diameter (rs = -0.2585; P = 0.006) and between proximal neck length and angle (rs = -0.2355; P = 0.013), and between proximal neck diameter and right iliac maximum diameter (rs = 0.2329; P = 0.014). Using fenestration to place an endograft above the LRA would create an ANL of >15 mm in 20 of 40 patients with aortic necks deemed too short to be eligible for EVAR using conventional infrarenal graft positioning. Extending the graft above the HRA would create an ANL of >15 mm in 36 of 40 patients. In this study, 41% of patients presented with neck lengths outside that of the traditional IFU for most aortic endografts. While there was wide variation from patient to patient, there was a general correlation between increasing AAA size and aneurysms that have shorter, wider, and more angulated proximal necks. Fenestration of even 1 renal artery could substantially increase the ANL. Additional study is warranted to determine if an increase in ANL in patients with otherwise short necks will positively impact long-term EVAR outcomes.