ARRS 2022 Abstracts

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E1228. Unstable Abdominal Aortic Aneurysm and Complications: Recognition of Imaging Findings
Authors
  1. Kaitlyn Samuels; University of Kentucky College of Medicine
  2. Jennifer True; Department of Radiology, University of Kentucky
  3. Marianna Zagurovskaya; Department of Radiology, University of Kentucky
Background
Abdominal aortic aneurysm (AAA) is a dilatation of abdominal aorta >1.5x normal diameter, more common in males. 90% of AAA are infrarenal, 80% are fusiform, most commonly (MC) due to atherosclerotic degeneration. Ruptured AAA (rAAA) carry high mortality risk, as 59-83% of patients succumb if not repaired within 24 hours. Risk of rupture is directly related to AAA sac size (0.3% <4cm, 1.5% 4-4.9cm, 6.5% 5-5.9cm) and growth rate. Other risk factors include inflammatory/infectious etiology, connective tissue disease (CTD), female gender (2-4x >M), age >60 years, hypertension (OR 8.65), COPD (OR 2.52), smoking (OR 2.7), prior cardiac or renal transplant. Multi-phase MDCTA is the mainstay AAA assessment and provides imaging criteria for instability and complications of AAA.

Educational Goals / Teaching Points
(i) identify MDCTA signs of unstable (uAAA) and complicated (cAAA), and correlate with relevant clinical scenario, (ii) understand management of AAA based on risk of rupture

Key Anatomic/Physiologic Issues and Imaging Findings/Techniques
(I) uAAA: (i) hyperattenuating crescent sign due to intramural and/or into pre-existing AAA thrombus hemorrhage (sens. 77%, spec. 93%), (ii) draped aorta sign due to intimal tear and reactive sac fibrosis (3%) and vertebral body erosion due to chronic water-hammer pulsatility from AAA or osseous destruction from infected AAA (30%), (iii) focal disruption of AAA wall calcification, (iv) growth of excluded/stented AAA. Of note, intraluminal thrombus (ILT) (>90% of AAA with MC eccentric-anterior location) in asymptomatic patient and ILT volume/aneurysm volume ratio (mean 0.47-0.49) are not significant predictors of rupture. (II)cAA: rAAA presents with abdominal pain, hypotension. CT: ill-defined retro- +/- intraperitoneal hemorrhage or more defined hematoma abutting AAA, often with wall discontinuity/outpouching; active contrast extravasation beyond AAA sac is infrequently seen due to hemodynamic collapse. Aorto-enteric fistula (MC 3rd-4th parts of duodenum) presents with abdominal pain, hematemesis, melena, and herald bleeding (60%). CT: gas within/around AAA sac, contrast extravasation into bowel. Aorto-venous fistula (<1% AAA, 3-4% rAAA) can present with syncope, hypotension, high output cardiac failure, pedal edema, renal insufficiency. CT: early enhancement of IVC/involved vein on arterial phase, delayed renal cortex enhancement. Other complications: peri-AAA inflammation, thrombosis of branch vessels, and compression of adjacent structures. Management: Ultrasound (US) is an initial screening method for AAA for men >65 years with smoking history, or patients with CTD, strong family history of AAA. Subsequently, US is used q6-12 months for known asymptomatic/stable AAA. MDCTA is mainstay of evaluation of symptomatic or rapidly enlarging AAA (for intervention planning) or post-interventional (to assess for endoleak). Generally, AAA diameter >5.5cm or rapid growth rate (5-7mm in 6months or 1cm/yr) warrants endovascular AAA repair (EVAR, preferred) or open surgical repair.

Conclusion
rAAA carries high mortality rate. MDCTA provides certain criteria of AAA instability and complications, thus impacting management and survival.