Natural history and growth rates of isolated common iliac artery aneurysms

Objective: The natural history of isolated common iliac artery aneurysms (CIAAs) has not been well-studied. The optimal size threshold for elective repair of isolated CIAAs is also not well-defined. We sought to determine the natural history and growth rates of isolated CIAAs to justify a surveillance protocol and size for elective repair. Methods: Isolated CIAAs (>2 cm) identified from January 1, 2008, through February 29, 2020, at a single center were reviewed. Patient demographics, comorbidities, and details of CIAA operative repairs were retrospectively collected. All available duplex ultrasound and computed tomography scans were reviewed from time of CIAA identification through June 2020. Results: There were 244 isolated CIAAs found in 167 patients. The cohort was 94% male with an average age of 68.1 +/- 8.8 years at the time of CIAA detection. CIAAs were identified with ultrasound examination 69% of the time with a mean CIAA diameter of 2.3 cm. Operative repair of a CIAA was performed in 11.4% of the cohort at an average diameter of 3.30 +/- 1.02 cm. The majority of these repairs were performed via an endovascular approach (73.7%; n = 14). There were no symptomatic or ruptured isolated CIAAs. Concurrent aortic growth that led to an abdominal aortic aneurysm with diameter of at least 3 cm occurred in 10.6% (n = 26) of isolated CIAAs. The average length of time from CIAA diagnosis to repair was 65.7 +/- 47.1 months. The overall CIAA growth rate was 0.4 mm/y. A subgroup analysis based on CIAA size demonstrated a growth rate of 0.2 mm/y fore CIAAs 2.00 to 2.49 cm, 0.3 mm/y for CIAAs 2.50 to 2.99cm, and 1.3 mm/y for CIAAs 3.0 cm or larger. There were two CIAAs greater than 3.0 cm with extreme growth, which significantly impacted the CIAA growth rate on sensitivity analysis. After excluding those two CIAAs from the model, the overall CIAA growth rate was 0.3 mm/y. The subgroup analysis then demonstrated a growth rate of 0.2 mm/y for CIAAs 2.00 to 2.49cm, 0.3 mm/y for CIAAs 2.50 to 2.99cm, and 0.5 mm/y for CIAAs 3 cm or larger. Conclusions: Isolated CIAAs are typically slow growing aneurysms that expectedly grow faster as they enlarge. Given the rare occurrence of rapid isolated CIAA growth, we recommend surveillance at 3 years for 2.00 to 2.49 cm isolated CIAAs, 2 years for 2.50 to 2.99 cm isolated CIAAs, and yearly for isolated CIAAs greater than 3.0 cm. The lack of symptomatic or ruptured isolated CIAAs in this study supports delaying elective repair until an isolated CIAA diameter reaches at least 3.5 cm. These recommendations should be considered for isolated CIAA practice guidelines.