title: Aortic Size Distribution in the General Population: Explaining the Size Paradox in Aortic Dissection.
abstract: BACKGROUND
  Current guidelines recommend a diameter of 5-5.5 cm as the threshold for surgery on the ascending aorta. However, a study from the International Registry of Acute Aortic Dissection showed that nearly 60% occurred at <5.5 cm (the 'aortic size paradox')--leading to a debate whether the size threshold should be lowered. However, the study showing dissection at small size had no knowledge of the population at risk. Herein, we aim to calculate the relative risk of aortic dissection at sizes<5.5 cm by analyzing both the number of occurring dissections (numerator) and the population at risk at each aortic size (denominator).
  
  
  METHODS
  Using a publicly available database of 3,573 multiethnic subjects (46% male, mean age 60.7 years) from the general population, we plotted a distribution curve of ascending aortic size (by magnetic resonance imaging). The relative risk of aortic dissection was calculated by dividing the proportion of dissections occurring at each size (numerator) by the proportion of aortas of that same size in the general population (denominator).
  
  
  RESULTS
  The mean ascending aortic diameter of the reference population was 3.2 cm (±0.4 cm). The largest diameter was 4.9 cm in women and 5.0 cm in men. The proportion of subjects with an aorta <3.5 cm was 79.2%, that of subjects with 3.5-3.9 cm was 18.0%, that of subjects with 4.0-4.4 cm was 2.6%, and that of subjects with ≥4.5 cm was 0.22%. The relative risk of dissection in those categories was found to be 0.055, 2.5, 4.9, and 346.8, respectively. Patients with an aorta≥4.5 cm were 6,305 times more likely to suffer aortic dissection than those with an aorta<3.5 cm.
  
  
  CONCLUSIONS
  The normal aorta is deceptively small, most commonly <3.5 cm. The aortic size paradox is a byproduct of the very large number of patients in small size ranges. This study fully supports current recommendations for surgical intervention at 5-5.5 cm.
authors.affiliation: Department of Cardiology, Winthrop University Hospital, Mineola, N.Y., USA.
authors.forename: Vijayapraveena
authors.initials: V
authors.lastname: Paruchuri
authors.forename: Khaled F
authors.initials: KF
authors.lastname: Salhab
authors.forename: Kahled F
authors.initials: KF
authors.lastname: Salhab
authors.forename: Gregory
authors.initials: G
authors.lastname: Kuzmik
authors.forename: George
authors.initials: G
authors.lastname: Gubernikoff
authors.forename: Hai
authors.initials: H
authors.lastname: Fang
authors.forename: John A
authors.initials: JA
authors.lastname: Rizzo
authors.forename: Bulat A
authors.initials: BA
authors.lastname: Ziganshin
authors.forename: John A
authors.initials: JA
authors.lastname: Elefteriades
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D000784:Aortic Dissection / Q000601:surgery*; D001013:Aorta, Thoracic / Q000473:pathology*; D017545:Aortic Aneurysm, Thoracic / Q000601:surgery*; D016208:Databases, Factual; D005260:Female; D006801:Humans; D008279:Magnetic Resonance Imaging; D008297:Male; D008875:Middle Aged; D009929:Organ Size; D012307:Risk Factors