title: Agreement between computed tomography and ultrasound on abdominal aortic aneurysms and implications on clinical decisions.
abstract: OBJECTIVE
  The United Kingdom abdominal aortic aneurysm (AAA) screening programme refers aneurysms with ultrasound (US) diameters of ≥5.5 cm to vascular services for consideration of computed tomography (CT) and intervention. We investigated the discrepancy between US and CT, implications on clinical decisions and question at which stage CT be used.
  
  
  METHODS
  AAA USs over 5 years were retrospectively analysed. Patients included had aneurysms measuring ≥5 cm on US with subsequent CT within 2 months (n = 123). Based on maximum US diameters, 44 patients had aneurysms between 5 and 5.4 cm (group I) and 79 patients ≥5.5 cm (group II). Results were cross-referenced. Correlation and limits of agreement were calculated. Two radiologists re-measured 44 pairs of CT/US scans and the inter-observer bias in determining discrepancies between imaging modalities calculated.
  
  
  RESULTS
  Mean difference between imaging modalities was 0.21 cm (±0.39 cm, p < 0.001). Limits of agreement were -0.55 to 0.96 cm, exceeding clinical acceptability. Mean difference was higher and significant in group I (0.39 cm, p < 0.001) compared to group II (0.10 cm, p > 0.05). Seventy-percent of group I patients had CT scans revealing diameters of ≥5.5 cm. Inter-observer bias was not significant.
  
  
  CONCLUSIONS
  Significant differences between imaging modalities, more in US diameters of below 5.5 cm, exist. We recommend AAAs measuring ≥5 cm on US should undergo earlier referral to a vascular service and CT.
authors.affiliation: Department of Vascular Surgery, Leeds Teaching Hospitals NHS Trust, UK.
authors.forename: F J
authors.initials: FJ
authors.lastname: Foo
authors.forename: C J
authors.initials: CJ
authors.lastname: Hammond
authors.forename: A R
authors.initials: AR
authors.lastname: Goldstone
authors.forename: M
authors.initials: M
authors.lastname: Abuhamdiah
authors.forename: S T
authors.initials: ST
authors.lastname: Rashid
authors.forename: R M
authors.initials: RM
authors.lastname: West
authors.forename: A A
authors.initials: AA
authors.lastname: Nicholson
authors.forename: D J A
authors.initials: DJ
authors.lastname: Scott
mesh_terms: D000368:Aged; D017544:Aortic Aneurysm, Abdominal / Q000000981:diagnostic imaging* / Q000628:therapy; D001027:Aortography; D005260:Female; D006801:Humans; D008297:Male; D015588:Observer Variation; D018579:Patient Selection; D015203:Reproducibility of Results; D012189:Retrospective Studies; D012680:Sensitivity and Specificity; D014057:Tomography, X-Ray Computed; D014463:Ultrasonography