The Impact of using Inner-to-Inner Wall Diameter Measurement of Abdominal Aortic Aneurysm

I read with interest the article by Sensier et al. ¹ ‘The impact of using inner-to-inner wall diameter measurement of abdominal aortic aneurysm’ in the February issue of Ultrasound. The authors are to be congratulated on their foresight, in designing an audit to evaluate the impact on their abdominal aortic aneurysm (AAA) screening and surveillance service, when introducing change to reflect national evidence-based practice.^{2, 3} This audit followed patients attending for AAA screening and surveillance ultrasound examinations in a hospital-based programme rather than in the National Abdominal Aorta Screening Programme (NAAASP). ² The study design was to compare their current practice of measuring outer-to-outer (OTO) abdominal aortic diameters with inner-to-inner (ITI) aortic diameter measurements.

Although the authors’ findings add to the knowledge base, the audit raises three issues. First, the recording of averaged, non-blind, longitudinal and transverse section aortic diameter measures, done by experienced vascular sonographers, in comparison to recording absolute measures, by screening technicians, will account for their precise and reliable values. Their values are comparable with the findings of a previous review of abdominal aortic diameter measurements. ⁴ It does not answer the question: Is the antero-posterior (A-P) abdominal aortic diameter ITI ⁵ or OTO ⁶ in longitudinal or transverse section more reproducible? ⁷

Second, their measuring of the abdominal aorta's lateral (transverse) diameter, in the coronal section, is at variance with NAAASP. ² The difference in practice between local and national screening services, within the same region, reflects the review by Long et al. ⁷ who found multiple techniques to measure the abdominal aortic diameter. This variance may have an impact on decision making, patient pathways and treatment outcomes for men with AAA.

Third, the patients with AAA close to the threshold for surgery, when measured by ITI rather than OTO meant a delay in referral of roughly nine months. While not impacting on patient outcomes, in this small sample, it is an interesting concept. Taking these data into account, intra-observer repeatability ranges between 1.6 and 4.4 mm and inter-observer reproducibility from 1.9 to 10.5 mm in A-P diameter ⁴ and with average growth rates of 2.3 mm/year ⁸ this suggests further research is required to evaluate the necessity of a surveillance interval of three months for AAA of 45–54 mm.

It is my opinion that hospital-based AAA screening and surveillance programmes should be standardized to national guidelines such as NAAASP. ² This should ensure improved decision making for health-care practitioners and equality of patient pathways: entry onto programme, surveillance, referral for a surgical opinion and treatment outcomes.