Objectives: To determine the normal dimensions of the anal wall and if there were detectable differences in inflammatory disorders.
Methods: A cross-sectional survey was performed on all patients referred to a university anorectal ultrasound clinic who had either perianal Crohn's disease (17 patients), ileoanal pouches (15 patients), perianal fistula (15 patients), or previous radiation to the rectum (5 patients). Results were compared to 40 normal controls. Anal wall thickness (AWT), mucosa, submucosa, internal sphincter thickness (MSIT), and external sphincter thickness (EST) were measured or calculated. Intra- and interobserver reliability was assessed.
Results: The mean AWT was 14.8 mm (95% CI: 14.0-15.6), mean EST was 8.3 mm (95% CI: 7.6-9.0), and the mean MSIT was 6.5 mm (95% CI: 5.8-7.2) in the control subjects. Measurements did not differ significantly with sex or with an increase in age. Patients with perianal Crohn's disease, ileoanal pouches with septic complications, and previous local radiotherapy had significant increases in anal wall thickness. In Crohn's disease, the significant increase was in MSIT, whereas, in the pouch patients, the increase was in the EST. Reliability studies demonstrated a learning curve with experience and a better correlation with determination of AWT than MSIT.
Conclusions: Patients with anorectal inflammatory conditions have increased thickness in anal wall dimensions.