Evacuation disorders in constipation tied to rectal gas volume
Rectal gas volume in patients with constipation may be greater among those with rectal evacuation disorders than among those without these disorders, a study finds.
The study included 1,552 patients with constipation who were evaluated over 20 years. Of these, 141 had pelvic CT examinations, including anorectal manometry, balloon expulsion tests and colon transit tests. Patients were then grouped according to their condition: rectal evacuation disorders, slow transit constipation and normal transit constipation.
There were two observers who measured areas of gas on each image using standard CT software. Rectal gas volume, maximal rectal gas transaxial area and area of rectal gas were compared among the three patient groups.
The measurements of rectal gas volume by the two observers were positively correlated (inter-class correlation coefficient 0.99; p<0.001). Measurements of rectal gas volume and maximal rectal gas transaxial area differed among the groups (p<0.001 for both).
Patients with rectal evacuation disorders had higher median rectal gas volume compared with patients with slow transit or normal transit constipation (13.84 vs 2.51 and 1.33 cm3; p<0.05 for both).
Similarly, area of rectal gas, which was correlated with maximal rectal gas transaxial area (Spearman correlation coefficient, 0.7; p<0.001), differed among the three groups (p=0.033). Patients with rectal evacuation disorders showed greater areas of rectal gas on the abdominal scout film compared with patients with normal transit constipation.
The findings indicate that rectal gas volume may be used to identify evacuation disorders in patients with constipation.