Relevance of abdominal gas analysis and transit study after colorectal cancer surgery

Rectal Gas Volume Measured by Computerized Tomography Identifies Evacuation Disorders in Patients With Constipation

BACKGROUND & AIMS

Approximately one third of patients who present to gastroenterology care with constipation have rectal evacuation disorders. We aimed to compare rectal gas volume, measured by computerized tomography (CT), in constipated patients with and without rectal evacuation disorders.

METHODS

In a retrospective study, we collected data from 1553 patients with constipation, evaluated over 20 years. We analyzed data from 141 patients evaluated by anorectal manometry, balloon expulsion tests, and colon transit tests, collecting records of abdominal and pelvic CT examinations. Patients were classified into 3 subgroups: those with rectal evacuation disorders, slow-transit constipation, or normal-transit constipation. Two observers used standard CT software to identify variable regions of interest on each cross-sectional CT image that contained rectum and measured areas of gas in each slice; they then summated entire volumes of rectal gas. For the 3 groups, we compared rectal gas volume, maximal rectal gas transaxial area (measured by CT), and area of rectal gas (vertical) on the 2-dimensional abdominal film (scout) using the Kruskal-Wallis test.

RESULTS

The intraclass correlation coefficient between 2 observers' measurements of rectal gas volume was 0.99 (P < .001). There were overall group differences in rectal gas volume and the maximal rectal gas transaxial area (both P < .001). The median rectal gas volume was higher in patients with rectal evacuation disorders (13.84 cm³) than in patients with slow-transit (2.51 cm³) or normal-transit constipation (1.33 cm³, both P < .05). Similarly, the area of rectal gas, which correlated with the maximal rectal gas transaxial area (Spearman correlation coefficient, 0.7; P < .001), showed overall 3-group differences (P = .033), with greater areas of rectal gas on the abdominal scout film in patients with rectal evacuation disorders than in those with normal-transit constipation.

CONCLUSIONS

In an analysis of patients with constipation, we found rectal gas volume, determined by abdominal CT imaging, to be greater in patients with than without rectal evacuation disorders.

Relevance of Colonic Gas Analysis and Transit Study in Patients With Chronic Constipation

Background/Aims

Colon transit time (CTT) is a useful diagnostic tool in chronic constipation, but requires good patient compliance. We analyzed the correlation between the gas volume score (GVS) and CTT in patients with chronic constipation.

Methods

The study included 145 consecutive patients (65 men) with chronic constipation. The primary outcome was the correlation between the colon GVS and CTT. Secondary outcomes were the differences in colon GVS according to CTT and subtypes of chronic constipation.

Results

There were 81 patients with “CTT < 45 hours” and 64 patients with “CTT ≥ 45 hours.” In addition, 88 patients were classified as having functional constipation and 57 were classified as having constipation predominant irritable bowel syndrome (IBS-C). There was no significant correlation between CTT and colon GVS. However, the right colon GVS showed a positive correlation with right CTT (r = 0.255, P = 0.007). The median total colon GVS was significantly higher in patients with “CTT ≥ 45 hours” than in those with “CTT < 45 hours” (5.65% vs 4.15%, P = 0.010). There were no significant differences in colon GVS between the functional constipation and IBS-C.

Conclusions

We were unable to detect a correlation between GVS and CTT in patients with chronic constipation. However, total colon GVS may be a method of predicting slow transit in patients with chronic constipation.