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

Abstract

Background & Aims Approximately one-third of patients who present with constipation to gastroenterology care 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. Method 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 intra-class 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 maximal rectal gas transaxial area (both P<.001). 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<0.05). Similarly, area of rectal gas, which correlated with 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. Conclusion 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.

Rectal gas volume: Defining cut‐offs for screening for evacuation disorders in patients with constipation

“…Our study shows that an RGV of 20 or 30 mL and an MRGTA of 10 cm 2 have PPVs of ≥75% at ~90% specificity for RED in constipated patients. These data complement our previous study, as we have identified the cut‐off values that have high specificity and PPV to select patients with likelihood to suffer RED and, therefore, to pursue other physiologic studies to confirm RED.…”

“…In the future, we plan to perform prospective validation of RGV for screening of RED. As our prior study demonstrated validity of rectal area on the scout film of the CT scan to differentiate RED from non‐RED constipation and the current analysis shows the rectal gas area of 9 cm 2 may indicate RED, we recommend prospective validation of plain abdominal and/or pelvic radiograph instead of abdominopelvic CT, given the radiation exposure and cost of abdominopelvic CT . Given the lack of standardization of BET methodology and variable sensitivity and specificity of that test, we anticipate that, with further prospective validation, the measurement of rectal gas area on a plain abdominal and/or pelvic radiograph will become a useful screening test for RED in patients with constipation.…”

“…Among these modalities, abdominopelvic CT is commonly used to exclude organic problems such as an obstructing mass or stricture in patients presenting with constipation, or it may have been undertaken in different clinics for evaluation of many abdominopelvic organs, as in patients presenting with abdominal pain to clinics specializing in gastroenterology, nephrology, urology, and gynecology. Previously, we showed that RGV on abdomen CT was greater in RED than in non‐RED patients with constipation . We used the area of ROI on each cross‐sectional CT image computed automatically by a software program available in standard CT equipment.…”

“…We recently showed that, using abdomen and pelvis CT, the rectal gas volume (RGV) and maximal rectal gas transaxial area (MRGTA) were significantly greater in constipated patients with RED than in those without RED …”

Usefulness of ultrasonographic evaluation of stool and/or gas distribution for the treatment strategy of chronic constipation

“…A recent study demonstrated that the rectal gas volume, determined by abdominal computed tomography imaging, was greater in patients with a rectal evacuation disorder than in those without it, although the criterion of this study was not rectal evacuation disorders but chronic constipation. Other studies have shown that rectal evacuation disorders are the most common cause of refractory chronic constipation .…”