Computed tomography assessment of intestinal gas volumes in functional gastrointestinal disorders

The Emerging Role and Clinical Applications of Morphomics in Diagnostic Imaging

Analytic morphomics refers to the accurate measurement of specific biological markers of human body composition in diagnostic medical imaging. The increasing prevalence of disease processes that alter body composition including obesity, cachexia, and sarcopenia has generated interest in specific targeted measurement of these metrics to possibly prevent or reduce negative health outcomes. Typical morphomic measurements include the area and density of muscle, bone, vascular calcification, visceral fat, and subcutaneous fat on a specific validated axial level in the patient's cross-sectional diagnostic imaging. A distinct advantage of these measurements is that they can be made retrospectively and opportunistically with pre-existing datasets. We provide a narrative review of the current state of art in morphomics, but also consider some potential future directions for this exciting field. Imaging based quantitative assessment of body composition has enormous potential across the breadth and scope of modern clinical practice. From risk stratification to treatment planning, and outcome assessment, all can be enhanced with the use of analytic morphomics. Moreover, it is likely that many new opportunities for personalized medicine will emerge as the field evolves. As radiologists, embracing analytic morphomics will enable us to contribute added value in the care of every patient.

Evaluation of abdominal gas by plain abdominal radiographs

BACKGROUND

Our aim was to determine the reliability of plain abdominal radiographs for the evaluation of abdominal gas content in patients with functional digestive symptoms.

METHODS

Abdominal CT scan scout views, mimicking a conventional plain abdominal radiograph, were obtained from 30 patients both during episodes of abdominal distension and basal conditions. Physicians (n = 50) were instructed to rate the estimated volume of gas in the 60 images presented in random sequence using a scale graded from 0 to ≥600 ml.

KEY RESULTS

The gas volumes estimated in the scout views differed from those measured by CT by a median of 90 (95% CI 70-102) ml, and the misestimation was not related to the absolute volume in the image. The accuracy of the observers, measured by their mean misestimation, was not related to their specialty or the training status (misestimation by 96 (95% CI 85-104) ml in staff vs 78 (70-106) ml in residents; p = 0.297). The accuracy was independent of the order of presentation of the images. Gas volume measured by CT in the images obtained during episodes of abdominal distension differed by a median of 39 (95% CI 29-66) ml from those during basal conditions, and this difference was misestimated by a median of 107 (95% CI 94-119) ml. The accuracy of these estimations was not related to the absolute gas volumes (R = -0.352; p < 0.001) or the magnitude of the differences.

CONCLUSIONS & INFERENCES

Plain abdominal radiographs have limited value for the evaluation of abdominal gas volume in patients with functional gut disorders.

Visible abdominal distension in functional gut disorders: Objective evaluation

BACKGROUND

Visible abdominal distension has been attributed to: (A) distorted perception, (B) intestinal gas accumulation, or (C) abdominophrenic dyssynergia (diaphragmatic push and anterior wall relaxation).

METHODS

A pool of consecutive patients with functional gut disorders and visible abdominal distension included in previous studies (n = 139) was analyzed. Patients (61 functional bloating, 74 constipation-predominant irritable bowel syndrome and 4 with alternating bowel habit) were evaluated twice, under basal conditions and during a self-reported episode of visible abdominal distension; static abdominal CT images were taken in 104 patients, and dynamic EMG recordings of the abdominal walls in 76, with diaphragmatic activity valid for analysis in 35.

KEY RESULTS

(A) Objective evidence of abdominal distension was obtained by tape measure (increase in girth in 138 of 139 patients), by CT imaging (increased abdominal perimeter in 96 of 104 patients) and by abdominal EMG (reduced activity, i.e., relaxation, in 73 of 76 patients). (B) Intestinal gas volume was within ±300 ml from the basal value in 99 patients, and above in 5 patients, who nevertheless exhibited a diaphragmatic descent. (C) Diaphragmatic contraction was detected in 34 of 35 patients by EMG (increased activity) and in 82 of 103 patients by CT (diaphragmatic descent).

CONCLUSIONS AND INFERENCES

In most patients complaining of episodes of visible abdominal distention: (A) the subjective claim is substantiated by objective evidence; (B) an increase in intestinal gas does not justify visible abdominal distention; (C) abdominophrenic dyssynergia is consistently evidenced by dynamic EMG recording, but static CT imaging has less sensitivity.

Intestinal gases: influence on gut disorders and the role of dietary manipulations

The inner workings of the intestines, in which the body and microbiome intersect to influence gut function and systemic health, remain elusive. Carbon dioxide, hydrogen, methane and hydrogen sulfide, as well as a variety of trace gases, are generated by the chemical interactions and microbiota within the gut. Profiling of these intestinal gases and their responses to dietary changes can reveal the products and functions of the gut microbiota and their influence on human health. Indeed, different tools for measuring these intestinal gases have been developed, including newly developed gas-sensing capsule technology. Gases can, according to their type, concentration and volume, induce or relieve abdominal symptoms, and might also have physiological, pathogenic and therapeutic effects. Thus, profiling and modulating intestinal gases could be powerful tools for disease prevention and/or therapy. As the interactions between the microbiota, chemical constituents and fermentative substrates of the gut are principally influenced by dietary intake, altering the diet, which, in turn, changes gas profiles, is the main therapeutic approach for gastrointestinal disorders. An improved understanding of the complex interactions within the intestines that generate gases will enhance our ability to prevent, diagnose, treat and monitor many gastrointestinal disorders.

Gastrointestinal Gas and Abdominal Fat Quantity Measured by Three-Dimensional Abdominal Computed Tomography in Patients with Functional Bloating

Background/Aims

The aim of this study was to assess whether increased intestinal gas or fat content in the abdominal cavity is related to abdominal bloating, using three-dimensional abdominal computed tomography scan.

Methods

Twenty-nine healthy individuals without abdominal bloating and organic disease (15 women; mean age, 49 years; range of age, 23-73 years) and 30 patients with chronic recurrent abdominal bloating-diagnosed with functional bloating (10 women; mean age, 53 years; range of age, 35-75 years) - participated in this study. The mean values of measured parameters were compared using independent sample t-test.

Results

The mean volume of total colon gas in bloated patients was similar to that in control subjects. The distribution of intra-abdominal gas was also similar between the two groups. However, the amount of gas in the transverse colon tended to be significantly higher in patients with bloating than in controls (p=0.06). Body mass index was similar between the two groups (23.4±3.2 kg/m² and 22.3±3.1 kg/m², respectively). Moreover, no significant differences with respect to circumferential area, subcutaneous fat, visceral fat area, and total fat area were found between the two groups.

Conclusions

Bloating might not just be the result of gastrointestinal gas or intra-abdominal fat. Other contributing factors, such as localized abnormality in gas distribution and visceral hypersensitivity, may be involved.

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.

Management Strategies for Abdominal Bloating and Distension

Bloating and distension are among the most common gastrointestinal complaints reported by patients with functional gut disorders and by the general population. These 2 complaints are also among the most prevalent of the severe symptoms reported by patients with irritable bowel syndrome. Nonetheless, only a limited number of published studies have specifically addressed bloating; it is infrequently studied as a primary endpoint, and what little systematic information exists has often been garnered from the assessment of secondary endpoints or the dissection of composite endpoints. This lack of data, and our consequent limited understanding of the pathophysiology of bloating, had hampered the quest for effective and targeted therapies until recently. Advances in the knowledge of underlying mechanisms, particularly with regard to the roles of diet, poorly absorbed fermentable carbohydrates, dysbiosis of the gut bacteria, alterations in visceral hypersensitivity, and abnormal viscerosomatic reflexes, have enabled the development of improved treatment options. The most significant recent advance has been a diet low in fermentable oligosaccharides, disaccharides, monosaccharides, and polyols, which significantly reduces patients' symptoms and improves quality of life. Given the prevalence of bloating and its perceived severity, it is clear that further studies regarding the pathogenesis and treatment of this problem are needed.

Bugs on the brain; brain in the gut--seeking explanations for common gastrointestinal symptoms

INTRODUCTION

Gastrointestinal symptoms such as heartburn, indigestion (or dyspepsia), bloating, distension, constipation, abdominal pain, abdominal discomfort and diarrhoea are extremely common worldwide. For some, such symptoms can prove to be chronic and disabling.

METHODS

The recent literature on irritable bowel syndrome and, in particular, work emanating form this authors research group, was reviewed.

RESULTS

These functional symptoms commonly occur in aggregations, referred to as functional gastrointestinal disorders (FGIDs). Some of the FGIDs and, most notably irritable bowel syndrome (IBS), have achieved a degree of scientific and clinical credibility as coherent entities. Several lines of evidence ranging from gut motility to the microbiota are under investigation in attempts to explain IBS or its symptomatology.

CONCLUSION

Though biomarkers for IBS and other FGIDs have proven elusive, considerable progress has been made in understanding possible aetiological factors in IBS; progress which may well lead to better therapeutic strategies.