William C. Shiel Jr., MD, FACP, FACR
William C. Shiel Jr., MD, FACP, FACR
Dr. Shiel received a Bachelor of Science degree with honors from the University of Notre Dame. There he was involved in research in radiation biology and received the Huisking Scholarship. After graduating from St. Louis University School of Medicine, he completed his Internal Medicine residency and Rheumatology fellowship at the University of California, Irvine. He is board-certified in Internal Medicine and Rheumatology.
In this Article
Imaging studies and other tests
Colonic transit (marker) studies
Colonic transit studies are simple X-ray studies that determine how long it takes for food to travel through the intestines. For transit studies, individuals swallow capsules for one or more days. Inside the capsules are many small pieces of plastic that can be seen on X-rays. The gelatin capsules dissolve and release the plastic pieces into the small intestine. The pieces of plastic then travel (as would digesting food) through the small intestine and into the colon. After 5 or 7 days, an X-ray of the abdomen is taken and the pieces of plastic in the different parts of the colon are counted. From this count, it is possible to determine if and where there is a delay in the colon.
In non-constipated individuals, all of the plastic pieces are eliminated in the stool and none remain in the colon. When pieces are spread throughout the colon, it suggests that the muscles or nerves throughout the colon are not working, which is typical of colonic inertia. When pieces accumulate in the rectum, it suggests pelvic floor dysfunction.
Defecography is a modification of the barium enema examination. For this procedure, a thick paste of barium is inserted into the rectum of a patient through the anus. X-rays then are taken while the patient defecates the barium. The barium clearly outlines the rectum and anus and demonstrates the changes taking place in the muscles of the pelvic floor during defecation. Thus, defecography examines the process of defecation and provides information about anatomical abnormalities of the rectum and pelvic floor muscles during defecation.
Ano-rectal motility studies
Ano-rectal motility studies, which complement defecography tests, provide an assessment of the function of the muscles and nerves of the anus and rectum. For ano-rectal motility studies, a flexible tube, approximately an eighth of an inch in diameter, is inserted through the anus and into the rectum. Sensors within the tube measure the pressures that are generated by the muscles of the anus and rectum. With the tube in place, the patient performs several simple maneuvers such as voluntarily tightening the anal muscles. Ano-rectal motility studies can help determine if the muscles of the anus and rectum are working normally. When the function of these muscles is impaired, the flow of stool is obstructed, thereby causing a condition similar to pelvic floor dysfunction.
Magnetic resonance imaging defecography
The newest test for evaluating defecation and its disorders is magnetic resonance imaging defecography and is similar to barium defecography. However, magnetic resonance imaging (MRI) is used instead of X-rays to provide images of the rectum during defecation. MRI defecography appears to be an excellent way to study defecation, but the procedure is expensive and somewhat cumbersome. As a result, it is used in only a few institutions that have a particular interest in constipation and abnormalities of defecation.
Colonic motility studies
Colonic motility studies are similar to ano-rectal motility studies in many aspects. A very long, narrow (one-eighth inch in diameter), flexible tube is inserted through the anus and passed through part or the entire colon during a procedure called colonoscopy. Sensors within the tube measure the pressures that are generated by the contractions of the colonic muscles. These contractions are the result of coordinated activity of the colonic nerves and muscles. If the activity of the nerves or muscles is abnormal, the pattern of colonic pressures will be abnormal. Colonic motility studies are most useful in defining colonic inertia. These studies are considered research tools, but they can be helpful in making decisions regarding treatment in patients with severe constipation.
Medically Reviewed by a Doctor on 7/16/2015
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