We described fecal retention during the defecation cycles of adults with functional constipation via ultrasonography (US) of the large intestine. US was performed continuously after the last defecation until the next defecation. We defined the fecal finding level on US as follows: weak fecal retention, a marginally high echo in the colonic lumen; or strong fecal retention, a strongly echoic colon lumen with showing a crescent-shaped acoustic shadow on transverse images and haustrations on longitudinal images. The findings confirmed weak fecal retention in the colon throughout the defecation cycle and a pattern of strong fecal retention in the descending and sigmoid colon and over the colon, including the transverse colon and ascending colon, in patients with functional constipation.
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