Microcolon is the term used to describe a colon of abnormally small caliber, typically seen in neonatal contrast enema studies.
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Pathology
In a normal fetus, succus entericus is secreted by the proximal small bowel to nourish and distend the colon. Microcolon occurs when there is functional disuse and these fluids fail to reach the colon 1,2. A relatively distal obstruction is therefore required to develop a microcolon.
Radiographic features
Fluoroscopy
On contrast enema, the entire colon is small in caliber, typically <1 cm in diameter 1, or smaller than the height of an upper lumbar vertebral body 3.
Ultrasound
In the setting of small bowel atresia, ultrasound shows a gasless colon that is <0.65 cm in diameter 4.
Differential diagnosis
meconium ileus: (most common cause 1) shows filling defects in the bowel
ileal atresia: (second most common cause 1) shows an abrupt cut-off at the site of atresia
distal jejunal atresia
total colonic Hirschprung disease: rare
megacystis microcolon intestinal hypoperistalsis syndrome (MMIHS)
NB: small left colon syndrome does not cause a true microcolon, and the small colon usually resolves during the enema.