The document compares and contrasts the small bowel and large bowel. The small bowel lies more centrally and has mucosal folds called valvulae conniventes that cross its full width. The large bowel has pouches called haustra and spaces called plicae semilunaris between them. The haustra are thicker than the valvulae conniventes and do not fully traverse the bowel. Normal diameter limits are 3cm for the small bowel and 6cm for the colon, with the caecum at 9cm. Small bowel obstruction appears as dilated loops over 3cm in diameter with prominent valvulae, while large bowel obstruction shows colonic distension proximal to the obstruction and collapse

1. Small bowel vs. Large bowel
• The small bowel usually lies more centrally, with the large
bowel framing it.
• The small bowel’s mucosal folds are known as valvulae
conniventes and are visible across the full width of the
bowel.
• The large bowel wall features pouches or sacculations that
protrude into the lumen, known as haustra. In between the
haustra are spaces known as plicae semilunaris. The
haustra are thicker than the valvulae conniventes of the
small bowel and typically do not appear to completely
traverse the bowel.
• Faeces have a mottled appearance and are most often
visible in the colon, due to trapped gas within solid faeces
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2. Bowel diameter
• The upper limits for the normal diameter of
different bowel segments are as follows:
• Small bowel: 3cm
• Colon: 6 cm
• Caecum: 9 cm
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3. A normal
abdominal X-ray
showing large
bowel (white
arrow) framing the
small bowel (black
arrow)
Example of faeces
and its typical
mottled
appearance
The small bowel’s
mucosal folds are
called valvulae
conniventes and
cross the full
width of the
bowel
Haustra (white
arrow) and plicae
semilunaris (black
arrow)
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4. Small bowel obstruction
• Typical abdominal X-ray features of small bowel
obstruction include dilation of the small
bowel (>3cm diameter) and much
more prominent valvulae conniventes creating a
‘coiled-spring appearance‘.
• When interpreting an abdominal X-ray you
should always inspect the inguinal regions,
particularly if considering a hernia as a cause of
small bowel obstruction, as they are often fairly
obvious (even on plain abdominal X-rays).
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5. Small bowel obstruction (note the
dilated loops of small bowel
creating a “coiled-spring”
appearance)
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6. Large bowel obstruction
• Characterised by colonic distension proximal
to the obstruction, with collapse distally.
• Considered dilated if it is over 6 cm in
diameter, with the caecum having an upper
limit of 9 cm.
• Very few or no air-fluid levels are found in the
large bowel because water is reabsorbed.
• rectum has little or no air.
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7. Large bowel obstruction
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