GI Radiology > Small Bowel > Anatomy > General
Anatomy
General |
·
The small bowel, derived from the fetal foregut and midgut,
is comprised of duodenum, jejunum, ileum. The small bowel
generally lies centrally within the abdomen, “framed” by the large
bowel. On imaging, the small
bowel can be differentiated from the large bowel based on the presence of
plicae circulares (circular folds), which traverse the entire diameter of the
lumen. The large bowel does not possess these circular folds, but rather has
saccular dividers called haustra. The normal dimensions of the small bowel
can be remembered by the “Rule of 3’s”– ·
Bowel wall < 3mm
thick ·
Bowel folds < 3mm
thick ·
Bowel diameter <
3cm wide ·
No more than 3
air-fluid levels should be present
·
The majority of the
small bowel is comprised of the jejunum and ileum. Both segments derive their blood supply from branches of
the SMA and have very similar appearances. Some guidelines, however, when
applied to film interpretation, can aid in differentiating these two segments
of bowel. The jejunum begins at
Ligament of Treitz and resides predominantly in the left upper quadrant. It possesses a feathery mucosal
pattern (appreciated best on fluoroscopy studies) and is usually larger In
caliber than the ileum. Coversely, the ileum resides predominantly in the
right lower quadrant, terminating at the ileocecal junction. It is usually
larger in caliber than the jejunum, with fewer folds and a smoother (more
featureless) mucosal pattern. |
Normal small bowel follow-through demonstrates the normal
anatomy of the small bowel. |
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