ABDOMINAL X-RAYS
Plain abdominal X-rays not as useful as plain
chest X-rays because of contrast factors
Lung pathology (pneumonia, CA, effusion, etc.) is
usually of soft tissue/fluid density and is visible on
X-ray against natural contrast agent of air in lungs
In abdomen, background is soft tissue/fluid
density, and pathology is often of same density,
hence usually invisible on X-ray
Plain abd. X-rays usually will be of help only for
pathology involving gas/air or calcium
– Gas/air: e.g., bowel obstruction, free air
– Calcium: e.g., renal stones
Following shows calcified gallbladder
stones (visible against soft tissue
background)
Although these stones are atypical in that
most gallstones are not visible on X-ray
(only 10-15% have enough calcium salts
to be seen), they are otherwise typical (in
location of GB, the calcium is layered, the
stones have facets or flat sides)
The following 3 images constitute a 3-way
of the abdomen
– Supine abdomen (KUB, flat plate of abd.)
– Upright abdomen
– Upright CXR
Each of the 3 images has key role to play
– Supine abd.: best detail image
– Upright abd.: shows air-fluid levels
– Upright CXR: shows free air under diaphragm
If patient can’t be positioned for upright
imaging, lateral decubitus abdomen is
done with right side up and horizontal
beam X-ray to look for free air and air-fluid
levels
Following lateral decubitus image shows a
large amount of free intraperitoneal air and
fluid
Following 2 images are 2-way of the abdomen (supine and upright
abdomen)
Note the dilated loops of small bowel containing air-fluid levels, but
with small amounts of air in non-dilated colon which has no air-fluid
levels, indicating a small bowel obstruction
The findings of obstruction (regardless of level of GI tract, on X-ray
or CT)
– Dilated bowel
– Air-fluid levels
– A transition (dilated bowel and levels proximally, but not distally),
although on X-ray the lesion and transition are usually not directly
visible)
Although CT is usually used when there is a high suspicion of bowel
obstruction, plain X-rays are still used frequently for cases of lower
suspicion (as a “rule-out”)
Distinguish bowel obstruction from ileus,
because patient with mechanical
obstruction should be on surgical service
and may need surgery, but not ileus
Both have dilated bowel and air-fluid
levels, but ileus lacks a transition (tends to
have dilatation and levels throughout)
Following is a case of ileus. Although there
is a lot of bowel gas, it extends throughout
the small and large bowel, without a
transition
Also, the small bowel loops have a
polygonal pattern rather than showing
longer distended loops as would be typical
of mechanical obstruction
Causes of paralytic ileus
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Peritoneal irritation (peritonitis, pancreatitis, hemoperitoneum,)
Recent abdominal surgery
Hypokalemia
Acute bowel ischemia
? Neurologic mechanism (spinal fracture, passing ureteral stone, baby delivery)
Causes of mechanical small bowel obstruction
– Adhesions from prior abdominal surgery
– Incarcerated hernia
– Tumor
Primary (carcinoid, lymphoma, adenocarcinoma)
Metastatic (e.g., ovarian CA)
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Stricture (chronic ischemia, Crohn dis., radiation, endometriosis)
Secondary involvement in adjacent inflammation (appendicitis, diverticulitis)
Gallstone ileus
Volvulus
Intussusception
Bezoar
Following 2-way of the abdomen shows large
bowel obstruction
Note dilated colon, air-fluid levels, and a transition
(sigmoid colon is not dilated), the 3 elements of
obstruction
More important to promptly diagnose large bowel
compared to small bowel obstruction
– SBO can be decompressed by NG tube, but harder to
do for LBO, especially with competent ileocecal valve
(50%of time)
– Cecum may rupture (Laplace’s Law), sending feces
into peritoneal cavity
To confirm colonic obstruction, a limited
barium enema is a quick, simple, cheap,
definitive exam, not requiring bowel prep
Following are images of barium enema on
same patient who had preceding 2-way of
abdomen
BE shows a short-segment obstructing lesion
with a polypoid intraluminal component,
indicating a sigmoid colon cancer
For comparison to the colon obstruction on
the prior patient, following is a 2-way of the
abdomen on a patient with toxic megacolon
due to ulcerative colitis
Although similar to the LBO, note distension
of sigmoid and very irregular, nodular,
thickened mucosa (clinical presentation
would be different also)
Patient had colectomy shortly after these Xrays because of progressive dilation of
cecum
Causes of sigmoid colon obstruction
– Adenocarcinoma of colon
– Diverticulitis
– Sigmoid volvulus
Following is KUB on patient with sigmoid
volvulus
– Two-part obstruction (closed loop obstruction of
twisted sigmoid and upstream colon obstruction)
– Note massively dilated sigmoid, because acute
obstruction typically occurs on background of
chronic constipation and chronic colonic
dilatation)
Gas “out of place” may be seen on
abdominal X-rays
– Bowel wall
– Portal vein
– GB and biliary tree
– Urinary tract
Following shows gas in wall of small
bowel, usually indicating dead bowel,
particularly if patient looks sick
Following case shows gas in portal vein
branches in liver, usually due to dead
bowel in a very sick patient, and often
followed by death
Branching pattern of gas in liver can also
be in biliary tree, but most commonly this
is incidental finding in patients with prior
papillotomy or biliary bypass surgery.
On following KUB most remarkable finding is
easy visibility of outside wall of some of the
bowel loops, indicating that outside wall is
outlined by air (pneumoperitoneum)
The upright CXR confirms a large amount of
free intraperitoneal air (secondary to
perforated diverticulitis)
Note the widened superior mediastinum on
the CXR, an incidental old finding on this
elderly female, due to intrathoracic goiter.