Plain Radiographs in the acute abdomen

65 Pages·2011·3.31 MB·English

Plain Radiographs in the acute abdomen - do they still have
a role?
Poster No.: C-1841
Congress: ECR 2011
Type: Educational Exhibit
Authors: L. Batista, J. T. Soares, J. Ressureição, F. C. Pires, A. B. Almeida;
Vila Nova de Gaia/PT
Keywords: Abdomen, Pelvis, Plain radiographic studies, Diagnostic
procedure, Acute
DOI: 10.1594/ecr2011/C-1841
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Learning objectives
To review the imaging findings on plain radiographs that can be helpful in the diagnosis
and management of the acute abdomen.
To present the rationale for the use of plain radiographs as the first imaging modality in
the evaluation of the patient with acute abdomen.
Background
Acute abdominal pain is one of the leading causes of admission in the emergency
department.
The most common etiology of acute abdominal pain is functional but several disorders
need urgent management.
A very large percentage of these patients are first evaluated with conventional
radiographs.
Imaging findings OR Procedure details
The distribution of gas or its presence in unusual locations, abnormal distention or
location of bowel loops and the presence and location of calcifications can all be used to
suggest and sometimes clinch the correct diagnosis.
Although the imaging findings in plain radiographs of the acute abdomen are often
nonspecific, they are still very important in the subsequent management of the patient
and they can sometimes reach to a specific diagnosis.
1. Technique
An anteroposterior (AP) view in the supine position is the most often plain abdominal
radiograph obtained. In the setting of acute abdominal disease, an erect film of the
abdomen should be obtained. The supine radiograph should include the diaphragm
superiorly and the hernia orifices inferiorly.
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In the patient who is too ill and cannot stand for an erect film, a lateral decubitus with
horizontal ray can be achieved to look for pneumoperitoneu or air-fluid levels. As little as
1 ml of free gas can be seen in the lateral decubitus abdominal radiograph.
2. Anatomy
The abdomen is divided into four quadrants: right upper quadrant (RUQ), left upper
quadrant (LUQ), right lower quadrant (RLQ) and left lower quadrant (LLQ).
We can also divide the abdomen into two cavities: the peritoneal cavity and the
retroperitoneal cavity.
The peritoneum is a thin layer of tissue that involve several organs like the spleen, almost
all liver and most of the bowel; in the lateral borders of the abdomen, the peritoneum
creates a recess lateral to the right and left colon which is called a paracolic gutter.
The retroperitoneum is a space located behind the peritoneal cavity and contains the
pancreas, kidneys, abdominal aorta, psoas muscles, bladder, ascending and descending
colon and the rectum.
The abdomen is composed in its majority by soft tissue. In plain radiograph, the soft tissue
density is equal to the density of water, so we cannot distinguish between solid and liquid.
In the majority of the population, the contour of the solid abdominal organs or muscle can
be seen in plain abdominal radiograph because of the fat that surrounds them that has
a different density than that of soft tissue. The fat lines can be displaced by enlargement
of the organs or effaced because of fluid or inflammation.
The flank stripe is also called properitoneal fat stripe and has a concave shape. As this
stripe is located adjacent to the ascending and descending colon and these structures
are filled with gas, if we detect a widening of the distance between the fat stripe and the
colon it means that fluid is filling the paracolic gutter (Fig. 5).
As said before, the outline of the muscles can also be accessed. The retroperitoneal
psoas muscle shadow can be seen lateral to the spine (Fig. 1). The absence of one or
both the shadows suggests inflammation, retroperitoneal tumor or hemorrhage. If the
outline of one of the psoas muscles appears convex it can be caused by an abscess or,
alternatively, an intramuscular mass.
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Fig.: Normal plain film of the abdomen. We can see the hepatic angle (H), the splenic
angle (S). The psoas muscle (arrows) and the kidneys (K) shadows are delineated by a
fat shadow. The blue arrowheads show the properitoneal fat stripes.
References: L. Batista; RADIOLOGY, Centro Hosp. Vila Nova de Gaia, Vila Nova de
Gaia, PORTUGAL
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In the RUQ we can see the liver shadow that is of fluid density (Fig.2). We cannot see
the portal vein and bile duct in normal conditions because they have the same density
in the plain radiograph as the liver.
Fig.: The lower margin of the liver (arrows) outlined by a fat shadow.
References: L. Batista; RADIOLOGY, Centro Hosp. Vila Nova de Gaia, Vila Nova de
Gaia, PORTUGAL
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The spleen is located at the LUQ. In plain radiographs the splenic angle can be visualized
because of the fat shadow that surrounds it.
The gastric bubble is a small amount of gas that can be seen in the LUQ (Fig. 3).
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Fig.: The gastric bubble (arrow) in the left lower quadrant.
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References: L. Batista; RADIOLOGY, Centro Hosp. Vila Nova de Gaia, Vila Nova de
Gaia, PORTUGAL
The renal contour also can be visualized in both flanks.
When the liver and the spleen enlarge they displace the bowel loops near them and cause
obliteration of the normal fat and of the normal gas pattern.
In the pelvis, the dome of the urinary bladder can be seen as it is delineated by fat. The
fat that involves the obturador internus muscle can be visualized on the inner surface of
the pelvic inlet.
Gas is present in the stomach, colon and in minimal quantities in the small bowel and it
has the lowest density in the abdomen.
The small bowel is composed of the duodenum, jejunum and ileum and is located in the
middle of the abdomen. It has fluid density and contains thin folds that cross the entire
width of the bowel (the valvulae coniventes) and are much closer together than colonic
haustra. The jejunum has numerous mucosal folds compared with the ileum. Short fluid
levels of the small bowel can be normally visualized on an erect abdominal film.
The colon is composed, from most proximal to distal, of the appendix, the cecum, the
ascending colon, hepatic flexure, transverse colon, splenic flexure, descending colon,
sigmoid colon and rectum. It is located in the periphery of the abdomen and has thick
incomplete folds, the haustra, that do not cross the lumen. The presence of solid feces
is a reliable sign that the loop is large bowel (Fig. 4).
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Fig.: The colon is located in the periphery of the abdomen (arrows) and has mucosa
folds that do not cross the entire lumen. Sometimes solid material can be seen with a
mottled appearance.
References: L. Batista; RADIOLOGY, Centro Hosp. Vila Nova de Gaia, Vila Nova de
Gaia, PORTUGAL
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The bones and the calcifications have the highest density in the plain abdominal films.
Bony structures that can be seen are: the ribs, the spine and the pelvic bones. Sometimes
calcifications can be visualized like calcified arteries, pancreatic calcifications and calculi
in the urinary tract.
3. Abnormal findings
3.1 Free fluid
The presence of free fluid (sterile reactive fluid, pus, blood, bile, urine) is a nonspecific
sign of abdominal pathology that requires an investigation with more techniques.
Free fluid (ascites) and blood can be suspect in the plain abdominal radiograph if there
is a widening of the distance between the fat stripe and the ascending or descending
colon shadow being these two portions of the large bowel displaced medially (Fig. 5).
The hepatic angle may be obscured or displaced medially, the "Hellmer`s sign".
A diffuse increase density of the pelvis or of all the abdomen is suggestive of large
amounts of free fluid.
Fig.: In the plain abdominal radiograph we can see a diffuse increase density of the
abdomen suggesting the presence of free fluid. There is a widening of the distance
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