Dr. Curry, Dr. Urban,
are with The Russell H. Morgan Department of Radiology and
Radiological Science, The Johns Hopkins Medical Institutions,
variety of processes involving the gastrointestinal tract can cause
acute abdominal pain. There is often overlap in the clinical
presentation of many entities that may not be distinguishable based
on clinical findings or laboratory results. Additionally, even when
the diagnosis is certain, the underlying etiology and associated
complications which will affect patient management may remain
unknown. Therefore, a rapid and accurate diagnosis in patients
presenting with an acute abdomen is essential for appropriate
triage and care.
Computed tomography has gained widespread acceptance as a rapid,
reliable, highly accurate, and cost-effective modality in the
evaluation of patients presenting with an acute abdomen. It is
often used in the work-up of many gastrointestinal causes of
abdominal pain, including bowel obstruction, inflammation,
appendicitis, diverticulitis, and ischemia.
With recent advances in volumetric data acquisition provided by
helical (spiral) computed tomography, CT continues to provide an
increasingly important role in the evaluation of the acute abdomen.
This article reviews the application of CT for acute GI conditions
which may present with acute abdominal pain.
Helical CT is the technique of choice when performing computed
tomography. When possible, it is important to tailor the helical CT
protocol to the working clinical diagnosis.
For most GI conditions, both oral and intravenous contrast are
utilized; 750 to 1000 cc of a 3% iodinated, water-soluble oral
contrast is typically given by mouth in divided doses over 30 to 45
minutes. In cases of suspected appendicitis, at least 1 hour of
transit time is needed for opacification of the distal small bowel
and right colon. Alternatively, contrast can be administered per
rectum for colonic opacification. In patients with high-grade
small-bowel obstruction, studies can be performed without oral
contrast, as the obstructed, fluid-filled loops provide "natural"
contrast when combined with an intravenous contrast injection.
Similarly, water can be ingested and utilized as a negative
contrast agent in evaluation of patients with suspected gastric
pathology, including peptic ulcer disease.
We recommend IV contrast injections for most patients, although in
many cases of appendicitis and diverticulitis the diagnosis can be
made accurately without it. The rate and amount of IV contrast
administration varies, but generally 120 cc of iodinated contrast
is administered at a rate of 2 to 3 cc per second via a peripheral
vein. Usually, images are obtained with a single-phase helical
acquisition 70 seconds after the initiation of injection; 5 mm
collimation with a pitch of 1.6 is adequate in most patients.
Images are reconstructed every 5 to 8 mm.
Acute appendicitis is a very common cause of acute abdominal
pain. Patients classically present with pain in the periumbilical
region, which typically localizes over several hours to the right
lower quadrant. Nausea, vomiting, and an elevated white blood cell
count are often seen. Symptoms are sometimes nonspecific and can be
mimicked by a variety of inflammatory processes including pelvic
inflammatory disease, diverticulitis, and inflammatory bowel
disease. CT is often utilized to confirm diagnosis, to quantify the
extent of inflammation, and identify complications, such as
perforation and abscess formation.
Studies have demonstrated that helical CT utilizing 5 mm
collimation, with or without oral or IV contrast, is very accurate
(94% to 100%) for the diagnosis of appendicitis.
A noncontrast CT exam is the study of choice in patients with renal
impairment, a history of prior reaction, or increased risk of
adverse reaction to iodinated contrast. A noncontrast exam is quick
and easy to perform. However, a noncontrast exam can be more
difficult to interpret as subtle findings may be obscured,
particularly in patients with minimal intra-abdominal fat. In
addition, other inflammatory processes that clinically mimic
appendicitis are often better evaluated with the use of IV and oral
contrast. Therefore, we routinely use both IV and oral contrast if
at all possible.
Signs of acute appendicitis on helical CT include a dilated,
fluid-filled appendix, stranding of the fat around the appendix, an
enhancing appendiceal wall, and a calcified appendicolith (figure
A dilated, fluid-filled appendix, the most specific sign for
appendicitis, is not always seen due to superimposed inflammation
or perforation or abscess formation. Enhancement of the appendiceal
wall can be quite subtle and may be the only sign of inflammation
(figure 2). Other conditions can lead to inflammation in the right
lower quadrant and mimic findings of acute appendicitis, including
Crohn's disease and cecal diverticulitis. In fact, any inflammatory
processes in the right lower quadrant can cause inflammatory
stranding in the mesenteric fat, and secondary signs specific to
the appendix should be seen before making the diagnosis of acute
US is also useful in patients with clinically suspected
appendicitis, particularly in women and children. However, in most
patients, CT is still the preferred modality of choice. Balthazar
prospectively compared CT with graded-compression US and
demonstrated increased sensitivity (96% vs. 76%), negative
predictive value (95% vs. 76%), and accuracy (94% vs. 83%) of CT
relative to US. The normal appendix, when present, was seen 48% at
CT compared to only 4% at US.
CT is also very helpful in evaluation of the obese patient, in whom
US evaluation can be very difficult.
Diverticular disease is very common in patients over the age of
60 and most commonly involves the sigmoid colon. Typical presenting
symptoms include left lower quadrant pain, fever, and elevated
white blood cell count. CT is very sensitive (93%) and specific
(nearly 100%) for diagnosing diverticulitis.
Oral, rectal, and/or IV contrast are helpful for diagnosing
diverticulitis, but often diagnosis is possible without contrast.
However, contrast is most beneficial for the detection of
complications, including perforation and abscess formation, and is
therefore recommended for most patients.
CT findings of acute diverticulitis include colonic wall
thickening, diverticula, and pericolonic fatty stranding. Luminal
opacification is important for depiction of wall thickening, and is
best obtained by contrast administration via an enema.
Helical CT obtained after enema is 99% accurate for confirming or
excluding the diagnosis of diverticulitis.
CT is also very sensitive to the presence and nature of pericolic
complications, including extraluminal air, enterovesical fistula,
and abscess formation (figure 3).
CT with IV contrast accentuates the rim enhancement of pericolic
abscesses, and helps differentiate neighboring bowel loops from the
inflammatory changes. In addition, CT is an excellent modality for
detecting other causes of left lower quadrant pain that may mimic
diverticulitis, and can suggest alternative diagnoses in 78% of
cases when they are present.
Small bowel obstruction
Small bowel obstruction (SBO) is a common cause of acute
abdominal pain in patients presenting with symptoms such as nausea
and vomiting. The common causes of SBO are adhesions, hernias, and
Complete or high-grade SBO is detected by CT with an accuracy of
However, when low-grade or partial obstructions are included, the
accuracy decreases to 66%.
In these cases, a small bowel series is often indicated to define
the level of obstruction. Routine helical CT evaluation in
suspected SBO is used following the administration of IV contrast.
In general, oral contrast is not necessary prior to CT evaluation
of the abdomen when a high-grade obstruction is suspected. In these
cases, the bowel is distended with fluid, providing excellent
delineation of bowel loops.
The most common CT findings in a patient with a high-grade
obstruction include dilated loops of bowel with a discrete
transition point, followed by decompressed loops of small bowel.
Careful evaluation of the bowel loops in the region of the
transition point will often reveal the underlying pathologic
Hernias are usually seen in the inguinal region or the abdominal
wall (figure 4).
Incisional hernias, parastomal hernias, and spigelian hernias
constitute other types of abdominal wall hernias.
The presence of a strangulated obstruction should be entertained
when there is engorgement of the mesenteric vessels and poor
enhancement of the bowel wall.
Occasionally, two limbs of a bowel loop will be obstructed
producing what is called a "closed-loop" obstruction.
The bowel loops and associated mesentery will be oriented in a
radial pattern converging toward the point of obstruction (figure
5). An obstructing mass, tumor implant, or intussusception can also
present with a SBO and should be searched for and excluded in all
patients presenting with a bowel obstruction (figure 6). The
absence of mass, hernia, intussusception, or other pathology is
usually indicative of an adhesion, particularly when the patient
has a history of abdominal surgery (figure 7).
Patients with acute bowel ischemia often present with severe
abdominal pain and hemodynamic instability. These patients are
diagnostically challenging from a clinical and radiographic
perspective. Although CT may play a vital role in identifying bowel
abnormalities associated with ischemia, the findings are often
nonspecific and must be correlated with the patient's clinical
history and physical exam.
Rapid IV contrast administration (at least 3 cc/sec) is
essential in the CT evaluation of mesenteric ischemia. Helical CT
can verify confidently the patency of the celiac and superior
mesenteric arteries and can depict bowel wall thickening, which
typically demonstrates a low-density ring of edema in cases of
(figures 8 and 9). Bowel wall edema is non-specific, however, and
can be seen with inflammatory or infectious etiologies as well.
Nonenhancement of mesenteric arteries and veins indicates
thrombosis and is diagnostic of ischemic bowel when seen in the
presence of bowel wall edema, pneumatosis, or other signs of
ischemia (figure 10).
Late signs of mesenteric ischemia include pneumatosis intestinalis
and air within the mesenteric vein and portal venous system (figure
11). Isolated pneumatosis intestinalis is a nonspecific
radiographic sign, however, and can be seen in a variety of
non-ischemic benign processes such as COPD, collagen vascular
disorders, and steroid administration. When present, pneumatosis
intestinalis should always be correlated with other CT findings and
the patient's symptoms.
Peptic ulcer disease
Patients with peptic ulcer disease present with epigastric pain,
nausea, and vomiting, although patients may lack a clinical history
of ulcer disease. Symptoms can be indistinguishable from those of
acute pancreatitis or cholecystitis. Adequate gastric distention
with either water or oral contrast is essential, and IV contrast
administration is also necessary if water is used.
The primary findings on CT exam are nonspecific and include
focal thickening of the gastric or duodenal wall, which may be
obscured in patients with chronic gastritis.
Findings can be normal or undetectable with CT. Penetrating ulcers
are difficult to visualize and the only CT clue to diagnosis may be
pneumoperitoneum (figure 12). Subtle stranding in the fat adjacent
to the ulcer may also be seen.
CT is often most helpful in patients with peptic ulcer disease for
excluding alternative diagnoses and detecting complications.
Usually patients with perforated bowel present with obvious
signs of peritonitis, often as a complication of peptic ulcer
disease or diverticulitis, or following endoscopic procedures.
Clinical symptoms are often misleading in patients who are
immunosuppressed or receiving steroid therapy, who are more likely
to present late in the course of their illness with symptoms
related to sepsis rather than pain.
Ideally, evaluation should be performed after the administration
of both oral and IV contrast. However, often this is omitted in the
critically ill patient to expedite the exam, and the diagnosis can
be made easily with a noncontrast study. CT is known to be more
sensitive than conventional radiographs in detecting subtle
pneumoperitoneum, and can detect free air despite a normal
Extraluminal air will accumulate in nondependent regions of the
abdomen, and location of air is usually not helpful in identifying
the site of perforation. The location of the pneumoperitoneum
varies depending on the position of the patient, and is commonly
seen along the anterior peritoneal surface of the liver (figure
13). If present, oral contrast extravasation, focal fluid, or
inflammatory changes are the most helpful signs for localizing the
site of perforation.
CT scanning, in particular helical CT, is very helpful in the
evaluation of the patient presenting with acute abdominal pain,
particularly in the diagnosis of acute gastrointestinal disorders
including appendicitis, diverticulitis, small-bowel obstruction,
and ischemia. It is often the screening modality of choice for
these conditions. In most cases, CT will enable the correct
diagnosis and dictate appropriate treatment decisions.
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