Acute appendicitis is the most common identifiable cause of an acute abdomen, yet accurate diagnosis of acute appendicitis is often difficult clinically. Increasing evidence suggests that computed tomography (CT) plays an important diagnostic role for many patients with suspected appendicitis. This article reviews the use of CT in such patients, including CT protocols and CT findings that must be properly considered.
is Vice Chair of the Department of Radiology, Winthrop-University
Hospital and Professor of Clinical Radiology, SUNY at Stony
is a second-year Radiology Resident and
is an Attending Gastroenterologist, Winthrop-University Hospital,
Conflict of interest disclaimer: No specific CT vendor is
mentioned in this article. The authors have no actual, potential,
or apparent conflicts of interest regarding the material covered
in this article.
Portions of the material covered in this article have been
previously presented at the American Roentgen Ray Society 103rd
Annual Meeting, May 4-9, 2003, San Diego, CA; and the Society of
Gastrointestinal Radiologists Annual Meeting, March 7-12, 2004,
Scottsdale, AZ, but this material has
Acute appendicitis represents the most common specific
identifiable cause of an acute abdomen worldwide. There is an
estimated 7% lifetime incidence of appendicitis in the United
States, with more than 250,000 appendectomies performed each year.
Accurate diagnosis of acute appendicitis is often difficult
clinically. The classic triad of right lower quadrant abdominal
pain (most typically beginning in the umbilical region and then
migrating to the right lower quadrant), fever, and leukocytosis may
be absent and may also be secondary to a wide variety of other
Accurate clinical diagnosis is particularly challenging in older
individuals. The negative appendectomy rate (NAR) in women of
child-bearing age who do not undergo preoperative imaging is upward
of 40% to 45%.
This article will: 1) review the rationale for routine computed
tomographic (CT) imaging of adult patients with suspected
appendicitis; 2) explain the advantages and disadvantages of
various CT protocols; 3) review the CT findings of appendicitis and
normal appendices; 4) review the controversies regarding
techniques; and 5) describe the complications of appendicitis.
Rationale for routine use of CT in adults with suspected
There is continuing controversy in the surgical/clinical
literature regarding which adult patients with suspected
appendicitis should undergo CT scanning versus initial surgical
exploration. The historically accepted trade-off between a NAR of
up to 20% and an increased perforation rate in patients without
definitive appendicitis who are clinically observed has recently
Since 1997, increased attention has focused on the routine use of
CT in clinical practice, as more accurate diagnosis and prompt
surgery, when indicated, have decreased the complication rate
associated with appendicitis. Additionally, alternative diagnoses
may be suggested or established using CT. In contrast to a 20% NAR
cited above, the overall accuracy of CT ranges from 93% to 98% in
most major published series.
In a retrospective series of 650 patients who underwent CT of the
abdomen and pelvis with oral and intravenous (IV) contrast, a 98%
accuracy rate was achieved.
In a study of 146 patients who underwent CT, the NAR was reduced to
4% and the perforation rate was 22%.
In another study, the NAR was reduced to 7% and the perforation
rate was only 14%.
When one examines the cost-effectiveness of utilization of CT
versus direct surgical exploration, the cost of a negative
appendectomy has been found to be many times that of a CT scan.
In one study that involved 100 consecutive patients, routine CT
changed management in 59% of patients, with a cost savings of $447
Rationale for routine CT: Controversy in the clinical
Several studies published in the surgical/clinical literature in
the past several years concluded that the use of CT did not improve
the diagnosis and treatment of acute appendicitis in adults.
However, the conclusions of these studies are seriously fiawed.
Specifically, only a small percentage of patients actually had a CT
there was absence of published information on CT usage,
or there was lack of analysis of the impact of CT on the patients
who did not undergo appendectomy but who had an alternate diagnosis
However, the majority of recent studies in the literature stress
the correlation of CT findings with patient examination by a
surgeon, with the brunt of the data supporting routine CT use.
In a randomized trial in which 65 patients with suspected
appendicitis underwent CT were compared with 63 patients managed
using clinical judgment alone, management changed in 26% in the
former group. Based on these findings, the authors recommended CT
for all patients with suspected appendicitis.
In another prospective study involving >100 patients,
emergency-department physicians and surgeons recorded their
respective management plans for each patient before and after CT
(discharge, admit/ observe, or operate). The emergency-department
physician plan changed in 35% of patients, and the attending
surgeon's plan changed in 27%, with 20 more patients than
originally planned undergoing surgery following CT. An alternate
diagnosis was made on CT in 20%.
There have, however, been some recent dissenting clinical
In one study of 110 patients, CT was only 89% accurate, and the
authors recommended it only if clinical findings were equivocal.
In a larger randomized study of 182 patients, 90% accuracy was
observed in both the group who underwent CT and the group who did
not. The time to the operating room was shorter in the non-CT
Many questions regarding the routine use of CT for suspected
appendicitis remain: Specifically, in terms of the reproducibility
of the much more accurate results published in the radiology
literature in the community, whether and when women of
child-bearing age should undergo initial sonography and/or magnetic
resonance imaging instead of CT, and the paradox of initial CT
triage despite the call in the surgical literature for careful
surgical evaluation of all patients. Additionally, the
responsibility with the routine use of CT is transferred to the
radiologist, along with potential liability, and if read as
equivocal, the workup before definitive diagnosis may be prolonged.
However, based on our own experience as well as our review of the
literature, we favor the routine use of CT in adults with suspected
CT protocols: Overview
The more recent CT literature supports the use of thin-section
imaging of the entire abdomen and pelvis, rather than just CT
"focused" on the right lower quadrant, and cine review of the
images at a monitor or workstation. There is a learning curve
involved, regardless of the CT protocol, if one is initially
interpreting CT scans for suspected appendicitis. It is important
to attempt to identify the cecum, terminal ileum, and appendix on
every CT scan, regardless of the protocol used. The choice of a
specific protocol may depend on the expertise and preference of the
radiologist and that of the ordering physician as well as the need
for an urgent answer, the patient's body habitus, and any
contraindications to contrast. However, in general, most practices
now routinely use oral and IV contrast for most-if not
The accuracy of CT is improved significantly when 5-mm as
opposed to 10-mm images are performed in the same group of
Currently, we reconstruct and review thinner (2 to 3 mm) images
from a multidetector CT data set if the appendix is difficult to
identify or evaluate on initial 5-mm images. We have found this to
be particularly helpful in a subset of patients.
In a landmark study by Balthazar et al,
100 patients with clinically equivocal appendicitis underwent CT
with oral and IV contrast. The authors stressed the importance of
ileal opacification with oral contrast, the use of CT as a road map
for surgical planning, and the use of CT for establishing
alternative diagnoses (in 17 of 31 patients without a CT diagnosis
of appendicitis). They also described the subtle findings of early
appendicitis, including only slight appendiceal distension and wall
An appendicolith may or may not be present/identifiable. All of
these principles remain very important to date.
Oral and IV contrast
In the original series by Balthazar et al,
800 mL of oral barium, given at least 1 hour prior to CT, achieved
an accuracy rate of 93%. The abnormal appendix was usually
fiuid-filled and revealed an enhancing and slightly thickened wall
(Figure 1). There were often associated infiammatory changes in the
adjacent fat, and associated fiuid collections or abscesses were
seen in cases with more advanced disease. In 2002, the vast
majority of U.S. radiology practices always or usually used both
oral and IV contrast for imaging patients with suspected
We suspect that this percentage has further increased in the last 3
The advantages of routine IV contrast use include identification
of earlier disease, easier identification of the appendix
(especially in thin patients or patients with little fat in the
right lower quadrant region), and potentially better
characterization of nonappendiceal disease. Disadvantages include
the additional time required for patients to drink oral contrast
(and the potential unpleasantness for patients who may already be
nauseous), slightly increased cost, and the small risk of a
reaction to IV contrast.
Rectal and/or oral contrast only
In 1997, Rao et al published accuracy rates of 98% for CT with
oral and rectal contrast
and then with rectal contrast only.
Up to 1 L of 3% water-soluble iodinated contrast was given rectally
via a small-bore catheter immediately prior to scanning without
additional patient preparation. A 15-cm-long "focused" region was
then scanned centered above the cecal tip (based on the scout
digital radiograph). The appendix was considered normal if the
lumen filled completely with bowel contrast, air, or a combination
of both, and the wall was ≤2 mm in thickness, regardless of maximum
Advantages of this technique include speed, decreased cost, and
reduction in overall radiation dose. Disadvantages include the
potential unpleasantness of routine rectal contrast use from the
viewpoint of patients, technologists, and radiologists (contrast
leaked externally in 24% of patients in one series
), and the risk of missing pathology outside the right lower
quadrant (ie, alternative diagnoses
) or appendicitis itself (2 of 51 cases in another series
As of 2002, only 1% of residency radiology programs and 8% of
private radiology practices in the United States responding to a
survey were always or usually using rectal contrast on their
patients with suspected appendicitis.
Although a recent article also showed very good results with
"focused" CT scans obtained with rectal contrast only,
we are not aware of many practices currently using this protocol
routinely. Oral contrast alone has been studied to a much more
limited extent, but in one series a 96% accuracy rate was achieved
CT without oral, rectal, or IV contrast (ie, nonenhanced or
noncontrast) was first attempted by a community hospital radiology
group led by Malone et al
in 1993. In their series of 211 patients, 93% accuracy was achieved
using this protocol. Similar or higher accuracy rates were obtained
in subsequent series.
In a study of 300 patients published by Lane et al,
a 97% accuracy rate was achieved and 63 (21%) alternative diagnoses
were correctly established prospectively.
The advantages of noncontrast CT include speed, decreased cost
(as contrast is not given), elimination of the risk of an IV
contrast reaction, and the ability to monitor the scan remotely
without having to supervise IV contrast administration.
Disadvantages include a steeper learning curve, difficulty in
interpretation in thin patients, and a higher false-negative rate
for earlier cases.
More recent investigations have yielded lower accuracy rates for
noncontrast CT for suspected acute appendicitis-78% (in 199
patients imaged at a community hospital
) and approximately 90% (in 95 patients imaged with both low-dose
and standard-dose CT
). Additionally, as of 2002, only 2% of radiology residency
programs and 12% of private radiology practices always or usually
used unenhanced CT.
However, since unenhanced CT is the test of choice for suspected
renal colic, and because appendicitis and right renal colic may
mimic each other clinically,
radiologists should be familiar with the appearance of the normal
and abnormal appendix on unenhanced CT (Figure 3).
CT protocols: Comparisons
Raptopoulos et al
compared 2 cohorts of 50 consecutive patients who underwent CT
(with oral and IV contrast) prior to appendectomy in 1997 and 2000.
During that time, the use of CT for suspected appendicitis
increased by 79%. In the second group, there were less severe
imaging findings, including absence of periappendiceal stranding,
with a corresponding decrease in pathological severity of
Jacobs et al
imaged 228 patients initially using oral contrast only with
"focused" right lower-quadrant CT followed immediately by a CT of
the entire abdomen and pelvis with IV contrast. Three radiologists
all had higher sensitivity for detection of appendicitis with the
second protocol, and increased confidence for alternative
diagnoses. Of the 51 patients with appendicitis as the final
diagnosis, 22% had no periappendiceal changes, which led to more
false-negative diagnoses with the first protocol. The diagnosis of
appendicitis was established in some of these cases based on
abnormal enhancement of the appendiceal wall.
These studies suggest that because patients are being scanned
earlier and with less stringent selection, IV contrast should be
CT findings of normal and abnormal appendices
The goal of CT interpretation is to identify the appendix and to
characterize it as normal or abnormal. This can be surprisingly
difficult in a minority of cases, even with optimized technique.
The appendix arises from the medial cecal wall, approximately 3 cm
below the ileocecal valve, although the location of the tip is
variable (Figure 4).
The percentage of cases in which a normal appendix is identified
increases with the routine use of thin sections, and the highest
reported identification rates have been noted with rectal contrast.
Pitfalls include: Misinterpretation of a transversely lying
ileocolic vessel as an appendix; missed identification of the
appendix because of a low-lying cecum; and mistaken identification
of an isolated appendicolith as a sign of appendicitis. In a recent
series of 366 consecutive patients with possible appendicitis who
underwent CT with oral and IV contrast using a slice thickness of 5
mm, the appendix could not be identified retrospectively in 46
(13%) patients, but only 1 of these patients proved to have
When determining if appendicitis is present, all of the CT
findings should be integrated in making this determination. Size
alone cannot be used as a criterion for appendicitis, as pointed
out in the initial work of Balthazar et al.
The mean transverse diameter of the normal appendix is as high as 7
to 8 mm on noncontrast CT.
The individual wall of the appendix is usually "pencil thin,"
regardless of the CT protocol used. Intraluminal gas is seen within
the lumen of 75% of identifiable appendices on noncontrast CT, but
may be present in >25% of cases of proven appendicitis.
In a series of rectal contrast CT cases, gas was present in the
lumen in 57% of normal appendices, versus 19% in infiamed
An appendicolith (Figure 5) may be present in up to 10% of normal
appendices on noncontrast CT
and in 47% of positive cases on noncontrast CT.
In some cases, oral contrast may obscure identification of an
appendicolith. Review of the images using bone windows may be
Misinterpreting periappendiceal infiammatory changes secondary to a
process centered outside the appendix-particularly infiammatory
bowel disease-is another potential pitfall.
Perforation is common in elderly patients who often have
atypical presentations, but it may be seen at any age.
Although still somewhat controversial, there is consensus in the
literature that it is the delay in initial diagnosis, rather than
the waiting time in the emergency department or the radiology
department, that increases the perforation rate. Additionally, when
the CT and clinical findings are initially equivocal for
appendicitis, repeat imaging of the right lower quadrant can be
performed. Multiple series have shown that intensive observation
does not increase appendiceal perforation rates significantly.
Accurate diagnosis of perforated appendicitis may be difficult in
some cases, as the CT findings may be confused with other disease
processes. Identifying residual portions of the appendix, and
particularly an appendicolith, adds specificity. To the authors'
knowledge, there have not yet been any large series conducted on
perforated appendicitis on CT, although smaller series have been
CT findings include phlegmonous changes or an abscess in the right
lower quadrant, secondary changes involving the terminal ileum and
cecum, a break in the enhancement of the appendiceal wall,
extraluminal gas or extraluminal appendicolith, and associated
small-bowel obstruction or other findings consistent with
peritonitis (Figures 6 and 7).
Regardless of the specific protocol used, many alternate
diagnoses have been suggested or established in the recent
literature using CT for imaging adults with suspected acute
appendicitis (Figures 8 and 9). The percentage of alternative
diagnoses ultimately made ranges from slightly greater than 25% to
35% of all patients imaged.
This has a major impact on the management of patients, as they can
be triaged to the appropriate therapy and specialist.
Although there is some continuing controversy in the surgical
and clinical literature, a consensus is emerging regarding the
utility of routine CT for most, if not all, adult patients with
suspected acute appendicitis. Increasing evidence suggests that
even young adult men should routinely undergo CT rather than
initial surgical exploration, and there is no convincing
evidence-based data that the routine use of CT increases the
perforation rate. CT, regardless of the protocol used, permits
diagnosis or exclusion of appendicitis and alternative diagnoses
accurately compared with the historical 20% negative appendectomy
rate. Furthermore, CT establishes the severity of appendicitis. The
paradox is that the increased use of CT may have made accurate
diagnosis more difficult in some patients, especially those in the
earlier stages of appendicitis. Because patients are being scanned
earlier, and because findings may therefore be more subtle or
false-negative on unenhanced CT or on CT with oral/rectal contrast
only, IV contrast should be considered routinely for imaging all
patients with suspected appendicitis. Thin cuts, cine review of
images on a monitor, and careful review of the right lower quadrant
anatomy, as well as routine scanning of the entire abdomen and
pelvis, should be performed in all cases. Radiologists need to
appreciate the overlap of normal and abnormal appendiceal sizes,
and should use all the CT findings present to make or exclude the
diagnosis of appendicitis.