received his MD from Jefferson Medical College, Philadelphia, PA,
in 1998. In 1999, he completed an internship in Internal Medicine
and is now a third-year Diagnostic Radiology Resident at YaleNew
Haven Hospital, New Haven, CT. In 2003 he plans to begin an MRI
fellowship at Jefferson University Hospital, Philadelphia, PA.
Computed tomography (CT) has become a critical tool in
the diagnostic algorithm for acute appendicitis. For the
clinician, history and physical examination alone are frequently
not accurate enough to evaluate diseases such as appendicitis,
where emergent decisions must be made about patient treatment.
Compared with clinical assessment alone, CT increases the
sensitivity, specificity, and accuracy of diagnosing acute
appendicitis. Radiologists are constantly seeking ways to further
optimize CT protocols and improve diagnostic accuracy. CT has
dramatically decreased the morbidity, mortality, and healthcare
costs associated with acute appendicitis, and will likely
maintain its role as an important tool for diagnosing acute
appendicitis in the forseeable future.
Appendicitis extracts a heavy burden in the United States, in
terms of patient morbidity and mortality, as well as in
hospital-based resources, contributing to as many as 250,000 cases
and 1 million hospital inpatient days a year.
These cases may be difficult to diagnose on clinical exam, and they
place a tremendous burden on U.S. hospital-based resources.
Computed tomography (CT) is an important diagnostic tool for
appendicitis that can decrease patient morbidity and healthcare
The diagnostic algorithm for appendicitis
When should the clinician suspect appendicitis? In a
meta-analysis of 10 studies involving 4000 patients, the three most
prominent clinical findings that indicate a high probability of
appendicitis are right lower quadrant pain, rigidity of the lower
abdominal wall, and migration of pain from a generalized location
in the abdomen to the right lower quadrant. Other signs and
symptoms are pain before vomiting, psoas muscle irritation, fever,
rebound tenderness, guarding, rectal tenderness, anorexia, nausea,
Traditionally, history and physical examination have been the
most commonly used tools in developing a differential diagnosis of
appendicitis. Unfortunately, these methods are often not sensitive
or specific enough.
In fact, missed appendicitis based on only history and physical
examination has become one of the most successful claims of
malpractice against emergency physicians.
Thus, the clinician must choose the best method to further evaluate
patients with suspected appendicitis. The choices at the
physician's disposal at this juncture are observation, imaging, or
In the current U.S. healthcare system, observing a patient with
suspected appendicitis as an inpatient has become cost prohibitive
and is done only on a highly selective basis. In addition, the
delay can be deadly for a patient with acute appendicitis. It has
been well established that the longer the delay to diagnosis, the
higher the risk of appendiceal perforation, which increases the
risk of postoperative complications (figure 1).
Open (surgical) appendectomy and laparoscopy have been shown to
have high negative appendectomy rates when appendicitis is
diagnosed on clinical grounds alone. In a literature review from
1978 to 1988, negative appendectomy rates ranged from 15% to 22% in
studies designed to compare open appendectomy with laparoscopy.
Despite its associated morbidity, in the past, exploratory
laparotomy could be justified because it provided prompt therapy,
mitigating against perforation and its associated risks. Today, few
cases of clinically suspected appendicitis go directly to surgery
without being evaluated by diagnostic imaging. After the history
and physical examination have been performed, diagnostic imaging is
frequently the next step in the diagnosis of clinically suspected
Two imaging modalities predominate in the diagnosis of
appendicitis. Ultrasound, with graded compression of the right
lower quadrant, is often utilized for diagnosing appendicitis in
the pediatric and pregnant population. CT is used commonly in
adults. One of the benefits of ultrasound is its greater
availability, and possible decreased time to patient imaging.
Another is its reasonably high accuracy.
A study in the pediatric surgery literature examined the results
of 2056 ultrasound examinations performed by radiologists on
children with suspected appendicitis. Statistical analysis revealed
a sensitivity of 89%, a specificity of 95%, a positive predictive
value of 86%, and a negative predictive value of 96%. An alternate
ultrasound diagnosis was made in 157 children.
Some of the benefits of ultrasound over CT have been called into
question. One study indicated that when compared with children who
underwent ultrasound, children who underwent CT had a significantly
lower negative appendectomy rate while maintaining a statistically
equivalent perforation rate.
Those who favor CT over ultrasound claim it has higher diagnostic
accuracy. One study compared 76 children in whom a noncontrast,
focused CT scan of the abdomen was performed with 86 children who
underwent graded compression ultrasound for suspected appendicitis.
Sensitivity, specificity, and accuracy for CT were 97%, 100%, 99%,
respectively, and for ultrasound were 100%, 88%, and 91%.
However, the lack of radiation and fairly good sensitivity and
specificity of ultrasound have made it the more common initial
imaging modality for children and pregnant women. Radiation
concerns with CT in the pediatric age group have been much
publicized in current literature.
Also, ultrasound requires no intravenous (IV) contrast, and is an
efficient and relatively inexpensive technique. At our institution,
ultrasound is the initial imaging modality of choice for the
pediatric and pregnant population.
Technical advancements have made CT the preferred study in cases
of clinically suspected appendicitis in adults. High-resolution
images and shorter scanning times provided by helical CT equipment
are important contributors to the modality's effectiveness in the
diagnosis of appendicitis. Modern multidetector helical CT systems
can perform a standard CT of the abdomen and pelvis in <10
minutes of table time.
A variety of helical CT protocols are currently utilized for
optimal evaluation of appendicitis. Some protocols include the use
of oral or rectal contrast agents. Some image the entire abdomen
and pelvis, others image only the inferior abdomen and pelvis, and
still others image only a focused area covering the right lower
quadrant. Some include IV contrast, others do not. Many protocols
require a collimation of ¾ 5 mm or less, particularly through the
appendiceal region. A 5-mm slice thickness has proven to
significantly decrease false negative evaluations when compared
with 10-mm images.
The ability of modern helical CT to acquire volumetric data has
greatly aided radiological diagnosis of many diseases, including
appendicitis. If the radiologist cannot adequately visualize the
appendix with 5-mm images, the stored volumetric data may serve as
a convenient diagnostic aid. The radiologist can request image
reconstruction in the area of the appendix at less than 5-mm
intervals using this stored data.
With multidetector row helical CT, overlapping images that are
thinner than those reviewed initially may be reconstructed (figure
2). These methods may reveal an appendix previously "hidden" in the
computer's data banks.
The protocol used at our institution includes imaging the entire
abdomen and pelvis using a multidetector helical CT scanner. Using
a detector group thickness of 2.5 mm, 5-mm thick sections are
reconstructed every 5 mm from data obtained with a beam pitch of
1.5 [detector pitch of 6, table feed per rotation of 15 mm].
Nonionic IV contrast and oral contrast are given to the patient.
Nonionic contrast material (300 mgI/mL) administered at 3.0 mL/sec
and scanning is begun 60 sec after initiation of the contrast
bolus. Our oral contrast solutions consist of 900 mL of 2%
diatrizoate sodium (Hypaque, Amersham Health, Princeton, NJ) or 30
mL of diatrizoate meglumine (Gastrografin, Bracco Diagnostics,
Inc., Princeton, NJ) in 900 mL of water. If contrast is
administered rectally, it is important to elicit any
contraindications to this method, such as toxic megacolon,
neutropenic colitis, or ischemic colitis.
After drinking the oral contrast, the patient waits
approximately 60 to 90 minutes for the contrast to arrive at the
cecum. The patient is then put on the scanner and a scout film is
obtained. The radiologist can then examine the scout images and
localize the oral contrast. If the distal portion of the oral
contrast is still in the small bowel, then the study may be delayed
for a short while until the cecum is contrast-filled. Oral contrast
can be an important component of CT protocols, because nonfilling
of the appendix with contrast is one important sign of appendicitis
(figure 3). A recent Australian study examined 100 patients with
clinically equivocal cases of appendicitis. Using focused
appendiceal CT and no IV contrast, they obtained a 93% sensitivity,
a 97% specificity, and a 96% accuracy.
Other studies have stressed the importance of IV contrast for an
accurate diagnostic evaluation of appendicitis. A recent article
compared focused, right lower quadrant helical CT technique with
oral contrast only to a nonfocused CT of the abdomen and pelvis
with both oral and IV contrast material. In this study, the
accuracy for diagnosing appendicitis increased significantly with
use of both IV and oral contrast agents. The three radiologists who
read the nonfocused, enhanced CTs also reported greater confidence
in diagnosing alternative conditions. Of the greatest concern was
the fact that when using the focused CTs the diagnosis of
appendicitis was missed entirely in two patients whose inflamed
appendices were not included in the images.
The clinician's perspective
Although the optimal protocol remains debatable, the use of
helical CT in the clinician's diagnostic algorithm for acute
appendicitis has become commonplace. Recent articles in the
emergency and surgical literature have supported the use of CT for
A study based in Taiwan compared the abilities of both
surgically trained and non-surgically trained residents to diagnose
appendicitis in the Emergency Department.
Under the supervision of board-certified emergency physicians,
there was no significant difference between surgically based and
non-surgically based residents in their ability to make the
diagnosis of appendicitis. However, non-surgically based residents
ordered more CT studies (12% versus 5.1%). Significantly, CT was
found to lower the negative appendectomy rate from 23% to12%.
Another study in the emergency literature examined the
effectiveness of diagnosing appendicitis clinically. This study
compared the accuracy of clinical assessment alone with clinical
assessment combined with CT imaging in a patient with clinically
suspected appendicitis. Clinical assessment alone, based on
specific criteria, had a sensitivity of 91.6% and a specificity of
84.7%. With the assistance of CT scanning, sensitivity and
specificity increased to 98.3% and 95.8%, respectively.
The surgical literature also has significant data supporting the
use of CT for appendicitis. In one study, surgically trained
physicians gave 99 patients with clinically suspected appendicitis
a physical examination before and after CT scan.
Diagnostic accuracy and management of acute appendicitis was
significantly improved when the results of the first physical exam
were compared with second physical exam after CT. Patients were
advanced from observation status to either operative appendectomy
or discharge more efficiently. In this study, the most convincing
evidence for the utility of CT in the diagnosis of appendicitis
comes from the 18 patients who were diagnosed correctly on CT
findings alone, and 6 patients who were spared from surgery
following the CT scan and second examination.
Benefits for the healthcare system
The increased efficiency of helical CT and the significant
decreases in healthcare spending associated with its use are two
important factors in its acceptance in diagnosing clinically
suspected appendicitis. One study explored the utility of focused
appendiceal CT with rectal contrast in 100 consecutive emergency
Prior to CT imaging, history, physical exam, and laboratory results
were used to determine if patients were to be observed for
suspected appendicitis or sent to the operating room for surgical
appendectomy. Following CT studies, the preliminary treatment plans
were compared with the patient's eventual real treatment. The
appendiceal CT was 98% accurate, with treatment plans changing in
59 patients based on the CT results.
The financial savings related to the use of CT in this study
were significant. A total of 13 patients were spared needless
appendectomy, for a savings of $47,281. In addition, 50 hospital
inpatients days were avoided, for further savings of $20,250. After
subtracting the $22,800 expenditure for the appendiceal CT scans,
total savings for the 100 patients was $44,731. If 250,000 cases of
appendicitis occur per year,
the use of appendiceal CT in cases of clinically suspected
appendicitis could save the U.S. economy $111,827,500 annually in
One limitation to the above-mentioned study is that an academic
emergency department radiologist interpreted all the appendiceal CT
scans. Can emergency department physicians, surgeons, and other
clinicians expect the same accuracy if helical CT studies are read
by community radiologists? The following study addressed this
concern. Radiologists working in a community hospital in Hawaii
read 100 CT studies.
Significantly, none of the radiologists had prior experience
reading appendiceal CT scans. Focused appendiceal CT scans were
obtained with enteric contrast for appendicitis. A total of 33 CT
scans were evaluated as positive for appendicitis and 67 were
considered negative. Statistical analysis revealed a sensitivity of
97%, a specificity of 94%, and an accuracy of 95%.
Thus, excellent diagnostic performance can be expected in the
university or community hospital setting when CT is performed for
the diagnosis of appendicitis.
Significantly, in this community hospital study, CT led to a
different diagnosis in 36 patients. The high-resolution images that
modern CT equipment provides permit excellent anatomic and
pathologic evaluation of the abdomen and pelvis. Many alternative
diagnoses have been made at our institution in the month prior to
submission of this article as well. These diagnoses have included
sigmoid diverticulitis, tubo-ovarian abscess, and right
ureterovesicular junction calculus with associated forniceal
rupture. Mesenteric adenitis and terminal ileitis are two of the
many other common conditions that can be indistinguishable
clinically from appendicitis, but are readily diagnosable by
Appendicitis and its mimics
To adequately understand how to characterize an inflamed
appendix by its appearance on CT, it is first important to
understand the features of a normal appendix. The vermiform
, worm, and
, form) averages 8 cm in length and no more than 6 mm in width.
Superior to the appendix, the ileum partly invaginates into the
cecum, forming the ileocecal valve. Two to three centimeters
inferior to the ileocecal valve, the three teniae coli of the cecum
merge at the base of the appendix and form its outer longitudinal
muscle coat. Two thirds of the time, the body of the appendix is in
a retrocecal position (figure 4). When retrocecal, the appendix may
be intraperitoneal or extraperitoneal.
When extraperitoneal, the appendix can be seen at or near the
convergence of the perinephric and lateral conal fascia. The
appendiceal mesentery, or mesoappendix, suspends the appendix from
the mesentery of the terminal ileum. The lymphatic vessels of the
cecum and appendix drain into mesoappendiceal, ileocolic, and
superior mesenteric lymph nodes. Cases of appendicitis are
occasionally associated with small lymph nodes in these regions
Appendicitis is most often caused by fecal obstruction of the
appendix. Normally, appendiceal secretions build up and decompress
into the cecum. In cases of obstruction, these secretions cannot
escape and the appendix becomes swollen, edematous, and inflamed
(figure 6). This inflammation and swelling causes the pain of acute
What are the signs of acute appendicitis by helical CT? One
study examined nonenhanced CT scans in 120 consecutive patients
with acute appendicitis in the differential diagnosis. In this
population, the most significant signs of appendicitis were fat
stranding (100%), enlarged appendix (>6 mm) (97%), adenopathy
(63%), appendicoliths (43%), abscess (10%), and phlegmon (5%)
(figures 3, 5, and 7).
Enhancement of a thickened appendiceal wall is another important
sign of acute appendicitis when IV contrast is administered
(figures 2B, 4A, 6B, and 7).
Nonfilling of the inflamed appendix with oral contrast is also a
useful sign. Cecal wall thickening adjacent to the inflamed
appendix may be seen (figure 7). Other important CT signs are
present when appendicitis is complicated by perforation. These
signs are periappendiceal abscess, phlegmon, free intraperitoneal
fluid, free air, and inflammatory changes of adjacent bowel
(figures 1B and 8).
Optimization of technique is essential to identify the CT signs
of acute appendicitis. If oral contrast does not opacify the
terminal ileum or cecum adequately, a false-positive result may
ensue. A nonopacified, thickened appendix often indicates
appendicitis and is difficult to differentiate from nonopacified
loops of distal and terminal ileum (figure 3). Without IV contrast,
mesenteric vessels in the lower quadrant may be confused with
mesenteric adenopathy, especially if these vessels cannot be
adequately followed to their origin.
The radiologist must also determine if the inflamed appendix has
been included in the images when using the focused right lower
quadrant technique. A false-negative result may be reported without
Appendicitis should be diagnosed definitively only if the
radiologist sees an abnormal appendix, or a calcified appendicolith
associated with pericecal fat stranding or fluid collections.
Without either of these two signs present, the reader can include
appendicitis as only one of many differential possibilities.
Certain pathological processes may mimic appendicitis by causing
thickening of the appendix itself. Some of these processes include
appendiceal or cecal tumors, mucoceles, and endometriosis.
Appendiceal tumors, such as carcinoid, and cecal tumors can
directly obstruct the appendix, causing a secondary appendicitis.
Mucin secreting tumors of the appendix can also cause obstruction
and bloating of the mucin-filled appendix, or mucocele. Mucoceles
are not usually associated with an appendicolith or pericecal
inflammation. Endometriosis may cause luminal fibrosis and
obstruction, leading to a picture that may mimic a mucocele.
Inflammatory changes in the pericecal fat can be found with
common mimickers of appendicitis such as cecal diverticulitis,
epiploic appendagitis, mesenteric adenitis, pelvic inflammatory
disease, transmural ileitis, and perforation of cecal carcinoma.
These processes are often indistinguishable from acute appendicitis
if a normal appendix is not visualized. Cecal diverticulitis may be
diagnosed if discrete cecal diverticula or an intramural abscess
with adjacent inflammation is present.
Epiploic appendagitis results from torsion of an epiploic
appendage, resulting in inflammation and abdominal pain. In a
series of five patients with epiploic appendagitis, all had CT
findings of a pericolic fatty mass with increased attenuation
compared with normal mesenteric fat. In each case, the fatty mass
had a high attenuation rim with focal fatty stranding.
Mesenteric adenitis is another important clinical mimicker of
appendicitis. In one study, a series of 18 CT scans among patients
with a discharge diagnosis of mesenteric adenitis were reviewed.
All 18 had a cluster of nodes in the right lower quadrant measuring
a minimum of 5 mm in short axis, associated with a normal appendix.
Eight had associated ileal or ileocecal wall thickening.
An infectious, inflammatory, or ischemic process in adjacent bowel
may also secondarily inflame the pericecal fat and the appendix
Helical CT has become a critical diagnostic tool in the
evaluation of the adult patient with clinically suspected
appendicitis. Many current techniques and protocols have an
impressive diagnostic performance record in identifying
appendicitis. CT has also proven to be a cost-effective method of
diagnosing appendicitis and its clinical mimics. The excellent
sensitivity and specificity of CT for appendicitis have many direct
benefits to the patient. When a CT study is interpreted as
negative, it spares patients the unnecessary morbidity of a
laparoscopic or open surgical procedure. When a study is positive
for appendicitis, the patient most often undergoes appropriate
The author wishes to thank James A. Brink, MD, from YaleNew
Haven Hospital, for his thoughtful input, insight, and assistance
with this manuscript.