Dr. Daily is a Senior Radiology Resident; Dr. Danton is an Assistant Professor of Clinical Radiology, Director of Radiology Residency Program; and Dr. Munera is an Associate Professor of Clinical Radiology, Director of Patient Safety and Image Quality, University of Miami Miller School of Medicine-Jackson Memorial Hospital, Miami, FL.
Acute appendicitis is the most common surgical condition associated with
nontraumatic acute abdominal pain. Accurate diagnosis in the emergency
room (ER) is important as patients who are not diagnosed early risk
perforation with an associated increase in morbidity and surgical
complication rate. For this reason, appendicitis is one of the top 5
diagnoses involved in ER malpractice claims.1 Fortunately,
radiologists do quite well at identifying acute appendicitis in
patients. Additionally, radiologists have been successful at excluding
appendicitis, and the negative appendectomy rate has decreased to less
than 5% with the use of increasingly accurate imaging, particularly
preoperative computed tomography (CT).2,3 The use of CT preceding emergent appendectomy has increased from 18.5% of cases in 1998 to 93.2% in 2007.4
MDCT technique for appendicitis
technique we use to evaluate patients with suspected appendicitis
involves scanning from the diaphragm to the symphysis pubis using
automatic exposure control on a 64-slice MDCT scanner with a 1.2-mm
configuration. The patient is injected intravenously with 100 mL
of iodinated contrast at 3 mL/sec, and acquisition is initiated at 60
sec after the start of intravenous (IV) contrast infusion. CT images are
routinely reconstructed at 3 x 3-mm sections (thickness multiplied by
interval). In patients with a body mass index (BMI) <25, our protocol includes oral and IV contrast, since appendicitis may be more difficult to diagnose in patients with very little abdominal fat.
Value of thin-slice and reformatted images
et al in a study with 212 patients reported that reconstruction
thickness was not related to diagnostic accuracy when comparing images
that measure 5 x 5 mm, 3 x 3 mm, and 2 x 1 mm (section thickness
multiplied by interval). However, visualization of the appendix,
visualization confidence, and impression confidence all improved with
thinner-slice images.5 Paulson et al in a study of 100
patients,demonstrated no difference in sensitivity or specificity with
the addition of coronal reformatted images, but did report increased
reader confidence in both identification of the appendix and
diagnosis/exclusion of appendicitis.6 While radiologists were
typically accurate when asked to decide on the presence or absence of
appendicitis for study purposes, a radiologist’s confidence is important
when surgeons decide whether to perform surgery in the setting of weak
or atypical clinical symptoms. A radiologist’s confidence is also
important when recommending conservative management if the appendix is
In our emergency department, we routinely use 3-mm
axial, coronal and sagittal reconstructions. When the appendix is
difficult to visualize, we also use incorporated thin-client software
for reformations in nonstandard planes (oblique or curved) to
demonstrate the tortuous appendix in one image so our surgical
colleagues better appreciate the findings (Figure 1). This can be useful
when identification of the appendix is difficult, spans multiple
slices, or requires viewing in multiple planes. This is performed by
manually inserting a centerline through the middle of the appendix using
the CPR functionality. Brackets can be placed at the base and tip of
the appendix. Utilizing a surface-rendered template allows the surgeon
to see the location of the appendix with respect to surface anatomy
Value of oral contrast
Oral contrast is
not required to diagnose appendicitis. It does not reliably fill the
normal appendix and its absence does not diagnose appendiceal
Oral contrast is frequently (70%) present in the cecum in cases where
the appendix is not visualized. It also often does not reach
right colon within a 2-hour preparatory time. Anderson et al found no
statistical difference in specificity for diagnosing appendicitis with or
without oral contrast.7 Mun et al also demonstrated good
sensitivity and specificity for diagnosing appendictis in 173 patients
using a protocol of IV contrast only.8 In addition to similar
accuracy, an IV contrast-only protocol has been associated with shorter
length of stay and less patient discomfort.9
Radiation dose concerns and the use of ultrasound and low-dose CT
CT is the imaging test of choice for adults with suspected appendicitis
given its high accuracy for diagnosing appendicitis and its
ability to evaluate for other alternative diagnoses. Disadvantages of
ultrasound include poor identification of the normal appendix, decreased ability
to detect perforation, decreased sensitivity to alternative diagnoses,
and limited utility in obese patients. There is a clear increase in the
negative appendectomy rate when only ultrasound is substituted for CT.10
A stronger argument for ultrasound exists in children, however, as the
modality lacks ionizing radiation and does not require sedation.
Additionally, many of the alternative diagnoses for which CT is useful
in adults are less common in children. High sensitivities and
specificities have been achieved with ultrasound in children in
experienced institutions.11 Ideally, skilled ultrasound can
precede CT in children to spare them ionizing radiation, with follow-up
CT in cases of high suspicion but equivocal or even negative ultrasound
findings.12 Still, potential reduction of radiation risks
will mean little to patients and surgeons in cases of subsequent
perforation or negative appendectomy. For this reason, low-dose CT
protocols have been explored and studies have demonstrated similar
diagnostic performance to standard dose CT.13,14
is the preferred modality for evaluating the appendix during pregnancy
because it is widely available, efficient, and safe to use in pregnancy.15
Currently, the American College of Radiology (ACR) Appropriateness
Criteria favor magnetic resonance (MR) imaging over CT for pregnant
patients with right lower quadrant pain, fever, and leukocytosis with
equivocal ultrasound. This recommendation is due to studies reporting
similar sensitivity and specificity to CT. MR has a reported sensitivity
of 97% to 100% and specificity of 92% to94% for diagnosing acute
appendicitis (Figure 2).16,17 Noncontrast MR is used since gadolinium is a class C drug and contraindicated in early pregnancy.
Imaging findings of the appendix and acute appendicitis
ileocecal valve can be used as a point of reference to identify the
base of the appendix. The appendix arises from the wall of the cecum
and, in 96% of patients, lies below the ileocecal valve, typically 1-2
cm.18 The tip of the appendix can be found in a variety of
directions with relation to the base (Figure 3). The most common
positions of the appendix are retrocecal and inferomedial to the cecum.19,20
Early studies with ultrasound suggested a 6-mm diameter cutoff for distinguishing the normal appendix from appendicitis.21
However, subsequent studies, particularly with MDCT, have concluded
that this measurement is unreliable. The normal appendix frequently
distends to greater than 6 mm in diameter when measured from outer wall
to outer wall on thin-slice MDCT (Figure 4). A study with 150 control
patients demonstrated that 45% of these normal patients had an
appendiceal diameter greater than 6 mm.22 Distinguishing an
enlarged appendix becomes particularly important in the subset of cases
where periappendiceal inflammation is not present or is obscured by lack
of abdominal fat. A measurement of 1 cm is a more reliable upper limit
of normal for the appendix. The Webb et al study identified no normal
appendix with a diameter>10 mm, and Benjiminov et al, in a review of
187 patients, found only 1 normal appendix with a diameter >10 mm.19,22 Size alone should not determine the diagnosis in the 6 to 10-mm range.
calcified appendicoliths are frequently discussed with appendicitis,
lymphoid hyperplasia and fecaliths are also common causes of appendiceal
obstruction. Calcified appendicoliths are identified in 10% to 34% of
appendicitis cases.19,23 They are important to mention in the
report. In a review of 380 patients, Shindoh et al reported that the
presence of an appendicolith correlated with negative outcome in
non-operative management.23 Additionally, extraluminal
appendicolith after perforation is associated with recurrent abscess and
poorer prognosis. It can act as a nidus for infection and may require
surgical or CT-guided removal.24,25
Several studies have noted the likelihood that the appendix will be filled with fluid in acute appendicitis.22, 26 The fluid represents intraluminal mucoid material that accumulates following obstruction. Studies by Moteki et al26-28 quantified
this fluid and found that intraluminal appendiceal fluid greater than
2.6 mm in diameter had high sensitivity and specificity for acute
appendicitis (Figure 5). This is particularly useful in the 6- to 10-mm
equivocal diameter range when periappendiceal inflammatory findings are
not seen. False positives in Moteki’s study included cases with
enteritis and cecal diverticulitis where there was a large cecal fluid
collection that filled the appendix as well.26
Other diagnostic findings
other criteria have been described when evaluating appendicitis,
including wall thickening, wall enhancement, extraluminal
air,periappendiceal fluid, periappendiceal fat stranding, abscess,
phlegmon, and cecal wall thickening. These are frequently seen together
and used to make a confident diagnosis (Figure 5). As isolated findings,
however, they are less reliable. Choi et al reviewed 238 patients with
suspected appendicitis and recorded that, in addition to an enlarged
appendix, wall thickening (sensitivity 66%, specificity 96%),
periappendiceal fat stranding (sensitivity 87%, specificity 74%), and
wall enhancement (sensitivity 87%, specificity 74%), were associated
with appendicitis over alternative diagnoses.29 Moteki et al
reported that periappendiceal inflammation is reliable in diagnosing
appendicitis. However, its absence does not exclude the diagnosis; 31%
of 112 patients with appendicitis showed no periappendiceal
The nonvisualized appendix
nonvisualized appendix is becoming less common as more emergency rooms
are using thin-slice, multidetector CT with reformatted images. In
studies of patients examined for renal colic, 13% to 14% of appendices
were recorded as nonvisualized.19,20 In patients with right
lower quadrant pain, Ganguli et al reported that a nonvisualized
appendix on an otherwise normal MDCT scan is a reliable indicator of the
absence of acute appendicitis.30 In a study of 156 children,
Garcia et al reported the negative predictive value only dropped 2%
when the appendix was not visualized.31 A thorough search,
however, is required. Eighteen percent of appendices not visualized by
the initial reader in the Nikolaidis study were identified by a
retrospective reviewer.20 False negatives were recorded in cases when there was near complete absence of pericecal fat.20,30 Caution is warranted in these thin patients if clinical suspicion is high.
will commonly be asked whether the appendix is perforated. Perforation
occurs in approximately 25% of cases of acute appendicitis and is
associated with higher rates of postoperative complications if not
identified preoperatively.32 The appendix does not deflate
significantly after perforation and is typically larger in patients with
perforated appendicitis (mean 15.1 mm) versus nonperforated (mean 11mm)
(Figure 6).33 Abscess is the most specific finding for
perforation (99%), but extraluminal gas and small bowel ileus also have
specificities >90%.33 There are no CT findings that are particularly sensitive; these include abscess, which has a sensitivity of 34%.33 Fluid surrounding the appendix and mesenteric fat stranding had less than 50% sensitivity and less than 80% specificity.33 There
is conflicting information on an enhancement defect in the wall of the
appendix. Bixby, in a study of 244 patients, determined it was neither
sensitive nor specific,while Tsuboi, in a study of 102 patients, found
an accuracy of 96%.33,34 Neither of these studies, however,
correlated the size of perforation at pathology with the imaging
findings, and the clinical significance of under-diagnosing
microperforation is unclear.
of prior appendectomy should not dissuade the radiologist from
diagnosing appendicitis with the appropriate imaging findings.Stump
appendicitis occurs when the residual appendix at the base following
appendectomy becomes inflamed (Figure 7). This is a rare diagnosis, but
it can happen at any time after surgery and it is increasing in
incidence.35 This increase may correspond with the greater
number of appendectomies performed with laparoscopy. Diagnoses may be
delayed, as clinical suspicion is low in patients with a history of
appendectomy; consequently, association with gangrene and perforation is
found exclusively at the distal appendix is characteristic of “tip”
appendicitis. Appropriate management is unclear as it is a rare entity,
seen in only 4% to 8% of appendicitis cases.36 It appears,
however, that many of these patients do well if managed conservatively.
Mazeh et al found equivocal imaging results between patients that were
treated surgically and conservatively for radiologically diagnosed tip
appendicitis.36 Clinical findings should take precedence in
these cases, and radiologists should be clear when appendicitis only
affects the tip. Note that contrast often only partially fills the lumen
of the appendix, and this should not raise suspicion of tip
appendicitis asan isolated finding (Figure 8).
appendix occurs where there is a significant abnormal accumulation of
mucus secondary to chronic obstruction of the appendix. Types of
mucocele depend on the mucosa associated with overproduction of mucus.
This includes normal mucosa, hyperplastic mucosa, cystadenoma, and
cystadenocarcinoma. Preoperative imaging diagnosis can affect surgical
management, as the laparoscopic approach has greater risk for
perforation and pseudomyxoma peritonei.37 Identifying reliable characteristics has been difficult, as it occurs in only 0.1% of appendectomies.37 However, a diameter of greater than 1.3 cm and “cystic” dilatation of the appendix are suspicious for mucocele.38 Mural calcification is not consistently identified, but when seen is associated with mucocele (Figure 9).38
Neoplasms of the appendix
of the appendix include colonic adenocarcinoma, mucinous adenoma,
mucinous adenocarcinoma, lymphoma, and carcinoid.Neoplasms of the
appendix are rare and found in fewer than 1% of appendectomies; however,
when they do occur, 30% to 50% of patients present with symptoms of
acute appendicitis.39 Findings associated with neoplasm are a diameter >15 mm, cystic dilatation, and the presence of a soft tissue mass.39 Also, 11% of right-sided colon cancers manifest as appendicitis (Figure 10).39
The peak incidence for appendicitis is between 10 and 30 years,
however, neoplasms of the appendix are more frequently associated with
an older age group.39
to surgical complications from perforated appendix, image-guided
drainage and antibiotics have become a popular bridge to delayed surgery
(Figure 6). Marin et al, in a study of 41 patients, demonstrated a 90%
technical success rate for image-guided drainage.40 They
stressed the importance of draining multiple abscesses if they do not
communicate. The clinical success rate was 92% when the abscess was
well-circumscribed, but drainage was less successful for large, poorly
defined abscesses and patients with extraluminal appendicolith.40
Percutaneous retrieval of extraluminal appendicolith has even been
performed with a sheath and stone basket to remove this problematic
nidus of infection.24
Incongruent clinical findings
occasionally find themselves at odds with clinicians after making an
unexpected diagnosis of appendicitis. While a complete lack of clinical
findings is worrisome, if accurate imaging findings are noted, the
radiologist can still defend the diagnosis if the clinical findings are
weak or improving. In a review of supposed “false-positive” CT diagnosis
of acute appendicitis, Stengal et al found it rare for the
radiologist’s diagnosis of appendicitis to be disregarded, occurring in
only 13 of 2,283 cases.41 However, of these 13 patients, 5 (38%) later required appendectomy.41
In these cases, the typical history was right lower quadrant tenderness
that improved in the ER or with hospitalization. These patients may
have had chronic or recurrent appendicitis.
Right lower quadrant alternative diagnoses
pain is a frequent and common complaint in the emergency room, and
diagnoses for CTs ordered to evaluate appendicitis are often unrelated
to the appendix. Reviewing 2 of the larger appendicitis studies where
alternative diagnoses were recorded reveals that 22%to 41% of patients
with normal or nonvisualized appendix had no other cause for their
abdominal pain identified by imaging.28,29 Other common alternative diagnoses are listed below with their frequencies reported in these studies.
Ileocolitis (7% to 29%)
Infection of the terminal ileum is usually caused by Yersinia, Campylobacter and Salmonella
and can be a source of right lower quadrant pain (Figure 11). The
typical CT findings are circumferential wall thickening of the terminal
ileum. Regional lymph nodes are typically enlarged.42 Be
careful with fluid filling the appendix in cases of ileocolitis, as this
was a source of false positives for Moteki’s depth criteria.
Cecal diverticulitis (11% to 20%)
with right-sided diverticulitis are typically younger than those
presenting with left diverticulitis and overlap exists in demographics
with acute appendicitis.43 The associated wall thickening of
the colon can be eccentric or circumferential (Figure 12).The key to
diagnosis is identifying the inflamed diverticulum and the normal
appendix. Other diverticula in the right colon may raise suspicion for
Crohn’s disease (0% to 2%)
findings for Crohn’s disease include bowel wall thickening, a “double
halo” sign of bowel wall stratification, mesenteric fat proliferation
(“creeping fat”), skip lesions, and fistula tracts (Figure 13). Since
Crohn’s patients often require repeat CT evaluations, follow up with
low-dose protocols should be considered. Kambadakone et al report the
ability to reduce doses substantially without compromising the
Mesenteric lymphadenitis (0% to 10%)
mesenteric lymphadenitis is diagnosed when the only findings are
enlarged mesenteric lymph nodes. Wall thickening of terminal ileum may
be seen but should be less than 5 mm to consider a “primary” diagnosis.45 Many times, however, another inflammatory cause is identified to explain mesenteric lymphadenopathy.
Typhlitis (Neutropenic enterocolitis) (0% to 1%)
is an inflammatory condition of the cecum and ascending colon in
immunocompromised patients (Figure 14). The length of colon affected
should be greater than the typical reactive changes in the colon to
appendicitis. Typhlitis typically has circumferential symmetric
thickening. Treatment is typically nonsurgical, however, necrosis and
perforation can occur.43
Ischemic colitis (0% to 2%)
colitis etiologies include vascular occlusion from thrombosis, emboli,
or tumor. Right-sided ischemia is also associated with hypovolemic
shock. Associated findings include a double halo of edema and hemorrhage
in the bowel wall, pneumatosis, or portal venous system air (Figure
Ureteral stone (4% to 7%)
is excellent at diagnosing renal stones and urolithiasis should always
be excluded as the cause for abdominal pain if the appendix is normal.
Altering the CT window should allow adequate visualization of ureteral
stones despite the presence of excreted contrast. MDCT allows for more
accurate tracing of the ureter and differentiation from phleboliths. The
most common locations for ureteral stones are the pelvic brim, the
iliac vessel crossing, and the ureterovesicular junction.
Pelvic inflammatory disease (4% to 8%)
CT findings include dilated fallopian tubes and thick-walled, low-attenuation adnexal masses (Figure 16).47
Usually, bilateral adnexa are affected. Multiplanar reconstructions
help to distinguish pyosalpinx from multiloculated abscess. This
inflammatory process may secondarily involve the surrounding bowel,
including the appendix.
Ovarian hemorrhage (3%)
may occur in both follicular and corpus luteal cysts. CT will show an
adnexal mass with dense blood products and may show a fluid-fluid level
(Figure 17). Blood is identified in the pelvis in the case of rupture.
Anticoagulation is a risk factor for hemorrhagic cyst formation and cyst
Ovarian torsion (0% to 1%)
CT, suspicious findings include a smooth adnexal mass, deviation of the
uterus to the side of torsion, and abnormal location of the torsed
ovary.49 Ultrasound is also frequently used in cases of
suspected torsion. Suspicious findings include peripherally distributed
follicles and lack of color flow (Figure 18).47 A reliable
but uncommon imaging finding is the “whirlpool sign,” a swirling of the
vascular pedicle supplying the torsed ovary. However, normal color flow
does not exclude torsion and may be seen in cases of partial torsion,
intermittent torsion, or collateral blood supply.50
summary, accurate evaluation of the appendix is an important skill for
the radiologist working in the emergency setting. CT is the preferred
first-line diagnostic modality for adults and can be performed without
oral contrast. Ultrasound, in experienced hands, can be used to evaluate
children, and MRI is a viable alternative in pregnancy. While
thin-slice images and reconstructions have not substantially improved
accuracy, they have proven useful in surgical planning and increasing
diagnostic confidence.The most accurate imaging finding for appendicitis
is fluid distending the appendiceal lumen more than 2.6 mm. Relying on
appendiceal diameter alone is a potential diagnostic pitfall and will
result in false-positive interpretations. Being unable to visualize the
appendix is frustrating, but it rarely occurs in patients with acute
appendicitis. CT is not sensitive for detecting perforated appendix.
When diagnosing perforation, periappendiceal fluid should not be
misinterpreted as an abscess, which has a higher diagnostic specificity.
appendicitis can be managed conservatively in some patients.
Appendicitis can occur in the postappendectomy stump; therefore, a
history of prior appendectomy does not exclude the diagnosis.
Appendiceal neoplasm can mimic the clinical presentation of
appendicitis,but it should be distinguishable based on imaging findings.
many other causes of right lower quadrant pain should be specifically
excluded in the setting of a normal or nonvisualized appendix.
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