DOI:10.2214/AJR.05.0085
AJR 2006; 186:1103-1112
© American Roentgen Ray Society
Mimics of Appendicitis: Alternative Nonsurgical Diagnoses with Sonography and CT
Adriaan C. van Breda Vriesman1 and
Julien B. C. M. Puylaert2
1 Department of Radiology, Rijnland Hospital, Simon Smitweg 1, P.O. Box 4220,
NL-2350 CC, Leiderdorp, The Netherlands.
2 Department of Radiology, MCH Westeinde Hospital, The Hague, The
Netherlands.
Received January 17, 2005;
accepted after revision March 2, 2005.
Address correspondence to A. C. van Breda Vriesman
(adriaanbreda{at}hotmail.com).
Abstract
OBJECTIVE. Our objective was to illustrate the imaging features of
alternative nonsurgical disorders in patients presenting with clinical signs
of appendicitis.
CONCLUSION. This article illustrates the sonographic and CT features
of various appendicitis-mimicking conditions that are self-limiting or that
can be treated conservatively. A correct imaging diagnosis of these disorders
may prevent a nontherapeutic appendectomy and unnecessary hospitalization.
Keywords: abdominal imaging • appendicitis • CT • differential diagnosis • emergency radiology • gastrointestinal radiology • sonography
Introduction
Acute appendicitis is a common diagnostic problem. Clinically, appendicitis
can mimic various diseases, which may lead to a false-negative diagnosis.
Conversely, many conditions are initially incorrectly diagnosed as
appendicitis. Such a misdiagnosis may result in delayed treatment in patients
with appendicitis or lead to the removal of a normal appendix in patients with
other causes of abdominal pain. A prompt and accurate diagnosis is essential
to minimize morbidity.
Sonography and CT have assumed critical roles as highly accurate diagnostic
techniques in patients suspected of having appendicitis
[1]. Both imaging techniques
can definitively confirm or exclude appendicitis and detect alternative
pathologic conditions that may explain the patient's symptoms. Many of these
nonappendiceal alternative disorders are self-limiting or can initially be
managed with medical therapy. We focus on these nonsurgical
appendicitis-mimicking diseases because in those patients, a correct imaging
diagnosis prevents an unnecessary operation or costly in-hospital
observation.
Normal and Inflamed Appendix
Sonography and CT allow direct visualization of the normal or inflamed
appendix, seen as a blind-ended tubular structure arising from the base of the
cecum. The normal appendix can be identified in 67-100% of patients without
appendicitis who undergo CT
[1]. On sonography, the normal
appendix is less frequently visualized, with results varying between 0-82%
[1], reflecting the operator
dependency of sonography.
One of the most important imaging criteria in the evaluation of
appendicitis is the outer diameter of the appendix. Although an overlap of
appendiceal diameters in normal and inflamed appendixes has been reported, a
threshold value of 6-7 mm is most commonly used
[1]. A normal appendix has a
maximum outer diameter of 6 mm, is surrounded by homogeneous noninflamed fat,
is compressible on sonography, and often contains intraluminal gas
[1,
2] (Figs.
1A,
1B, and
2). An inflamed appendix has a
diameter larger than 6 mm and is usually surrounded by hyperechoic inflamed
fat on sonography (Figs. 3A and
3B) or extramural changes with
fat stranding on CT (Fig. 4).
Other strongly supportive signs of inflammation include the presence of an
appendicolith, cecal apical thickening, and hypervascularity of the appendix
wall on color Doppler sonography
[1]
(Fig. 3B).
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Fig. 1A —34-year-old healthy volunteer with normal appendix. Longitudinal
(A) and transverse (B) sonograms show appendix as blind-ended
compressible tubular structure with gut signature (arrowheads) with
diameter less than 7-mm cutoff point, surrounded by normal noninflamed
fat.
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Fig. 1B —34-year-old healthy volunteer with normal appendix. Longitudinal
(A) and transverse (B) sonograms show appendix as blind-ended
compressible tubular structure with gut signature (arrowheads) with
diameter less than 7-mm cutoff point, surrounded by normal noninflamed
fat.
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Nonsurgical Mimics of Appendicitis
Gastrointestinal Tract
Mesenteric adenitis has been reported as the second most common cause of
right lower quadrant pain after appendicitis, accounting for 2-14% of the
discharge diagnoses in patients with a clinical suspicion of appendicitis
[3]. It is defined as a benign
self-limiting inflammation of right-sided mesenteric lymph nodes without an
identifiable underlying inflammatory process, occurring more often in children
than adults. Sonography and CT show clustered adenopathy
(Fig. 5). Because adenopathy
also frequently occurs with appendicitis, the normal appendix must be
confidently visualized on imaging studies before assigning a diagnosis of
mesenteric adenitis.
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Fig. 5 —14-year-old boy with mesenteric adenitis. Sonogram of right lower
quadrant shows cluster of enlarged mesenteric lymph nodes
(arrowheads). Appendix was normal (not shown) and no other
abnormalities were found. IVC = inferior vena cava.
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Infectious enterocolitis can cause mild symptoms resembling common viral
gastroenteritis, but it can also clinically present with features
indistinguishable from appendicitis
[4]. This latter presentation
may occur in bacterial ileocecitis caused by Yersinia, Campylobacter,
or Salmonella spp. Imaging studies show mural thickening of the
terminal ileum and cecum without inflammation of the surrounding fat (Figs.
6A and
6B) and moderate mesenteric
adenopathy.
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Fig. 6A —39-year-old man with bacterial ileocecitis. Sonograms show moderate
mural thickening of terminal ileum and cecum surrounded by normal noninflamed
fat. Moderate mesenteric lymphadenopathy was also present (not shown).
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Fig. 6B —39-year-old man with bacterial ileocecitis. Sonograms show moderate
mural thickening of terminal ileum and cecum surrounded by normal noninflamed
fat. Moderate mesenteric lymphadenopathy was also present (not shown).
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Epiploic appendages are small adipose protrusions from the serosal surface
of the colon. An epiploic appendage may undergo torsion and secondary
inflammation, causing focal abdominal pain that simulates appendicitis when
located in the right lower quadrant. Epiploic appendagitis is a self-limiting
disease that has been reported in approximately 1% of patients clinically
suspected of having appendicitis
[5]. Sonography and CT depict
an inflamed fatty mass adjacent to the colon (Figs.
7A and
7B) containing a
characteristic hyperattenuating ring of thickened visceral peritoneal lining
and an occasional dense central focus caused by a thrombosed vessel or
hemorrhagic changes on CT.
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Fig. 7A —29-year-old woman with epiploic appendagitis. Sonogram of right
lower quadrant reveals hyperechoic inflamed fatty mass (arrowheads)
adjacent to colon (arrow) at spot of maximum tenderness.
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Fig. 7B —29-year-old woman with epiploic appendagitis. On unenhanced CT,
fatty lesion contains characteristic hyperattenuating ring (arrows)
corresponding to thickened visceral peritoneal lining.
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Omental infarction has a pathophysiology and clinical presentation similar
to that of epiploic appendagitis, with the infarcted fatty tissue being a
right-sided segment of the omentum. Imaging shows a cakelike inflamed fatty
mass (Figs. 8A and
8B) larger than in epiploic
appendagitis and lacking a hyperattenuating ring on CT. In some cases it may
be difficult to distinguish epiploic appendagitis from omental infarction
(Fig. 9); however, this
distinction has no clinical importance as both have a similar benign natural
history [5].
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Fig. 8B —41-year-old man with omental infarction. Unenhanced CT depicts
lesion as cakelike area of slightly dense inflamed omental fat
(arrowheads) larger than in epiploic appendagitis and lacking
hyperattenuating ring.
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Fig. 9 —47-year-old woman with acute right lower quadrant pain. Unenhanced
CT shows ovoid inflamed fatty mass (arrowhead) with normal regional
bowel loops. Shape and size of lesion suggest epiploic appendagitis, but
lesion does not contain hyperattenuating ring. In this case, it is difficult
to discriminate between epiploic appendagitis or small omental infarction.
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Right-sided colonic diverticulitis may clinically mimic appendicitis or
cholecystitis, although the patient's history is generally more protracted. In
comparison with sigmoid diverticula, right-sided colonic diverticula are
usually true diverticula, that is, outpouchings of the colonic wall containing
all layers of the wall. This may explain the essentially benign self-limiting
character of right-sided diverticulitis
[6]. Sonography and CT findings
consist of inflammatory changes in the pericolic fat with segmental thickening
of the colonic wall at the level of an inflamed diverticulum (Figs.
10A,
10B, and
11).
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Fig. 10B —51-year-old man with right-sided colonic diverticulitis. Sonogram
proves to be valuable adjunct to CT, revealing cause of inflammation by
depicting inflamed cecal diverticulum (arrow) surrounded by
hyperechoic fat.
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Crohn's disease often causes long-standing symptoms, but up to one-third of
patients with ileocecal Crohn's disease present with initial symptoms so acute
that they are misdiagnosed as appendicitis
[7]. In the acute active phase
of ileocecal Crohn's disease, imaging shows transmural bowel wall thickening,
often predominantly of the submucosal layer, with frequent inflammatory
changes of the surrounding fat (Figs.
12A,
12B, and
12C). Uncomplicated Crohn's
disease can initially be treated with antiinflammatory drugs.
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Fig. 12A —28-year-old man with acute ileocecal Crohn's disease. Sonograms show
transmural wall thickening of terminal ileum (arrows) in longitudinal
(A) and transverse (B) section with hyperechoic inflammatory
changes of surrounding fat (arrowheads).
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Fig. 12B —28-year-old man with acute ileocecal Crohn's disease. Sonograms show
transmural wall thickening of terminal ileum (arrows) in longitudinal
(A) and transverse (B) section with hyperechoic inflammatory
changes of surrounding fat (arrowheads).
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Fig. 12C —28-year-old man with acute ileocecal Crohn's disease.
Contrast-enhanced CT confirms wall thickening and luminal narrowing of
terminal and preterminal ileum (arrowheads) with regional fat
stranding.
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Ileocecal intussusception predominantly occurs in young children with a
history of gastroenteritis and can present with right lower quadrant symptoms.
Enlarged mesenteric lymph nodes or lymphoid hyperplasia of the distal ileum
often acts as a lead point for intussusception. Imaging shows a
bowel-within-bowel configuration with a targetlike mass on sonography
consisting of multiple concentric rings related to the invaginating layers of
the bowel wall [8]
(Fig. 13). Nonoperative
hydrostatic reduction is the treatment of preference.
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Fig. 13 —2-year-old boy with ileocecal intussusception. Transverse sonogram
of right lower abdomen shows targetlike mass representing intussusception of
distal ileum (arrowhead) into cecum (arrow).
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Genitourinary Tract
Gynecologic conditions such as pelvic inflammatory disease or a hemorrhagic
functional ovarian cyst can cause acute pelvic pain that may simulate
appendicitis. In the evaluation of these disorders, transvaginal sonography is
superior to a transabdominal approach because of the proximity of the
transducer to the internal genital organs. In pelvic inflammatory disease, the
imaging findings vary according to the severity of the disease and may be
normal in early conditions. In more advanced stages, findings may include
enlargement of the internal genital organs with indistinct contours and free
pelvic fluid (Figs. 14A,
14B, and
14C). In the absence of a
drainable tuboovarian abscess, treatment is medical with antibiotics. A
hemorrhagic ovarian cyst appears as a complicated cyst on sonography and a
high-attenuation adnexal mass on unenhanced CT and does not require
treatment.
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Fig. 14B —39-year-old woman with pelvic inflammatory disease.
Contrast-enhanced CT shows enlargement of ovaries (B, arrows)
with ill-defined contours of ovaries and uterus and some free pelvic fluid
(C, arrow).
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Fig. 14C —39-year-old woman with pelvic inflammatory disease.
Contrast-enhanced CT shows enlargement of ovaries (B, arrows)
with ill-defined contours of ovaries and uterus and some free pelvic fluid
(C, arrow).
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Urolithiasis may present with right lower quadrant pain when obstruction is
caused by a distal ureteral stone. Unenhanced CT
(Fig. 15) is more accurate in
detecting ureteral stones than sonography, both often showing hydronephrosis
and a hydroureter as signs of obstruction (Figs.
16A and
16B).
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Fig. 16A —40-year-old woman with right ureteral stone. Sonograms show
right-sided hydronephrosis (A) and obstructing calculus (B,
arrow) in distal ureter at level of iliac artery (A) and iliac vein
(V).
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Fig. 16B —40-year-old woman with right ureteral stone. Sonograms show
right-sided hydronephrosis (A) and obstructing calculus (B,
arrow) in distal ureter at level of iliac artery (A) and iliac vein
(V).
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Musculoskeletal Tract
A rectus sheath hematoma may be easy to diagnose in patients presenting
with a painful palpable mass under anticoagulant therapy; however, small
nonpalpable hematomas can clinically masquerade as appendicitis and also occur
in patients without anticoagulantia
[9]. Sonography and CT show a
hemorrhagic mass within the sheath of the rectus abdominis muscle (Figs.
17A and
17B). No treatment is required
other than adjusting any anticoagulant therapy.
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Fig. 17A —68-year-old woman with rectus sheath hematoma. Sonogram depicts
small painful lesion (arrow) within sheath of rectus abdominis muscle
in right lower quadrant. Lesion contains fluid-fluid level.
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In conclusion, this review illustrates the sonographic and CT features of a
broad spectrum of nonsurgical diseases that may clinically present as
appendicitis in patients without appendicitis. A correct imaging diagnosis of
these alternative disorders may have a major impact on patient management
because it prevents an unnecessary operation or hospitalization.
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Abstract
Introduction
