AJR 2005; 184:1136-1142
© American Roentgen Ray Society
Helical CT Evaluation of Acute Right Lower Quadrant Pain: Part I, Common Mimics of Appendicitis
Jinxing Yu,
Ann S. Fulcher,
Mary Ann Turner and
Robert A. Halvorsen
Department of Radiology, Virginia Commonwealth University, Medical
College of Virginia, 401 N 12th St., PO Box 980615, Main Hospital, Third
Floor, Richmond, VA 23298-0615.
Received July 21, 2004;
accepted after revision September 28, 2004.
Address correspondence to J. Yu
(jyu1{at}vcu.edu).
Abstract
OBJECTIVE. The purpose of our pictorial essay is to present common
mimics of appendicitis as noted on helical CT in patients with right lower
quadrant pain and to highlight the features that provide clues to the
diagnosis.
CONCLUSION. Recognition of the findings of common diseases that
simulate acute appendicitis on helical CT, along with features that help to
differentiate these entities from appendicitis, is important in establishing a
correct diagnosis and in guiding appropriate therapy.
Introduction
Helical CT plays an important role in the evaluation of patients
with right lower quadrant (RLQ) pain and suspected acute appendicitis. Many
conditions can produce RLQ pain or inflammatory changes similar to those of
acute appendicitis resulting in a diagnostic challenge on CT
[1,
2]. Common diseases that mimic
appendicitis include Crohn's disease, pelvic inflammatory disease, acute
pyelonephritis, renal and urinary tract obstruction, hemorrhagic ovarian cyst,
right-sided diverticulitis, mesenteric adenitis, epiploic appendagitis, bowel
ischemia, right colonic neoplasia, and infectious ileocolitis. Helical CT
findings of these common mimics along with features that help to differentiate
them from appendicitis are emphasized in these proven cases.
Acute Appendicitis
Acute appendicitis (Figs.
1A, and
1B) manifests on CT as
enlargement of the appendix with a diameter greater than 6 mm, thickened wall
with enhancement, periappendiceal fatty stranding, and sometimes with an
appendicolith, or focal thickening of terminal ileum or cecum
[1-3].
In early or mild appendicitis, the appendix may remain normal in size. The
thickened wall with enhancement may be the only major finding on CT
(Fig. 2). A focal defect in the
wall of the inflamed appendix (Figs.
3A, and
3B), appendicolith outside the
appendix, periappendiceal fluid collection, or extraluminal air near the
appendix indicates perforation of the appendix.
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Fig. 1A. —22-year-old man with acute appendicitis. C = cecum. Axial CT
image shows enlarged appendix (arrow) and fat stranding in right
lower quadrant (arrowheads) posterior and medial to cecum.
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Fig. 2. —27-year-old man with right lower quadrant pain for 1 day and
low-grade fever. Axial CT image shows mildly enhanced appendix
(arrows) with diameter of 6 mm and minimal periappendiceal fatty
stranding consistent with early acute appendicitis.
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Fig. 3A. —27-year-old man with perforated acute appendicitis. Axial CT
scan shows extensive fat stranding and fluid collection (arrows)
surrounding enhanced and dilated appendix (A). Adjacent small bowel (sb) shows
wall thickening.
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Fig. 3B. —27-year-old man with perforated acute appendicitis. Axial CT
scan obtained inferior to A shows defect (arrowheads) in
inflamed appendiceal wall (A), indicating perforation. Extensive fat stranding
and fluid collection (arrows) are present.
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Crohn's Disease
Crohn's disease may present as acute RLQ pain with fever and elevated WBC,
mimicking appendicitis. Helical CT findings in Crohn's disease include bowel
wall thickening, narrowing of the lumen, mesenteric fatty stranding, creeping
fat, and skip lesions [4]
(Fig. 4). Abdominal abscesses
may develop adjacent to segments of bowel severely affected by Crohn's disease
(Figs. 5A, and
5B). The long segmental wall
thickening of the terminal ileum, the center of inflammation away from the
appendix, and circumferential symmetric thickening of the cecum are the major
features that differentiate Crohn's disease from appendicitis.
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Fig. 5A. —24-year-old woman with Crohn's disease and abscess. sb =
small bowel. Axial CT scan shows circumferential wall thickening of distal
small bowel and cecum (C) with adjacent fat stranding (arrow).
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Fig. 5B. —24-year-old woman with Crohn's disease and abscess. sb =
small bowel. Axial CT scan obtained inferior to A shows large abscess
(arrows) in mesentery adjacent to long segment of distal small bowel
with wall thickening.
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Pelvic Inflammatory Disease
Pelvic inflammatory disease represents a spectrum of infection within the
female reproductive system. Hydrosalpinx, especially when involvement is
limited to the right fallopian tube, may be confused with a dilated appendix
on CT (Figs. 6A, and
6B). The extrinsic
inflammation from a tuboovarian abscess, if it lies adjacent to the appendix,
may cause serosal edema and mural thickening of the appendix, which create a
diagnostic challenge. Recognizing that the inflammation is centered in the
adnexa rather than in the appendix assists in making the correct
diagnosis.
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Fig. 6A. —34-year-old woman with acute right lower quadrant pain. Axial
CT scan shows dilated tubular fluid-density structure in right adnexa
(arrows) medial to cecum (C) consistent with right hydrosalpinx.
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Fig. 6B. —34-year-old woman with acute right lower quadrant pain. Axial
CT scan obtained inferior to A shows fat stranding (open
arrows) surrounding right ovary (O). Physical examination showed vaginal
discharge and cervical motion tenderness consistent with pelvic inflammatory
disease. Uterus (U) is noted.
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Acute Pyelonephritis
Acute pyelonephritis may present with appendicitis-like symptoms. However,
on contrast-enhanced helical CT, numerous low-attenuation wedges and streaks
in the renal parenchyma with associated focal or diffuse enlargement and
perinephric fat stranding readily allow the differentiation of this entity
from appendicitis (Figs. 7A,
and 7B).
Renal and Urinary Tract Obstruction
Urinary tract disorders commonly present with acute right lower
abdominopelvic pain [5].
Occasionally, urine extravasation may occur from the renal collecting system
or ureter if the obstruction is acute and severe and may extend into RLQ,
resulting in fat stranding mimicking acute appendicitis (Figs.
8A, and
8B). Identifying the normal
appendix and tracing the fat stranding back to the urinary tract may help in
differentiating this entity from acute appendicitis.
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Fig. 8B. —41-year-old man with right lower quadrant (RLQ) pain. Axial
CT scan obtained superior to A shows dilatation of right renal
collecting system (arrows) consistent with obstruction. Final
diagnosis was right ureteropelvic obstruction.
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Hemorrhagic Ovarian Cyst
Hemorrhagic ovarian cyst is the most frequent gynecologic condition
presenting with lower abdominopelvic pain that may simulate appendicitis,
especially when it occurs on the right side. On helical CT, a hemorrhagic
ovarian cyst appears as a well-circumscribed structure with attenuation
greater than that of simple fluid (Fig.
9). Rupture of the ovarian cyst resulting in free pelvic fluid
and/or fat stranding may mimic acute appendicitis. Identification of a normal
appendix in conjunction with an ovarian cyst and associated inflammatory
changes centered in the adnexa is helpful in establishing the correct
diagnosis.
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Fig. 9. —28-year-old woman with acute right lower quadrant pain. Axial
CT scan shows cystic structure in right adnexa (arrows) with
well-defined wall most likely representing hemorrhagic cyst. Follow-up pelvic
sonography performed 6 weeks later (not shown) showed interval resolution of
cyst.
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Right-Sided Diverticulitis
Right colonic diverticulitis may be mistaken clinically for acute
appendicitis. The helical CT findings usually consist of asymmetric thickening
of the cecal wall, pericolonic inflammation, and the presence of diverticula
[6] (Figs.
10A, and
10B). Identifying pericolonic
inflammation centered above the ileocecal valve or adjacent to a diverticulum
is helpful in differentiating diverticulitis from appendicitis.
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Fig. 10B. —42-year-old man with right-sided diverticulitis. Axial CT
scan obtained superior to A shows inflamed diverticulum
(arrowhead) in medial aspect of right colon (C) with extensive
pericolonic fat stranding (arrows).
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Mesenteric Adenitis
Mesenteric adenitis represents a benign infection or inflammation of the
lymph nodes within the mesentery that results in abdominal pain, often
mimicking appendicitis clinically
[7]. If the sole finding in
patients with RLQ pain is enlarged mesenteric lymph nodes clustered in the RLQ
seen in association with a normal appendix, the diagnosis of mesenteric
adenitis is highly likely (Fig.
11).
Epiploic Appendagitis
Epiploic appendagitis is thought to occur as a result of spontaneous
torsion, ischemia, or inflammation of an epiploic appendage of the colon. The
condition presents with acute abdominal pain that can mimic appendicitis
[8]. On helical CT, the lesion
shows a characteristic appearance as an ovoid fat-attenuation focus with a
hyperattenuating rim associated with the serosal surface of the adjacent colon
(Fig. 12). Mild inflammatory
changes of the surrounding fat may be seen.
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Fig. 12. —42-year-old woman with right abdominal pain. Axial CT scan
shows fat-containing lesion (asterisk) with hyperattenuating rim and
fat stranding (arrows) in right lower quadrant right lateral to cecum
(C), consistent with epiploic appendagitis.
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Bowel Ischemia
Bowel ischemia is a common cause of abdominal pain in the elderly. Helical
CT findings include symmetric bowel wall thickening, mucosal thumbprinting,
and pneumatosis coli if infarction occurs
(Fig. 13). When these findings
are localized to the distal ileum, differentiation from acute appendicitis
resulting in reactive changes of the ileum may be difficult, especially if a
normal appendix is not visualized.
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Fig. 13. —58-year-old man with acute right lower quadrant pain. Axial
CT scan shows wall thickening of cecum (C) with pneumatosis (open
arrows) and pericecal fat stranding (solid arrows). Loops of
small bowel (S) are dilated, consistent with ileus. Surgery confirmed
infarction of cecum.
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Right Colonic Carcinoma
Right colonic carcinoma may present with acute lower abdominal pain,
usually due to obstruction or perforation. On helical CT, marked asymmetric
colonic wall thickening, short segment involvement, and abrupt change from a
normal to an abnormal segment of colon are the key features that help to
distinguish this from other entities. However, the diagnosis becomes more
challenging and may mimic appendicitis when perforation occurs and results in
fat stranding, fluid collections, and abscess formation in the RLQ (Figs.
14A, and
14B).
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Fig. 14A. —59-year-old woman with fever and acute right abdominal pain.
Axial CT image shows mass in right abdomen, containing gas and fluid with
adjacent fatty stranding (solid arrows) consistent with abscess.
Right renal hemorrhagic cyst (open arrows) was noted and confirmed on
follow-up sonography (not shown).
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Fig. 14B. —59-year-old woman with fever and acute right abdominal pain.
Axial CT image obtained 1 cm inferior to A shows marked wall thickening
of short segment of right colon (arrows). Right colonic carcinoma
with perforation was confirmed surgically.
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Infectious Ileocolitis
Infectious ileocolitis is usually caused by Yersinia,
Campylobacter, or Salmonella organisms. The characteristic CT
features of infectious ileocolitis include wall thickening of the terminal
ileum, cecum, and a portion of the ascending colon
(Fig. 15) and enlargement of
the mesenteric lymph nodes. Identification of the normal appendix and lack of
periappendiceal fat stranding help to exclude appendicitis.
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Abstract
Introduction
