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1 Department of Radiology, Mayo Clinic College of Medicine, Scottsdale, AZ
85259.
2 Department of Radiology, University of Washington Harborview Medical Center,
Box 359728, 325 Ninth Ave., Seattle, WA 98104.
3 Department of Radiology, University of Washington, Box 354755, 4245 Roosevelt
Way, NE, Seattle, WA 98105.
Received June 16, 2006;
accepted after revision June 16, 2006.
Address correspondence to C. C. Roberts
(roberts.catherine{at}mayo.edu).
Abstract
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Keywords: abdominal imaging • appendicitis • mimics of appendicitis • right lower quadrant pain
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| QUESTION 1 A primary appendiceal neoplasm underlying acute appendicitis would be suggested by which imaging finding?
QUESTION 2 Which is the most likely explanation for right hydronephrosis and right hydroureter that occur in the setting of acute appendicitis with perforation and abscess formation?
QUESTION 3 Which statement is true regarding recurrent appendicitis?
QUESTION 4 Which gynecologic condition most commonly mimics appendicitis both clinically and on CT?
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| QUESTION 5 Which CT finding helps differentiate acute appendicitis from Crohn's disease?
QUESTION 6 On CT of the abdomen in a woman with clinically suspected appendicitis, which diagnosis is suggested by a right lower quadrant lesion with a fat-fluid level?
QUESTION 7 An enlarged appendix in the right lower quadrant of the abdomen can be simulated on CT by which condition?
QUESTION 8 On CT of the pelvis in a postpartum woman, a dilated tubular structure extending caudad from the inferior vena cava into the pelvis most strongly suggests which diagnosis?
QUESTION 9 In a patient with suspected appendicitis, layered densities of fat and soft tissue inside the bowel lumen on CT of the abdomen suggest which diagnosis?
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Solution to Question 1
A dilated appendix occurs with acute appendicitis but will also be seen
with primary tumors of the appendix
[1,
2]. An appendiceal mucocele
typically presents with diffuse distention of the appendix and the presence of
low-density material. Lymphoma of the appendix will show an enlarged appendix
with diffuse wall thickening and maintenance of its vermiform shape. Goblet
cell tumors have an infiltrative growth pattern resulting in circumferential
wall thickening. Option A is not the best response.
An appendiceal soft-tissue mass may be seen with colonic-type primary appendiceal neoplasms. These neoplasms may also be locally infiltrative into the periappendiceal fat and adjacent organs. Appendiceal carcinoid tumors are usually small and distal in the appendix and are typically not directly detected during imaging. Option B is the best response.
Inflammation surrounding the appendix can be seen with primary tumors of the appendix such as a colonic-type tumor with local infiltrative growth. More often, however, inflammation is seen with obstruction of the appendix and secondary infection from any neoplastic or nonneoplastic cause, such as an appendicolith or mucinous neoplasms. Option C is not the best response.
Calcifications in the appendix are often seen secondary to an appendicolith, which may be an incidental finding in some patients. Curvilinear mural calcifications also are associated with neoplastic and nonneoplastic mucoceles of the appendix. Option D is not the best response.
Free air in the peritoneum is an indication of bowel perforation, but not specifically the presence of a neoplasm. Option E is not the best response.
Solution to Question 2
Hydronephrosis and hydroureter are caused by ureteral obstruction. In
general, the most common intraluminal cause would be an obstructing urinary
tract calculus, with an intrinsic urothelial malignancy being less likely.
However, neither one of these lesions is associated with appendicitis. Option
A is not the best response.
Pyelonephritis may present with right flank pain that radiates to the right lower quadrant, simulating acute appendicitis. Although pyuria may occur in acute appendicitis as a result of periureteral inflammation, pyelonephritis is not associated with acute appendicitis. Option B is not the best response.
Mucinous tumors are the most common type of primary tumors of the appendix. They typically occur as cystic masses that may affect adjacent structures by mass effect but not by surrounding and engulfing them [1, 2]. Option C is not the best response.
Right ureteral obstruction may result from extrinsic compression. As in the case discussed here, perforation of an acutely inflamed appendix results in abscess formation. The right lower quadrant abscess may surround and obstruct the distal ureter, leading to hydronephrosis and hydroureter. Periureteral inflammation may also result in pyuria and hematuria, which may confuse the clinical picture. Option D is the best response.
Although a ureteral stone can occur coincidentally with appendicitis, the two conditions are unrelated. Option E is not the best response.
Solution to Question 3
Clinical and histopathologic evidence of one or more previous episodes of
appendicitis may be found in as many as 7% of appendectomy specimens from
patients with appendicitis, suggesting that recurrent appendicitis is not rare
[3]. Option A is not the best
response.
The CT findings of acute appendicitis and of recurrent appendicitis are indistinguishable. These findings include an enlarged, fluid-filled appendix, periappendiceal fat stranding, and frank abscess formation [4]. Option B is the best response.
The recurrence rate for acute appendicitis treated with nonoperative percutaneous drainage is approximately 14% in large series [5]. Elective appendectomy generally is recommended after nonoperative management of acute appendicitis. Option C is not the best response.
Unrecognized malignancy is found in 0.5-1% of surgical specimens for acute appendicitis; 30-50% of patients with a primary appendiceal malignancy will present similarly to those with typical acute appendicitis [1, 2]. Option D is not the best response.
The recurrence rate of appendicitis after appendectomy is considered to be zero, although the recurrence rate after nonoperative percutaneous drainage is approximately 14% [5]. Option E is not the best response.
Solution to Question 4
Hemorrhagic ovarian cysts are the most common gynecologic condition that
mimics appendicitis [6].
Option C is the best response. An unruptured hemorrhagic cyst appears
as an ovarian mass with a density higher than that of fluid. When a
hemorrhagic cyst ruptures, the resultant free fluid and fat stranding can
simulate changes seen with appendicitis.
Uncomplicated uterine leiomyomas or fibroids tend to have an innocuous appearance on CT. They appear as soft-tissue density or calcified masses within or exophytic from the uterus. Option A is not the best response. Endometriosis is less common than hemorrhagic ovarian cysts. The endometrial implants of endometriosis can cause thickening of the terminal ileum and inflammatory stranding in the fat of the right lower quadrant. Option B is not the best response. Cervical carcinoma causes masslike changes in the cervix. Changes in the uterine wall from adenomyosis are best shown on MRI. Options D and E are not the best responses.
Solution to Question 5
Crohn's disease and appendicitis have several imaging features in common,
sometimes making the two entities difficult to differentiate. One of the major
differentiating features is long-segment thickening of the terminal ileum
[6]. Option A is the best
response. This finding would be uncommon in appendicitis.
Both entities can cause inflammatory stranding in the fat of the right lower quadrant of the abdomen. Option C is not the best response. Inflammatory changes associated with these entities can cause increased enhancement of the cecal wall. Option D is not the best response. Ruptured appendicitis and Crohn's disease can both cause intraabdominal abscesses and free intraperitoneal air. Options B and E are not the best responses.
Solution to Question 6
Ovarian dermoid tumors classically contain fat admixed with other solid,
fluid, and calcified elements. When these tumors rupture, they can produce a
fat-fluid level in the peritoneum
[7]. Option B is the best
response.
Perforated peptic ulcer, acute pancreatitis, ovarian torsion, and ruptured ectopic pregnancy can cause free fluid in the abdomen but would not be expected to produce a fat-fluid level. Options A, C, D, and E are not the best responses.
Solution to Question 7
A dilated fallopian tube, or hydrosalpinx, associated with pelvic
inflammatory disease can mimic an enlarged appendix
[6]. This is especially true
when the changes predominantly involve the right fallopian tube. Option D
is the best response.
Epiploic appendagitis typically appears as a fat-containing lesion with a hyperdense rim and surrounding inflammatory change. Option A is not the best response. Pyelonephritis simulates appendicitis clinically but has a distinctly different imaging appearance. Pyelonephritis on CT appears as renal enlargement with streaks of low attenuation and perinephric fat stranding. Option B is not the best response. Diverticulitis does not produce an enlarged tubular structure. CT findings in diverticulitis include bowel wall thickening, diverticula, and surrounding inflammatory change. Option C is not the best response. Multiple enlarged mesenteric lymph nodes are seen in mesenteric adenitis. Option E is not the best response.
Solution to Question 8
Ovarian vein thrombosis is associated with several gynecologic conditions,
including pregnancy. The right ovarian vein is involved in most cases. On CT,
a thrombosed right ovarian vein will extend from the pelvis cephalad to the
junction with the inferior vena cava
[7]. Option E is the best
response.
Ureteral obstruction will also produce a dilated tubular structure that extends cephalad, but the ureter will extend to the renal hilum. Option B is not the best response A dilated fallopian tube from pelvic inflammatory disease will remain in the pelvis or low abdomen. Option A is not the best response. Crohn's disease and typhlitis produce bowel wall thickening and surrounding inflammatory change. Options C and D are not the best responses.
Solution to Question 9
Intussusception of the bowel occurs when a segment of bowel and surrounding
fat extends into an adjacent segment of bowel. The appearance on CT is that of
a loop of bowel containing another loop of bowel with mesenteric fat
interposed between the bowel walls
[7]. Option A is the best
response.
Pseudomembranous colitis and cytomegalovirus colitis cause marked thickening of the colon wall. Options B and D are not the best responses. The colonic wall thickening is of low attenuation but not as low as fat. A mucocele of the appendix may cause low-density contents in the appendix lumen but would not have as low a density as fat. Option C is not the best response. A Meckel's diverticulum has a similar appearance to a normal appendix. Option E is not the best response. A Meckel's diverticulum may be the lead point of an intussusception.
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