(Radiographics. 2001;21:247-262.)
© RSNA, 2001
When Appendicitis Is Suspected in Children1
Carlos J. Sivit, MD,
Marilyn J. Siegel, MD,
Kimberly E. Applegate, MD and
Kurt D. Newman, MD
1 From the Department of Radiology, Rainbow Babies and Children's Hospital of the University Hospitals of Cleveland and Case Western Reserve School of Medicine, 11100 Euclid Ave, Cleveland, OH 44106-5056 (C.J.S., K.E.A.); the Mallinckrodt Institute of Radiology, Washington University School of Medicine, St Louis, Mo (M.J.S.); and the Department of Surgery, Children's National Medical Center and George Washington University School of Medicine, Washington, DC (K.D.N.). Received February 2, 2000; revision requested March 28 and received April 6; accepted April 11. Address correspondence to C.J.S. (e-mail: sivit@uhrad.com).
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Abstract
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Acute appendicitis is the most common condition requiring emergent abdominal surgery in childhood. The clinical diagnosis of acute appendicitis is often not straightforward because approximately one-third of children with the condition have atypical clinical findings. The delayed diagnosis of this condition has serious consequences, including appendiceal perforation, abscess formation, peritonitis, sepsis, bowel obstruction, and death. Cross-sectional imaging with ultrasonography (US) and computed tomography (CT) have proved useful for the evaluation of suspected acute appendicitis. There has been a great deal of variability in the utilization of these modalities for such diagnosis in the pediatric population. The principal advantages of US are its lower cost, lack of ionizing radiation, and ability to assess vascularity through color Doppler techniques and to provide dynamic information through graded compression. The principal advantages of CT include less operator dependency than US, as reflected by a higher diagnostic accuracy, and enhanced delineation of disease extent in a perforated appendix.
Index Terms: Appendicitis, 751.291 • Appendix, CT, 751.12118 • Appendix, US, 751.1298 • Children, gastrointestinal tract, 751.291
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LEARNING OBJECTIVES FOR TEST 6
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After reading this article and taking the test, the reader will be able to:
- Describe the role of cross-sectional imaging in the evaluation of suspected acute appendicitis.
- List the relative advantages and disadvantages of US and CT for the diagnosis of acute appendicitis.
- Identify important technical factors in the performance of US and CT in children with suspected acute appendicitis.
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Introduction
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Acute appendicitis is the most common condition requiring emergency abdominal surgery in the pediatric population, with 60,000–80,000 cases annually in the United States (1,2). It is one of the major causes of hospitalization in children (3). The condition typically develops in older children and young adults. It is rare under the age of 2 years. The lifetime risk of acute appendicitis ranges from 7% to 9% (4). Acute appendicitis presents a challenging problem to caregivers because it must be differentiated from a variety of other conditions that result in acute abdominal pain in childhood.
Acute abdominal pain is a common complaint in the pediatric age group, accounting for approximately 4% of office encounters in children aged 5–14 years (5). The majority of children with acute abdominal pain have self-limited nonsurgical disease. The most common associated conditions noted in these children include upper respiratory tract infection, pharyngitis, viral syndrome, gastroenteritis, and constipation (5). The prevalence of acute appendicitis in children presenting in the outpatient setting with acute abdominal pain ranges from 1% to 4% (5–7).
In this article, we review current practice with respect to the assessment of suspected acute appendicitis in children, including the role of imaging in patient assessment, the diagnostic efficacy of graded-compression ultrasonography (US) and helical computed tomography (CT) for diagnosis, the characteristic imaging appearance of acute appendicitis at US and CT, and the effect of cross-sectional imaging on patient outcomes.
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Clinical Assessment of Acute Appendicitis
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Clinical signs and symptoms associated with acute appendicitis include crampy, periumbilical or right lower quadrant pain; nausea; vomiting; point tenderness in the right lower quadrant; rebound tenderness; and leukocytosis with a left shift. Although knowledge of the classic findings is important, the clinical diagnosis of acute appendicitis in children is not always straightforward. Approximately one-third of children with acute appendicitis have atypical clinical findings (8). Younger children are not able to clearly describe their symptoms. In addition, the presenting signs and symptoms of many nonsurgical conditions may mimic those of acute appendicitis, and most children with a suspected diagnosis of appendicitis do not have it. Further evidence of the difficulty of diagnosing appendicitis is the 5%–25% false-negative appendectomy rates reported for the pediatric population (9–16).
Various objective clinical scoring systems have been devised to stratify patient risk of appendicitis (17,18). The most widely used clinical scoring system is the MANTRELS score (Table) (18). It incorporates eight clinical and laboratory factors that were found to be useful in making the diagnosis of acute appendicitis (18). The MANTRELS score has been shown to be useful in discriminating between children with acute appendicitis and those without the disease (18).
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Morbidity and Mortality Associated with Acute Appendicitis
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There are serious consequences to the delayed diagnosis of acute appendicitis. Reported complications include perforation, abscess formation, peritonitis, wound infection, sepsis, infertility, adhesions, bowel obstruction, and death. Acute appendicitis is among the five leading causes of litigation against emergency room physicians, accounting for 5% of the dollars lost by insurers of such physicians (19–21).
Morbidity and mortality in acute appendicitis is related almost entirely to appendiceal perforation. The prevalence of appendiceal perforation in various pediatric series has ranged from 23% to 73% (11,12,15,22–28). The perforation rate is even higher in younger children, with rates of 62%–88% being reported in preschool children (22,23). Up to one-half of patients with perforated appendicitis may experience a complication (22). In comparison, the mortality rate following acute appendicitis in a general population is approximately 1% (29). Nearly all deaths are associated with a perforated appendix.
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Imaging Assessment of Acute Appendicitis
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Although abdominal radiography remains a widely used examination in children with acute abdominal pain, it has been shown to be a relatively insensitive and nonspecific means for evaluating this condition, and its use adds unnecessary cost and radiation exposure (30,31). Routine use of abdominal radiography in these children has little value unless bowel obstruction or perforation is suspected (31). Therefore, conventional radiography is not discussed here, and we focus on the cross-sectional imaging assessment of acute appendicitis with graded-compression US and helical CT.
There has been a great deal of variability in the utilization of cross-sectional imaging for the diagnosis of acute appendicitis in children. The goals of imaging in this condition are to (a) facilitate an earlier diagnosis of acute appendicitis or other conditions that it may mimic, (b) reduce negative laparotomy and perforation rates, and (c) reduce the intensity and cost of care. The principal imaging technique over the past decade for evaluating children with suspected appendicitis has been graded-compression US (8,13,14,28,32–37). A number of reports detailing the use of helical CT in adult patients for the diagnosis of acute appendicitis have been published (38–42). Recently, there have been reports on the utility of helical CT for the assessment of acute appendicitis in children as well (43–47).
Graded-compression US
The reported diagnostic accuracy of US in the diagnosis of acute appendicitis has varied greatly. The sensitivity of US in children has ranged from 44% to 94%, and the specificity has ranged from 47% to 95% (8,13,32–35,45,48). An overall sensitivity of 85% and specificity of 92% has been reported for US based on meta-analysis of pediatric and adult studies published between 1986 and 1994 (49). The clinical utility of US lies primarily in the subgroup of children in whom the clinical findings are equivocal, both to establish the diagnosis of appendicitis and to aid in the diagnosis of other abdominal and pelvic conditions that may mimic the disorder, particularly gynecologic diseases (8).
The graded-compression technique of US is performed with a high-resolution, linear array transducer. Gentle, gradual pressure is used to compress the anterior abdominal wall, resulting in displacement and compression of normal bowel loops. Adequate compression has been achieved if the iliac vessels and psoas muscle are visualized, since the appendix will be anterior to these structures. Scanning is performed in both longitudinal and transverse planes, and the examination begins with identification of the ascending colon, which appears as a nonperistaltic structure containing gas and fluid. The transducer is then moved inferiorly to identify the terminal ileum, which is easily compressible and displays active peristalsis. The cecal tip where the appendix arises is approximately 1–2 cm below the terminal ileum. A technically adequate examination can be achieved in over 95% of patients. Technical failures are due to the presence of severe pain or patient obesity that preclude satisfactory graded-compression.
At the start of the examination, the patient is asked to point to the site of maximal tenderness. This is useful to expedite the examination and to aid in locating a retrocecal appendix. On longitudinal images, the inflamed, nonperforated appendix appears as a fluid-filled, noncompressible, blind-ending tubular structure (Fig 1). The maximal appendiceal diameter, from outside wall to outside wall, is greater than 6 mm. In early nonperforated appendicitis, an inner echogenic lining representing submucosa can be identified (Fig 1). If fluid is present within the appendiceal lumen, a target appearance, characterized by a fluid-filled center and surrounded by a echogenic mucosa and submucosa and hypoechoic muscularis, may be seen when imaging in the axial plane (Fig 2). Other findings of appendicitis include an appendicolith, which appears as an echogenic foci with acoustic shadowing (Fig 3); pericecal or periappendiceal fluid; increased periappendiceal echogenicity representing fat infiltration (Fig 4); and enlarged mesenteric lymph nodes. The only US sign that is specific for appendicitis is an enlarged, noncompressible appendix measuring greater than 6 mm in maximal diameter.
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Figure 1a. Acute appendicitis. Longitudinal (a) and transverse (b) US scans through an inflamed appendix (between electronic calipers) show that it is enlarged. Note the central echogenic mucosal lining.
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Figure 1b. Acute appendicitis. Longitudinal (a) and transverse (b) US scans through an inflamed appendix (between electronic calipers) show that it is enlarged. Note the central echogenic mucosal lining.
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Figure 2. Acute appendicitis with target sign. Transverse US scan through an inflamed appendix shows an intact echogenic submucosal layer and a fluid-filled lumen (F), resulting in a "target" appearance.
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Figure 3a. Acute appendicitis with an appendicolith. Longitudinal (a) and transverse (b) US scans through an inflamed appendix show an echogenic appendicolith with acoustic shadowing.
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Figure 3b. Acute appendicitis with an appendicolith. Longitudinal (a) and transverse (b) US scans through an inflamed appendix show an echogenic appendicolith with acoustic shadowing.
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Figure 4. Acute appendicitis with increased periappendiceal echogenicity. Longitudinal US scan through the right lower quadrant shows an area of increased echogenicity (arrows) representing infiltration of mesenteric fat surrounding an enlarged appendix (between electronic calipers).
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Perforation occurs in 23%–73% of children with acute appendicitis (11,12,15,22–28). The US features of perforation include loss of the echogenic submucosal layer (Fig 5) and presence of a loculated periappendiceal or pelvic fluid collection (Fig 6) or abscess (Fig 7) (50,51). These findings occur in 50%–70% of cases of perforated appendicitis. The appendix itself is visible in only 40%–60% of patients with appendiceal perforation.
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Figure 5a. Acute appendicitis with loss of the echogenic submucosal layer. Longitudinal (a) and transverse (b) US scans through an inflamed appendix show a diffuse hypoechoic and enlarged appendix (between electronic calipers), with loss of the normally echogenic submucosal layer. At surgery, appendiceal perforation was noted.
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Figure 5b. Acute appendicitis with loss of the echogenic submucosal layer. Longitudinal (a) and transverse (b) US scans through an inflamed appendix show a diffuse hypoechoic and enlarged appendix (between electronic calipers), with loss of the normally echogenic submucosal layer. At surgery, appendiceal perforation was noted.
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Figure 6. Acute appendicitis with loculated periappendiceal fluid. Longitudinal US scan through the right lower quadrant shows an enlarged appendix (between electronic calipers) with surrounding loculated fluid. Appendiceal perforation was noted at surgery.
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Figure 7. Perforated appendicitis with intraperitoneal abscess. Longitudinal US scan through the pelvis demonstrates an oval, complex mass immediately above the bladder (B), which proved to be an abscess. Note the echogenic appendicolith within the mass.
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The use of color Doppler US provides a useful adjunct in the evaluation of suspected acute appendicitis. Although color Doppler US does not increase the sensitivity of the examination, it makes interpretation of the gray-scale US findings easier and can increase observer confidence in the diagnosis of acute appendicitis. Color Doppler US of nonperforated appendicitis typically demonstrates peripheral wall hyperemia, reflecting inflammatory hyperperfusion (Fig 8) (34,52,53). In early inflammation, color flow may be absent or limited to the appendiceal tip. Color flow may also be absent in gangrenous appendicitis. Color Doppler findings of appendiceal perforation include hyperemia in the periappendiceal soft tissues or within a well-defined abscess (54).
Most false-negative diagnoses at US result from failure to visualize the appendix (55). Causes of nonvisualization include (a) the inability to compress the right lower quadrant adequately; (b) an aberrant location of the appendix, such as retrocecal position; and (c) appendiceal perforation. The problem of a retrocecal appendix can be minimized by having the patient identify the site of maximal tenderness and by scanning in a coronal plane with the transducer parallel to the iliac wing. If the psoas muscle is visualized, a retrocecal appendix should be seen. Although the appendix is not recognizable in many patients with perforation, the identification of secondary findings can help to suggest the diagnosis. Another pitfall is early inflammation limited to the appendiceal tip, which can be missed if only the proximal appendix is imaged (Fig 9) (56,57). Therefore, it is important to visualize the entire length of the appendix.
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Figure 9a. Distal appendicitis. (a) Transverse US image through the proximal appendix (between electronic calipers) demonstrates a normal appendiceal diameter less than 6 mm. (b) Transverse US scan through the distal appendix (between electronic calipers) demonstrates appendiceal enlargement. The distal appendix measures 8.1 mm.
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Figure 9b. Distal appendicitis. (a) Transverse US image through the proximal appendix (between electronic calipers) demonstrates a normal appendiceal diameter less than 6 mm. (b) Transverse US scan through the distal appendix (between electronic calipers) demonstrates appendiceal enlargement. The distal appendix measures 8.1 mm.
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Several causes of false-positive diagnoses have been reported. First, the normal appendix may be visible with graded-compression US in 10%–50% of children and adolescents and mistaken for appendicitis (Fig 10). The normal appendix measures 6 mm or less in maximal outer diameter, is compressible, and lacks adjacent inflammatory changes. In addition, it has no demonstrable flow at color flow Doppler imaging. A second cause of a false-positive examination is periappendiceal inflammation due to Crohn disease or pelvic inflammatory disease. An inflamed Meckel diverticulum also may mimic acute appendicitis. Finally, false-positive studies can be the result of spontaneous resolution of acute appendicitis (58).
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Figure 10a. Normal appendix. Longitudinal (a) and transverse (b) US images through the right lower quadrant demonstrate a normal appendix (between electronic calipers) measuring less than 6 mm in diameter.
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Figure 10b. Normal appendix. Longitudinal (a) and transverse (b) US images through the right lower quadrant demonstrate a normal appendix (between electronic calipers) measuring less than 6 mm in diameter.
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Several reports have suggested that use of US has not improved outcomes in children with suspected acute appendicitis (14,28,59). Roosevelt and Reynolds (28) showed no significant differences in the perforation rate, complication rate, or cost of care in children who underwent US compared with those who did not. Ford et al (59) showed a significantly higher negative appendectomy rate in children with suspected acute appendicitis following the introduction of US at their institution compared with the "pre-sonography" era (23% versus 14%). The cost of care was also higher after the introduction of US (59). Davidson et al (14) also showed a higher negative appendectomy rate in children who underwent US compared with those who did not (12% vs 9%).
Helical CT
Helical CT has been shown to be a highly sensitive and specific modality for the diagnosis of acute appendicitis in children and adults. The reported sensitivity of CT for the diagnosis of acute appendicitis has ranged from 87% to 100%, and the specificity has ranged from 89% to 98% (38–43,45,46). The advantages of CT over US are reduced operator dependence, superior contrast sensitivity, and the capability for viewing the entire range of air, soft-tissue, fat, and bone attenuation values inherent to the abdomen. CT is also more useful than US for evaluating complications of acute appendicitis, such as phlegmon and abscess formation. It can precisely delineate the location and extent of associated fluid collections including interloop abscesses, which facilitates drainage procedures.
A variety of techniques have been used in the performance of appendiceal CT. These include (a) full abdominopelvic scanning after intravenous and oral administration of contrast material (38), (b) imaging limited to the lower abdomen and pelvis without any contrast material (39,42), (c) imaging limited to the lower abdomen and pelvis with the use of oral and rectal contrast material (41), and (d) imaging of the lower abdomen and pelvis with the use of only rectal contrast material (40,43,45,46). The highest diagnostic efficacy at CT has been obtained with the use of rectal contrast material and thin collimation through the lower abdomen and pelvis. The reported sensitivity of CT when such techniques are used has ranged from 97% to 100%, and the specificity has ranged from 94% to 98% (40,41,43,45,46).
Rectal administration of contrast material is generally well tolerated in children, and sedation is not typically required. A 3% diatrizoate meglumine solution is administered intracolonically through a rectal catheter. The amount of contrast material administered varies according to the size of the patient and the degree of fullness and discomfort that the patient can tolerate when the fluid is instilled. The administered volume of fluid ranges from 500 mL in small children to 1,000 mL in adolescents. Thin-collimation scanning is performed with 4-mm collimation, 4-mm/sec table speed (1.0 pitch), and 4-mm reconstruction beginning 2–3 cm above the iliac wing.
The normal appendix can be identified at CT in over three-fourths of children (45). The appendix arises from the posteromedial aspect of the cecum, approximately 1–2 cm below the ileocecal junction (Fig 11). The relationship of the base of the appendix to the cecum is constant, but the free end of the appendix is mobile and can be directed medially, caudally, laterally, or retrocecally. The appendix is usually curved and may be tortuous. A segment of the appendix is commonly noted at a level higher than the ileocecal valve. The maximal normal appendiceal diameter is quite variable; although it usually is 7 mm or less, it may occasionally be larger (Fig 12). The lumen of the normal appendix may fill with contrast material (Fig 13), or it may contain intraluminal air (Fig 14) or fluid. It may occasionally be difficult to differentiate the normal appendix from adjacent unopacified bowel loops. Therefore, optimal cecal opacification and distension are essential to maximize the diagnostic yield of the examination. In addition, thin collimation helps to distinguish adjacent bowel loops from the appendix (Fig 15). This is especially true in children who often have much less intraperitoneal and retroperitoneal fat to delineate the cecum and appendix compared with adults.
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Figure 11a. Normal appendix. (a) Axial CT scan obtained through the lower abdomen with thin collimation following the intravenous and rectal administration of contrast material demonstrates the normal terminal ileum (arrows). (b) Axial CT scan obtained 2 cm below a demonstrates the normal proximal appendix (arrow) originating from the cecal apex. (c) Axial CT scan obtained 2 cm below b demonstrates the normal distal appendix (arrow). Note that the appendix does not fill with contrast material.
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Figure 11b. Normal appendix. (a) Axial CT scan obtained through the lower abdomen with thin collimation following the intravenous and rectal administration of contrast material demonstrates the normal terminal ileum (arrows). (b) Axial CT scan obtained 2 cm below a demonstrates the normal proximal appendix (arrow) originating from the cecal apex. (c) Axial CT scan obtained 2 cm below b demonstrates the normal distal appendix (arrow). Note that the appendix does not fill with contrast material.
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Figure 11c. Normal appendix. (a) Axial CT scan obtained through the lower abdomen with thin collimation following the intravenous and rectal administration of contrast material demonstrates the normal terminal ileum (arrows). (b) Axial CT scan obtained 2 cm below a demonstrates the normal proximal appendix (arrow) originating from the cecal apex. (c) Axial CT scan obtained 2 cm below b demonstrates the normal distal appendix (arrow). Note that the appendix does not fill with contrast material.
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Figure 12. Normal appendix measuring 10 mm in maximal diameter. Axial CT scan obtained through the upper pelvis with thin collimation following the intravenous and rectal administration of contrast material demonstrates an enlarged appendix measuring 10 mm (arrows).
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Figure 13a. Normal contrast materialfilled appendix. (a) Axial CT scan obtained through the lower abdomen with thin collimation following the intravenous and rectal administration of contrast material demonstrates a contrast materialfilled normal proximal appendix (arrow). (b) Axial CT image obtained 1 cm below a shows the normal contrast materialfilled distal appendix (arrow). C = cecum.
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Figure 13b. Normal contrast materialfilled appendix. (a) Axial CT scan obtained through the lower abdomen with thin collimation following the intravenous and rectal administration of contrast material demonstrates a contrast materialfilled normal proximal appendix (arrow). (b) Axial CT image obtained 1 cm below a shows the normal contrast materialfilled distal appendix (arrow). C = cecum.
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Figure 14a. Normal appendix containing intraluminal air. (a) Axial CT scan obtained through the lower abdomen with thin collimation following the intravenous and rectal administration of contrast material demonstrates air within the normal proximal appendix (arrow). (b) Axial CT image obtained 2 cm below a shows air within segments of the more distal appendix (arrow).
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Figure 14b. Normal appendix containing intraluminal air. (a) Axial CT scan obtained through the lower abdomen with thin collimation following the intravenous and rectal administration of contrast material demonstrates air within the normal proximal appendix (arrow). (b) Axial CT image obtained 2 cm below a shows air within segments of the more distal appendix (arrow).
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Figure 15a. Enlarged appendix on thick and thin collimation sections. (a) Axial CT scan obtained through the upper pelvis with 8-mm collimation following the intravenous and oral administration of contrast material. The borders of the enlarged appendix (arrows) are not well seen, and it is difficult to distinguish from surrounding bowel loops. (b) Axial CT scan obtained with 4-mm collimation through the same location demonstrates enhanced definition of the appendix (arrows). Note the curvilinear appearance and low-attenuation fluid within the lumen.
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Figure 15b. Enlarged appendix on thick and thin collimation sections. (a) Axial CT scan obtained through the upper pelvis with 8-mm collimation following the intravenous and oral administration of contrast material. The borders of the enlarged appendix (arrows) are not well seen, and it is difficult to distinguish from surrounding bowel loops. (b) Axial CT scan obtained with 4-mm collimation through the same location demonstrates enhanced definition of the appendix (arrows). Note the curvilinear appearance and low-attenuation fluid within the lumen.
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CT features of acute appendicitis include a distended appendix greater than 7 mm in maximal diameter (Fig 16), appendiceal wall thickening (Fig 16) and enhancement (Fig 17), an appendicolith (Fig 18), circumferential or focal apical cecal thickening (Fig 19), pericecal fat stranding (Fig 16), adjacent bowel wall thickening, free peritoneal fluid, mesenteric lymphadenopathy, intraperitoneal phlegmon, or abscess (Fig 20). The only CT findings specific for appendicitis are an enlarged appendix and cecal apical changes, which represent contiguous spread of the inflammatory process to the cecum. The identification of cecal apical changes is particularly useful in allowing a confident diagnosis of acute appendicitis if there is difficulty in identifying an enlarged appendix (Fig 21). Identification of an appendicolith in an individual with acute right lower quadrant pain is also considered highly suggestive of acute appendicitis. Care should be taken not to confuse retained barium in a normal appendix with an appendicolith. It may be easier to differentiate retained barium from an appendicolith by viewing the digital scout radiograph, since retained barium will have a higher attenuation. The remaining CT findings are nonspecific and may be seen with a variety of right lower quadrant and pelvic infectious or inflammatory conditions.
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Figure 16. Acute appendicitis. Axial CT scan obtained through the lower abdomen with thin collimation following the intravenous and rectal administration of contrast material demonstrates an enlarged appendix with marked stranding of the periappendiceal fat.
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Figure 17a. Acute appendicitis with appendiceal wall enhancement. (a) Axial CT scan obtained through the lower abdomen with thin collimation following the intravenous and rectal administration of contrast material demonstrates an enlarged proximal appendix with intense enhancement of the appendiceal wall. (b) Axial CT scan obtained 1 cm below a demonstrates intense contrast material enhancement of the distal appendix.
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Figure 17b. Acute appendicitis with appendiceal wall enhancement. (a) Axial CT scan obtained through the lower abdomen with thin collimation following the intravenous and rectal administration of contrast material demonstrates an enlarged proximal appendix with intense enhancement of the appendiceal wall. (b) Axial CT scan obtained 1 cm below a demonstrates intense contrast material enhancement of the distal appendix.
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Figure 18. Acute appendicitis with an appendicolith. Axial CT scan obtained through the upper pelvis with thin collimation following the intravenous and rectal administration of contrast material demonstrates an appendicolith within the appendix (arrow).
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Figure 19a. Acute appendicitis with cecal apical thickening. (a) Axial CT scan obtained through the upper pelvis with thin collimation following the intravenous and oral administration of contrast material demonstrates focal thickening at the cecal apex (arrow). (b) Axial CT scan obtained 2 cm below a shows an enlarged appendix (arrow).
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Figure 19b. Acute appendicitis with cecal apical thickening. (a) Axial CT scan obtained through the upper pelvis with thin collimation following the intravenous and oral administration of contrast material demonstrates focal thickening at the cecal apex (arrow). (b) Axial CT scan obtained 2 cm below a shows an enlarged appendix (arrow).
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Figure 20. Perforated appendicitis. Axial CT scan obtained through the upper pelvis with thin collimation following the intravenous and rectal administration of contrast material demonstrates a complex mass containing fluid and air representing a periappendiceal abscess.
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Figure 21a. Acute appendicitis with cecal apical thickening. (a) Axial CT scan obtained through the upper pelvis with thin collimation following the intravenous and rectal administration of contrast material demonstrates focal cecal apical thickening (arrow). (b) Axial CT scan obtained 1 cm below a demonstrates an enlarged curvilinear appendix (arrow). Note that there is not a good plane of separation between the appendix and adjacent unopacified small bowel loops. The cecal apical thickening was helpful in calling attention to the abnormal appendix.
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Figure 21b. Acute appendicitis with cecal apical thickening. (a) Axial CT scan obtained through the upper pelvis with thin collimation following the intravenous and rectal administration of contrast material demonstrates focal cecal apical thickening (arrow). (b) Axial CT scan obtained 1 cm below a demonstrates an enlarged curvilinear appendix (arrow). Note that there is not a good plane of separation between the appendix and adjacent unopacified small bowel loops. The cecal apical thickening was helpful in calling attention to the abnormal appendix.
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One potential pitfall in the CT diagnosis of acute appendicitis results from the overlapping range in maximal appendiceal diameter between inflamed and uninflamed appendices. In contrast to the US examination, the compressibility of the appendix cannot be used as a distinguishing feature. Therefore, it is important to assess for associated secondary changes, including cecal apical thickening and infiltration of periappendiceal fat. Another potential pitfall at CT is that an inflamed appendix may be mistaken for unopacified bowel loops. Therefore, it is essential to optimize cecal and colonic opacification. Finally, as previously discussed, early appendiceal inflammation may be limited to the appendiceal tip (Fig 22) (60,61). Therefore, it is important to identify the entire appendix at CT.
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Figure 22a. Distal appendicitis. (a) Axial CT scan obtained through the upper pelvis with thin collimation following the intravenous and rectal administration of contrast material demonstrates a normal-appearing proximal appendix originating from the cecal apex (arrow). (b) Axial CT scan obtained 2 cm below a shows a dilated, fluid-filled appendix.
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Figure 22b. Distal appendicitis. (a) Axial CT scan obtained through the upper pelvis with thin collimation following the intravenous and rectal administration of contrast material demonstrates a normal-appearing proximal appendix originating from the cecal apex (arrow). (b) Axial CT scan obtained 2 cm below a shows a dilated, fluid-filled appendix.
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There is evidence supporting improved patient outcomes in children with suspected acute appendicitis who undergo CT (45,62). Garcia-Pena et al (45) have shown a significant decrease in the negative appendectomy rate in children with suspected acute appendicitis who underwent CT before surgery compared with those who did not (7% vs 13%). Rao et al (62) have also shown a significant decrease in the negative appendectomy rate in children with suspected acute appendicitis who underwent CT also as part of a protocol compared with those who did not (6% vs 12%). The study by Rao et al (62) also showed a decrease in the perforation rate in children who underwent CT compared with those who did not (15% vs 23%). Another study by Garcia-Pena et al (46) showed that the use of CT in children with suspected appendicitis who are candidates for inpatient observation reduces the number of days of inpatient diagnostic evaluation prior to surgery and the cost of care per patient.
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Alternative Diagnoses in Children with Suspected Acute Appendicitis
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Most children referred for US or CT evaluation of suspected acute appendicitis will not have the condition. In a study of 178 patients, Siegel et al (63) found that only 22% of children referred for US for suspected acute appendicitis actually had appendicitis; 29% had other specific diagnoses, usually gastrointestinal and gynecologic abnormalities (Fig 23). US aided in the diagnosis of other conditions in approximately 60% of these patients (63). Sivit et al (8) found appendicitis in 29% of 180 patients referred for US because of suspected acute appendicitis. Alternative diagnoses were established at US in 25% of patients in that series who did not have appendicitis (8). Therefore, a survey of the pelvis and upper abdomen should be performed in patients who have normal results from US examination of the right lower quadrant. This is also a relevant issue for CT evaluation, since controversy exists on whether to perform a focused or targeted CT examination of the right lower quadrant and pelvis to assess only for appendicitis versus complete abdominopelvic scanning. Sivit et al (47) found appendicitis in 38% of patients referred for CT because of suspected acute appendicitis. In 37% of patients with a true-negative diagnosis for appendicitis at CT, an alternative diagnosis was established on the basis of CT findings (47).
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Figure 23a. Ureteral calculi. (a) Axial CT scan obtained through the upper abdomen following the intravenous and rectal administration of contrast material in a child with acute right lower quadrant pain demonstrates dilatation of the right intrarenal collecting system. Also note decreased right renal parenchymal enhancement. (b) Axial CT scan obtained through the pelvis shows a calculi in the right distal ureter.
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Figure 23b. Ureteral calculi. (a) Axial CT scan obtained through the upper abdomen following the intravenous and rectal administration of contrast material in a child with acute right lower quadrant pain demonstrates dilatation of the right intrarenal collecting system. Also note decreased right renal parenchymal enhancement. (b) Axial CT scan obtained through the pelvis shows a calculi in the right distal ureter.
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Summary
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Both graded-compression US and helical CT have been shown to have potential utility in the evaluation of suspected acute appendicitis in children. The principal advantages of US are its lower cost; lack of ionizing radiation; and its ability to assess vascularity through color Doppler analysis, provide dynamic information through graded-compression, and delineate gynecologic disease which is a common mimic of acute appendicitis. The principal advantages of CT include less operator dependency than US, as reflected by a higher diagnostic accuracy in most published studies, and enhanced delineation of disease extent in perforated appendicitis. CT is particularly valuable in obese patients, since they are typically difficult to evaluate with US.
A few studies have shown improved patient outcome measures in children with acute appendicitis (45,62). It should be noted, however, that these studies which demonstrated improved outcomes in children with this condition undergoing cross-sectional imaging have used imaging protocols developed by multidisciplinary teams of emergency physicians, surgeons, and radiologists (45,62). Such protocols go beyond technology assessment and precisely define which patients undergo a specific diagnostic test. More work is needed to better define how cross-sectional imaging affects the cost of care, negative appendectomy rates, appendiceal perforation, and complication rates. This information is critical to reduce health care costs and improve patient outcomes.
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References
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Pieper R, Kager L
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Abstract
LEARNING OBJECTIVES FOR TEST...
