DOI: 10.1148/rg.282075039
RadioGraphics 2008;28:393-405
© RSNA, 2008
Added Diagnostic Value of Multiplanar Reformation of Multidetector CT Data in Patients with Suspected Appendicitis1
Hyun Cheol Kim, MD,
Dal Mo Yang, MD,
Wook Jin, MD, and
Seong Jin Park, MD
1 From the Department of Radiology, East-West Neo Medical Center, Kyung-Hee University, 149 Sangil-dong, Gangdong-gu, Seoul 134-727, South Korea (H.C.K., D.M.Y., W.J.); and Department of Diagnostic Radiology, Soonchunhyang University, Bucheon Hospital, Bucheon, Gyeonggi, South Korea (S.J.P.). Presented as an education exhibit at the 2006 RSNA Annual Meeting. Received March 6, 2007; revision requested June 15 and received July 10; accepted July 20. All authors have no financial relationships to disclose.
Address correspondence to H.C.K. (e-mail: khcppp{at}lycos.co.kr).
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Abstract
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Computed tomography (CT) is an accurate and effective modality for the diagnosis and staging of appendicitis. CT provides rapid and complete evaluation of patients with suspected appendicitis and clearly demonstrates the typical findings of appendicitis, including a distended appendix, periappendiceal fat stranding, an appendicolith, and focal thickening of the cecum. Identification of an inflamed appendix at CT may be difficult in certain patients (eg, patients with scanty intraabdominal fat, an unusual location of the cecum and appendix, prominent cecal wall thickening and pericecal fat stranding, small bowel dilatation, or abscess formation adjacent to the right adnexa). In such cases, multiplanar reformation (MPR) of multidetector CT data may provide improved appendiceal visualization and increase the physician’s confidence in diagnosing appendicitis. Moreover, the use of MPR in addition to conventional CT may provide improved visualization of the normal appendix and thereby enhance confidence in excluding appendicitis and diagnosing diseases that mimic appendicitis. Consequently, the radiologist should obtain MPR images in the evaluation of patients with suspected appendicitis to help ensure the correct diagnosis.
© RSNA, 2008
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Introduction
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Computed tomography (CT) has proved capable of rapidly and effectively revealing the presence of appendicitis in patients in whom this condition is clinically suspected (1). The definitive diagnostic criterion for acute appendicitis is visualization of an inflamed appendix at CT (2). With use of a modern multidetector CT scanner, multiplanar reformatted (MPR) images in any desired plane will have a spatial resolution similar to that of the axial images. 
In patients with suspected appendicitis, MPR images can serve as a useful adjunct to the axial images for detecting an inflamed appendix, especially in patients in whom the diagnosis may be difficult to make with conventional CT alone (3). In patients with conditions that mimic appendicitis, MPR images can provide improved visualization of the normal appendix and increase the physician’s confidence in ruling out acute appendicitis (4). MPR images might also be particularly helpful for clinicians who are less experienced in evaluating CT scans in that they are analogous to conventional abdominal radiographs (5). In this article, we review CT technique in patients with suspected appendicitis. In addition, we discuss and illustrate various appearances of the normal appendix and the typical features of appendicitis. We also discuss some of the factors that cause difficulty in diagnosing appendicitis at conventional CT (scanty intraabdominal fat, unusual location of the cecum and appendix, prominent cecal wall thickening and pericecal fat stranding, small bowel dilatation, abscess formation adjacent to the right adnexa, diseases that mimic appendicitis) and the role of MPR in overcoming these difficulties.
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CT Technique
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The optimal CT technique in patients with suspected appendicitis remains controversial. A variety of methods have been advocated (6,7), the most commonly used of which continues to be CT with oral and intravenous administration of contrast material (6). CT with intravenous contrast material has been shown to aid in subtle cases and in patients with scanty mesenteric fat by showing enhancement of the appendiceal wall (2,6). It can also be helpful in the diagnosis and assessment of numerous inflammatory and ischemic conditions, as well as of a neoplasm that may be causing acute abdominal pain and simulating appendicitis. Oral contrast material has been used to enhance the terminal ileum and cecum and to avoid false-positive results caused by the misdiagnosis of a fluid-filled terminal ileum as a distended appendix (2). Enhancement of the appendix has served to exclude appendicitis (2). In some cases, however, the appendix may partially fill proximal to the area of appendiceal obstruction, leading to a false-negative interpretation (8). In addition, nonfilling of the appendix should not be interpreted as an abnormal finding; up to 76% of normal appendixes do not fill with oral contrast material (9). Furthermore, oral contrast material administration delays the CT examination by 1–2 hours or more, taking longer in patients with abdominal pain who are nauseous and cannot tolerate the contrast agent. Therefore, some authors have recently suggested that elimination or selective use of oral contrast material may be suitable for the rapid diagnosis of patients in a busy emergency department setting (6,10, 11). Our institution also performs CT without oral contrast material due to the emergency nature of suspected appendicitis.
At our institution, CT was performed on an eight-channel (LightSpeed Ultra; GE Medical Systems, Milwaukee, Wis) or 16-channel (Brilliance 16; Philips Medical Systems, Best, the Netherlands) multidetector CT scanner. Post-contrast scanning was performed 70 seconds after the start of infusion of 120 mL of nonionic contrast material (Iomeprol; Bracco, Milano, Italy) through the antecubital vein at a rate of 3 mL/sec. With the LightSpeed Ultra CT scanner, the technical parameters were as follows: collimation of 1.25 or 2.5 mm, table speed of 33.5 or 16.75 mm per rotation, pitch of 1.675, rotation time of 0.8 seconds, 120 kVp, and 200 mAs. The axial section data were reconstructed twice: first with a 5-mm thickness at 5-mm intervals, and then with a 1.25-mm thickness at 1.25-mm intervals or a 2.5-mm thickness at 2.5-mm intervals. With the Brilliance 16 CT scanner, the technical parameters were as follows: collimation of 1.5 mm, table speed of 22.51 mm per rotation, pitch of 0.938, rotation time of 0.75 seconds, 120 kVp, and 200 mAs. The axial section data were reconstructed with a 5-mm thickness at 5-mm intervals and with a 2-mm thickness at 1-mm intervals. The thin-section reconstructed images were then transferred to a satellite workstation (AW 4.1 on HP x 4000, GE Medical Systems; Extended Brilliance Workspace: Philips Medical Systems, Haifa, Israel) and were processed in the coronal, sagittal, and oblique planes. MPR images of the appendix were interactively created with special consideration given to the anatomic relationship between the cecum and the ileocecal valve. Most of the reformatted images that were created along the tortuous course of the appendix were in the coronal oblique or sagittal oblique plane.
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Various Appearances of the Normal Appendix
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The appendix arises from the posteromedial aspect of the cecum, approximately 3 cm below the ileocecal valve (12). The relationship of the base of the appendix to the cecum is constant, but the free end of the appendix is mobile, which accounts for its variable location in the abdominopelvic cavity. Relative to the cecum, the appendix is most commonly either retrocecal (about two-thirds of patients) or inferomedial (about one-third of patients) (13). The appendix can have a retroileal or preileal location or extend to the pelvis (13,14). The tip of the appendix sometimes extends into the subhepatic space (Fig 1). In some cases, a bowel obstruction can distort the anatomy and lead to difficulty in visualizing the appendix (Fig 2). The lumen of the normal appendix is totally collapsed or partially filled with fluid or air. The maximum diameter of the normal appendix is highly variable, ranging from 3 to 11 mm in published reports (4,9). Although a threshold diameter of 6 mm is important for diagnosing appendicitis (2,7), a high percentage (24%–42%) of the population has an appendiceal diameter greater than 6 mm (4,9). Therefore, in the absence of any other CT signs of appendicitis, a threshold diameter of 6 mm is not a reliable indicator. The normal appendiceal wall measures less than 1–2 mm in thickness.
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Figure 1. Subhepatic location of a normal appendix. Coronal oblique reformatted image clearly shows the entire length of a normal appendix (arrows), which in this case arises from the cecum and extends into the subhepatic space.
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Figure 2a. Appendiceal displacement due to bowel obstruction in a 57-year-old woman with ascending colon cancer. (a) CT scan shows a subtle tubular structure (arrows) that is suspected of being the appendix in the context of bowel dilatation. (b) Coronal oblique reformatted image clearly shows a normal appendix (solid arrows) arising from the cecum. The appendix is slightly deviated toward the left side due to bowel obstruction. Note the focal wall thickening with enhancement (open arrow), which represents a portion of the ascending colon cancer.
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Figure 2b. Appendiceal displacement due to bowel obstruction in a 57-year-old woman with ascending colon cancer. (a) CT scan shows a subtle tubular structure (arrows) that is suspected of being the appendix in the context of bowel dilatation. (b) Coronal oblique reformatted image clearly shows a normal appendix (solid arrows) arising from the cecum. The appendix is slightly deviated toward the left side due to bowel obstruction. Note the focal wall thickening with enhancement (open arrow), which represents a portion of the ascending colon cancer.
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A normal appendix is identified in 82% of patients who undergo thin-section CT of the right lower quadrant (9). However, because the appendix usually has a curved and tortuous course, axial images alone are of limited value in tracing its course. MPR images from multidetector CT data demonstrate an even higher visualization rate (93%) of the normal appendix than do axial images, thereby increasing the physician’s confidence that the finding in question is indeed the appendix (4). Visualization of the normal appendix at axial CT largely depends on the location of the appendix, the amount of periappendiceal or mesenteric fat, and the presence of small bowel dilatation. MPR images can facilitate the search for the appendix in spite of an unusual location, a paucity of intraabdominal fat, and small bowel dilatation (Fig 3).
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Figure 3a. Nonvisualization of a normal appendix. (a, b) CT scans do not show the normal appendix due to relatively scanty intraabdominal fat, dilatation of a small bowel loop, downward displacement of the ileocecal valve (arrowheads in a) and terminal ileum (arrows in a), and a distended cecum (* in b). (c) Coronal oblique reformatted image clearly shows the entire length of the normal appendix (arrows), which arises from the lower-lying cecum (*). Note the indistinct appendiceal tip, which blends with the adjacent right ovarian vein (arrowheads). Adjacent images were needed for conclusive identification.
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Figure 3b. Nonvisualization of a normal appendix. (a, b) CT scans do not show the normal appendix due to relatively scanty intraabdominal fat, dilatation of a small bowel loop, downward displacement of the ileocecal valve (arrowheads in a) and terminal ileum (arrows in a), and a distended cecum (* in b). (c) Coronal oblique reformatted image clearly shows the entire length of the normal appendix (arrows), which arises from the lower-lying cecum (*). Note the indistinct appendiceal tip, which blends with the adjacent right ovarian vein (arrowheads). Adjacent images were needed for conclusive identification.
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Figure 3c. Nonvisualization of a normal appendix. (a, b) CT scans do not show the normal appendix due to relatively scanty intraabdominal fat, dilatation of a small bowel loop, downward displacement of the ileocecal valve (arrowheads in a) and terminal ileum (arrows in a), and a distended cecum (* in b). (c) Coronal oblique reformatted image clearly shows the entire length of the normal appendix (arrows), which arises from the lower-lying cecum (*). Note the indistinct appendiceal tip, which blends with the adjacent right ovarian vein (arrowheads). Adjacent images were needed for conclusive identification.
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Typical CT Features of Appendicitis
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As stated earlier, a definitive CT diagnosis of acute appendicitis can be made when an inflamed appendix is identified (2). In mild cases, an inflamed appendix appears as a slightly distended, fluid-filled tubular structure, usually measuring 6–7 mm in diameter. In most patients, acute appendicitis manifests at CT as enlargement of the appendix (diameter >7 mm); a thickened wall with enhancement; periappendiceal fat stranding, sometimes with an appendicolith; and, in some cases, focal thickening of the terminal ileum or cecum (Fig 4) (2). Distal appendicitis is diagnosed when CT reveals appendicitis involving the distal aspect of the appendix with a normal appearance of the proximal appendix (8). An obstructing appendicolith is often detected at the transition point between the collapsed proximal appendix and the inflamed distal appendix (Fig 5). The normal appearance of the proximal appendix may lead to a missed diagnosis of distal appendicitis at axial CT alone. MPR images can allow more confident identification of an inflamed distal appendix by facilitating the tracing of the entire course of the appendix.
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Figure 4. Typical appendicitis in a 37-year-old woman. Coronal oblique reformatted image shows the full length of a distended appendix (solid arrows), appendiceal wall thickening with enhancement, periappendiceal fat stranding, and thickening of the cecal base (open arrow), findings that indicate appendicitis.
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Figure 5. Distal appendicitis with an appendicolith in a 22-year-old man. Coronal oblique reformatted image clearly shows the entire length of the appendix, with an obstructing appendicolith (open arrow) between the collapsed proximal portion (arrowheads) and the inflamed distal portion (solid arrows).
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A focal defect in an enhancing appendiceal wall, a periappendiceal fluid collection, a pericecal phlegmon, an extraluminal appendicolith, or air near the appendix indicates perforated appendicitis (15). Although axial CT scans demonstrate these findings, MPR images depict them even more clearly and provide a quick anatomic overview of perforated appendicitis (Fig 6). A pericecal phlegmon or abscess is strongly suggestive of perforated appendicitis. However, these findings are nonspecific and may be seen with other disease entities involving the cecum and terminal ileum. In cases in which a pericecal phlegmon or abscess is observed, MPR images may demonstrate an inflamed appendix that is not seen on axial CT scans because it courses primarily in a coronal plane (Fig 7). Multidetector CT can be used to accurately stage the extent of periappendiceal inflammation and to help diagnose complications of periappendiceal abscess such as hydronephrosis (Fig 8).
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Figure 6. Perforated appendicitis in a 47-year-old woman. Coronal oblique reformatted image clearly shows a distended appendix (solid arrows), an appendicolith (open arrow), and a focal defect (arrowhead) of the enhancing appendiceal wall, thereby providing a quick anatomic overview of perforated appendicitis.
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Figure 7a. Perforated appendicitis with periappendiceal abscess formation in an 85-year-old man. (a, b) CT scans do not show an inflamed appendix. However, severe pericecal fat stranding (arrowheads in a) with adjacent abscess formation (arrows) suggest the diagnosis of perforated appendicitis. (c) Coronal oblique reformatted image shows a tubular area of increased enhancement (solid arrows) surrounded by the abscess (open arrows) and representing an inflamed appendix. These findings give the physician more confidence in making the diagnosis of appendicitis.
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Figure 7b. Perforated appendicitis with periappendiceal abscess formation in an 85-year-old man. (a, b) CT scans do not show an inflamed appendix. However, severe pericecal fat stranding (arrowheads in a) with adjacent abscess formation (arrows) suggest the diagnosis of perforated appendicitis. (c) Coronal oblique reformatted image shows a tubular area of increased enhancement (solid arrows) surrounded by the abscess (open arrows) and representing an inflamed appendix. These findings give the physician more confidence in making the diagnosis of appendicitis.
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Figure 7c. Perforated appendicitis with periappendiceal abscess formation in an 85-year-old man. (a, b) CT scans do not show an inflamed appendix. However, severe pericecal fat stranding (arrowheads in a) with adjacent abscess formation (arrows) suggest the diagnosis of perforated appendicitis. (c) Coronal oblique reformatted image shows a tubular area of increased enhancement (solid arrows) surrounded by the abscess (open arrows) and representing an inflamed appendix. These findings give the physician more confidence in making the diagnosis of appendicitis.
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Figure 8a. Perforated appendicitis complicated by hydronephrosis in a 28-year-old man. Coronal oblique reformatted images clearly show an inflamed appendix (white arrows in a), as well as a periappendiceal abscess (black arrows) and hydroureter (arrowheads in b) and the relationship between the two.
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Figure 8b. Perforated appendicitis complicated by hydronephrosis in a 28-year-old man. Coronal oblique reformatted images clearly show an inflamed appendix (white arrows in a), as well as a periappendiceal abscess (black arrows) and hydroureter (arrowheads in b) and the relationship between the two.
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Although axial scans are sensitive and specific for the diagnosis and staging of appendicitis, MPR images can be particularly helpful for clinicians with less experience in evaluating CT scans by providing a brief anatomic overview of the relationship between the inflamed appendix and the surrounding structures.
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Factors That Complicate the CT Diagnosis of Appendicitis
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Scanty Intraabdominal Fat
The most common reason for a false-negative diagnosis of appendicitis at CT is related to scanty intraabdominal fat (16). More specifically, the amount of fat surrounding the cecum influences the ability to visualize the inflamed appendix (17,18). The intraabdominal fat serves as a natural contrast agent, allowing inflammatory changes in the pericecal and periappendiceal areas to be detected easily. Thus, it is difficult to areas to be detected easily. Thus, it is difficult to detect an inflamed appendix on axial CT scans obtained in slender patients with appendicitis, especially young women with little intraabdominal fat, and the diagnosis is sometimes missed. MPR images may provide improved appendiceal visualization and increase the physician’s confidence in making the diagnosis of or excluding acute appendicitis (Fig 9).
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Figure 9a. Acute appendicitis in a 15-year-old girl. (a) CT scan shows a suspect inflamed appendix (arrow), which is hard to distinguish from adjacent collapsed bowel due to scanty intraabdominal fat. (b) Coronal oblique reformatted image clearly shows the full length of an inflamed appendix (arrows), which originates from the cecum.
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Figure 9b. Acute appendicitis in a 15-year-old girl. (a) CT scan shows a suspect inflamed appendix (arrow), which is hard to distinguish from adjacent collapsed bowel due to scanty intraabdominal fat. (b) Coronal oblique reformatted image clearly shows the full length of an inflamed appendix (arrows), which originates from the cecum.
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Unusual Location of Cecum and Appendix
The cecum is a highly mobile structure whose position can vary due to variations in the posterior peritoneal attachment. The cecum may occasionally be seen in the subhepatic area, the midline of the abdomen, or even within the pelvic cavity. In such instances, identification of the appendix arising from the cecum can be difficult on axial CT scans, and a false-negative diagnosis of appendicitis may occur (19). Misdiagnosis can be avoided if the physician is familiar with searching for the ileocecal valve during CT interpretation, which helps define the contour of the cecum and consequently facilitates the search for the appendiceal base. MPR images, especially coronal images, more easily demonstrate the anatomic configurations of the entire ileocecal valve, cecum, and appendiceal base, all of which are quite helpful in making the correct diagnosis of appendicitis (Fig 10) (4).
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Figure 10a. Acute appendicitis in a 53-year-old woman. (a) CT scan shows an enhancing tubular structure with wall thickening (arrows), with adjacent fat stranding in the right midabdomen. Although the lesion is suggestive of an inflamed appendix, the relationship between the cecum and the appendix is unclear at axial CT alone. (b) Coronal oblique reformatted image clearly shows an inflamed appendix (solid arrows) originating from the high-positioned cecum (open arrows).
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Figure 10b. Acute appendicitis in a 53-year-old woman. (a) CT scan shows an enhancing tubular structure with wall thickening (arrows), with adjacent fat stranding in the right midabdomen. Although the lesion is suggestive of an inflamed appendix, the relationship between the cecum and the appendix is unclear at axial CT alone. (b) Coronal oblique reformatted image clearly shows an inflamed appendix (solid arrows) originating from the high-positioned cecum (open arrows).
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In adults, the appendix is a long diverticulum with a variable length (5–35 cm). Although the base of the appendix originating from the cecum is relatively constant, the remainder of the appendix has wide individual variability (2). The use of axial CT alone is particularly limited in tracing the course of a retrocecal appendix or an appendix extending to the pelvis (3), since these appendixes course mainly in a coronal plane. Therefore, coronal or coronal oblique MPR images help greatly in tracing and demonstrating an inflamed appendix (Fig 11). Sagittal or sagittal oblique MPR images are also helpful in some cases of retrocecal appendicitis.
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Figure 11a. Acute appendicitis in a 41-year-old woman. (a) CT scan does not show an inflamed appendix. (b) Coronal oblique reformatted image clearly shows an inflamed appendix (arrows) located in the pelvic cavity and extending into the left side.
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Figure 11b. Acute appendicitis in a 41-year-old woman. (a) CT scan does not show an inflamed appendix. (b) Coronal oblique reformatted image clearly shows an inflamed appendix (arrows) located in the pelvic cavity and extending into the left side.
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Patients with intestinal malrotation are not only at increased risk for volvulus or intestinal obstruction, but may also have atypical clinical symptoms of relatively common intestinal disorders due to altered anatomy (20). An atypical manifestation of appendicitis associated with intestinal malrotation may be misleading, thereby delaying therapeutic management. Although axial CT demonstrates this unusual location of appendicitis and the associated rotational anomaly of the intestine, MPR images may be more helpful in making the diagnosis (Fig 12).
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Figure 12a. Perforated appendicitis with periappendiceal abscess formation in a 33-year-old man who presented with periumbilical pain. (a) CT scan shows a left-sided ileocecal valve and the terminal ileum (arrowheads). (b) CT scan obtained at a lower level shows abscess formation (arrows) in the midline lower abdomen. (c) Coronal oblique reformatted image clearly shows an inflamed appendix (solid arrow) originating from the cecum in the context of nonrotation anomaly, as well as the periappendiceal abscess (open arrows).
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Figure 12b. Perforated appendicitis with periappendiceal abscess formation in a 33-year-old man who presented with periumbilical pain. (a) CT scan shows a left-sided ileocecal valve and the terminal ileum (arrowheads). (b) CT scan obtained at a lower level shows abscess formation (arrows) in the midline lower abdomen. (c) Coronal oblique reformatted image clearly shows an inflamed appendix (solid arrow) originating from the cecum in the context of nonrotation anomaly, as well as the periappendiceal abscess (open arrows).
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Figure 12c. Perforated appendicitis with periappendiceal abscess formation in a 33-year-old man who presented with periumbilical pain. (a) CT scan shows a left-sided ileocecal valve and the terminal ileum (arrowheads). (b) CT scan obtained at a lower level shows abscess formation (arrows) in the midline lower abdomen. (c) Coronal oblique reformatted image clearly shows an inflamed appendix (solid arrow) originating from the cecum in the context of nonrotation anomaly, as well as the periappendiceal abscess (open arrows).
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Prominent Cecal Wall Thickening and Pericecal Fat Stranding
In some patients with appendicitis, appendiceal wall inflammation can spread contiguously into the cecum. Pericecal fat stranding is a sensitive finding of appendicitis (21). Cecal wall thickening and pericecal fat stranding without definite visualization of an inflamed appendix are suggestive of but not diagnostic for acute appendicitis because many other conditions, including cecal diverticulitis, perforated cecal tumor, nonspecific cecal inflammation, and Crohn disease, may demonstrate these findings (22). In particular, perforated appendicitis without abscess formation may not be seen as an inflamed appendix at CT due to the collapsed appendix being obscured by cecal wall thickening and pericecal inflammatory changes (23). In such cases, MPR images may help demonstrate the suspect appendiceal course and some fragments of the inflamed appendix by facilitating localization of the ileocecal valve and identification of the expected location of the appendiceal orifice (Fig 13).
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Figure 13a. Perforated appendicitis in a 15-year-old boy. (a, b) CT scans show thickening of the cecal wall (arrows in a) but do not depict the appendix. Note the appendicolith (arrowhead in b), a finding that is suggestive of appendicitis. (c) Sagittal oblique reformatted image clearly shows an inflamed appendix (solid arrows) arising from the cecum (open arrows), the appendicolith (white arrowhead), and a surrounding fluid collection (black arrowheads).
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Figure 13b. Perforated appendicitis in a 15-year-old boy. (a, b) CT scans show thickening of the cecal wall (arrows in a) but do not depict the appendix. Note the appendicolith (arrowhead in b), a finding that is suggestive of appendicitis. (c) Sagittal oblique reformatted image clearly shows an inflamed appendix (solid arrows) arising from the cecum (open arrows), the appendicolith (white arrowhead), and a surrounding fluid collection (black arrowheads).
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Figure 13c. Perforated appendicitis in a 15-year-old boy. (a, b) CT scans show thickening of the cecal wall (arrows in a) but do not depict the appendix. Note the appendicolith (arrowhead in b), a finding that is suggestive of appendicitis. (c) Sagittal oblique reformatted image clearly shows an inflamed appendix (solid arrows) arising from the cecum (open arrows), the appendicolith (white arrowhead), and a surrounding fluid collection (black arrowheads).
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Small Bowel Dilatation
Appendicitis with its secondary inflammatory changes may result in reactive dilatation of small bowel loops in the right lower quadrant (16). A dilated fluid- or air-filled small bowel may encroach on the pericecal or periappendiceal fat, making visualization of the appendix more difficult. In addition, a distended appendix can occasionally be confused with or obscured by a fluid-filled small bowel loop (16). In such cases, MPR images clearly demonstrate a distended appendix arising from the cecum (Fig 14).
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Figure 14a. Perforated appendicitis with small bowel dilatation in a 58-year-old man. (a) CT scan shows a suspect distended appendix (arrow) that may be obscured by a dilated, fluid-filled small bowel. (b) Coronal oblique reformatted image clearly shows a distended inflamed appendix (solid arrows) arising from the cecum (open arrows).
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Figure 14b. Perforated appendicitis with small bowel dilatation in a 58-year-old man. (a) CT scan shows a suspect distended appendix (arrow) that may be obscured by a dilated, fluid-filled small bowel. (b) Coronal oblique reformatted image clearly shows a distended inflamed appendix (solid arrows) arising from the cecum (open arrows).
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Abscess Formation Adjacent to the Right Adnexa
Abscess formation may occur after appendiceal perforation, often at some distance from the appendix and sometimes in association with a collapsed or fragmented appendix. If the abscess formation results from perforation of the appendiceal tip proximal to the right ovary, it may mimic a tubo-ovarian abscess, especially in young women. Identification of an inflamed appendix in conjunction with an abscess and delineation of the anatomic relationship between the right ovary and the appendix may be achieved more easily with MPR images than with axial images (Fig 15).
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Figure 15a. Perforated appendicitis with abscess formation adjacent to the right adnexa in a 54-year-old woman. (a, b) CT scans show an abscess (arrows) adjacent to the uterus (* in b) and a suspect right adnexa (arrowheads in b). An inflamed appendix is not identified. These findings suggest that the abscess originated from the right adnexa. Note the associated thickening of the rectal and sigmoid colon walls. (c) Coronal oblique reformatted image clearly shows an inflamed appendix (solid arrows) surrounded by the abscess (open arrows).
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Figure 15b. Perforated appendicitis with abscess formation adjacent to the right adnexa in a 54-year-old woman. (a, b) CT scans show an abscess (arrows) adjacent to the uterus (* in b) and a suspect right adnexa (arrowheads in b). An inflamed appendix is not identified. These findings suggest that the abscess originated from the right adnexa. Note the associated thickening of the rectal and sigmoid colon walls. (c) Coronal oblique reformatted image clearly shows an inflamed appendix (solid arrows) surrounded by the abscess (open arrows).
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Figure 15c. Perforated appendicitis with abscess formation adjacent to the right adnexa in a 54-year-old woman. (a, b) CT scans show an abscess (arrows) adjacent to the uterus (* in b) and a suspect right adnexa (arrowheads in b). An inflamed appendix is not identified. These findings suggest that the abscess originated from the right adnexa. Note the associated thickening of the rectal and sigmoid colon walls. (c) Coronal oblique reformatted image clearly shows an inflamed appendix (solid arrows) surrounded by the abscess (open arrows).
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Diseases That Mimic Appendicitis
Patients with right lower quadrant pain who are referred for CT owing to a clinical diagnosis of appendicitis may in fact have some other condition that mimics appendicitis (24). A wide variety of disease entities may mimic appendicitis, including mesenteric adenitis, infectious ileocolitis, cecal diverticulitis, Crohn disease, tuberculous enterocolitis, right colonic neoplasia, pelvic inflammatory disease, torsion caused by an ovarian cystic lesion (Fig 16), ectopic pregnancy, and urolithiasis (25). The nonspecific signs seen with appendicitis, such as pericecal fat stranding, adjacent bowel wall thickening, and fluid collection, also occur in these conditions. Identification of the normal appendix is very important for excluding appendicitis (3). Multidetector CT can help definitely confirm or exclude appendicitis and can help detect alternative pathologic conditions that may cause right lower quadrant pain. In particular, MPR images may provide improved visualization of the normal appendix and enhance the physician’s confidence in excluding appendicitis. Furthermore, MPR images may often help clarify the confusing anatomy of the ileocolic area and the female pelvis at axial CT, thereby increasing confidence in diagnosing those diseases that mimic appendicitis.
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Figure 16a. Torsion from right ovarian teratoma in a 66-year-old woman who presented with right lower quadrant pain. (a, b) Axial CT scan (a) and axial oblique reformatted image (b) show a huge cystic mass (arrows) containing fat and calcification. Note the tortuous, thickened right fallopian tube (arrowheads), which is suspected of connecting with the ipsilateral side of a deviated uterus (* in b). (c) Coronal oblique reformatted image clearly shows an air-filled normal appendix (solid arrows) arising from the cecum, which is medially and inferiorly indented by the cystic mass (open arrows). Torsion from ovarian teratoma was confirmed surgically.
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Figure 16b. Torsion from right ovarian teratoma in a 66-year-old woman who presented with right lower quadrant pain. (a, b) Axial CT scan (a) and axial oblique reformatted image (b) show a huge cystic mass (arrows) containing fat and calcification. Note the tortuous, thickened right fallopian tube (arrowheads), which is suspected of connecting with the ipsilateral side of a deviated uterus (* in b). (c) Coronal oblique reformatted image clearly shows an air-filled normal appendix (solid arrows) arising from the cecum, which is medially and inferiorly indented by the cystic mass (open arrows). Torsion from ovarian teratoma was confirmed surgically.
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Figure 16c. Torsion from right ovarian teratoma in a 66-year-old woman who presented with right lower quadrant pain. (a, b) Axial CT scan (a) and axial oblique reformatted image (b) show a huge cystic mass (arrows) containing fat and calcification. Note the tortuous, thickened right fallopian tube (arrowheads), which is suspected of connecting with the ipsilateral side of a deviated uterus (* in b). (c) Coronal oblique reformatted image clearly shows an air-filled normal appendix (solid arrows) arising from the cecum, which is medially and inferiorly indented by the cystic mass (open arrows). Torsion from ovarian teratoma was confirmed surgically.
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Conclusions
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The introduction of multidetector CT has transformed an axial imaging modality into a volumetric one and allows the radiologist to display a finding in any desired plane. The creation of MPR images increases confidence in identifying the appendix and in diagnosing or excluding acute appendicitis. Some of the factors that cause difficulty in the diagnosis of appendicitis at axial CT can be overcome with MPR. In addition, a coronal MPR image can help clinicians and radiologists, since it is analogous to a conventional abdominal radiograph. Understanding the underlying factors that complicate the CT diagnosis of appendicitis and the appropriate use of MPR can further improve diagnostic accuracy in this setting.
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Footnotes
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Abbreviations: MPR = multiplanar reformation
See the commentary by Rhea following this article.
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References
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Abstract
Introduction
