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Fig. 1.59a-g. Several different evolutive patterns of appendicitis with the lumen collapsed: axial US scans, diagrams, and histologic specimen. Early appendicitis. Axial US (a) and diagram (b) showing a "three-rings" pattern. The three hyperechoic rings represent the mucosal surface, the thickened submucosa, and the serosa layers. The transmural inflammation stresses the stratification of the appendix. The relative mucosal predominance of the normal appendix changes to a submucosal predominance. Advanced appendicitis. Axial US (c) and diagram (d) showing a "two-rings" pattern. Notice the preserved submucosa and serosa, and the associated prominent periappendicular fat. The central ring or "spot", that represents the mucosal surface, cannot be identified. Axial US (e) and diagram (f) showing a "one-ring" pattern corresponding to the serosa (arrows). Note the presence of thickened omentum (O) and the intraperitoneal echogenic free fluid as purulent peritonitis (A). The appendix appears homogeneously hypoechoic due to the loss of submucosal hyperechogenicity. d The specimen corroborates US findings show-g ing not only a dilated but also collapsed appendix in appendicitis tive mucosal to a submucosal predominance. In this early stage the appendix may be found with the lumen collapsed appearing as a target or a three-ring pattern (Fig. 1.59a,b), or with the lumen dilated and some grade of wall thinning, which would lead to a thin-rings pattern on axial US scan (Fig. 1.56). In this last appearance, the layers are expanded by a usually hypoechoic purulent content. In a more advanced stage the appendiceal diameter increases and the central ring or "spot" corresponding to the mucosal surface cannot be identified, making it difficult to evaluate whether the hypoechoic center corresponds to the inflamed mucosa or to the intraluminal content. The serosa and submu-cosa are preserved giving rise a two-rings pattern (dei Pozo et al. 1994) (Fig. 1.59c,d). Finally, necrosis and suppuration lead to the loss of the submu-cosa hyperechogenicity, and the appendix tends to appear homogeneously hypoechoic surrounded by the serosa: one-ring pattern (Figs. 1.59e-g and 1.60) (Borushok et al. 1990; Vignault et al. 1990). The accurate identification of the different appendiceal layers demands a careful technique examination and the use of an appropriate transducer. Otherwise, we can easily mistake thin rings for a one-ring pattern, misinterpreting as a higher grade of involvement than really exists. Because of fluid content, the structure should have posterior enhancement, but its identification is often impaired due to the small appendiceal size and the particular echogenic quality of the surrounding structures.

All patterns may coexist in the same appendix. Furthermore, one of the appendiceal ends may remain normal while the opposite is inflamed, so it is very important to image the full appendix (Nghiem and Jeffrey 1992). An appendicolith may also be identified coexisting with each pattern, even in normal appendices. Appendicoliths appear as bright, echogenic foci with clean distal acoustic shadowing. Their identification within the appendix or in the adjacent perienteric soft tissue after perforation is highly associated with a positive diagnosis. Failure to see an appendicolith, in contrast, is noncontributory (BirNbaum and Wiison 2000) (Fig. 1.56).

A significant number of appendicitis may have an atypical location, producing a long-standing process and, less frequently, involving other organs. If the appendix cannot be identified in the RLQ, the entire abdomen should be systematically examined, because it may locate retrocecally (20%-25% of cases) or pelvic (7.9% of cases) (Coiiins 1932). Lateral approach through the flank may facilitate the US identification of retrocecal appendix, which lies posterolaterally to the cecum and would be hidden by the cecal air (Ceres et al. 1990).

Loss of visualization of submucosa layer, prominent periappendicular fat and periappendicular fluid (loculated fluid collection) have been related to a higher rate of perforation (Borushok et al. 1990) (Fig. 1.61). Perforation is more frequent in infants and small children and, at these ages, it is often free. The pneumoperitoneum secondary to an appendi-ceal perforation is extremely rare. Echogenic ascites implies purulent peritonitis in a free perforation, being the most important finding. A perforated

Fig. 1.60. Several patterns of appendicitis in the same appendix. Longitudinal US scan, from the right lower quadrant to the subhepatic region summarizes all the different appearances of appendicitis, showing at the base (arrows) the five conspicuous appendiceal layers with the patent mucosal surface and the prominent submucosa layer. These layers begin disappearing from the appendiceal base to the tip. Notice the associated thickened omentum encircling the appendix and trying to prevent the dissemination of the process. Also note the irregularity at the tip contour due to discrete inflammatory collection in the appendicular periphery (arrowhead). L, liver

Fig. 1.61a-d. Perforated appendicitis: phlegmon and abscess. a,b Phlegmon. Inflammatory mass composed of a complex fluid collection (C), prominent mesenteric fat (M), and adjacent thickened poorly defined intestinal bowel loops (B) just close to the appendiceal remnants (arrows). c,d Abscesses. Distant multiple abscesses in the pouch of Douglas and in the subhepatic region. A, abscess

Fig. 1.61a-d. Perforated appendicitis: phlegmon and abscess. a,b Phlegmon. Inflammatory mass composed of a complex fluid collection (C), prominent mesenteric fat (M), and adjacent thickened poorly defined intestinal bowel loops (B) just close to the appendiceal remnants (arrows). c,d Abscesses. Distant multiple abscesses in the pouch of Douglas and in the subhepatic region. A, abscess appendix is difficult to identify, as it tends to be collapsed, partially destroyed, and generally hidden behind the dilated loops. Generalized peritonitis can produce distant abscesses (Fig. 1.61c,d).

Appendicitis may resolve spontaneously either in noncomplicated or perforated forms. Follow-up US examinations have shown these infrequent spontaneous resolutions. They are considered as a false positive diagnosis in most of the published studies, due to unavailability of surgical and pathological confirmation (Jeffrey et al. 1987). Spontaneously resolving appendicitis occurs in at least 1 in 13 cases of appendicitis and has an overall recurrence rate of 38%, with the majority of cases recurring within 1 year. It is difficult to make therapeutic recom mendations with this intermediate recurrence rate (Cobben et al. 2000). The lack of US criteria in predicting the evolution of these cases leaves conservative management an alternative. On the other hand, when resolution is achieved, recurrence is not the rule, and interval or prophylactic appendectomies may be unnecessary (Püylaert 1990).

Color Doppler US may be useful in easily identifying the inflamed appendix. Color Doppler US is useful as an additional positive finding of appendicitis in uncertain cases of borderline appendiceal size (around 6 mm). Circumferential color in the wall of the inflamed appendix on color Doppler US images reflecting inflammatory hyperperfusion is strongly supportive evidence of active inflamma tion (Birnbaum and Wilson 2000) (Fig. 1.62). With gangrene, color Doppler US may show decreased or no perfusion. With perforation of the appendix, the hyperemia seen in the inflamed appendix extends to the inflamed periappendiceal fat, as seen at color Doppler US (Fig. 1.63).

CT is a highly accurate and effective cross-sectional imaging technique for diagnosing and staging acute appendicitis. The advantages 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 (Sivit et al. 2000). CT is also more useful than US for evaluating com plications such as phlegmon and abscess formation, as well as for delineating the location and extent of associated fluid collections. The smaller amount of intraabdominal fat in children compared with that of adults may contribute to the relative low rate of normal appendix detection at CT (12%) published in some studies (Kaiser et al. 2002) (Fig. 1.64). Controversy remains in the literature regarding the use of oral, rectal, or intravenous contrast agents and the question of whether the area scanned should be limited to the lower abdomen and pelvis or extended to the full abdominopelvic cavity (Taylor 2004). The highest diagnostic efficacy has been obtained with the use of rectal contrast material and thin collima-

Fig. 1.62a,b. Acute appendicitis on color Doppler US. a B-mode US axial scan showing a two-ring-pattern appendicitis. b Color Doppler demonstrates hyperemia of the appendiceal wall manifested as an increased circumferential color flow, mostly in the submucosal layer

Fig. 1.62a,b. Acute appendicitis on color Doppler US. a B-mode US axial scan showing a two-ring-pattern appendicitis. b Color Doppler demonstrates hyperemia of the appendiceal wall manifested as an increased circumferential color flow, mostly in the submucosal layer b a a

Fig. 1.63a,b. Perforated appendicitis. a Axial US scan shows air within the appendiceal dilated lumen (arrow) and enlargement of the periappendicular fat. b Color Doppler demonstrates the enlarged periappendicular tissue to correspond to an inflammatory mass

Fig. 1.63a,b. Perforated appendicitis. a Axial US scan shows air within the appendiceal dilated lumen (arrow) and enlargement of the periappendicular fat. b Color Doppler demonstrates the enlarged periappendicular tissue to correspond to an inflammatory mass b a

Fig. 1.64. Normal gas-filled appendix (arrow) on CT. Some dilated bowel loops filled with oral contrast are depicted. Note the small amount of intraabdominal fat that contributes to the low rate of normal appendix detection in children at CT

tion through the lower abdomen and pelvis (Rao et al. 1998; Garcia-Pena et al. 1999). The amount of intracolonic contrast material administered depends on the size of the patient, ranging from 500 ml in small children to 1000 ml in adolescents. Thin-collimation scanning is performed with 4-mm collimation, 4-mm/s table speed (1.0 pitch), and 4mm reconstruction beginning 2-3 cm above the iliac wing (Sivit et al. 2001). Visualization of the appendix is strongly dependent on the type and quality of the CT examination, although appendiceal size, the amount of periappendicular fat, and the degree of bowel opacification are important influencing factors (Birnbaum and JeFFreY 1998). Optimal cecal opacification and distension are essential to maximize the diagnostic yield of the examination. When seen, the normal appendix appears as a tubular or ring-like pericecal structure that is either totally collapsed or partially filled with fluid, contrast material, or air. The periappendiceal fat should appear homogeneous, although a thin mesoappendix may be present. The appearance of the abnormal appendix varies with the stage and severity of the disease process. In patients with mild, nonperforating appendicitis the appendix may appear as minimally distended, fluid-filled, tubular structure 5 mm in diameter surrounded by the homogeneous fat attenuation of the normal mesentery. This appearance, however, occurs in less than 5% of patients. Most patients demonstrate greater degrees of luminal dis-tention and evidence of transmural inflammation (Fig. 1.65). The inflamed appendix usually measures 7-15 mm in diameter. Circumferential and symmetric wall thickening is nearly always present and is best demonstrated on images obtained with intravenous contrast material enhancement (Birnbaum and Wilson 2000). The thickened wall is usually homogeneously enhanced, although mural stratification in the form of a target sign may be noted. Other common findings include an appendicolith, circumferential or focal apical cecal thickening, pericecal fat thickening, and the arrowhead sign. The latter finding occurs when cecal contrast material funnels symmetrically at the cecal apex to the point of the appendiceal occlusion (Rao et al. 1997). Perforated appendicitis is usually accompanied by pericecal phlegmon or abscess formation (Fig. 1.65). Associated findings include extraluminal air, marked ileocecal thickening, peritonitis, and small bowel obstruction.

The only CT features 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. Identification of an appendicolith in an individual with acute right lower quadrant pain is also considered highly suggestive of acute appendicitis. The remaining CT findings are nonspecific and may be seen with a variety of right lower quadrant and pelvic infectious or inflammatory conditions. The main disadvantage of CT remains the radiation dose to the patient. The emergence of helical and multidetector CT technology has been followed by higher diagnostic efficacy, with no increase in the ionizing radiation exposure. Low-dose CT protocols a

Fig. 1.65a-c. CT in appendicitis. A 13-year-old girl treated with antibiotics for pelvic pain and fever. a US shows a non-specific cystic mass (M) cranial to the uterus (U). No flow was observed on color Doppler study. b,c CT clearly demonstrates the close relationship between the mass (A) and the enlarged appendix (arrow) with an appendicolith (arrowhead). An appendiceal abscess was demonstrated at surgery. B, Bladder; A, abscess b a c using an effective current-time product of 30 mAs have proven to be highly accurate (Keyzer et al. 2004). In spite of these considerations, as stated by Kaiser et al. (2004), "the greatest possible decrease in risk from ionizing radiation at CT is a result of an unnecessary study not being performed". In the interests of radiation protection CT scanning should be reserved for complex problems or for patients whose body habitus precludes adequate US examination.

In conclusion, in cases of high clinical suspicion of appendicitis, surgery is indicated without cross-sectional imaging examination. When clinical presentation is unclear, US should be performed. A positive diagnosis followed by a prompt appendectomy decreases the complication rate. Additionally, a conservative treatment alternative to the surgical option can be used: antibiotics, occasionally followed by delayed appendectomy in cases of phlegmon, and percutaneous drainage in abscess formation. If US examination is accurately shown to be negative for appendicitis, no further studies are required, except for those indicated for the proper management of other possible diagnoses (intussusception, ovarian cyst, etc.). If a nonconclusive diagnosis is made (bowel air interposition, obesity, etc.), different options should be considered, depending on the clinical findings and on the resources available in each institution: observation followed by a second US examination (Kosloske et al. 2004), or CT in order to obtain the most accurate diagnosis. Protocol-based in-patient clinical evaluations by pediatric surgeons, with selective use of diagnostic imaging methods, have shown high accuracy in the diagnosis of appendicitis. Low negative appendicectomy rates (5%) and perforation rates (17%) have been achieved without the radiation exposure and potential costs derived from excessive use of radiological examinations (Kosloske et al. 2004; Ziegler 2004). On the other hand, lower negative appendicectomy rates have been demonstrated in high volume hospitals (Smink et al. 2004).

Several non-surgical abdominal processes such as enteritis (ileocecitis, inflammatory bowel disease), mesenteric adenitis, primary fat epiploic lesions (right segmentary omental infarction and epiploic appendagitis), typhlitis, peritonitis, and functional gynecologic pathology may clinically mimic appen dicitis. A precise diagnosis to avoid unnecessary surgery is essential in these cases.

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