Fig. 10.1
Normal appendix on US in an 8-year-old-boy. The multilayered structure measures 5 mm in diameter and presents a blind ending (yellow arrow). It has to be demonstrated all along up to the cecum to establish its normality
On US, signs to be considered as evidence (with different positive and negative predictive values) for appendicitis include:
The visualization of an enlarged and blind bowel-type structure connected to the cecum. The diameter considered as a significant abnormal enlargement is debated. Normal appendix diameter has been reported as below 6 mm [8–10] independently of the patient’s age. Above 6 mm, the diameter is usually considered abnormal but this by itself is not a highly specific sign [11]. A diameter up to 7 mm can be a normal finding [12, 13] or associated with asymptomatic lymphoid hyperplasia (thickening of the lamina propria) (Fig. 10.2) [14]. Still, a diameter equal or superior to 7 mm increases the specificity of this sign for diagnosing appendicitis [13].
In our experience, the thickness of the appendiceal wall is a more reliable sign than the diameter itself since it is less dependent on the lumen content which may increase the whole diameter of the appendix. There are controversies whether this wall thickness is age dependent [8, 9]. Above 3 mm, the wall thickening is definitely abnormal.
Peri-appendiceal fat inflammation appearing as increased hyperechogenicity is an important positive sign even if it can be found in other all inflammatory processes surrounding the appendix or even rarely in normal children. Its specificity increases when this echogenic fat surrounds circumferentially the appendix [11].
The presence of an appendicolith has a low predictive value. Indeed, it can be visualized in asymptomatic patients [15, 16].
A small amount of fluid within the lumen of the appendix [17].
An increased flow in the appendiceal wall as demonstrated by color Doppler US is a non-specific sign. However, its absence associated with the previous described positive signs would favor a perforation.
Lack of compressibility of the appendix has a poor positive predictive value. It has been reported to be the most commonly false-positive finding (80%) [11].
Local sonographic tenderness, presence of gas within the lumen of the appendix and lymph nodes within the root of the mesentery are not considered as accurate positive diagnosis signs.
Fig. 10.2
Lymphoid hyperplasia of the appendix in US in an asymptomatic 6-year-old patient: the appendix is enlarged only on the mucosal layer with preservation of the multilayer differentiation
In summary, the association of several different US signs increases the accuracy of US and ascertains the diagnosis (Fig. 10.3). Once confirmed, it becomes mandatory to search for potential complications.
Fig. 10.3
Non-perforated acute appendicitis on US-Color Doppler in a 12-year-old-girl. (a) US sagittal scan: The appendix is enlarged surrounded by an increased echogenic fat. (b) Color Doppler: Hypervascularization is demonstrated within the appendix wall
Of course, if an alternative diagnosis is identified during the US exploration, it rules out the diagnosis of appendicitis.
10.3.2 Complications
Perforation of the appendix is a major pejorative stage in the evolution of appendicitis; its frequency increases as the age at presentation decreases since the classic clinical signs and symptoms tend to be absent. Therefore, the diagnosis might be delayed in youngest patients [18].
The prevalence of perforation has been reported to range from 23 to 88% [19]. Perforation opens the way to the two most major life-threatening complications, abscesses and peritonitis. Noteworthy, the therapeutic options have recently evolved and there is a wide discussion regarding the optimal treatment (medical vs surgical treatment) of a simple acute appendicitis [20]. Even perforation with abscesses would now be treated with antibiotics first [21]. In order to decrease surgical complications, an appendectomy will be performed in a second stage after disappearance of infection and inflammation. A clinical, biological, and ultrasound follow-up will confirm the regression of the abscesses. In case of absence of response to the antibiotic treatment, a percutaneous drainage can be performed before to finally consider a surgical option.
US features suggesting perforation (isolated or complicated) include [19, 22–24] (Fig. 10.4):
A focal loss of differentiation of the appendix wall.
An appendicolith outside the lumen of the appendix.
The absence of appendiceal hyperhemia on color Doppler.
A hypoechoic and hyperhemic ill-defined fatty infiltration surrounding the abnormal appendix (=phlegmon)
A well-limited heterogeneous collection containing or not air bubbles (with comet-type hyperechogenicities) and surrounded by a hyperemic capsule of variable thickness (=abscess)
Due to the peritonitis, US may demonstrate several associated features
Loculated echogenic fluid collection(s) within the peritoneum
A hyperechogenicity of the periportal space
A diffuse increase of thickness and echogenicity of the peritoneal fat
A diffuse thickening of the outer layers (serosa, muscularis propria) of the small bowel
A small bowel ileus
Free air bubble(s) in the peritoneal cavity (=pneumoperitoneum). These bubbles appear as hyperechoic isolated spots and must be searched within the surrounding inflammatory fat, close to the anterior liver capsule and under the anterior peritoneal surface.
Fig. 10.4
US of a perforated appendix in an 11-year-old-boy: a heterogeneous well-limited fluid collection surrounds an inflamed appendix; part of the perforated appendix wall is not visible anymore (yellow arrow). The adjacent mesenteric fat is inflamed and hyperechoic
The complexity of appendicitis and its complications highlights once again the need for the exploration of the entire abdomen when performing US.
10.4 Appendicitis and CT
The lack of peritoneal fat in children younger than 10 years is an important limitation to visualize the appendix on CT [25]. A normal appendix is demonstrated on CT in 55.6% of patients older than 10-year but only in 38.7% in younger patients [25]. However, the absence of the visualization of the appendix has been reported to have a very high negative predictive value up to 98.7% as for the diagnosis of appendicitis [26].
CT has numerous advocates and has demonstrated in a meta-analysis high sensitivity and specificity, respectively 94 and 95%—for the diagnosis of appendicitis in children [3].
Yet, there is a raising concern in relation with the potential radiation risk associated with the use of CT. It has been calculated that 10,000 CT scans would increase the risk of cancer in 13 children; but conversely, not performing these 10,000 CT would lead to 280 missed diagnoses of appendicitis [3].
Whatever the arguments leading to perform CT, an optimized dose reduction strategy needs to be applied in order to minimize the patient’s exposure while maintaining a diagnostic level quality of images. The aim is being to obtain the best diagnosis accuracy.
There is no well-established CT protocol in the literature to explore a child with suspected appendicitis.
Adaptation of the tube current (mA) to the child body weight has been proposed by Donnelly et al. [27]. For instance, in a patient between 27 and 36 kg, 100 mA is sufficient while between 45.1 and 70 kg the mA can range between 140 and 150 mA.
Recommendations from the SFIPP society propose for a 10-year-old child, 32 kg weight, a CTDI of 7 ± 3 mGy for exploring a body of 35 cm (www.sfip-radiopediatrie.org).
Some authors prefer to limit the exploration from the lower pole of the right kidney [28] down to the pubic symphysis while others start the acquisition at the level of the diaphragm in order to consider all possible differential diagnoses [6].
Agreement does exist to perform the acquisition after IV contrast injection contrast media during the portal phase (1.5–2 cm3/kg with a maximum of 140 cm3).
No oral or rectal opacification is usually recommended [29].
Slice thickness varies in the literature from 1.5 to 5 mm [26].
Coronal and sagittal reconstructions are recommended mostly to increase the level of confidence for the diagnosis.
10.4.1 Classical Presentation
Diagnosis criteria’s include the following [30]
An appendiceal caliber >6 mm: This measurement has been questioned in the literature since normal caliber of the appendix may raise above 7 mm and increases from birth till 6–7 years [31].
An increased appendiceal wall enhancement.
A peri-appendicular fat stranding.
An appendicolith. However, Lowe et al. [32] report the presence of such finding in 3% of completely asymptomatic children.
The presence of fluid of more than 2.6 mm of thickness within the lumen of the appendix [33].
A focal symmetric thickening of the ceco-appendiceal junction (arrowhead sign) or a mass effect on the cecum [34].
None of these signs are highly specific, but the accuracy of diagnosis increases when a combination of signs is observed (Fig. 10.5).
Fig. 10.5
Retro-cecal sub-hepatic appendicitis (yellow arrow) on coronal reformatted CE-CT in a 16-year-old-boy
Noteworthy, the presence of gas within the lumen of the appendix does not exclude acute inflammation.
As mentioned, the visualization of a normal appendix on its whole length excludes the diagnosis of appendicitis.
10.4.2 Complications
Peritonitis is more frequent in children due to more rapid perforation than in adults.
Arguments for perforation include:
Focal loss of enhancement of the wall of the appendix; this sign has the best accuracy
The demonstration of a phlegmon: ill-defined inflammatory mass of heterogeneous density with an increased volume of inflamed fat associated with a various amount of fluid.
The presence of an abscess: well-limited fluid collection of various densities surrounded by an enhancing wall of variable thickness (Fig. 10.6).
Extra-luminal air
Appendicolith outside the appendix
Fig. 10.6
CE-CT on a 15-year-old-boy. Perforated appendicitis surrounded by an abscess (large air fluid level collection on the midline)
Using these criteria the overall accuracy of CT is reported as higher than 96% [35].
10.5 MR Imaging and Appendicitis
In order to avoid irradiation hazards, MR imaging has gained acceptance for the evaluation of suspected appendicitis as a first line imaging exploration or when the contribution US is limited especially in obese children [36–39].
Using either a 1.5 or a 3 T unit magnet, a fast MR imaging protocol is performed without the need for IV injection. Three Tesla allows shorter examination time and higher resolution images. The MR imaging examination time ranges from 8 to 35 min.
The use of multi-channel phased array coils with large coverage and parallel processing is mandatory.
Three-plans single-shot turbo spin-echo sequences associated with axial T2-weighted fat saturation acquisitions are obtained with free breathing. Alternative protocols replace the sagittal single-shot TSE by a coronal T2-weighted fat saturation sequence [38, 39].
A respiratory triggering may be used. Slice thickness can range from to 3 to 5 mm.
In more complex cases, the use of DWI sequences and Gadolinium IV injection T1 Fat-Saturation sequences may be required.
The normal appendix in asymptomatic patient can be demonstrated in 48% [40] to 86% [41] of patients while using an upper limit diameter of 7 mm [40].
10.5.1 Classical Presentation
MR imaging signs for appendicitis include: (Fig. 10.7)
Markedly hyperintense T2-weighted thickened wall of the appendix
Markedly hyperintense T2-weighted peri-appendicular tissues
Dilated appendix >6 mm
Presence of an appendicolith appearing as a focal signal void in T2-weighted sequences in a dependent position.
Free fluid in the pelvis
Fig. 10.7
MR imaging Axial T2-weighted fat saturation sequence: Enlarged inflamed appendix (yellow arrow) with a small appendicolith in a 12-year-old obese patient
10.5.2 Complications
Perforation must be considered in case of [37] (Fig. 10.8):
Localized fluid collection(s): they appear as hypersignal on T2-weighted sequences with or without heterogeneous content, with or without air fluid level or entrapped air within a thick fluid. The collections being surrounded by a hyposignal rim of various thicknesses.
Free peritoneal air appearing as a signal void outside the bowel lumen in a non-dependent position.
Direct visualization of the perforation of the appendicular wall
Fig. 10.8
Perforated appendix in a 5-year-old girl: MR imaging T2-weighted sequences. (a) Deep perforated appendicitis (yellow arrow). (b) Associated pelvic abscess (yellow arrow)
10.6 Unusual Presentations
10.6.1 Appendicitis in Infant and Neonates
Less than 3% of appendicitis occur in children younger than 3 years. Symptoms are non-specific, including abdominal pain, diarrhea, vomiting, abdominal distension, and fever. Due to a delayed diagnosis, the perforation rate is higher and the perforation occurs more rapidly in this age group.
10.6.2 Ectopic Locations
Due to wide variation in its length and position and due to the variable positions of the cecum itself, the symptoms related to appendicitis may be very atypical.
Retrocecal appendix: it is the second most frequent appendix location [42]. Due to this anatomical position, symptoms may mimic cholecystitis or pyelonephritis. Perforation may lead to abscesses in the pararenal space and/or in the perihepatic spaces.
Left side appendix: it can be associated with malrotation, situs inversus, or mobile cecum.
Amyand hernia: It is defined by the presence of the appendix within the inguinal canal. The appendix can be located in the inguinal canal in 1% of children but less than 0.1% will be complicated by an inflammation [43].
De Garangeot hernia: It is referred to an appendicitis within the femoral canal.
Intrathoracic appendix is associated with a diaphragmatic herniaRelated posts:
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