SonoTutorial: Appendicitis assessment by ultrasound #FOAMed #FOAMus

In a recent article in Insights into Imaging, there is a great pictorial and descriptive review of the how-to of appendicitis assessment by ultrasound. The authors are radiologists from the UK and they provide an excellent description of its assessment. As they state, if appendicitis is not evaluated in patients with right lower quadrant pain or any of the other signs of appendicitis (either by the Alvarado Score or other decision rule… or even just your clinical judgement) complications can occur: “Potential complications include perforation, peritonitis, abscess formation and death. Because of atypical presentations and the risk of potential complications, imaging is often requested. In children, this imaging technique is usually US.” For SonoSpot cases for appendix US, go here. For SonoSpot studies’ reviews in appendicits, go here.

Their specific teaching points:

• A step-wise technique improves the chances of visualisation of the appendix.
• There are often several causes for the non-visualisation of the appendix in children.
• A pathological appendix has characteristic US signs, with several secondary features also identified.
• There are multiple common differentials to consider in the paediatric patient.
Their technique as described in the free article published:
1. Ask where it hurts and start there
2. Graded compression
3. Find the appendix using specific landmarks (psoas muscle and iiacs vessels)
4. Look for signs of appendicitis (noncompressible, tubular, >6mm diameter, aperistaltic) – other signs described below

“Setting the scene: contact with the patient and parents

When meeting the paediatric patient for the first time, the patient should be asked where the point of maximum tenderness is located. The examination is explained to the patient. The patient is usually accompanied by a parent or guardian. In optimal conditions, the patient is fasted and has a full bladder to help in the exclusion of any ovarian or other pelvic pathology.

Graded compression US

The scan is continued with a planar higher frequency probe, which allows higher resolution of more superficial structures. The frequency used depends on the size and age of the child (between 5 and 12 MHz).

Step 1:

Displacing small bowel loops out of the way
Normal bowel loops are displaced by gentle compression of the anterior abdominal wall using the US probe. These loops should be easily compressed and displaced away. The displacement of the bowel structures should allow the visualisation of the iliac vessels in the right iliac fossa as well as the psoas muscle. Two-plane scanning is performed (longitudinal and transverse).
Step 2:

Visualisation of the ascending colon and caecum
The ascending colon is visualised as a non-peristalsing structure containing gas and fluid in the right side of the abdomen. The probe is then moved inferiorly toward the caecum, using repeated compression and release to express gas and fluid from the bowel (Fig. 1a, b). The right psoas muscle should also be visualised (Fig. 2). The adjacent terminal ileum should be identified as a compressible structure that is undergoing peristalsis.

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Fig. 1

Longitudinal (a) and transverse (b) views using high frequency linear-array probe showing the caecum (small white arrows in b) and ascending colon in a 15-year-old girl
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Fig. 2

Longitudinal image showing the caecum and ascending colon, as well as the adjacent psoas muscle posteriorly (small white arrows) in a 15-year-old girl
Step 3:

Identification of the appendix
Once the caecum has been seen, the appendix should be visualised arising from it, separate to the terminal ileum (Fig. 3). The appendix should be followed along its whole length. A normal appendix should measure 6 mm or less in diameter from outside wall to outside wall. It should have a thin wall (less than 3 mm), be empty or gas/faecal-filled and compressible, and there should be no evidence of hypervascularisation [2326].

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Fig. 3

A normal appendix is seen draped over the iliac vessels in a 10-year-old girl. This is thin-walled, measuring less than 6 mm in diameter (A width of 3 mm). The caecum can be seen in continuity with the appendix superior to it
Step 4:

Assessment for features of acute appendicitis
An abnormal appendix can have any of the following characteristics which should be actively considered:

  • Compressibility: in acute appendicitis, the appendix is non-compressible [24]. One caveat here is perforation when the appendix can become compressible.
  • Maximum diameter: a maximum diameter of greater than 6 mm is considered abnormal (Figs. 4 and 5) [52425].
  • Wall thickness: a single wall thickness of 3 mm or more is considered abnormal (Fig. 6) [2427].
  • Target sign appearance: this is caused by a fluid-filled centre (hypoechoic centre), surrounded by a hyperechoic ring (mucosa/submucosa) which is surrounded by a hypoechic muscularis layer giving a target sign on axial imaging (Fig. 7a, b) [1528].
  • The presence of an appendicolith (this will appear as an echogenic focus with posterior acoustic shadowing) (Fig. 8a, b) [1528].
  • Vascularity: peripheral appendiceal wall hyperaemia is seen in the early stages of acute appendicitis (Fig. 9a, b); this may not be seen with progression to necrosis [1529].
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Fig. 4

Longitudinal view of a thickened, oedematous appendix measuring 10 mm in diameter with surrounding increased echogenic omentum in an 8-year-old boy with confirmed appendicitis. Absent intraluminal gas is noted
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Fig. 5

Transverse view of a thickened, oedematous appendix measuring 10 mm in diameter in an 8-year-old boy with confirmed appendicitis. Again, surrounding omentum of increased echogenicity is noted
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Fig. 6

The wall of this oedematous appendix measures 4 mm in an 8-year-old boy with confirmed appendicitis. Increased echogenic omentum is seen adjacent to the appendix
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Fig. 7

a A transverse view of an inflamed appendix in a 15-year-girl, showing the target sign appearance. bSimilar appearances in an 11-year-old boy. This target sign comprises a hypoechoic fluid-filled centre (white arrow), inner hyperechoic mucosal/submucosal ring (white asterisk), and outer hypoechoic ring (dashed white arrow)
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Fig. 8

Appendicoliths (labelled) causing posterior acoustic shadowing in two patients, a 15-year-old girl (a) and a 10-year-old boy (b). The thickened, fluid-filled appendix is labelled in b (small white arrows)
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Fig. 9

a Increased Doppler signal in a thickened, oedematous appendix in an 8 year-old-boy. b Similar appearances noted in a 10-year-old girl. The increased Doppler signal indicates hyperaemia
Secondary features can be observed around the inflamed appendix; these should be actively sought:

  • Free fluid or abscess in the periappendiceal region (Fig. 10) [61528].
  • Increased echogenicity of the adjacent periappendiceal fat (Fig. 11) [61528].
  • Enlarged mesenteric lymph nodes (Fig. 12) [15].
  • Thickening and hyperechogenicity of the overlying peritoneum (Fig. 13).
  • Dilated hyperactive small bowel from secondary small bowel obstruction (Fig. 14).
  • Focal apical caecal pole thickening or thickening of the adjacent small bowel can be seen as a secondary response [630].
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Fig. 10

Small pocket of free fluid in the region of the appendix (white arrow) in a 10-year-old girl with confirmed appendicitis
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Fig. 11

Omental fat with increased echogenicity with a mass-like appearance (small white arrows) in a 12-year-old boy with confirmed appendicitis
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Fig. 12

Multiple lymph nodes (arrows) in the mesentery of the periappendiceal region in an 8-year-old girl with confirmed appendicitis
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Fig. 13

Increased echogenic free fluid in the right iliac fossa (indicating pus) with adjacent thickening of the peritoneum in a 2-year-old girl with confirmed appendicitis
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Fig. 14

Loops of dilated, fluid-filled small bowel in a 2-year-old girl with confirmed appendicitis. Echogenic free fluid is seen adjacent to the bowel indicating pus (white arrow)
It is not uncommon that the appendix cannot be identified. There are varying rates quoted in the literature for the appendix being seen, between 24.4 % and 69.3 % [61323]. In this situation, it is important to actively assess for the secondary features often seen which may help direct further management. Repeating the examination after a few hours has been shown to significantly increase the sensitivity of US [31].
Read on more to hear about the complications of appendicitis,  the causes of inadequate visualization, and other etiologies as seen on ultrasound for right lower quadrant pain. Trust me, its worth the viewing.

SonoCase from EPMonthly: 19 yr old with food poisoning? hmm….by B. Pregerson and T. Wu

Merry Christmas everyone! For your reading pleasure this week, Id thought we would discuss a case whose topic is near and dear to my heart. In the most recent issue of EPMonthly, there is a great case and interesting “internal” discussion made quite humorously public by Drs. Pregerson and T. Wu of a young healthy male with right lower quadrant abdominal pain after eating at a “Roach Coach”…. which just so happen to have the best breakfast burritos, but I digress… The case discussion involves how the history and physical may help, how labs may (or may not) help and how an ultrasound can be of use to make you and your surgical colleagues feel better in taking the patient to the OR. There was a recent post on SonoSpot about ultrasound in appendicitis sharing data from a study about the CT findings when US “equivocal” cases arise.  When the ultrasound is positive – how great is that?! Quite a few studies recently on the topic and some of the more recent ones can be found here.

The case is followed by an extensive (and great) discussion of the technique, pearls and pitfalls of ultrasound in evaluating the appendix – because we all know there are quite a few. As far as the sensitivity ad specificity go, they state it best:

“Sensitivity & Specificity: Both the sensitivity & specificity of ultrasound for appendicitis are less than that of CT. In pediatrics the values are about 88% and 94% respectively, and in adults about 83% and 93%. (These numbers may vary depending on the experience of the ultrasonographer.) There are studies from Europe and Israel where they have used the “ultrasound first” approach for many, many years that show even better test characteristics. These values are actually not that bad when compared to CT scan whose sensitivity and specificity are around 94% and 95% respectively. Remember, however, that the performance characteristics for ultrasound can be significantly worse in overweight patients or those with overlying bowel gas. In addition, if the appendix is retrocecal or is lying in a difficult anatomical plane, the study will be more challenging.  Unfortunately, you may still have to do a CT scan if your ultrasound is non-diagnostic and your clinical suspicion is moderate to high, but the strategy of ultrasound first would likely decrease CTs by about 50%.”

And in kids…”You should be aware of the most recent recommendation of the American College of Radiology from the “Choosing Wisely” campaign, which states, “Don’t do computed tomography (CT) for the evaluation of suspected appendicitis in children until after ultrasound has been considered as an option.” Although CT is accurate in the evaluation of suspected appendicitis in the pediatric population, ultrasound is nearly as good in experienced hands. Since ultrasound will reduce radiation exposure, ultrasound is the preferred initial consideration for imaging examination in children. If the results of the ultrasound exam are equivocal, it may be followed by CT. This approach is cost-effective, reduces potential radiation risks and has excellent accuracy, with reported sensitivity and specificity of 94 percent.”

To diagnose appendicitis: look for a noncompressible a-peristaltic structure that attaches to the cecum that is larger than 7mm in diameter.

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A great tutorial of ultrasound for the appendix can be found here by the UltrasoundPodcast guys:

SonoInterview by Medscape: A Radiologist’s perspective of Appendix US…replacing CT? Yes!

This comes in great timing as a prior SonoSpot post describing recent studies evaluating CT findings in appendicitis rule-outs show that the majority ( 80-90% ) are negative…. US, clinical judgement, and a possible observation period can go a long way in radiation reduction.

Expert Interview: Stephanie Wilson, MD, on the Value of Ultrasonography for Imaging Appendicitis

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