Appendicitis

Images and text Genevieve Carbonatto

A 14 year old boy presents to the Emergency Department with abdominal pain. The pain had started acutely the day before and he had been unable to sleep because of the pain. As you lead the patient to the examination room you note his antalgic gait. He states that while on his way to hospital, in the car, after every bump or sudden movement his pain was more severe. He has had no fever, no vomiting, no diarrhea.

On examination his abdomen is soft but he is tender in the RIF. You examine him using ultrasound.

In the short axis, a “target “sign is visible, which with Colour Doppler shows increased wall vascularity. This is referred to as the “ring of fire”.

The appendix is surrounded by a hyperechoic (brighter) mesentery which has been described as “creeping fat”. This indicates the presence of inflammation.

A clip in the longitudinal plane below demonstrates  the appendix which is clearly visible with its thickened wall and increased hypoechoic muscularis from the small bowel above it. Note the small bowel wall has a normal “gut signature” or gut wall stratification and exhibits normal peristalsis. The appendix does not show any peristalsis and has a thicker wall with a prominent hypoechoic muscularis.

The appendix is considered inflamed if the total diameter of the appendix exceeds 6mm. In the case below the appendix measures 1.35 cm

The boy has clearly got an inflamed appendix. He is taken to theatre without further imaging.

Discussion:

The best technique to examine for appendicitis is to get the patient to localise his/her area of pain. Staring in the RIF, localise the CFV and CFA and the psoas muscle. The appendix usually lies above this. Keep moving towards the RUQ using graded compression. If you are unable to localise the appendix, get the patient to hold the probe and put the probe on top of the area that is causing pain.

Which probe to use?

Start by using a curvilinear probe to get a sense of where you are and once you have identified the appendix switch to a linear probe. If the patient is obese or the appendix is deep, then go back to  the curvilinear probe.

What does a normal appendix look like?

  • A normal appendix should be less than 6mm in diameter
  • It is associated with peristalsis
  • It is a tubular structure with a blind end. This is the clincher when identifying the appendix
  • It is compressible

What does appendicitis look like?

  • The appendix measures more than 6mm in diameter.
  • It is often associated with surrounding “creeping fat”, which is the hyperechoic inflammed mesentery surrounding the appendix.
  • It can be associated with an appendicolith.

Appendicolith in the short axis above

Appendicolith in long axis view above

  • With colour Doppler or power Doppler the thickened bowel wall – especially the submucosa, lights up. This is the “ring of fire” appearance in the short axis
  • It is non compressible
  • There may be surrounding fluid if the appendix has ruptured.

Free fluid surrounding appendix – appendix rupture

  • There may be a complex abscess formation adjacent to the inflamed appendix

Manoeuvres which improve the visualisation of the appendix (2)

Jong et al (2) in 2005   evaluated the value of various operator- dependent techniques to improve visualisation of the appendix other than the simple use of graded compression. Graded compression is firm compression with the probe to displace bowel which may hinder the visualisation of the appendix. These techniques included

  1. Posterior manual compression
  2. Low frequency transducer
  3. Upward graded compression technique
  4. Left lateral decubitus change of body position

Using these techniques they were able in this prospective study of 877 subjects, 202 of which were in the control group and 675 patients in the patient group, to detect the appendix using ultrasound from 84% of the 202 in the control group to 98% and from 89%  of the 675 patients in the patient group to 99%, clearly indicating that these techniques are helpful in identifying the appendix.

What are these techniques?

Posterior manual compression (2,3)

  • Forced extrinsic compression of the opposite side of the right lower quadrant abdomen in the anterior or anteromedial direction using the left hand, thereby allowing forced compression of the posterior aspects of the cecum or pericaecal space with or without anteromedial displacement of the right lower quadrant bowel structures onto the psoas muscle
  • Best used in poorly compressible bowel structure or in obese or muscular patients

American Journal of Roentgenology. 2002;178: 863-868. 10.2214/ajr.178.4.1780863

Low frequency transducer

  • Best used in obese patients
  • I use it as the initial probe to “scout” around and identify landmarks and then move to the linear probe

Upward graded compression technique

  • Most useful for false or true pelvic appendices
  • It consists of forced upwards sweepings of the high frequency probe to move upward the low lying caecum and appendix
  • Squeezes the caecum and appendix onto the psoas muscle or anterior verterbral body reducing the distance between the probe and the appendix

Left lateral decubitus change of body position

  • Helpful for visualising retrocaecal appendix
  • Causes the caecum and the appendix to be displaced medially onto the psoas reducing the distance between the probe and the retrocaecal colic area, improving the visualisation of the appendix.

Teaching point: There is plenty of evidence to suggest that ultrasound should be the first imaging modality for acute appendicitis (4). With practice this is an easy skill to learn and a valuable one for both the patient’s journey and to reduce CT scanning .

References

  1. Insights imaging:2016 Apr; 7(2): 255–263.Published online 2016 Feb 16. doi: 10.1007/s13244-016-0469-6 How to diagnose acute appendicitis: ultrasound first Gerhard Mostbeck,corresponding author E. Jane Adam, Michael Bachmann Nielsen, Michel Claudon, Dirk Clevert, Carlos Nicolau, Christiane Nyhsen, and Catherine M. Owens
  2. American Journal of Roentgenology. 2005;184: 91-97. 10.2214/ajr.184.1.01840091 Gastrointestinal Imaging
    Operator-Dependent Techniques for Graded Compression Sonography to Detect the Appendix and Diagnose Acute Appendicitis
    Jong Hwa Lee1, Yoong Ki Jeong, Kwang Bo Park, Ji Kang Park
  3. American Journal of Roentgenology. 2002;178: 863-868. 10.2214/ajr.178.4.1780863 Gastrointestinal Imaging
    Graded Compression Sonography with Adjuvant Use of a Posterior Manual Compression Technique in the Sonographic Diagnosis of Acute AppendicitisJong-Hwa Lee1, Yoong Ki Jeong, Jae Cheol Hwang, Soo Youn Ham
  4. Insights Imaging: 2016 Feb 16. doi: 10.1007/s13244-016-0469-6PMCID: PMC4805616 How to diagnose acute appendicitis: ultrasound first
    Gerhard Mostbeck,corresponding author E. Jane Adam, Michael Bachmann Nielsen, Michel Claudon, Dirk Clevert, Carlos Nicolau, Christiane Nyhsen, and Catherine M. Owens

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