Ultrasound examination (ultrasound)
Scanning of the right iliac fossa in the transverse plane is the method of choice for children (when the diagnosis is doubtful), young women (due to the high incidence of concomitant fallopian tube pathologies), and pregnant patients. The method is well suited for patients with an asthenic body habitus.
Key sonographic signs:
- Presence of a blind-ending tubular structure with a diameter of 7 mm or more.
- Non-compressibility of the appendix upon transducer compression and absence of peristalsis within it.
- Visualization of an appendicolith producing a clear acoustic shadow.
- Changes in surrounding tissues: high echogenicity of adipose tissue (indicates infiltration), free fluid or abscess, as well as edema of the cecal pole.
- Local tenderness strictly upon transducer pressure over the appendix area.
In the presence of an experienced specialist, the sensitivity of ultrasound is 78–98%, and specificity reaches 98%.
Limitations and pitfalls of ultrasound
The main drawback of the ultrasound method is that in most cases, the normal vermiform appendix is simply not visualized. Therefore, if the diagnostician has not found the appendix, this does not rule out the development of appendicitis.
False-negative results may be associated with focal inflammation of the tip, retrocecal location, or gas-filled lumen. Less commonly, the cause of error is a massively enlarged appendix. Special pitfall: in gangrenous or perforated processes, the appendix may lose its «non-compressibility». This paradoxical compressibility occurs in 55% of adult patients with perforation and in 38% of children.
False-positive diagnoses on ultrasound are most frequently provoked by:
- Adnexal pathologies (dilated fallopian tube).
- Compacted stool, which mimics an appendicolith on the monitor.
- Inflammatory bowel diseases and periappendicitis.
Computed tomography (CT)
CT is a high-precision tool with a sensitivity of up to 100% and a specificity of 95% (according to expert centers). Unlike ultrasound, CT more often succeeds in visualizing even a normal appendix, which yields a high percentage of true-negative findings.
Tomographic signs of inflammation:
- Appendix diameter greater than 6 mm.
- Active contrast enhancement of the wall after intravenous administration.
- Appendicolith (radiopaque density at the base of the edematous appendix).
- Increased density of the surrounding periappendiceal adipose tissue.
- Extraluminal gas (a reliable sign of perforation).
- «Cecal bar» sign — local thickening of the cecal wall due to edema at the site of appendix insertion.
The widespread adoption of CT in the USA has helped reduce the rate of negative appendectomies from over 20% to less than 9%, although some studies dispute these statistics.
Search for alternative diagnoses
The most important advantage of CT in right iliac fossa pain is the ability to establish the correct alternative diagnosis (achieved in 89% of cases). Conditions clinically mimicking appendicitis include:
- Mesenteric adenitis and terminal ileitis.
- Meckel's diverticulitis.
- Typhlitis.
- Omental infarction and epiploic appendagitis.
For comparison, in pain of the left iliac fossa, CT is the gold standard for diagnosing acute diverticulitis, allowing immediate assessment of the risk of perforation or fistula formation.
Plain radiography and management
A plain abdominal radiograph is taken in the supine position. Its independent value is small, but it can reveal a radiopaque shadow of an appendicolith, supplementing the overall picture.
When choosing a method (ultrasound or CT), one must rely on the clinical task at hand, the patient's body habitus, equipment availability, and the radiologist's qualifications. The main rule: diagnostic imaging must not replace a thorough clinical evaluation by the surgeon. Waiting for a CT scan queue should not lead to delayed surgical treatment and worse outcomes.
Briefly: answers to topical questions
What direct and indirect radiographic signs of acute appendicitis can be detected on a plain abdominal radiograph?
- Appendicolith (appendicolith) — a radiopaque shadow in the projection of the right iliac fossa may be visualized.
Plain radiography for suspected appendicitis has limited value because specific diagnostic features are lacking, and the study has no independent decisive significance.
What MRI signs are characteristic of acute appendicitis in pregnant patients?
- Wall thickening (thickening of appendix walls) — T2-weighted fat-suppressed images show thickening of the vermiform appendix walls.
- Appendicoliths (appendicoliths) — multiple filling defects are defined within the lumen of the appendix.
- Inflammatory edema (inflammatory oedema) — the surrounding hyperintense signal corresponds to free fluid and inflammatory edema.
Ultrasound triad of appendicitis: blind-ending tube, greater than 7 mm thick, non-compressible by the transducer.
Class and exam questions
Can acute appendicitis be ruled out if the appendix is not visualized on ultrasound?
No. Normally, the appendix is often not visualized on ultrasound. A negative study result does not rule out the presence of inflammation.
Does an inflamed appendix always fail to compress under pressure?
In most cases it is non-compressible, but in perforation or gangrenous process, the appendix may become compressible again (observed in 38% of children and 55% of adults with perforation).
What is the «cecal bar» sign on CT?
This is a focal thickening of the cecal wall that occurs due to pronounced edema at the site of origin of the inflamed vermiform appendix.
Which method is preferred in suspected appendicitis in young women?
The method of choice is ultrasound, as it allows ruling out gynecological pathologies (e.g., fallopian tube dilation) that often mimic the clinical presentation of appendicitis, and carries no radiation exposure.
What else to study on this topic
- Focal appendicitis of the appendiceal tip: diagnostic challenges
- Differential diagnostic imaging with Meckel's diverticulitis
- Comparison of CT and ultrasound in the diagnosis of terminal ileitis and typhlitis
- Epiploic appendagitis and omental infarction: CT semiotics
- Acute colonic diverticulitis: classification and complications on CT
- Radiation dose optimization in abdominal CT
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