This is a basic article for medical students and other non-radiologists

Appendicitis occurs when there is inflammation of the vermiform appendix. It is a very common condition and is a major cause of abdominal surgery in young patients. CT is the most sensitive modality to detect appendicitis although its use should be limited because of the radiation dose required and ultrasound should be employed as first-line where possible.

Reference article

This is a summary article; read more in our article on appendicitis.

Summary

• anatomy

  • appendix

• epidemiology

  • typically children and young adults

  • peak incidence 2nd to 3rd decade of life

• presentation

  • initial periumbilical pain with fever, nausea and vomiting

  • progresses to localised right iliac fossa pain

• pathophysiology

  • obstruction of the appendiceal lumen

    • fluid accumulation, infection, venous congestion, ischaemia/necrosis

    • causes

      • lymphoid hyperplasia (60%)

      • appendicolith (33%)

      • rare: foreign body, Crohn's disease, tumour

• investigation

  • US is often all that is required (quick, dynamic and no ionising radiation)

  • cross-sectional imaging is more sensitive (CT and MRI)

• treatment

  • appendicectomy (laparoscopic or open)

• prognosis

  • prognosis is very good and mortality very low (0.1%)

  • complications include:

    • perforation and abscess formation

    • generalised peritonitis

Role of imaging

• confirm appendicitis

• assess for peri-appendiceal collection

• assess for perforation

• determine if there is another cause for symptoms

Radiographic features

Ultrasound

Graded compression, and uses the linear probe over the site of maximal tenderness, with gradually increasing pressure to displace normal overlying bowel gas. Always used in young patients because of the lack of ionising radiation.

• distended appendix

• surrounding (echogenic) inflamed fat

• thickening (oedema) and then later, thinning (pre-rupture) of the appendix wall

• increased appendix wall vascularity

• collections (hypoechoic areas) around the appendix

In one meta-analysis, ultrasound has sensitivity and specificity of 69% and 81%, respectively, for the diagnosis of acute appendicitis.¹

CT

CT is highly sensitive (94-98%) and specific (up to 97%) for the diagnosis of acute appendicitis and allows other causes of abdominal pain to be diagnosed. Usually performed with IV contrast (no oral contrast required).

• dilated appendix with a distended lumen ( >6 mm diameter)

• thickened and enhancing wall

• thickening of the caecal apex (up to 80%)

• peri-appendiceal inflammation (stranding of the adjacent fat)

• extraluminal fluid

• inflammatory phlegmon

• abscess formation

• appendicolith may also be identified

MRI

In one study, the sensitivity and specificity of MRI for the diagnosis of acute appendicitis are 96% and 96%, respectively. The appearance of appendicitis on MRI has many similarities to the CT appearance ².