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AbdomenDemonstration data

Graded-Compression Appendix Ultrasound

Graded-compression ultrasound is a first-line, radiation-free test for suspected acute appendicitis, particularly in children, adolescents, thin adults and pregnant patients. Gentle progressive transducer pressure displaces overlying gas-filled bowel to reveal the appendix. A blind-ending, non-compressible tubular structure with an outer diameter of 6 mm or more is the principal diagnostic criterion.

Indications

  • Suspected acute appendicitis with right iliac fossa pain
  • Children and adolescents in whom ionising radiation is best avoided
  • Pregnant patients with right-sided abdominal pain
  • Thin adults and equivocal clinical presentations
  • Follow-up of a treated appendiceal mass or abscess

Contraindications & Cautions

  • No absolute contraindications; ultrasound is safe and non-ionising
  • Marked obesity, extensive bowel gas and guarding limit visualisation and compression
  • A retrocaecal or pelvic appendix may be difficult or impossible to identify
  • A non-visualised appendix does not exclude appendicitis; consider MRI (pregnancy/children) or CT (adults)

Patient Preparation

  • No specific preparation required; the patient can indicate the point of maximal tenderness
  • Supine position, sometimes with left lateral decubitus to access a retrocaecal appendix
  • Begin scanning at the site the patient localises as most painful
  • Apply gentle, progressively increasing (graded) compression to displace bowel gas
  • Explain that mild pressure discomfort is expected

Technique & Parameters

  • High-frequency linear 7-15 MHz probe; switch to curvilinear 3-6 MHz for deep or retrocaecal appendix or larger patients
  • Identify the ascending colon and follow the caecum to the appendiceal base
  • Trace the blind-ending, non-peristaltic tubular structure to its tip in transverse and longitudinal planes
  • Apply graded compression to displace gas and assess compressibility
  • Measure the maximal outer-to-outer diameter perpendicular to the long axis
  • Add colour Doppler to demonstrate mural hyperaemia and survey for secondary signs

Systematic Review

  • Identify the appendix as a blind-ending, non-peristaltic, gut-signature tubular structure from the caecal base
  • Measure the maximal outer diameter and assess compressibility
  • Assess wall thickness, layering and mural hyperaemia on Doppler
  • Look for an appendicolith with posterior acoustic shadowing
  • Evaluate periappendiceal echogenic fat, free/loculated fluid and phlegmon or abscess
  • Consider alternative diagnoses in the right iliac fossa and pelvis

Key Findings & Significance

  • Non-compressible, blind-ending tubular structure with outer diameter >=6 mm is the primary criterion for appendicitis
  • Aperistaltic appendix with wall thickening and mural hyperaemia on colour Doppler
  • Appendicolith with posterior shadowing, often associated with complicated appendicitis
  • Periappendiceal inflamed echogenic fat and free fluid as secondary signs
  • Loss of wall layering, loculated fluid or a phlegmon/abscess indicates perforation
  • A fully compressible appendix under 6 mm with no secondary signs argues against appendicitis

Differential Considerations

  • Right iliac fossa pain: appendicitis vs mesenteric adenitis vs terminal ileitis (Crohn/infective) vs typhlitis
  • Gynaecological: ovarian torsion, ruptured cyst, ectopic pregnancy, tubo-ovarian abscess
  • Urological: ureteric colic, pyelonephritis
  • Appendiceal diameter 6-7 mm borderline: early appendicitis vs normal variant; use secondary signs and re-evaluation
  • Right-sided diverticulitis and epiploic appendagitis

Pearls & Pitfalls

  • Scan directly over the point of maximal tenderness; the sonographic Murphy sign supports the diagnosis
  • Graded compression is key: gentle progressive pressure displaces gas and tests compressibility
  • A diameter of 6-7 mm is borderline; weight secondary signs (hyperaemia, fat, fluid) and consider short-interval re-scan
  • A non-visualised appendix is non-diagnostic, not negative; escalate to MRI (pregnancy/children) or CT as appropriate
  • Always look for an alternative cause, especially gynaecological pathology in women

Structured Report

  • State transducer, technique and whether the appendix was visualised in full
  • Report maximal outer diameter, compressibility, wall changes and mural hyperaemia
  • Note appendicolith, periappendiceal fat, fluid and any phlegmon or abscess
  • Describe relevant alternative diagnoses when the appendix is normal or not seen
  • Give an impression (positive, negative or equivocal) and recommend further imaging when non-diagnostic

References

  • ACR Appropriateness Criteria: Right Lower Quadrant Pain - Suspected Appendicitis
  • Puylaert JB. Acute Appendicitis: US Evaluation Using Graded Compression. Radiology 1986
  • AIUM Practice Parameter for the Performance of an Ultrasound Examination of the Abdomen
  • Trout AT et al. Sonographic Diagnosis of Appendicitis in Children. Radiographics

Educational clinical decision support only. Protocols vary by institution and equipment; always confirm with a qualified radiologist and local guidelines before clinical use.