Appendix Ultrasound

Appendix Ultrasound

Introduction

Appendix ultrasound is the first-line imaging modality for suspected appendicitis, especially in children and young adults, due to its:

  • High sensitivity (75-90%) and specificity (90-95%) in experienced hands
  • Real-time imaging capabilities with graded compression
  • Absence of ionizing radiation
  • Bedside availability

Limitations: Operator-dependent technique, may be limited by patient body habitus and bowel gas.

Appendiceal Anatomy

Location: Arises from posteromedial cecum, typically in right lower quadrant (RLQ).

Normal Characteristics:

  • Blind-ending tubular structure
  • Diameter <6 mm (outer wall to outer wall)
  • Wall thickness <3 mm
  • Compressible with no surrounding inflammation
  • No internal vascularity on Doppler

Variants: Retrocecal (most common variant), pelvic, subhepatic positions



Clinical Indications

1. Common Indications

  • Right lower quadrant pain
  • Suspected acute appendicitis
  • Evaluation of appendiceal abscess
  • Pediatric abdominal pain
  • Pregnant patients with RLQ pain

2. Specific Clinical Scenarios

  • Classic appendicitis: Periumbilical pain migrating to RLQ + rebound tenderness
  • Atypical presentations: Pelvic pain, flank pain, or diffuse abdominal pain
  • Pediatric cases: Non-specific symptoms (anorexia, vomiting, low-grade fever)

Scanning Technique

1. Patient Preparation

  • No fasting required is required
  • Patient positioning: Supine, with slight left lateral decubitus tilt if needed
  • Communication: Explain graded compression to patient

2. Equipment Settings

  • Transducer: High-frequency linear (7-15 MHz) for optimal resolution
  • Depth: Adjust to include entire appendix and surrounding structures
  • Harmonic imaging: Improves tissue contrast
  • Doppler settings: Low PRF (500-1000 Hz) for slow flow detection

3. Systematic Scanning Approach

  • Begin at point of maximal tenderness: Usually McBurney's point
  • Graded compression technique: Gradually increase pressure to displace bowel gas
  • Identify landmarks: Psoas muscle, iliac vessels, cecum
  • Trace terminal ileum: To locate appendiceal origin
  • Assess entire length: From base to tip

Normal Sonographic Findings

1. Normal Appendix

  • Blind-ending tubular structure arising from cecum
  • Diameter <6 mm (outer wall to outer wall)
  • Wall thickness <3 mm
  • Compressible with transducer pressure
  • No periappendiceal fat inflammation

2. Surrounding Structures

  • Normal echogenic periappendiceal fat
  • No free fluid in RLQ
  • Normal bowel peristalsis adjacent to appendix
  • No lymphadenopathy
Normal appendix longitudinal

Normal Appendix (Longitudinal)

Blind-ending tubular structure (A) with thin walls (<3mm) and diameter <6mm, originating from the caecum (C).

Normal appendix transverse

Normal Appendix (Transverse)

Target appearance with concentric wall layers, fully compressible appendix (A).



Pathological Findings

1. Acute Appendicitis

  • Primary signs:
    • Non-compressible, blind-ending tube >6mm diameter
    • Wall thickening (>3mm)
    • Hyperemia on Doppler
  • Secondary signs:
    • Periappendiceal fat inflammation (hyperechoic fat)
    • Free fluid in RLQ
    • Appendicolith (hyperechoic focus with shadowing)

2. Perforated Appendicitis

  • Loss of continuity of appendiceal wall
  • Periappendiceal abscess (complex fluid collection)
  • Increased surrounding inflammatory changes
  • Possible localized pneumoperitoneum

3. Appendiceal Abscess

  • Complex fluid collection adjacent to cecum
  • Thick, irregular walls with increased vascularity
  • Possible gas bubbles within collection
  • May contain appendicolith

4. Mucocele of Appendix

  • Dilated, fluid-filled appendix without inflammation
  • Diameter typically >15mm
  • May contain echogenic mucin
  • Wall calcifications in some cases

5. Appendiceal Neoplasms

  • Carcinoid tumor: Hypoechoic nodule at tip of appendix
  • Adenocarcinoma: Irregular wall thickening with loss of layers
  • Metastases: Rare, usually from GI or ovarian primaries
Acute appendicitis longitudinal

Acute Appendicitis (Longitudinal)

  • Non-compressible, dilated appendix (>6mm)
  • Wall thickening (>3mm)
  • Surrounding hyperechoic fat
Acute appendicitis transverse

Acute Appendicitis (Transverse)

  • Target sign with thickened walls
  • Hyperemic wall on Doppler
  • Appendicolith with shadowing
Perforated appendicitis

Perforated Appendicitis

  • Wall defect
  • Periappendiceal abscess
  • Marked surrounding inflammation
Appendiceal abscess

Appendiceal Abscess

  • Complex fluid collection (A)
  • Thick, irregular walls
  • Adjacent inflamed fat
Appendiceal mucocele

Appendiceal Mucocele

  • Markedly dilated appendix
  • Thin walls without inflammation
  • Echogenic mucin content
Appendiceal carcinoid

Appendiceal Carcinoid

  • Hypoechoic nodule at tip (arrows)
  • Preserved wall layers of the appendix (A)
  • No significant inflammation
.

References

  1. American College of Radiology (ACR). (2023). ACR Appropriateness Criteria® Right Lower Quadrant Pain. Journal of the American College of Radiology, 20(1S), S78-S92.
  2. Puylaert, J. B. (2022). Ultrasonography of the Acute Abdomen (2nd ed.). Springer.
  3. Rumack, C. M., & Levine, D. (2021). Diagnostic Ultrasound (6th ed.). Elsevier.
  4. World Society of Emergency Surgery (WSES). (2023). Guidelines for diagnosis and treatment of acute appendicitis. World Journal of Emergency Surgery, 18(1), 1-25.
  5. European Society of Pediatric Radiology (ESPR). (2022). Imaging guidelines for pediatric appendicitis. Pediatric Radiology, 52(3), 425-438.