What diagnostics are used for appendicitis?

Diagnostic Approach for Appendicitis

CT scan with IV contrast is the recommended initial imaging modality for diagnosing appendicitis in non-pregnant adults due to its high sensitivity (96-100%) and specificity (93-95%). 1

Clinical Evaluation

• Early clinical evaluation is essential for diagnosing intra-abdominal infections like appendicitis, helping to optimize diagnostic testing and implement appropriate management plans 2
• Classic symptoms include vague periumbilical pain, anorexia/nausea/vomiting, migration of pain to the right lower quadrant, and low-grade fever 3
• The presence of a positive psoas sign, fever, or migratory pain to the right lower quadrant suggests an increased likelihood of appendicitis 2
• Conversely, vomiting before pain makes appendicitis less likely 2

Diagnostic Algorithm

Step 1: Initial Assessment

• Use a step-up approach tailored to clinical setting, resources, and patient's age, beginning with clinical and laboratory examination and progressing to imaging 2
• Laboratory tests including white blood cell count can assist in diagnosis 4

Step 2: Imaging Selection Based on Patient Population

For Non-Pregnant Adults:

• CT abdomen with IV contrast is recommended as the initial imaging modality 1
• Technical considerations:
  • IV contrast improves sensitivity to 96% compared to unenhanced CT 1
  • Oral contrast is generally not necessary and may delay diagnosis 1

For Children and Adolescents:

• Ultrasound is suggested as the initial imaging modality 2, 5
• If initial ultrasound is equivocal/non-diagnostic and clinical suspicion persists, obtain abdominal MRI or CT as subsequent imaging 2
• CT involves radiation exposure and may require IV contrast or sedation, which should be considered when selecting imaging 2

For Pregnant Patients:

• Ultrasound is recommended as the initial imaging modality 2, 5
• If ultrasound is inconclusive, MRI without IV contrast is preferred over CT 1

Ultrasound Parameters for Diagnosis

• Key findings include:
  • Appendiceal diameter ≥7 mm (most consistent finding) 5
  • Non-compressibility of the appendix 5
  • Appendiceal tenderness during examination (sonographic McBurney's sign) 5
• Ultrasound has approximately 76% sensitivity and 95% specificity for diagnosing acute appendicitis 5
• Point-of-care ultrasound performed by emergency physicians or surgeons shows higher sensitivity (91%) and specificity (97%) 5

CT Findings

• Diagnostic criteria for appendicitis on CT include:
  • Appendiceal dilatation (diameter ≥7 mm) 3
  • Presence of appendicoliths 3
• CT findings suggestive of complicated appendicitis include:
  • Extraluminal appendicolith 2
  • Abscess 2
  • Extraluminal air 2
  • Appendiceal wall enhancement defect 2
  • Periappendiceal fat stranding 2

MRI Considerations

• MRI is comparable to ultrasound with conditional use of CT in identifying perforated appendicitis 2
• MRI shows high diagnostic accuracy with sensitivity of 94% and specificity of 96% for acute appendicitis 2
• MRI is particularly valuable for pregnant patients when ultrasound is inconclusive 2

Special Considerations

Elderly Patients

• CT scan with IV contrast is strongly recommended for patients older than 60 years with an Alvarado score ≥5 and negative ultrasound 2
• Elderly patients have higher rates of complicated appendicitis and mortality, making accurate diagnosis crucial 2

Management After Inconclusive Imaging

• If imaging is negative but clinical suspicion remains high, consider:
  • Observation and supportive care, with or without antibiotics 2
  • Surgical intervention if clinical suspicion is very high despite negative imaging 2
  • Follow-up within 24 hours if discharged 2

Common Pitfalls

• Ultrasound accuracy is highly operator-dependent and the appendix may be obscured by bowel gas or difficult to locate in a retrocecal position 5
• Both MRI and ultrasound may incorrectly classify up to half of all patients with perforated appendicitis as having simple appendicitis 2
• Concerns about radiation exposure with CT should be balanced against the need for accurate and timely diagnosis, especially in elderly patients with higher risk of complications 2