Can lymphocytic appendicitis be detected on Computed Tomography (CT) or Ultrasound Scan (USS)?

Detection of Lymphocytic Appendicitis on CT and USS

Lymphocytic appendicitis cannot be reliably detected or differentiated from other forms of appendicitis on CT or ultrasound imaging, as these modalities lack the resolution to visualize the specific histopathological changes that characterize lymphocytic appendicitis.

Imaging Capabilities for Appendicitis

CT Imaging

• CT is highly accurate for detecting acute appendicitis in general, with sensitivity of 95% (95% CI: 93-96%) and specificity of 94% (95% CI: 92-95%) 1
• CT can identify:
  • Thickened appendiceal wall (>2 mm)
  • Increased appendiceal diameter (>6 mm)
  • Periappendicitis
  • Abscess formation
  • Appendicoliths 2
• However, CT cannot visualize the microscopic lymphocytic infiltration that defines lymphocytic appendicitis

Ultrasound Imaging

• Ultrasound has more variable performance for appendicitis detection:
  • When results are definitive: high sensitivity (99%) and specificity (97%) 3
  • When including equivocal results: lower sensitivity (82%) 3
• Ultrasound limitations include:
  • Operator dependency
  • Limited visualization of retrocecal appendix
  • Reduced sensitivity for perforated appendicitis 4
  • Inability to detect microscopic lymphocytic infiltration

Imaging Recommendations by Patient Population

Adults

• CT with IV contrast is the preferred first-line imaging for suspected appendicitis in adults 3, 4
• Benefits include:
  • High diagnostic accuracy
  • Ability to identify alternative diagnoses
  • Reduction in negative appendectomy rates 4

Children

• Ultrasound is recommended as first-line imaging 3
• If ultrasound is equivocal/indeterminate, either MRI or CT is suggested as follow-up imaging 3
• CT has shown 96.2% sensitivity and 94.6% specificity as second-line imaging after ultrasound in children 5

Pregnant Patients

• Ultrasound is suggested as initial imaging 3
• If ultrasound is equivocal, MRI is recommended as subsequent imaging 3
• MRI has demonstrated 100% sensitivity and 98% specificity as second-line imaging in pregnant patients 3

Clinical Implications

• Neither CT nor ultrasound can specifically diagnose lymphocytic appendicitis, as this is a histopathological diagnosis made after appendectomy
• The diagnosis of lymphocytic appendicitis requires microscopic examination showing lymphocytic infiltration of the appendiceal wall without neutrophilic inflammation
• Imaging can only detect appendiceal inflammation in general, not the specific cellular composition of the inflammatory infiltrate
• Patients with suspected appendicitis should undergo standard imaging protocols based on their age and pregnancy status, with the understanding that the specific subtype of appendicitis will be determined histologically after surgery

Pitfalls and Caveats

• Relying on imaging alone to diagnose or exclude lymphocytic appendicitis is not appropriate
• A normal-appearing appendix on imaging does not exclude lymphocytic appendicitis
• Clinical correlation remains essential, as patients with lymphocytic appendicitis may present with typical symptoms of acute appendicitis despite more subtle imaging findings
• The definitive diagnosis of lymphocytic appendicitis can only be made histopathologically after appendectomy