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

Lymphocytic Appendicitis Cannot Be Reliably Distinguished on CT or Ultrasound

Lymphocytic appendicitis cannot be reliably distinguished from other forms of appendicitis on either CT or ultrasound imaging. 1 While both imaging modalities can detect general appendicitis with good accuracy, they lack the specificity to identify the lymphocytic subtype, which requires histopathological examination.

Imaging Capabilities for Appendicitis Detection

CT Scan Performance

• CT with IV contrast is the preferred first-line imaging for adults with suspected appendicitis due to its high diagnostic accuracy (96% sensitivity, 93% specificity) 1
• CT provides superior anatomic coverage, allowing visualization of the appendix regardless of its position, including retrocecal appendix which ultrasound often misses 1
• Key CT findings for general appendicitis include:
  • Maximum external appendiceal diameter ≥8.2mm (optimal cutoff for specificity) 1
  • Appendiceal wall thickening
  • Periappendiceal inflammation
  • Presence of appendicolith

Ultrasound Performance

• Ultrasound shows lower overall sensitivity (83.7%) compared to CT (93.4%) for appendicitis 2
• Ultrasound criteria for general appendicitis include:
  • Maximum outer diameter ≥7mm or wall thickness >1.7mm (sensitivity 98.7%, specificity 95.4%) 3
  • Non-compressibility of the appendix
  • Hyperemia on color Doppler
  • Periappendiceal fluid or fat stranding

Limitations in Identifying Lymphocytic Appendicitis

Neither CT nor ultrasound can reliably distinguish the specific histological subtype of appendicitis. Lymphocytic appendicitis, characterized by lymphocytic infiltration of the appendiceal wall without neutrophils, presents with imaging findings similar to other forms of appendicitis.

The American College of Radiology guidelines make no distinction between imaging findings for different histological subtypes of appendicitis 1, as this differentiation requires microscopic examination of tissue samples after appendectomy.

Clinical Implications

• Definitive diagnosis of lymphocytic appendicitis requires histopathological examination
• Imaging should focus on detecting appendicitis generally, not on subtyping
• Both CT and ultrasound should be interpreted in conjunction with clinical findings
• A combined clinical-sonographic approach may improve overall diagnostic accuracy for appendicitis (sensitivity 98%, specificity 82% when combining ultrasound findings with Alvarado score) 4

Practical Approach to Suspected Appendicitis

1. For adults: CT with IV contrast is recommended as first-line imaging 1
2. For children and pregnant patients: Ultrasound is recommended as first-line imaging 1
3. If ultrasound is equivocal or non-diagnostic and clinical suspicion remains high, proceed to CT 1, 5

Common Pitfalls to Avoid

• Relying solely on imaging to determine the histological subtype of appendicitis
• Assuming a normal-appearing appendix on imaging excludes lymphocytic appendicitis
• Overlooking clinical correlation when interpreting imaging findings
• Failing to consider CT when ultrasound is equivocal in cases with high clinical suspicion

In summary, while imaging is valuable for detecting appendicitis, the specific diagnosis of lymphocytic appendicitis requires histopathological examination of the surgical specimen.