What are the differences in diagnosis and treatment between appendicitis and mesenteric adenitis?

Differentiating Appendicitis from Mesenteric Adenitis

Mesenteric adenitis presents with longer symptom duration (2.4 vs 1.4 days), multiple emergency department visits, lymphocyte-predominant leukocytosis, and absence of classic peritoneal signs, while appendicitis shows rapid progression, neutrophil-predominant leukocytosis, pain migration, and definitive peritoneal findings. 1

Clinical Presentation Differences

Symptom Duration and Pattern

• Mesenteric adenitis patients have significantly longer symptom duration before presentation (average 2.4 days) and require multiple ED visits (1.3 visits on average) before diagnosis 1
• Appendicitis patients present earlier (average 1.4 days) with more acute progression and typically present once 1
• Classic pain migration from periumbilical to right lower quadrant occurs in 28% of appendicitis cases but only 7% of mesenteric adenitis 1

Physical Examination Findings

• Appendicitis demonstrates classic peritoneal signs (rebound tenderness, guarding, rigidity) in 72% of cases 1
• Mesenteric adenitis shows these classic findings in only 20% of cases, with more diffuse tenderness and less localization 1
• Vomiting is significantly more common in appendicitis (62%) compared to mesenteric adenitis (34%) 1

Laboratory Differentiation

White Blood Cell Count Pattern

• Appendicitis: Elevated WBC (mean 15.8 × 10³/dL) with neutrophil predominance (87% neutrophils) 1
• Mesenteric adenitis: Lower WBC (mean 10.16 × 10³/dL) with lymphocyte predominance (24.6% lymphocytes vs 13% in appendicitis) 1
• This lymphocyte predominance is a critical distinguishing feature that reflects the viral or bacterial lymphadenopathy rather than acute suppurative inflammation 2, 1

Inflammatory Markers

• Appendicitis: Elevated CRP (mean 1.6 mg/dL) indicating acute inflammation 1
• Mesenteric adenitis: Lower CRP (mean 0.48 mg/dL) suggesting less severe inflammatory response 1

Imaging Characteristics

Ultrasound Findings

• Mesenteric adenitis shows three or more enlarged lymph nodes (≥5 mm in shortest axis) clustered in the right lower quadrant with a normal, compressible appendix 3, 4
• Terminal ileal wall thickening is present in approximately 44% of mesenteric adenitis cases 3
• Appendicitis demonstrates a non-compressible appendix >6 mm diameter, target sign, and periappendiceal fluid 5

CT Scan Features

• Mesenteric adenitis: Multiple enlarged mesenteric nodes (≥5 mm), normal appendix visualization, possible ileocecal wall thickening in 44% of cases 3
• Appendicitis: Appendiceal diameter >6 mm, periappendiceal fat stranding, appendicolith (if present), and inability to visualize normal appendix 5
• The lymph node size itself (small vs large) does not significantly differentiate between conditions 1

Diagnostic Algorithm

Initial Assessment

• Use clinical scoring systems (AIR score or AAS) to stratify risk—scores suggesting low probability warrant observation rather than immediate imaging 5
• Point-of-care ultrasound (POCUS) should be the first-line imaging modality in both adults and children 5

When Ultrasound is Inconclusive

• Proceed to contrast-enhanced low-dose CT scan if ultrasound is non-diagnostic 5
• In pregnant patients or children, use MRI as second-line imaging to avoid radiation 5

Imaging Interpretation

• If imaging shows normal appendix with clustered enlarged lymph nodes: Diagnose mesenteric adenitis and pursue conservative management 3, 4
• If imaging shows abnormal appendix: Proceed with appendectomy planning 5, 6

Treatment Differences

Mesenteric Adenitis Management

• Self-limited condition requiring only symptomatic treatment with resolution typically within 2-3 days 7, 1
• Consider stool cultures for Yersinia enterocolitica or Salmonella species, particularly in endemic areas 7, 4
• Avoid appendectomy when diagnosis is confirmed by imaging 4

Appendicitis Management

• Immediate broad-spectrum antibiotics (ticarcillin-clavulanate, cefoxitin, ertapenem, or metronidazole plus cephalosporin) 8
• Appendectomy remains the definitive treatment, preferably laparoscopic when expertise available 6
• For uncomplicated appendicitis, no postoperative antibiotics are needed; for complicated cases, limit antibiotics to 3-5 days postoperatively 8

Critical Pitfalls to Avoid

• Never proceed to appendectomy without imaging confirmation, especially in females where negative appendectomy rates historically exceed 40% 6, 2
• Do not dismiss mesenteric adenitis based solely on lymph node size—the presence of clustered nodes with normal appendix is diagnostic regardless of exact measurements 1, 3
• Recognize that mesenteric adenitis accounts for 19.8% of non-appendicitis diagnoses in patients admitted with suspected appendicitis 3
• In patients with lymphocyte-predominant leukocytosis and longer symptom duration, strongly consider mesenteric adenitis and avoid unnecessary surgery 1
• If explorative laparoscopy is performed for persistent pain with negative imaging, mesenteric adenitis can be confirmed visually and appendectomy avoided 5