What is the appropriate evaluation and management for a patient presenting with right lower quadrant abdominal pain, fever, nausea, and mild diarrhoea suggestive of mesenteric adenitis?

Mesenteric Adenitis: Evaluation and Management

Initial Diagnostic Approach

For patients presenting with right lower quadrant pain, fever, nausea, and mild diarrhea suggestive of mesenteric adenitis, stool testing for Yersinia enterocolitica should be performed, as this pathogen specifically causes mesenteric adenitis mimicking appendicitis, particularly in school-aged children and young adults. 1

Key Clinical Features to Assess

• Right lower quadrant pain without classic appendicitis features: Mesenteric adenitis typically presents with RLQ pain but lacks the classic migration from periumbilical region, and rebound tenderness is present in only 26.7% of cases (compared to typical appendicitis) 2
• Associated gastrointestinal symptoms: Diarrhea occurs in 80% of mesenteric adenitis cases, which is uncommon in appendicitis 2
• Fever pattern: Present in 73% of cases but may be absent 2
• Absence of anorexia: The preservation of appetite significantly decreases appendicitis likelihood 3

Critical Distinction from Appendicitis

The clinical presentation differs importantly from appendicitis: fever is absent in approximately 50% of appendicitis cases, while diarrhea is uncommon in appendicitis but present in 80% of mesenteric adenitis 1, 2. Clinical assessment alone misdiagnoses acute appendicitis in 34-68% of cases, making imaging essential when the diagnosis is uncertain. 3

Diagnostic Testing Algorithm

Stool Microbiology (First Priority)

Test specifically for Yersinia enterocolitica in patients with persistent abdominal pain, especially school-aged children with right lower quadrant pain mimicking appendicitis who may have mesenteric adenitis. 1

Additional stool testing should include:

• Salmonella species (second most common cause in some populations) 4, 2
• Shigella, Campylobacter, and STEC if bloody stools present 1
• Consider parasitic testing (Giardia, Entamoeba) if symptoms persist beyond 14 days 1

Epidemiologic Risk Assessment

• Exposure history: Inquire about raw or undercooked pork products (Yersinia risk), particularly in infants with direct or indirect exposures 1
• Travel history: Non-typhoidal Salmonella and typhoid fever are important considerations in endemic areas 2
• Age consideration: Mesenteric adenitis most commonly affects young adults (average age 29.9 years in Korean study) and school-aged children 2, 1

Imaging Strategy

When to Image

CT abdomen and pelvis with IV contrast should be obtained when clinical differentiation from appendicitis is uncertain, as it achieves 90-100% sensitivity and 94.8-100% specificity for appendicitis while also diagnosing mesenteric adenitis. 1, 5

Imaging is indicated when:

• Clinical presentation overlaps significantly with appendicitis 1, 3
• Symptoms worsen or fail to improve with supportive care 3
• Rebound tenderness develops (suggesting peritoneal irritation) 3
• Diagnostic uncertainty persists after initial evaluation 1

CT Findings of Mesenteric Adenitis

• Diagnostic criteria: Three or more lymph nodes measuring ≥5 mm in shortest axis clustered in the right lower quadrant mesentery 6, 7
• Normal appendix: Must be visualized and normal in appearance 7
• Associated findings: Ileal or ileocecal wall thickening present in 44% of cases 7
• Lymph node size: Long axis typically reaches minimum 10 mm in 66.9% of cases 8

Alternative to CT

Ultrasound may be used as first-line imaging in children to avoid radiation exposure, showing enlarged mesenteric lymph nodes with normal appendix. 3, 9 However, if ultrasound is nondiagnostic or equivocal, proceed directly to CT 3, 5.

Management Based on Etiology

Primary (Idioprimary) Mesenteric Adenitis

When no specific pathogen is identified (occurs in 21-30% of cases) 6, 8:

• Supportive care only: Maintain hydration, mild pain control 3
• Spontaneous resolution: Symptoms typically resolve within 2-7 days without antibiotics 4, 2
• Avoid unnecessary antibiotics: Most cases are self-limited 2

Pathogen-Specific Treatment

When Yersinia enterocolitica is identified:

• Most cases are self-limited and do not require antibiotics 2
• Consider antibiotics only for severe cases or immunocompromised patients 1

When Salmonella is identified:

• Critical distinction: Unlike Yersinia, Salmonella enterica carries potential risk for serious systemic complications including meningitis and septic arthritis 4
• Antimicrobial therapy should be considered based on severity and patient risk factors 1

When tuberculosis or typhoid fever is identified:

• Specific antibiotic therapy is mandatory as these do not resolve spontaneously 2

Observation and Follow-up Protocol

Hospital Observation Criteria

Consider 24-hour observation with serial abdominal examinations when:

• Diagnostic uncertainty persists despite imaging 3
• Pain severity is moderate to severe 3
• Patient cannot tolerate oral intake 3

Serial examinations every 6-12 hours assess for progression of peritoneal signs, with repeat complete blood count to monitor leukocytosis trend. 3

Discharge Criteria

Safe discharge requires:

• Normal CT scan without evidence of appendicitis 3
• Absence of peritoneal signs on physical examination 3
• Ability to tolerate oral intake 3
• Reliable access to follow-up 3

Mandatory Follow-up

All discharged patients require follow-up within 24 hours due to measurable false-negative rates in low-risk presentations. 3 Instruct patients to return immediately if:

• Symptoms worsen 3
• Fever develops or increases 3
• Vomiting occurs 3
• Abdominal tenderness increases 3

Critical Pitfalls to Avoid

• Do not rely on absence of fever to exclude appendicitis: Fever is absent in approximately 50% of appendicitis cases 1, 3
• Do not discharge without clear follow-up plan: False-negative rates exist even with imaging 3
• Do not delay imaging if symptoms worsen during observation: CT should be obtained promptly 3
• Do not assume all mesenteric adenitis is benign: Salmonella carries risk of systemic complications requiring different management than Yersinia 4
• Do not use NSAIDs liberally: They can mask evolving symptoms and delay diagnosis 3

Special Considerations

Secondary Mesenteric Adenitis

In 70% of cases, mesenteric adenitis is secondary to an identifiable inflammatory condition 6. Colonoscopy with mucosal biopsies should be considered when:

• Symptoms persist beyond expected self-limited course 2
• Inflammatory bowel disease is suspected 2
• Tuberculosis or other chronic infections are considerations 2

Active inflammation on colonoscopy was observed in 75% of cases in one series, confirming that mesenteric adenitis often represents a response to intestinal pathology 2.

Complications to Monitor

• Intussusception tendency: Observed in 3.9% of children with mesenteric adenitis, particularly with acute infection and high inflammatory parameters 8
• Conglomerate lymph nodes: Present in 7.1% of cases, associated with various diagnoses including acute diarrhea, ulcerative colitis, and celiac disease 8