Mesenteric Adenitis

Mesenteric adenitis is inflammation of the mesenteric lymph nodes, usually in the right lower quadrant, that mimics appendicitis in children and adolescents.

• It is the commonest cause of acute right iliac fossa pain with a normal appendix at surgery in children.
• It often follows an upper respiratory tract or gastrointestinal viral infection.
• Bacterial causes include Yersinia enterocolitica, Yersinia pseudotuberculosis, Salmonella and Campylobacter. Streptococcal throat infection can also be associated.
• Tuberculous mesenteric lymphadenitis occurs in endemic regions.
• It is self-limiting, usually settling within 1 to 4 weeks, but remains a diagnosis of exclusion.

Abdominal pain follows or accompanies a recent infection.

• Colicky or constant right lower abdominal pain, periumbilical at first.
• Fever, sore throat, cough or coryza within the past days.
• Nausea, and sometimes vomiting or diarrhoea.
• Tenderness in the right iliac fossa without marked guarding, and tenderness that shifts with change of position (shifting tenderness, as lymph nodes are mobile).
• Cervical lymphadenopathy may be present.
• Differential diagnosis: appendicitis, Crohn disease, terminal ileitis, intussusception, ovarian torsion, ovarian cyst, urinary tract infection, constipation, Meckel diverticulum, lymphoma, tuberculosis and Henoch-Schonlein purpura.
• Complications: usually none. Rarely mesenteric abscess, bowel obstruction from adhesions and chronic recurrent pain. Misdiagnosis of appendicitis is the main risk.

Diagnosis is by exclusion, supported by ultrasound.

• Abdominal ultrasound: three or more enlarged mesenteric lymph nodes in the right iliac fossa, each 8 to 10 mm or more in short axis, and a normal appendix (a non-compressible appendix wider than 6 mm points to appendicitis instead).
• Full blood count and C-reactive protein (often mildly raised).
• Urinalysis. Pregnancy test in adolescent girls.
• Stool culture if diarrhoea. Throat swab if sore throat. Yersinia serology or culture where indicated.
• Computed tomography when ultrasound is inconclusive and appendicitis remains likely.
• Observation with serial examination if uncertain.

Reassurance and symptomatic care after exclusion of appendicitis.

• Supportive: oral fluids, rest, and serial examination for 12 to 24 hours if there is any doubt.
• Pharmacological: paracetamol 15 mg/kg every 6 hours (maximum 1 g per dose, 4 g per day) or ibuprofen 5 to 10 mg/kg every 8 hours after food. Avoid unnecessary opioids that obscure examination.
• Antibiotics are not routine. For confirmed Yersinia in severe or bacteraemic disease: ciprofloxacin 10 to 15 mg/kg twice daily or cotrimoxazole for 5 to 7 days. For streptococcal pharyngitis: phenoxymethylpenicillin 250 mg twice daily (under 12 years) for 10 days.
• Tuberculous adenitis requires four-drug antituberculosis treatment (isoniazid, rifampicin, pyrazinamide and ethambutol for 2 months, then isoniazid and rifampicin for 4 months) under specialist care.
• Procedures: laparoscopy if appendicitis cannot be excluded. Lymph node biopsy for persistent, enlarging nodes.
• Special groups: adolescent girls need gynaecological causes excluded. Immunocompromised children need extended work-up.
• Red flags: persistent focal tenderness, guarding, fever above 39 °C, vomiting, peritonism, an abdominal mass, weight loss and symptoms beyond 4 weeks.
• Follow-up: review in 24 to 48 hours. Return if pain worsens or localises. Persistent symptoms over 4 weeks need further investigation.