Mesenteric adenitis

Mesenteric adenitis is a self-limiting inflammatory process that affects the mesenteric lymph nodes in the right lower quadrant, and is clinically often mistaken for acute appendicitis.

Epidemiology

Mesenteric adenitis is most common in children and adolescents although it may occasionally affect adults. 

Clinical presentation

Presentation is similar (or can be identical) to acute appendicitis, hence is a differential diagnosis for right iliac fossa (RIF) pain. 

Pathology

Pathogens are thought to gain access via intestinal lymphatics, and then multiply in mesenteric lymph nodes. On gross pathology, lymph nodes are enlarged and soft. On microscopy, there is non-specific hyperplasia and when suppurative, there is necrosis and pus.

Mesenteric adenitis has a number of causes:

• variety of viruses
• Yersinia enterocolitica
• Helicobacter jejuni
• Campylobacter jejuni
• Salmonella spp.
• Shigella spp.

Yersinia enterocolitica is considered the most common pathogen in temperate Europe, North America and Australia. It is more common in boys.

Occasionally in young children and infants, ileocolitis may be also present suggesting that the lymph node involvement may be secondary to a primary enteric pathogen.

Radiographic features

As mesenteric adenitis usually presents in the young, ultrasound is often the investigation of choice. CT is usually reserved for older patients, if needed at all. 

Features on either modality include: 

• enlarged lymph nodes
  • 3 or more nodes with a short-axis diameter of at least 5 mm clustered in the right lower quadrant (see normal mesenteric lymph nodes) ^1,2
    • ​​enlarged lymph nodes are located anterior to the right psoas in the majority of cases, or in the small bowel mesentery ⁶.
• ileal or ileocaecal wall thickening may be present
  • wall is thicker than 3 mm over at least 5 cm of the bowel despite bowel lumen opacification (CT) and distention
• a normal appendix (if able to be identifiedseen)

Treatment and prognosis

In most cases, mesenteric adenitis is self-limiting, and typically abates over the course of a few weeks. 

Interestingly, when mesenteric adenitis (or appendicitis) occurs in childhood or adolescence, there is a significantly reduced risk of ulcerative colitis later in life ³.

Differential diagnosis

The clinical differential includes:

• acute appendicitis
  • lymph nodes are generally smaller and fewer lymph nodes
  • abnormal appendix is abnormal
• intussusception
• Meckel diverticulitis