Mesenteric adenitis (rare plural: adenitides), less commonly called mesenteric lymphadenitis (rare plural: lymphadenitides), is a self-limiting inflammatory process that affects the mesenteric lymph nodes in the right lower quadrant and is clinically often thought initially to be acute appendicitis, a common diagnostic mimic.
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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 pain. Mesenteric adenitis is often a diagnosis of exclusion after 'more serious' etiologies have been ruled out. Definitive diagnosis at surgery is possible but is increasingly uncommon due to the ubiquity of modern imaging tools.
Pathology
The pathogenic micro-organisms 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, including Epstein-Barr virus and probably COVID-19 10
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:
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enlarged lymph nodes
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3 or more (very) tender 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 muscle in the majority of cases, or in the small bowel mesentery 6
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ileal or ileocecal wall thickening may be present
thicker than 3 mm over at least 5 cm of the bowel despite bowel lumen opacification (CT) and distention
a normal appendix (if seen)
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.
Complication
Occasionally, enlarged mesenteric lymph nodes may result in vascular compromise leading to ischemic colitis 9.
Differential diagnosis
The clinical differential includes:
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generally smaller and fewer lymph nodes
abnormal appendix
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