What are the differences between the gastrointestinal (GI) system of adults and children?

Differences Between Adult and Pediatric Gastrointestinal Systems

The pediatric gastrointestinal system differs significantly from adults in anatomical distribution, histological features, and microbiome composition, which impacts disease presentation and management.

Anatomical and Histological Differences

• Children, especially those under 10 years of age, show less architectural distortion and inflammation in the colonic mucosa compared to adolescents or adults 1
• Pediatric-onset inflammatory bowel disease (IBD) is characterized by more extensive colitis and less ileitis compared to adult-onset IBD 1, 2
• Children with IBD often have more upper gastrointestinal tract involvement than adults 1, 2
• In untreated children with ulcerative colitis (UC), unusual inflammation patterns may be present, including patchiness (21%) and relative rectal sparing (30%), which is uncommon in adults 1
• Rectal sparing is more commonly diagnosed in children less than 10 years of age with UC, whereas it's rare in adults with UC 1, 3

Histopathological Differences

• Granulomas are more frequent in children with Crohn's disease (CD) than in adults, with granulomas identified in 61% of untreated pediatric CD patients compared to lower rates in adults 1, 2
• Basal plasmocytosis is less common in children (58%) than in adults (38-100%) with IBD, though it remains an early feature in young children 1
• Upper gastrointestinal inflammation is present in up to 75% of children with UC, including esophagitis, mild non-specific gastritis, or focally enhanced gastritis 1
• Helicobacter pylori-negative focally enhanced gastritis is more common in children with CD (43-76%) than in those with UC (8-21%) 1

Microbiome Differences

• Children have significantly lower gut microbiome diversity compared to adults 4
• Children's gut microbiome shows higher relative abundances of genus Bacteroides, while adults have higher relative abundances of genus Blautia 4
• Pediatric gut microbiomes are enriched with Bifidobacterium spp., Faecalibacterium spp., and members of the Lachnospiraceae family, while adults harbor greater abundances of Bacteroides spp. 5, 6
• The gut microbiome of adolescents (11-18 years) differs from adults, with significantly higher abundance of genera Bifidobacterium and Clostridium 6

Functional Differences

• Children's gut microbiomes show overrepresentation of glycan degradation pathways and certain vitamin biosynthesis pathways (riboflavin, pyridoxine, folate) 4
• Adult gut microbiomes have higher abundances of carbohydrate metabolism pathways, beta-lactam resistance, and different vitamin biosynthesis pathways (thiamine, pantothenic acid) 4
• Children's gut microbiomes show predominance of catabolic pathways (amino acid degradation), while adults show more biosynthetic pathways, suggesting a functional switch occurs with aging 4, 5
• Children's gut communities are enriched in functions that support ongoing development, while adult communities show enrichment in functions associated with inflammation and increased risk of adiposity 5

Disease Presentation Differences

• Common causes of intestinal failure differ between children and adults: gastroschisis (21%), volvulus (17%), and necrotizing enterocolitis (12%) predominate in children, while ischemia (23%), Crohn's disease (14%), and trauma (10%) are more common in adults 1
• Very early onset IBD (occurring by 6 years of age) may represent a distinct entity with more severe disease behavior 2
• Children with severe CD may show chronic inflammation in all biopsies including the rectal mucosa, making differentiation from UC more challenging than in adults 1

Clinical Implications

• Pediatric patients require more careful evaluation of the upper gastrointestinal tract, as biopsies from this region are essential for identifying granulomas in 42% of children with CD 1
• Children under 6 years with IBD may have underlying immune deficiencies requiring special consideration 2
• Children with IBD are more susceptible to hepatic complications from total parenteral nutrition (TPN) than adults, with higher rates of simultaneous hepatic replacement needed during intestinal transplantation (50% in children vs. 21% in adults) 1
• Medication dosing must be adjusted for children, as demonstrated by specific pediatric dosing recommendations for drugs like omeprazole 7

Common Pitfalls to Avoid

• Failing to consider very early onset IBD as a potential manifestation of underlying immune deficiency in children under 6 years 2
• Overlooking the possibility of UC in young children with atypical histological presentation 1
• Missing granulomatous inflammation due to inadequate tissue sampling in pediatric patients 1
• Assuming that rectal sparing excludes UC in pediatric patients, as this feature is more common in children than adults 1, 3
• Failing to recognize that the pediatric gut microbiome continues to develop beyond early childhood, contrary to previous beliefs that it stabilizes after the first 1-3 years of life 5, 6