Small bowel mesentery internal hernias (alternative plural: herniae) are a form of internal bowel herniation, involving protrusions of viscera through defects in the peritoneum or bowel mesentery. This type of internal herniation is more often seen in neonates than in adults.
There are two types:
transmesenteric small bowel internal hernia
- much more common
- occurs through a defect in the mesentery
intramesenteric (mesenteric pouch hernia)
- occurs into the mesentery through a mesenteric defect
- predominantly in pediatric patients
The most common presentation is with small bowel obstruction. Sometimes they can have mostly silent symptoms of nausea and epigastric discomfort only.
In adults, transmesenteric hernias may be congenital, but may also result from mesenteric defects caused by trauma, inflammation, or surgery.
Small bowel internal mesenteric hernias manifest as proximal small bowel dilatation and an abrupt change in caliber at the level of the mesenteric defect. Mesenterial stranding sign is often associated. The mesenteric vascular pedicle can be engorged or stretched.
Transmesenteric small bowel internal hernias do not typically show a "sac-like" cluster of vessels (like a paraduodenal internal hernia), and differentiation between a transmesenteric internal hernia and a small bowel obstruction from other causes can sometimes be difficult.
Intramesenteric small bowel internal hernias may appear "sac-like", with anterior and superior displacement of the superior mesenteric artery.
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