From the Guidelines
An internal hernia on CT is characterized by a cluster of dilated bowel loops in an abnormal location, often with a sac-like collection of small bowel loops displaced from their normal anatomic position, and a visible constriction at the hernia orifice creating a "closed-loop" appearance. This diagnosis can be challenging due to the nonspecific clinical picture of internal hernias 1. The CT appearance of an internal hernia typically includes crowding of mesenteric vessels converging toward the hernia defect, wall thickening, mesenteric edema, and surrounding inflammatory changes. Key findings may also include signs of bowel obstruction, such as proximal bowel dilation and distal collapse. In severe cases, pneumatosis intestinalis, portal venous gas, or free intraperitoneal fluid may be observed, suggesting bowel ischemia or perforation 1. Multiplanar reformatted images are essential for diagnosis, as they better demonstrate the relationship between the herniated bowel and surrounding structures. The specific CT appearance can vary depending on the type of internal hernia, but the primary characteristic is always bowel located outside its normal anatomic compartment with evidence of transition through a defect. Accurate preoperative diagnosis of internal hernias is possible only with computed tomography, which can identify ischemia and necrosis, especially in adhesive small bowel obstruction and sigmoid volvulus 1.
From the Research
CT Findings of Internal Hernias
- Evidence of small bowel obstruction (SBO) is a common manifestation of internal hernias, with strangulating SBO being the most common type 2
- A saclike mass or cluster of dilated small bowel loops at an abnormal anatomic location in the presence of SBO can be indicative of an internal hernia 2
- An engorged, stretched, and displaced mesenteric vascular pedicle and converging vessels at the hernial orifice can also be seen on CT scans 2
- CT signs common to all types of internal hernia include evidence of small-bowel obstruction, clustering of small bowel, stretched, displaced, crowded, and engorged mesenteric vessels, and displacement of other bowel segments 3
Types of Internal Hernias and Their CT Appearance
- Paraduodenal hernias can demonstrate a sac-like mass of small-bowel loops interposed between the stomach and pancreatic tail and a posterior mass effect on the stomach 3
- Transmesenteric hernias can show clustered small-bowel loops adjacent to the abdominal wall without overlying omental fat and central displacement of colon, and are frequently complicated by small-bowel volvulus and bowel ischemia 3
- CT findings of internal hernias can vary depending on the type and location of the hernia, and knowledge of the normal anatomy of the peritoneal cavity and the characteristic anatomic location of each type of internal hernia is essential for preoperative diagnosis 2, 4
CT Criteria for Diagnosing Internal Hernias
- A cluster of small bowel segments, crowding and convergence of mesenteric vessels, mesenteric vessel engorgement, and mass effect to the surrounding bowels are CT features most suggestive of internal hernia versus adhesive small bowel obstruction 5
- The most specific CT criteria for the diagnosis of internal hernia, rather than adhesive small bowel obstruction, are engorged mesenteric vessels, mass effect to surrounding organs, and bowel wall thickening 5
- CT can also demonstrate signs of volvulus and bowel ischemia, such as localized mesenteric fluid, mesenteric infiltrates, bowel wall thickening, and intramural hemorrhage 5