Can CT Scan Diagnose Internal Hernia?
Yes, CT scan with IV contrast is the primary diagnostic imaging modality for internal hernias and can confidently diagnose most cases, though preoperative diagnosis remains challenging due to nonspecific clinical presentations. 1
Diagnostic Performance of CT for Internal Hernias
CT demonstrates high diagnostic capability for internal hernias with sensitivities ranging from 75-100% and specificities from 61-93% for small bowel obstruction, which is the most common presentation of internal hernias. 1 However, a critical caveat exists: despite CT's technical capabilities, preoperative diagnosis of internal hernia specifically is frequently missed—in one large series of 49 cases, while 16% of CT scans were suspicious for internal hernia, the actual preoperative diagnosis was made in zero cases. 2
Key CT Findings for Internal Hernias
CT signs that should raise suspicion for internal hernia include: 3, 4
- Clustered or sac-like mass of small bowel loops at an abnormal anatomic location in the presence of small bowel obstruction
- Stretched, displaced, crowded, and engorged mesenteric vessels converging at the hernial orifice
- Displacement of other bowel segments, particularly the transverse colon and fourth portion of the duodenum
- Clustered small bowel loops adjacent to the abdominal wall without overlying omental fat (characteristic of transmesenteric hernias)
Specific Hernia Types and CT Characteristics
Transmesenteric Hernias (Most Common)
Transmesenteric hernias account for 57-83% of internal hernias and are usually related to prior abdominal surgery, especially Roux-en-Y anastomosis creation. 2, 5 CT findings include clustered small bowel loops adjacent to the abdominal wall without overlying omental fat and central displacement of colon. 3 These hernias are frequently complicated by small bowel volvulus (36% of cases) and bowel ischemia (43% of cases). 3
Paraduodenal Hernias
Left-sided paraduodenal hernias demonstrate a sac-like mass of small bowel loops interposed between the stomach and pancreatic tail with posterior mass effect on the stomach. 3 All paraduodenal hernias in one series were diagnosed confidently at retrospective CT review. 3
Critical Imaging Protocol Considerations
CT with IV contrast is preferable for evaluating suspected internal hernias because it demonstrates whether bowel is perfusing normally or is potentially ischemic. 1 This is crucial because internal hernias lead directly to both obstruction and ischemia if untreated, representing closed-loop small bowel obstruction. 1
Multidetector CT with multiplanar reconstruction capabilities significantly increases accuracy and confidence in locating the transition zone in small bowel obstruction. 1 Multiplanar reformations are particularly useful adjuncts when surgical intervention is planned. 1
Signs of Bowel Ischemia on CT
When present, CT signs of ischemia are highly specific but unfortunately not sensitive (sensitivity only 14.8-51.9% in prospective studies). 1 CT signs of volvulus were demonstrated in 67% of patients with ischemia in internal hernia cases. 3 Key ischemic findings include: 1
- Reduced or absent bowel wall enhancement
- Bowel wall thickening with target enhancement
- Mesenteric edema and intraperitoneal fluid
- Absence of small bowel feces (suggesting early surgical intervention should be considered)
Clinical Context and Pitfalls
The diagnosis of internal hernias is very difficult because of their nonspecific clinical picture, and internal hernias account for only 0.5-5.8% of all intestinal obstruction cases. 1, 6 However, the incidence is increasing due to modern surgical procedures including liver transplantation and gastric bypass surgery. 6, 5
A critical pitfall is that the majority of patients (75%) present with acute small bowel obstruction symptoms, while 22% have intermittent symptoms. 2 The intermittent nature can lead to delayed diagnosis, and internal hernias are associated with high mortality rates exceeding 50% in some series when diagnosis is delayed. 6
Practical Diagnostic Algorithm
When CT demonstrates small bowel obstruction without prior surgical history or external hernia: 4
- Look for clustered dilated small bowel loops at abnormal anatomic locations (not typical for adhesive obstruction)
- Trace the mesenteric vessels to identify stretching, engorgement, or convergence at a hernial orifice
- Assess for closed-loop obstruction patterns which strongly suggest internal hernia
- Evaluate bowel wall enhancement to determine if ischemia is present, which mandates urgent surgical intervention
Knowledge of normal peritoneal cavity anatomy and characteristic anatomic locations of each internal hernia type is essential for accurate CT interpretation. 4 The radiologist must actively consider internal hernia in the differential diagnosis of small bowel obstruction, particularly in post-surgical patients or those with atypical obstruction patterns, as the diagnosis will be missed if not specifically sought. 2