Internal hernias represent a complex pathological entity with a subtle and often confusing clinical presentation, making radiologist’s role crucial in accurate patient assessment. As with many acute abdomen cases, ultrasound (US) and conventional radiography are typically the first-line imaging techniques, especially in the emergency setting, with CT often being considered only at a later stage of the diagnostic process.

Conventional radiology and/or US may show unspecific signs of small bowel obstruction, such as dilated bowel loops with enlarged walls and intraperitoneal fluid resulting from the possible ischemic lesion associated with the bowel herniation and strangulation.

CT scan certainly shows more specific findings such as enlarged dilated bowel loops with a sac-like appearance, with signs of ischemia such as lack of mural enhancement, pneumatosis, interloop fluid, and abnormal bowel wall thickness. Another typical sign of IH on CT is the swirl sign characterised by the twisting and stretched appearance of mesenteric vessels towards the site of herniation.

A series of clinical cases is presented to showcase the diverse imaging appearance of internal hernias ranging from incidental findings to acute surgical emergencies. These patients were evaluated at the emergency radiology department of Ospedale Maggiore di Bologna where they initially underwent US and/or conventional radiographic examinations followed by contrast-enhanced CT studies.

CASE 1.

Fig 8: Case 1: the abdominal x-ray (a), shows no specific gas pattern with a round opacity in the low abdomen (white arrows). The coronal CT view in portal-venous phase (b), demonstrates that the opacity seen on x-ray corresponds to a cluster of small intestinal bowel loops filled with fluid (white arrows). On the axial (b) and sagittal (d) view we can observe the presence of an herniation port (yellow arrow) with signs of ischemic associated lesion such as mesenteric effusion and wall thickening, leading to the diagnosis of a transmesenteric internal hernia.

67 years old, male patient, presenting to the emergency department with acute abdominal pain and spontaneous loss of urine with history of renal and vesical litiasis. Patient firstly underwent conventional abdominal x-ray (fig 8.a) demonstrating diffuse bowel dilatation with no specific gas pattern, and a round opacity in the low quadrants suspected as bladder outlet obstruction. Contrast enhanced CT (fig 8.b,c,d) found a clustered sac-like appearance of dilated bowel loops in the low abdominal quadrants with stretched and engorged mesenteric vessels towards the site of the bowel cluster suggesting an Internal Abdominal hernia.

CASE 2

Fig 9: Case 2: abdominal US (a) showing some dilated bowel loops in the low right flank with a thin fluid layer between them (white arrow). The axial (b) and coronal (b) view of the CT scan in portal-venous phase show an herniation port (white arrow) in the low right quadrant with the caecum displaced medially by the herniated loops suggesting the presence of a paracolic internal hernia.

43 years old woman with abdominal pain prevailing in the right flank. The abdominal US exam (Fig 9.a) shows fluid filled dilated bowel loops in the right flank with associated peritoneal effusion in the right parietocolic shower. CT scan (fig 9.b-c) reveals at the site of the ecographic findings, a small herniation port with engorged and stretched mesenteric vessels with dilated fluid-filled bowel loops adjacent to the latter, suggesting a small bowel occlusion (SBO) due to internal hernia. 

CASE 3

Fig 10: Case 3: abdominal x-ray (a) showing air-fluid levels in the middle abdomen (white arrows). US examination (b) in the same region shows fluid filled bowel loops with associated abdominal effusion in the explored quadrants. The axial (c) and sagittal (d) CT scans demonstrate an herniation port in the middle abdomen (orange dotted line) with a whirl appearance of the mesenteric vessels (yellow arrow) demonstrating a trans-mesenteric internal hernia.

Male patient, 46 years old, admitted to the emergency department with persisting headache and epigastric pain arising in the morning accompanied by nausea. In his medical history he reports a previous appendectomy. First an abdominal ultrasound was performed (fig. 10.b) which showed the presence of some dilated fluid-filled bowel loops in the left side with an associated minimal fluid effusion between them. An x-ray of the abdomen (fig 10.a) is then performed, which confirms the presence of a few small bowel loops with different fluid levels in the middle abdomen and left flank in the absence of free air. On CT examination (10.c-d) distressed loops with vascular engorgement are revealed, with an associated stretched vascular pedicle conforming the classic “whirl sign”, highly suggestive of an internal hernia.

CASE 4

Fig 11: Case 4: abdominal x-ray (a-b) shows dilated small bowel loops in the upper right quadrant with multiple air-fluid levels (white arrows). On the axial CT scan (b) there is a whirl of mesenteric vessels (yellow arrow) and dilated adjacent bowel loops. On the sagittal CT scan (c) we can better appreciate the herniation point with a caliber transition point of an herniated bowel loop (yellow arrow), suggesting a trans-mesenteric internal hernia.

A 48-year-old male patient presenting with abdominal pain and constipation, with previous right kidney transplant surgery. On X-ray examination of the abdomen (11.a-11.b) some dilated small bowel loops in the right hypochondrium with associated air-fluid levels are appreciated. The CT scan (11.c-11.d) confirms the presence of packed multiple loops of the small intestine in the right lower-middle abdominal quadrants with stretched appearance of the mesenteric vessels. Additionally there is a C-shaped calibre transition point suggestive of closed loop bowel occlusion caused by internal hernia.

CASE 5

Fig 12: Case 5: abdominal x-ray (a-b) showing no specific gas pattern. On the lateral view (b) there is a slight wall thickening of some dilated bowel loops in the anterior abdominal region (white arrows). On the axial and sagittal CT scans in portal-venous phase (c-d) we can appreciate a diffuse small bowel dilatation with signs of serious ischemic distress such as pneumatosis (white asterisk) and an herniation port on the sagittal view (orange dotted line). The MIP coronal recontruction of the CT scan in arterial phase (e) highlights the herniation point where the superior mesenteric artery abruptly closes (yellow arrow).

A 28-year-old female patient presents to the emergency department with diffuse abdominal pain. An initial abdominal X-ray in two projections (AP and tangential) (fig 12 a-b) shows a parietal thickening of some intestinal loops, likely of the small intestine, in the anterior abdominal regions. Subsequently, an abdominal CT scan with contrast (Fig. 12c–d-e) is performed, revealing a significant and widespread abdominal effusion with multiple dilated intestinal loops filled with fluid. The dilated loops also show signs of ischemic distress (parietal thickening and lack of contrast enhancement) associated with a stretched appearance of the mesenteric pedicle. The findings are highly suggestive of small bowel obstruction due to internal hernia with signs of advanced intestinal ischemia, requiring urgent surgical evaluation.

CASE 6

Fig 13: Case 6: Axial CT scan in the portal venous phase (a) shows lateral displacement of the pancreas (white arrow) due to an adjacent dilated small bowel loop near the liver hilum. A caudal slice of the same scan (b) reveals a twisted appearance of the mesenteric vessels (white arrow) associated with the dilated bowel loop. On the coronal reconstruction (c), the stretching and displacement of the mesenteric trunk (yellow arrow) are clearly appreciable. Axial (d) and coronal (e) views after oral contrast administration demonstrate the re-establishment of normal peritoneal anatomy, with the pancreas (yellow arrow) returning medially to its original position..

A 51-year-old woman presented to the emergency department with acute abdominal pain. An initial contrast-enhanced CT scan (Fig. 13 a-b-c) revealed a dilated small bowel loop in the mid-abdomen, near the liver hilum, displacing the pancreas laterally. The mesenteric vessels were also displaced laterally by the dilated loops and appeared stretched, with an associated twisting observed in the caudal slices.

The patient was then given an oral contrast solution, and a follow-up scan was performed (Fig. 13 d-e), showing resolution of the previous CT findings and re-establishment of normal anatomy, correlating with the patient’s clinical improvement. Further image evaluation confirmed the presence of a right paraduodenal internal hernia, which had spontaneously resolved after oral contrast administration.