Teaching Case

The patient presented with acute onset of severe abdominal pain with non-bilious vomiting, which was not responding to medication.

Plain radiograph of the abdomen taken in erect position showed non-specific findings with normal position of the stomach bubble, few air fluid levels in the small intestinal loops and no free gas under the diaphragm.
CT findings were characteristic for right paraduodenal hernia in which the herniated loop could be seen lying below the third part of the duodenum, behind the root of small bowel mesentery. Multiplanar reconstruction further clarified the relation of the loop and demonstrated the characteristic whirlpool sign. On contrast-enhanced imaging, the vascular relations of the hernia were appreciated in which the superior mesenteric artery and vein were noted along the free edge of the fossa of Waldeyer. The bowel wall thickness and attenuation further helped in assessing bowel viability and need for surgery. Hyperattenuation on NCCT pointed towards intramural haemorrhage or haemorrhagic infarction while mesenteric and bowel wall hyperemia on CECT denoted venous occlusion.

Internal hernias have been defined by Meyers et al [1] as protrusion of abdominal viscera through an opening within the confines of the peritoneal cavity. These orifices can be congenital or acquired. Internal hernias account for approximately 4% of cases of sudden onset small bowel obstruction (SBO) [2] and present with acute pain in the abdomen, abdominal distension, vomiting and nausea. Diagnosis of internal hernias if difficult clinically and warrants the need for imaging. Multidetector CT scan with intravenous contrast is an important diagnostic modality which points to the exact site of the hernia along with the status of the herniating bowel segment. [3]
Internal hernias have a broad spectrum and include herniating loops into the retroperitoneum through an orifice in the peritoneal cavity. One such hernia is paraduodenal hernia which can be either on the left or right of the duodenum and occurs through an unusual peritoneal recess into the retroperitoneum. [4] The orifice on the left is the fossa of Landzert, which is 3 times more common while the orifice on the right is the mesentericoparietal fossa of Waldeyer. [1]
The fossa of Waldeyer results from failure of fusion of the ascending mesocolon with the posterior parietal peritoneum. It is located below the third part of the duodenum with the superior mesenteric vessels running along the medial free edge of the fossa. It extends rightward and downward towards the ascending mesocolon, thus displacing the left colic vein anteriorly by the entrapped intestinal loops.
The diagnostic findings on CT include a herniated sac containing the bowel lying below the third part of the duodenum, behind the mesentery of the small bowel, displacing the left colic vein anteriorly with the superior mesenteric vessels running along its medial free edge. Presence of a whirlpool sign, which signifies bowel rotation around its mesentery, indicates that the patient is 25.3 times as likely as a patient without the sign to need surgery for SBO. [5] Hypoattenuation of bowel wall on NCCT indicated wall oedema which occurs due to venous congestion in case of strangulated hernia. Homogeneous/heterogeneous hyperattenuation of the bowel wall on NCCT denotes mural haemorrhage/haemorrhagic infarction. Diffuse or focal hyperaemia of the bowel wall and surrounding mesentery on CECT typically occurs in cases of mesenteric venous occlusion and subsequent outflow obstruction. CT findings help in the assessment of bowel wall viability and thus help in clinical decision making. [6]
Awareness about this entity is necessary to make ab accurate radiological diagnosis for appropriate patient management.

Written informed patient consent for publication has been obtained.