Introduction :

Internal hernias are protrusions of the viscera through the peritoneum or mesentery but remaining within the abdominal cavity.

The most common presentation is an acute obstruction of small bowel loops that pass through normal or abnormal apertures. Internal hernias not infrequently self-resolve, making imaging at the time of symptomatology vital. The orifice that the small bowel herniates through is usually a pre-existing anatomic structure, such as foramina, recesses, and fossae (e.g. fossa of Landzert),

This is a report of a patient with a transmesenteric hernia

Clinical Profile:

A 52-year-old man came with complaints of pain in the abdomen and vomiting for one week. There was no history of constipation or obstipation. There were no other co-morbidities. He had no history of TB or of prior surgery. 

Clinical examination revealed a slightly distended and non tender abdomen. There was no palpable lump.

Radiological findings:

1. Erect x-ray abdomen (Fig, 1)  The bowel loops are displaced to the periphery of the abdomen. There is paucity of the bowel loops in centre. There is a soft tissue opacity in the left paravertebral region at L2-L3 level displacing the bowel loops to the left.

Fig 1 The bowel loops are displaced to the periphery of the abdomen. There is paucity of the bowel loops in centre. There is a soft tissue opacity in the left paravertebral region at L2-L3 level displacing the bowel loops to the left.

CECT Abdomen (Fig 2 a-2f) - There is large sac measuring 11x10x13.5cm in the left upper quadrant of the abdomen containing undilated, enhancing small bowel loops. The neck of the hernia is wide measuring approximately 3.2cm, anterior to D3 segment of the duodenum, anterior to the IMV and adjacent to the SMV in the infra-mesocolic compartment. There is widening of the c-loop of the duodenum. 

There is cluster of undilated normally enhancing ileal loops in the right iliac fossa, contained in a sac. These two sacs communicate with each other.

There is well-defined round to oval hyperdense (+80HU), non-enhancing focal submucosal lesion measuring 2.2x1.9x2.1cm along the anterolateral aspect of caecum. No luminal narrowing of the bowel is noted at this site. This was interpreted as a calcified GIST.

Fig 2A, 2B - The large sac in the left upper quadrant of abdomen containing undilated, enhancing small bowel loops. The neck of the hernia is wide, anterior to D3 segment of the duodenum, anterior to the IMV and adjacent to the SMV in the infra-mesocolic compartment. 

Fig 2C - The cluster of undilated normally enhancing ileal loops in the right iliac fossa, contained in a sac.

Fig 2D – The communication between the sacs in right iliac fossa and left upper quadrant.

Fig 2E – The SMV and SMA relation is maintained. There is herniation of bowel loops through foramen of Winslow.

Fig 2F – A well-defined round to oval hyperdense(+80HU) non-enhancing focal submucosal lesion along the anterolateral aspect of caecum.

Radiological diagnosis:  

Internal transmesenteric hernia.

Management:

Elective hernial repair is planned.

Discussion

Internal hernias are protrusions of the viscera through the peritoneum or mesentery but remaining within the abdominal cavity.

The most common presentation is an acute obstruction of small bowel loops that develops through normal or abnormal apertures. Internal hernias not infrequently self-resolve, making imaging at the time of symptomatology vital. The orifice that the small bowel herniates through is usually a pre-existing anatomic structure, such as foramina, recesses, and fossae (e.g. fossa of Landzert). Pathologic defects of the mesentery and visceral peritoneum, such as from congenital maldevelopment of the mesenteries, and surgery also create potential internal herniation orifices. Internal hernias have a low incidence of < 1% and represent a relatively small proportion, up to 5.8%, of presentations with small bowel obstruction (1).

Types:

• left and right para-duodenal hernias (most common; ~55%1)

• lesser sac (foramen of Winslow) hernia

• peri-caecal hernia

• sigmoid mesocolon hernias

o intersigmoid hernia

o transmesosigmoid hernia

o intramesosigmoid hernia

• small bowel mesentery internal hernia

o intramesenteric hernia

• transomental hernia

• supravesical hernia

o internal supravesical hernia

• pelvic internal hernia

o broad ligament hernia

• falciform ligament hernia

• internal hernia due to gastric bypass surgery

1. Paraduodenal hernia:

Paraduodenal hernias are internal hernias due to failure of the descending or ascending colonic mesentery to fuse with the posterior parietal peritoneum. Left paraduodenal hernias are more common and can cause closed-loop bowel obstruction and infarction.

2. Transmesenteric Hernia

Transmesenteric hernias are a type of internal hernia, where abdominal contents protrude through the foramen of Winslow, hence they are also known as foramen of Winslow hernia. 

Plain radiograph shows gas-filled loops of small bowel in the upper abdomen.

CT scan findings (5)

-mesenteric fat/vessels posterior to portal vein, common bile duct, hepatic artery and anterior to the inferior vena cava.

-mesenteric vessels passing into the lesser sac via the foramen of Winslow.

-gas and/or fluid in the lesser sac with bird beak sign towards the foramen of Winslow.

Radiological features:

Plain radiograph may show signs of obstruction or gas filled bowel loops.

On ultrasonography, a cluster of bowel loops may see on one side of the abdomen.

CT is the gold standard imaging modality for the assessment of bowel obstruction and suspected internal hernias. The appearance depends on the particular internal hernia as described above. Common features include (6)

• encapsulation of distended bowel loops within an abnormal location

• arrangement or crowding of small bowel loops within a hernial sac

• evidence of obstruction with segmental dilatation and stasis

• mesenteric vessel abnormalities

o engorgement, crowding, twisting, stretching of mesenteric vessels.

Conclusion: 

Though the incidence of internal hernias is low, they should be considered as a differential diagnosis in patients with small bowel obstruction where transition point is not obvious.

References:

1) Martin LC, Merkle EM, Thompson WM. Review of internal hernias: radiographic and clinical findings. AJR Am J Roentgenol. 2006;186 (3): 703-17. doi:10.2214/AJR.05.0644 - Pubmed citation

2) Vanmali A, Maharajh J, Haines M. Left Paraduodenal Hernia: Embryological and Radiological Findings. S Afr J Radiol. 2021;25(1):1979. doi:10.4102/sajr.v25i1.1979 - Pubmed

3) Takeyama N, Gokan T, Ohgiya Y et-al. CT of internal hernias. Radiographics. 25 (4): 997-1015. doi:10.1148/rg.254045035 - Pubmed citation

4) Doishita S, Takeshita T, Uchima Y et-al. Internal Hernias in the Era of Multidetector CT: Correlation of Imaging and Surgical Findings. Radiographics. 2016;36 (1): 88-106. doi:10.1148/rg.2016150113 - Pubmed citation

5) Forbes SS, Stephen WJ. Herniation through the foramen of Winslow: radiographic and intraoperative findings. Can J Surg. 2006;49 (5): 362-3. Free text at pubmed - Pubmed citation

6) Fitzgibbons RJ, Greenburg AG. Nyhus and Condon? Hernia. Lippincott Williams & Wilkins. ISBN:0781719623.