CT Case 069

The stomach is extremely distended, with dependent contents within the stomach.

There is obstruction with transition point in the region of the second part of duodenum.

The head of the pancreas is seen partially encasing the duodenum at this region with the distal duodenum being collapsed.

This suggests the possibility of an incomplete annular pancreas causing gastric outlet obstruction.

In a complete annular pancreas, pancreatic parenchyma is seen to completely encase the duodenum, whereas in incomplete annular pancreas, it gives a “crocodile jaw” appearance.

Annular pancreas results from a failure of the ventral pancreatic bud to rotate with the duodenum, resulting in encasement of the duodenum.

This case demonstrates a patient with gastric outlet obstruction (GOO).

The aetiology of GOO has changed over the past decades.

Previously, peptic ulcer disease and its sequelae were responsible for up to 90% of cases.

However, with the eradication of H. Pylori and the advent of protein pump inhibitors it is now estimated that the majority of cases (between 50 and 80%) are attributed to malignancy.

Of the benign causes, PUD accounts for approximately 90% of cases. Caustic ingestions, inflammatory diseases such as Crohn’s and TB, and NSAID induced strictures are other causes to consider.

Pancreatic and gastric cancers are the most common malignant causes.

Duodenal, biliary tract, metastatic malignancy and lymphoma may also result in GOO.

Annular pancreas, is a non-malignant cause of GOO. Approximately two-thirds of patients with annular pancreas are asymptomatic.

When symptomatic, patients will present with abdominal pain, nausea, post-prandial fullness, and as in this case with gastric outlet obstruction.

Only symptomatic cases of annular pancreas will require intervention.

Surgery is the mainstay of treatment for symptomatic cases. The goal of surgery is to relieve the duodenal or gastric outlet obstruction.

Resection of the annulus is avoided as it can be associated with pancreatitis and pancreatic fistula formation.

Instead, a duodenojejunostomy or gastrojejunostomy is performed to bypass the annulus.

And what of his blood gas?

There is a hypokalaemic, hypochloraemic metabolic alkalosis with partial respiratory compensation.

This may seem familiar as the gas that if seen infants with pyloric stenosis. Indeed, it is the picture of gastric outlet obstruction with profuse vomiting.

The hypochloraemia, hypokalaemia and metabolic alkalosis are due to the loss of chloride, potassium and hydrogen in the vomitus.

• Mittal S, Jindal G, Mittal A, Singal R, Singal S. Partial annular pancreas. Proc (Bayl Univ Med Cent). 2016 Oct;29(4):402-403
• Jeong SJ, Lee J. Management of gastric outlet obstruction: Focusing on endoscopic approach. World J Gastrointest Pharmacol Ther. 2020 Jun 9;11(2):8-16.