Case 3:  Surgical anatomy -- Gastric Bypass with Afferent Loop Obstruction

This patient has suture lines dividing the proximal stomach.   There is distention of the stomach, duodenum, and proximal small bowel.  The distal small bowel is decompressed. Contrast has already passed through the terminal ileum and into the colon.  There is no free air, ascites, or bowel wall thickening.  This is an afferent loop obstruction in a patient post gastric bypass surgery.  Technically, the patient has had a Rouxen-Y gastrojejunostomy.

Small bowel obstructions are common in patients after abdominal surgery so it is useful to know the anatomy of many common small bowel procedures. One of the most common at elective procedures our institution is a gastric bypass.  A common way to perform this procedure is the Rouxen-Y gastrojejunostomy. 

The surgeon divides the stomach proximally, closing each half with a staple line.  You should always be able to see this staple line just anterior the GE junction.  The newer, smaller stomach is called the gastric remnant.  The pylorus and antrum are now called the excluded stomach. The excluded stomach, native duodenum, and native proximal small bowel constitute the afferent loop.  This loop delivers bile and pancreatic enzymes to the remainder of the small bowel.

A section of small bowel is anastamosed to the gastric remnant.  This is the gastrojejunostomy.  This segment of small bowel is called the efferent limb, and is usually about 40 cm long.  This is the expected path of food and oral contrast after surgery. The efferent loop in this example runs anterior to the stomach.  Sometimes it runs through the lesser sac posterior to the transverse mesocolon.  The distal jejuno-jejunal anastomosis is often hand sewn and the sutures are not always visible on either CT or flouroscopy.

The following still images show the staple lines anterior to the GE junction and the anterior path of the Rouxen-Y limb

Rouxen Y gastro-jejunostomies are also seen in patients who have had a partial gastrectomy for cancer or ulcer disease.  In this case, parts of the distal stomach are removed and there is no gastric remnant.  In the gastric bypass no stomach is removed.  Older partial gastrectomies were performed using the Bilroth II technique.  In this surgery the proximal small bowel is transfixed to the greater curvature with a side-to-side anastamosis.  There is no efferent limb; only an afferent limb.

In this case it is difficult to determine the anatomy because contrast has progressed distally.  The proximal bowel is dilated.  The distal bowel is decompressed and filled with contrast.  It looks like SBO but the contrast is in the wrong place.  The staple line in the proximal stomach should tell you the patient has had a surgical intervention.  By following the proximal bowel loops you can recognize the pattern of a Rouxen-Y gastrojejunostomy gastric bypass.

Obstruction of the afferent loop is a serious surgical matter.  Since the excluded stomach is no longer attached to the esophagus, nasogastric tube decompression will not work.  The patient either needs surgical decompression or placement of percutaneous gastrostomy tube.  Otherwise, the stomach will rupture.  Ascites is a worrisome sign and the surgeons should be notified.

An afferent loop obstruction usually occurs at the jejuno-jejunal anastamosis.  Causes include edema and adhesions.  In this case the cause of obstruction was an adhesion.  In a patient who has had a Bilroth II, the cause is usually recurrence of tumor or ulcer disease.

Take home points.

• If you see surgical staples at the GE junction or along the lesser curvature check to see if the patient has had Gastric Surgery.
• Obstructions of the afferent loop in a gastric bypass are an emergency becasue NGT decompression will not work.