Afferent Loop Syndrome

Updated: May 15, 2019
  • Author: Suresh Kumar Nayudu, MD; Chief Editor: BS Anand, MD  more...
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Afferent loop syndrome (ALS) is a purely mechanical complication that infrequently occurs following the construction of a gastrojejunostomy. Creation of an anastomosis between the stomach and jejunum leaves a segment of the small bowel, most commonly consisting of the duodenum and proximal jejunum, lying upstream from the gastrojejunostomy. This limb of the intestine transfers bile, pancreatic juices, and other proximal intestinal secretions toward the gastrojejunostomy and is thus termed the afferent loop. See the images below.

Afferent limb syndrome. Kinking of the afferent li Afferent limb syndrome. Kinking of the afferent limb at the gastrojejunostomy.
Afferent limb syndrome. Tracing of kinking of the Afferent limb syndrome. Tracing of kinking of the afferent limb at the gastrojejunostomy.

For patient education resources, see Digestive Disorders Center, as well as Peptic Ulcers and Anatomy of the Digestive System.


Relevant Anatomy

The afferent loop consists of the duodenal stump, the remainder of the duodenum, and the segment of jejunum proximal to the gastrojejunostomy. The clinically relevant portion of the loop pertaining to ALS is the jejunal portion of the afferent limb. The jejunal limb is subject to adhesion formation, internal herniation, volvulus, anastomotic obstruction, and other etiologies of ALS, as described below.




ALS manifests in acute and chronic forms. Acute ALS represents complete obstruction of the afferent loop and is a true surgical emergency. It must be diagnosed and corrected expeditiously. Chronic ALS is associated with partial obstruction. It is not a surgical emergency but does require corrective surgery.


An afferent loop is composed of the duodenal stump, the remainder of the duodenum, and the segment of jejunum located proximal to a Billroth II–type gastrojejunostomy. ALS is caused by complete or partial mechanical obstruction at the gastrojejunostomy or at a point along the jejunal portion of the afferent loop.

Passage of food and gastric secretions through the gastrojejunostomy and into the efferent loop triggers the release of secretin and cholecystokinin. These enteric hormones stimulate the secretion of bile, pancreatic enzymes, and pancreatic bicarbonate and water into the afferent loop. Under gastrointestinal hormonal influence, up to 1-2 L of pancreatic and biliary secretions can enter the afferent loop each day.

Symptoms associated with ALS are caused by increased intraluminal pressure and distention due to the accumulation of enteric secretions in a partially or completely obstructed afferent limb. ALS is one of the main causes of duodenal stump blowout in the early postoperative period and is also an etiology for postoperative obstructive jaundice, ascending cholangitis, and pancreatitis due to the transmission of high pressures back into the biliopancreatic ductal system. [1] High luminal pressures and distention increase bowel wall tension in the afferent loop (in accord with the Laplace law) and can lead to ischemia and gangrene with subsequent perforation and peritonitis.

Secondarily, prolonged stasis and pooling of secretions with partial obstruction facilitate bacterial overgrowth in the afferent loop. [2] Bacteria deconjugate bile acids, which can lead to steatorrhea, malnutrition, and vitamin B-12 deficiency leading to megaloblastic anemia.

A variety of investigations have been performed to confirm the diagnosis of bacterial overgrowth and include jejunal aspiration, 14 carbon D-xylose breath testing, hydrogen breath testing using glucose or galactose, and 14 carbon-glycocholic breath testing. However, as none of these investigations have been standardized, treatment is often initiated clinically when there is a high index of suspicion. Although the mechanism behind iron deficiency is complex, iron deficiency can also develop due to the bypassing of the proximal small bowel and achlorhydria which impairs iron solubility.

The severity at presentation mainly depends on the degree and duration of obstruction.


History of the Procedure

The surgical procedures most commonly associated with this complication include distal or subtotal gastrectomies for peptic ulcer disease or gastric malignancies with Billroth II reconstructions, pancreaticoduodenectomies, and gastrojejunostomies performed to bypass other foregut pathology. The pathophysiology and signs and symptoms associated with ALS result from partial or complete obstruction of the afferent loop.

ALS is included in the constellation of resectional gastric surgical complications known as the postgastrectomy syndromes. The following syndromes are included:

  • Early dumping syndrome [3]

  • Late dumping syndrome [4]

  • Postvagotomy diarrhea [5]

  • Chronic gastric atony [6]

  • Roux stasis syndrome [7]

  • Small gastric remnant syndrome [8]

  • Alkaline reflux gastritis [9]

  • Afferent loop syndrome [10]

  • Efferent loop syndrome [10]

Patients with ALS may present with an acute, completely obstructed form or with a chronic, partially obstructed form. The syndrome can manifest at any time from the first postoperative day to many years after surgery. The acute form usually occurs in the early postoperative period (1-2 wk), but it has been described to occur 30-40 years after surgery.

In 1942, McNealy first described acute ALS as a cause of early postoperative duodenal stump leakage. Lake is credited with recognizing the chronic form in 1948. Roux and coworkers coined the term afferent loop syndrome in 1950. [11] The first detailed description in the English literature of the etiology, clinical presentation, and treatment of ALS was contributed by Wells and Welbourn in 1951. [12]



Postoperative conditions

Each of the following postoperative conditions can cause ALS in a patient with a gastrojejunostomy:

  • Entrapment or compression of the afferent loop by postoperative adhesions

  • Internal hernia (eg, through a mesocolic defect) [13]

  • Volvulus of the intestinal segment

  • Enteroenteral or enterogastric intussusception

  • Kinking of the afferent limb at the gastrojejunostomy (see the following images)

    Afferent limb syndrome. Kinking of the afferent li Afferent limb syndrome. Kinking of the afferent limb at the gastrojejunostomy.
    Afferent limb syndrome. Tracing of kinking of the Afferent limb syndrome. Tracing of kinking of the afferent limb at the gastrojejunostomy.
  • Scarring due to marginal (stomal) ulceration [14]

  • Recurrence of cancer at or near the anastomotic site

  • Enteroliths in the afferent limb [15, 16, 17, 18]

  • Bezoars in the afferent limb or at the anastomosis [19]

  • Foreign bodies in the afferent limb or at the anastomosis

Surgical technique

Patients have an increased chance of developing ALS if one or more of the following conditions is met:

  • The jejunal portion of the afferent limb is longer than 30-40cm in length.

  • The gastrojejunostomy is placed in an antecolic position instead of a retrocolic position.

  • Mesocolic defects are not properly closed after construction of a retrocolic gastrojejunostomy.

Bushkin and Woodward reported an equal incidence of ALS in patients with short, retrocolic afferent limbs. [20] However, according to Eagon and coworkers, most authors opine that longer, redundant, and antecolic afferent limbs are more prone to kinking, volvulus, and entrapment by adhesions. [10]



United States and international data

In the United States, ALS affects approximately 1% of patients undergoing gastric resection and Billroth II gastrojejunostomy. This figure may be an underestimation because this complication is probably underdiagnosed. Overall, the incidence of this complication decreased dramatically during the final quarter of the 20th century as elective gastric surgery for complications of peptic ulcer disease underwent a logarithmic decline. [21, 22]

Internationally, rates for the development of this complication appear to be similar in other nations.

Sex- and age-related demographics

According to Tovey et al, one or more of the postgastrectomy syndromes is more likely to occur in female patients. [23]

ALS favors no particular age group on a per capita basis.



After a proper corrective procedure, the prognosis is usually very good, except in cases of advanced or recurrent malignancy.


Mortality rates of up to 57% have been reported for acute ALS. Mortality is most frequently associated with a delay in the diagnosis that leads to bowel infarction or rupture and peritonitis. Patients in whom a timely diagnosis is made or who present with chronic manifestations of the disease can undergo corrective surgery with acceptably low morbidity and mortality rates. 


Patients undergoing surgery for ALS are at risk of developing any of the following complications:

  • Wound infection

  • Wound dehiscence with or without evisceration

  • Urinary tract infection

  • Atelectasis

  • Pneumonia

  • Anastomotic disruption

  • Anastomotic stricture

  • Marginal ulceration

  • Intra-abdominal abscess formation

  • Cholangitis

  • Delayed gastric emptying/gastroparesis

  • Internal or enterocutaneous fistulae

  • Small bowel obstruction

  • Dumping syndrome

  • Alkaline reflux gastritis

  • Roux stasis syndrome

  • Cardiac arrhythmias

  • Deep venous thrombosis

  • Pulmonary embolism