Afferent Loop Syndrome Workup

Updated: May 15, 2019
  • Author: Suresh Kumar Nayudu, MD; Chief Editor: BS Anand, MD  more...
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Laboratory Studies

Complete blood count

Blood should be drawn for a complete blood count (CBC). Areas of interest include the hemoglobin and hematocrit values, white blood cell (WBC) count, and red blood cell (RBC) characteristics (eg, mean corpuscular volume, cell size, iron content).

These studies aid in confirming the diagnosis of anemia (hemoglobin and hematocrit), the possibility of infection or acute illness (WBC count), and a possible cause for anemia related to ALS (eg, vitamin B-12 deficiency anemia, iron deficiency anemia).

Liver function tests and pancreatic enzymes

Elevated levels of serum bilirubin, alkaline phosphatase, alanine aminotransferase, aspartate aminotransferase, amylase, and lipase may be detected when biliary and/or pancreatic duct obstruction is prominent.

Occasionally, abnormalities of these hepatic and pancreatic products are early clues to the diagnosis in the proper patient scenario (eg, those with a Billroth II gastrojejunostomy). [27]

Electrolyte panel

Serum electrolytes should be examined, especially in patients with prolonged vomiting and possible dehydration. These conditions can lead to hyponatremia or hypernatremia, hypokalemia, and hypochloremia. Metabolic alkalosis may be present.


Serum albumin levels should be measured, especially because ALS requires surgical correction.

In patients with chronic ALS and significant malnutrition, a period of preoperative specialized nutritional support might be appropriate.

Carbon 14 xylose breath test

When bacterial overgrowth is present, a carbon 14 xylose breath test reveals an increased concentration of hydrogen in exhaled gas following a glucose-containing meal. This test is mainly helpful in diagnostic dilemmas and has no role in acute ALS.



Imaging studies may be of greater utility in patients with chronic ALS in which the diagnosis is often elusive. Although imaging tests are often performed in patients with acute ALS, the vast majority of such patients require urgent surgery regardless of the results of the imaging tests.

Upper gastrointestinal series

Findings from an upper gastrointestinal series may suggest the diagnosis when orally administered contrast agents fail to provide adequate opacification of the afferent loop. However, test results are not specific because nonopacification of the afferent loop is not unusual in normally functioning Billroth II anastomoses.

Plain abdominal radiography

Plain abdominal radiographs can be helpful by demonstrating abnormal bowel gas patterns or air-fluid levels, but these findings are not specific to the diagnosis of ALS.


Abdominal Ultrasonography

Ultrasound may demonstrate a peripancreatic cystic mass or a fluid-filled tubular structure in the right upper abdominal quadrant that may cross the midline.

Kitamura and associates performed ultrasound as an adjunct to percutaneous small bowel drainage in patients with ALS. [28] They used ultrasound to identify a segment of the afferent limb in apposition to the abdominal wall in 3 patients with ALS. In each case, the small bowel segment was successfully cannulated and decompressed.

Derchi and colleagues reported their experience with ultrasound in 4 patients with ALS caused by tumor recurrence at or near a Billroth II gastrojejunostomy. [29] In each case, ultrasound was able to define the distended afferent limb as a fluid-filled structure with a multilayered wall and effacement of the mucosal folds. The investigators described being able to trace the obstructed afferent loop from the hepatic hilum to the anastomosis with the stomach.

Lee and coworkers reviewed the sonographic findings of ALS in 7 patients. [30] In their group of patients, the etiology of ALS was internal herniation in 3, recurrent cancer in 2, marginal ulceration in 1, and a new primary cancer at the anastomosis in 1. The obstructed afferent limb appeared as a dilated, fluid-filled structure in the upper abdominal quadrants, which crossed the midline. These investigators also described the ability to trace this distended bowel loop to the area of the gastrojejunostomy.

Matsusue and colleagues published their experience with ultrasound in 3 patients with ALS. [31] In their report, the salient features of ALS on ultrasound images included a dilated intestinal loop without accompanying gas echoes in the upper abdomen and associated echolucent, edematous swelling of the pancreas.


Nuclear Imaging Studies

Hepatobiliary scintigraphy

These investigations have been used with limited success in diagnosing chronic ALS. Normally, the radionuclide should pass from the afferent limb into the stomach or distal small bowel. Failure to do so may suggest the possibility of an afferent loop obstruction, although the medical usefulness of these studies remains to be determined.

Muthukrishnan and colleagues used technetium-99m (99m Tc) mebrofenin hepatobiliary scintigraphy to examine 2 patients with gastrojejunostomies who presented with bilious vomiting. [31] Findings from previous studies, including endoscopy and ultrasonography, had been nondiagnostic. The scintigraphic technique identified duodenal and extrahepatic biliary dilation in these patients, consistent with chronic ALS

Lai and coworkers performed99m Tc hepatoiminodiacetic acid scanning on a patient with a gastrojejunostomy and obstructive jaundice. [32] The main findings included a dilated afferent loop and dilated biliary radicles.

Sivelli and colleagues reported their experience with99m Tc hepatoiminodiacetic acid scanning in 50 patients with Billroth II gastrojejunostomies and postgastrectomy syndromes. [33] Based on clinical findings, 18 of these patients were thought to have ALS. In this subgroup, abnormal afferent loop emptying was demonstrated in 8 and atonic gallbladder distension without afferent loop abnormalities was found in 10. The authors stressed that clinical symptoms associated with ALS are not pathognomonic and that hepatobiliary scintigraphy can aid in the differential diagnosis of ALS and other conditions such as biliary dyskinesia.


Computed Tomography Scanning

Abdominal computed tomography (CT) scanning helps in the visualization of the obstructed segment directly and yields detailed information regarding the biliary tree, pancreas, and other structures. Yilmaz et al reported that CT scanning should be the radiographic study of choice in the diagnosis of ALS. [34, 35]

Zissin and coworkers reported salient CT scan features of ALS. [36] They described the typical appearance as that of a U-shaped, fluid-filled tubular structure crossing the midline of the abdomen between the abdominal aorta and the superior mesenteric artery.

Kim and coauthors demonstrated the accuracy of CT scanning not only in detecting ALS but also in predicting the underlying pathology causing the condition. [37] They performed helical CT scans on 18 patients presenting with ALS. CT scanning helped correctly predict locally recurrent gastric cancer or carcinomatosis as the cause in 16 patients and adhesion formation and internal herniation as the cause in the other 2 patients.

Gayer and colleagues described CT scan findings in 5 patients with ALS. [38] The afferent limb appeared as a dilated (average 5.3 cm diameter), fluid-filled tubular mass. Valvulae conniventes were observed in all cases, and intraluminal air was detected in 80%. The dilated loop was confined to the subhepatic area in 60%, but it crossed the midline in the other patients. Biliary dilation was identified in all patients, and radiographic evidence of pancreatitis was discovered in one. Notably, orally administered contrast opacified the afferent limb in just one patient.

Gale and coworkers stated that the afferent limb can appear as multiple, uniformly sized, peripancreatic cystic masses on CT scans. [39] This description was confirmed by Swayne and Love, who added that the cysts featured attenuation numbers consistent with water density. [40]

The initial description of ALS on CT scans was offered by Kuwabara and associates in 1980. [41] They characterized an obstructed afferent limb as a U-shaped cystic mass in continuity with the biliary system, appearing posterior to the superior mesenteric artery.


Magnetic Resonance Imaging and Magnetic Resonance Cholangiopancreatography

Chevallier and associates described a case of a 77-year-old man presenting with obstructive jaundice. [42] Magnetic resonance imaging (MRI) revealed biliary and pancreatic ductal dilation and a dilated afferent limb. A mass was visualized between the afferent loop and gastric remnant. Endoscopy with biopsy proved this mass to be an adenocarcinoma that was completely obstructing the afferent limb.

A variety of investigators have used magnetic resonance cholangiopancreatography (MRCP) to diagnose ALS. [43, 44, 45, 46] For example, McKee and coworkers described the use of MRCP in ALS manifesting with cholangitis. [43]


Upper Endoscopy

Esophagogastroduodenoscopy offers the advantage of direct visualization of the gastrojejunostomy and portions of its afferent and efferent limbs. The anastomosis can be inspected for kinking or marginal ulceration. A twist near the anastomosis suggests volvulus or internal herniation. Worrisome masses in the region of the anastomosis can be identified, and biopsy samples can be taken. In addition, enteroliths may also be present, which may mimic mitotic disease on imaging studies and can only be diagnosed with upper endoscopy as described by Yavuz et al. [47]

According to Eagon et al, esophagogastroduodenoscopy is helpful in discriminating between ALS and alkaline reflux gastritis, which is an important entity in the differential diagnosis. [10]


Radiographically Guided Interventional Techniques

The cornerstone of treatment in ALS remains corrective surgery. Occasionally, patients are too debilitated to withstand operative therapy or recurrent cancer may preclude a successful reoperation.

In 2002, Kim and associates published their results with palliative percutaneous tube enterostomy in patients with ALS who presented with a chief complaint of jaundice. [48] In each case, the dilated afferent loop was successfully cannulated and decompressed. Bilirubin levels returned to reference ranges in 5 (71%) of 7 patients.

Lee and coworkers described 2 patients with ALS due to recurrent gastric cancer who were deemed inoperable. [49] Both patients underwent percutaneous transhepatic drainage of the duodenum followed by weekly infusions of 5-fluorouracil and leucovorin. In both cases, afferent limb patency was reestablished, and the drainage catheters were subsequently removed. At the time of the report, the patients remained free of symptoms 16 and 17 months after drainage, respectively.

Caldicott and associates published the case report of a man who had undergone partial gastrectomy and later presented with distal common bile duct and duodenal obstruction due to an inoperable carcinoma of the head of the pancreas. [50] Using percutaneous transhepatic techniques, the patient was effectively palliated by placement of metallic stents across the biliary and duodenal strictures.

Yoshida and coauthors reported the case of a 77-year-old man presenting with fever, right upper quadrant abdominal pain, and jaundice 2 years after a distal gastrectomy for cancer. [51] CT scanning revealed a dilated afferent limb and intrahepatic biliary tree. ALS secondary to recurrent gastric cancer was diagnosed. The authors accessed the afferent limb via the ampulla of Vater, using percutaneous transhepatic biliary drainage techniques. One week after the initial drainage, a sheath introducer was inserted distal to the point of obstruction, and the stenotic area was successfully reopened with metallic stents. A double pigtail catheter was also deployed to prevent stent migration.

The same investigators further refined the above technique for afferent loop obstruction caused by recurrent gastric carcinoma. [52] Yoshida et al simultaneously deployed an expandable metal biliary stent percutaneously together with a double-pigtail catheter endoscopically to prevent migration of the metal stent.

Chevallier and colleagues described a patient in whom a malignant distal afferent loop obstruction developed 19 months after undergoing pancreaticoduodenectomy with Roux-en-Y reconstruction for pancreatic cancer. [53] The obstruction was too distal to be palliated by stent deployment via the transbiliary route. Successful palliation was achieved by percutaneous jejunostomy and stenting.

Song et al reported their experience with metallic stents in 39 consecutive patients who had undergone gastrojejunostomy. [54] The investigators reported that although placement of these stents was technically successful in 90% of patients, stent migration was more common with fully covered stents (4 of 24 cases) compared with no migration with the bare or partially covered stents. In addition, recurrent ALS occurred 10 days after stent placement in 1 patient. Tumor ingrowth occurred in 1 of 4 bare stents and tumor overgrowth in 1 of 29 partially covered stents requiring a second metal stent.