The afferent loop syndrome is a rare complication of surgeries in which a segment of the proximal small intestine (often the duodenum and a small portion of the small bowel) is bypassed, creating an "afferent loop" [1] [2] [3]. Billroth II or Roux-en-Y gastrectomy and subsequent gastrojejunostomy, or pancreaticoduodenectomy are procedures that result in the formation of an afferent loop [1] [3] [4]. Once this segment of the bowel is present, several triggers may lead to its either complete or partial obstruction - volvulus, intussusception, development of adhesions, hernias, recurrence of underlying disease (eg. malignancy or metastatic dissemination), and the formation of enteroliths (intestinal stones) in rare cases [2] [3] [7]. Once the loop is obstructed, symptoms appear due to the buildup of bile and pancreatic secretions, and two main forms are recognized in the literature [4] [5]:

• Acute - When complete or near-complete obstruction occurs, a sudden onset of epigastric pain, nausea, and vomiting developing approximately 1 week after surgery is the hallmark of acute afferent loop syndrome [3] [4]. Without early intervention, gangrene of the afferent loop with possible perforation, peritonitis, ascending cholangitis, and pancreatitis is reported [1], suggesting that patients may be at a life-threatening risk if not recognized promptly.
• Chronic - Contrary to acute forms, partial obstruction of the loop can cause subtle but prolonged complaints that start months or even years after surgery [3] [4]. In most patients, a periumbilical discomfort that lasts for several hours, starting about 15-30 minutes after a meal, is noted, and vomiting is not uncommon [1] [4] [6]. In addition, significant loss of weight is reported, while diarrhea, vitamin B12 deficiency, steatorrhea and iron-deficiency anemia are known complications [1] [2] [3] [4]. Like with acute forms, ascending cholangitis and infections are known complications.

• Anemia

  Burhenne Medicine Radiology 1968 Stasis in the proximal jejunal (afferent) loop after distal gastric resection and gastrojejunostomy (Billroth II) may result in intermittent bilious vomiting, malabsorption with steatorrhea, anemia, and weight loss. [semanticscholar.org]

  The macrocytic anemia appears related to binding of vitamin B12 by metabolites of Escherichia coli, and treatment with antibiotics frequently gives striking relief (7). [pubs.rsna.org]

  Bacteria deconjugate bile acids, which can lead to steatorrhea, malnutrition, and vitamin B-12 deficiency leading to megaloblastic anemia. [laparoscopyhospital.com]

  In addition, significant loss of weight is reported, while diarrhea, vitamin B12 deficiency, steatorrhea and iron-deficiency anemia are known complications. Like with acute forms, ascending cholangitis and infections are known complications. [symptoma.com]

In order to prevent the development of complications, some of which may be life-threatening, the diagnosis of afferent loop syndrome must be made as early as possible. Although the clinical presentation is often comprised of non-specific GI complaints [3], a carefully obtained patient history will reveal prior gastrointestinal surgery that must raise suspicion in the physician. Thus, adequate history taking is of vital importance. Moreover, physical examination can reveal abdominal distention and tenderness, involuntary guarding (if more severe obstruction or perforation has occurred), jaundice, and a projection of the obstructed afferent loop as a mass in the upper abdomen [1]. Because the differential diagnosis of such findings is broad, imaging studies are the mainstay in diagnosing afferent loop syndrome. Plain radiography is not favored because of inconclusive findings. For this reason, abdominal ultrasonography (US), but more commonly computed tomography (CT), are recommended diagnostic procedures [1] [3] [4]. In addition to clear visualization of the afferent loop, other notable features are obstruction and distension of the bowels proximally to the afferent loop, but also dilation of the pancreaticobiliary tract [1] [3] [4]. Thus, CT is the diagnostic modality of choice [7]. When the obstruction is partial, or when repeated vomiting causes decompression of the afferent loop, neither CT nor US may be as effective. [4]. Instead, cholangiography can be employed as a reliable procedure [4]. In fact, magnetic resonance cholangiopancreatography (MRCP) is also mentioned as a valid imaging study if preceding pancreaticoduodenectomy was performed [1].

• Macrocytic Anemia

  The macrocytic anemia appears related to binding of vitamin B12 by metabolites of Escherichia coli, and treatment with antibiotics frequently gives striking relief (7). [pubs.rsna.org]

• Macrocytosis

  Afferent loop syndrome should be suspected in case of malabsorption syndrome with chronic diarrhea, steatorrhea, iron-deficiency anemia, edema, emaciation, and osteomalacia and also in case of simple biological anomalies such as macrocytosis or megaloblastic [ncbi.nlm.nih.gov]

We highlight the importance of high clinical suspicion and individualized treatment according to the patient's condition, severity, ALS etiology and locally available treatment possibilities. [ncbi.nlm.nih.gov]

Treatment Medical Treatment Acute ALS requires immediate diagnosis and corrective surgery. Indeed, the major pitfall associated with ALS is a delay in diagnosis due to risk of intestinal perforation and sepsis [ 33 ]. [abdominalkey.com]

Prognosis After a corrective and proper method done, the prognosis of afferent loop syndrome is typically very good, except for those individuals who have advanced or recurrent malignancy. [syndromespedia.com]

[…] possible delayed filling of an enlarged afferent loop CT "U-shaped" loop of bowel, adjacent to the pancreas, usually containing water attenuation fluid common bile duct should enter into the loop possible gallbladder and biliary dilatation Treatment and prognosis [radiopaedia.org]

Prognosis After a proper corrective procedure, the prognosis is usually very good, except in cases of advanced or recurrent malignancy. Mortality/morbidity Mortality rates of up to 57% have been reported for acute ALS. [emedicine.medscape.com]

Malignant causes of ALS, such as local recurrence and carcinomatosis, are the most common etiologies of obstruction. These etiologies and associated complications can be predicted 100% by MDCT. [ncbi.nlm.nih.gov]

The jejunal limb is subject to adhesion formation, internal herniation, volvulus, anastomotic obstruction, and other etiologies of ALS, as described above. Contraindications Surgical correction of ALS has no absolute contraindications. [laparoscopyhospital.com]

Metallic stents have been used for the relief of afferent loop syndrome due to number of etiologies [ 35 – 37 ]. [abdominalkey.com]

The etiology wasn't entirely clear to me. It wasn't a volvulus. There wasn't an internal hernia. It just didn't seem to want to "lay right" without kinking (perhaps secondary to some redundancy in the afferent limb). [buckeyesurgeon.com]

Peptic ulcer surgery during the H2-receptor antagonist era: a population-based epidemiological study of ulcer surgery in Helsinki from 1972 to 1987. Br J Surg. 1991 Jan. 78(1):28-31. [Medline]. Tovey FI, Godfrey JE, Lewin MR. [emedicine.medscape.com]

From this point of view, we conclude as follows: 1) The pathophysiology of chronic ALS consists in not only mechanical obstruction but also functional dyskinesia of afferent loop in various degrees, and trimebutine maleate, recognized as gastrointestinal [jstage.jst.go.jp]

The pathophysiology and signs and symptoms associated with ALS result from partial or complete obstruction of the afferent loop. [laparoscopyhospital.com]

The pathophysiology and signs and symptoms associated with this syndrome result from partial or complete obstruction of the afferent loop. [usmleforum.com]

Thiamine deficiency is known to cause Wernicke’s syndrome, but the pathophysiology is still uncertain. The cerebellar vermis is sensitive to thiamine deficiency, in particular the Purkinje cells. [giornalechirurgia.it]

Direct percutaneous transperitoneal drainage may be impractical when overlying bowel loops prevent access to deeply located afferent loops. [ncbi.nlm.nih.gov]

In the early postoperative period, anastomotic edema, hemorrhage at the origin of the efferent limb, or both can prevent gastric emptying and, similarly, result in fluid accumulation in the afferent loop. [medicalgeek.com]

In order to prevent the development of complications, some of which may be life-threatening, the diagnosis of afferent loop syndrome must be made as early as possible. [symptoma.com]

1. Blouhos K, Boulas KA, Tsalis K, Hatzigeorgiadis A. Management of afferent loop obstruction: Reoperation or endoscopic and percutaneous interventions? World J Gastrointest Surg. 2015;7(9):190-195.
2. Kwong WT, Fehmi SM, Lowy AM, Savides TJ. Enteral stenting for gastric outlet obstruction and afferent limb syndrome following pancreaticoduodenectomy. Ann Gastroenterol. 2014;27:413–417.
3. Cho YS, Lee TH, Hwang SO, et al. Electrohydraulic Lithotripsy of an Impacted Enterolith Causing Acute Afferent Loop Syndrome. Clin Endosc. 2014;47(4):367-370.
4. Kim JK, Park CH, Huh JH, et al. Endoscopic Management of Afferent Loop Syndrome after a Pylorus Preserving Pancreatoduodenecotomy Presenting with Obstructive Jaundice and Ascending Cholangitis. Clin Endosc. 2011;44(1):59-64.
5. Wise SW. Case 24: Afferent loop syndrome. Radiology. 2000;216(1):142-145.
6. Gale ME, Gerzof SG, Kiser LC, et al. CT appearance of afferent loop obstruction. AJR Am J Roentgenol. 1982;138:1085–1088.
7. Nageswaran H, Belgaumkar A, Kumar R, et al. Acute afferent loop syndrome in the early postoperative period following pancreaticoduodenectomy. Ann R Coll Surg Engl. 2015;97(5):349-353..