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

  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]

  Patients with chronic ALS may develop malnutrition or anemia [ 22, 34 ], and may derive benefit from nutritional therapy or transfusion prior to surgery. [abdominalkey.com]

• Upper Abdominal Pain

  Our findings indicate that biliary vomiting, right upper abdominal pain pyrosis, and biliary diarrhea in Billroth II gastrectomized patients are not always pathognomonic symptoms of afferent loop syndrome. [ncbi.nlm.nih.gov]

  A female patient came to our department complaining of upper abdominal pain and she was diagnosed as having a bezoar that was causing afferent loop syndrome and pancreatitis. [e-ce.org]

  •Localized midepigastric or right upper abdominal quadrant tenderness •Peritonitis and/or a rigid abdomen if necrosis or perforation of the bowel wall has occurred •Jaundice •Signs of pancreatitis (eg, upper abdominal pain radiating to the flank or back [usmleforum.com]

  upper abdominal pain radiating to the flank or back Peritonitis and/or a rigid abdomen if necrosis or perforation of the bowel wall has occurred Differential diagnoses Benign gastric tumors Mesenteric tumors Bile duct tumors Anemia Intestinal perforation [laparoscopyhospital.com]

• Abdominal Tenderness

  Clinical findings Pain, bloating, abdominal tenderness, with bacterial overgrowth, malabsorption. afferent loop syndrome Blind loop syndrome A type of postgastrectomy syndrome, caused by partial or complete obstruction of the proximal portion–loop of [medical-dictionary.thefreedictionary.com]

• Hematochezia

  Abdominal hernia : Inguinal ( Indirect, Direct ) - Umbilical - Incisional - Femoral Obturator hernia Peritoneal Peritonitis ( Spontaneous bacterial peritonitis ) - Hemoperitoneum - Pneumoperitoneum GI bleeding Upper ( Hematemesis, Melena ) - Lower ( Hematochezia [wikidoc.org]

• Suggestibility

  We report here a patient with postgastrectomy afferent loop syndrome with a decreased number of c- kit-expressing cells in the external muscle layer of the dilated intestine, suggesting damage to the ICCs. [ncbi.nlm.nih.gov]

  Abstract We present a case of chronic pancreatitis (CP) accompanied by afferent loop syndrome (ALS) which suggested a new clue to treat an intractable type of the disease. [jstage.jst.go.jp]

• Impulsivity

  […] corpuscle. afferent loop syndrome chronic partial obstruction of the proximal loop (duodenum and jejunum) after gastrojejunostomy, resulting in duodenal distention, pain and nausea following ingestion of food. afferent nerve any nerve that transmits impulses [medical-dictionary.thefreedictionary.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].

• 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]

• 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]

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..