Pediatrics

Superior Mesenteric Artery Syndrome

OVERVIEW: What every practitioner needs to know

Superior mesenteric artery syndrome (SMAS) is an unusual presentation of small bowel obstruction that results from compression of the duodenum between the abdominal aorta, posteriorly, and the superior mesenteric artery, anteriorly. SMAS is more frequently found in females than males, can be found in every age category including infants, and typically affects slender individuals after acute weight loss.

Are you sure your patient has Superior Mesenteric Artery Syndrome? What are the typical findings for this disease?

Symptoms of SMAS may have an acute onset or a more insidious and chronic presentation.

Individuals with more acute onset tend to present with symptoms of small bowel obstruction including vomiting, nausea, anorexia, abdominal distention and abdominal pain.

A review of 22 cases reported that patients tended to present with more acute symptoms of epigastric abdominal pain, vomiting and early satiety. Symptoms developed 1 to 393 days before diagnosis (median 5 days). The most common presenting symptoms included abdominal pain (59%), vomiting (50%), nausea (40%) and early satiety (32%). Diagnosis was made by upper gastrointestinal radiography (82%), computed tomography (9%) and at laparotomy (9%). There were 21 out of 22 patients who responded to nutritional therapy.

Individuals with more chronic presentation demonstrate gradual onset of symptoms, including postprandial epigastric pain, early satiety and weight loss.

In severe cases, patients may present with acute metabolic acidosis, dehydration, and altered mental status from profuse vomiting.

Physical examination findings are nonspecific but can include abdominal distension, epigastric tenderness, a succussion splash and/or high pitched bowel sounds.

What other disease/condition shares some of these symptoms?

The differential diagnosis of SMAS is fairly broad due to the nonspecific nature of the symptoms and exam findings. Conditions that should be considered include anatomical causes of vomiting such as intestinal duplication, duodenal web or sling, malrotation with volvulus and intussusception. Other intestinal conditions which should also be considered include pancreatitis, acute or chronic gastritis with or without associated H. pylori infection, as well as duodenal or gastric ulcer. Extraintestinal conditions that cause similar symptoms include ovarian or testicular torsion, anorexia/bulimia, psychogenic vomiting, and cyclic vomiting. In addition SMAS should be considered in anyone with recent spinal surgery or orthopedic surgery resulting in serial casting of the abdomen that may have resulted in significant weight loss.

What caused this disease to develop at this time?

The etiology of SMAS is thought to be the loss of the duodenal fat pad, thus changing the angle between the aorta and the superior mesenteric artery. This allows the superior mesenteric artery to rest directly on the small intestine, resulting in obstruction.

The most common conditions predisposing patients to SMAS include orthopedic casting with incapacitation, spinal surgeries, anorexia nervosa and/or severe burns. SMAS has been associated with a variety of disease processes including fungal abscess, gastric bezoar, celiac disease, diabetes, pregnancy, and dialysis catheters.

A review of 22 cases of SMAS suggested that underlying neurological disability, such as severe cerebral palsy, may predispose an individual to SMAS. Individuals who have an existing neurological injury may develop SMAS after less weight loss compared with patients who develop SMAS without pre-existing neurological defects.

In summary, any process which changes the angle by which the superior mesenteric artery departs the aorta or results in the loss of the duodenal fat pad would predispose a patient to developing SMAS. The development of SMAS has been correlated to a reduction of the angle of the superior mesenteric artery to the aorta to less than 20 degrees.

What laboratory studies should you request to help confirm the diagnosis? How should you interpret the results?

There are no specific laboratory studies used to diagnose SMAS. Patients with profuse or chronic vomiting should have a basic metabolic panel to rule out electrolyte abnormalities or an acid/base disturbance.

Would imaging studies be helpful? If so, which ones?

SMAS can be diagnosed by upper gastrointestinal radiography, which demonstrates a dilated stomach and duodenum with an abrupt cut-off or narrowing of the duodenum at the level of the 3rd lumbar vertebra (Figure 1).

Figure 1.

Upper gastrointestinal radiography may also demonstrate intermittent reversal or "to-and-fro" peristaltic activity of the contrast as it passes through the obstruction.

A recent case series of 80 patients demonstrated that the majority of cases where diagnosed by abdominal CT ( Figure 2). MRI, endoscopic ultrasound, and laparotomy have all been described as a means of diagnosing SMAS.

Figure 2.

If you are able to confirm that the patient has Superior Mesenteric Artery Syndrome, what treatment should be initiated?

Acute treatment of SMAS involves gastric decompression and initiation of fluid resuscitation while maintaining appropriate electrolyte balance. Once the patient is stabilized, initiation of nutritional support and rehabilitation may begin.

When SMAS is associated with orthopedic body casting, it is recommended that the cast be removed in order to alleviate the obstruction.

Long-term treatment is focused on increasing caloric intake to rebuild the duodenal fat pads and thus cushion the superior mesenteric artery from obstructing the duodenum. This can be accomplished enterally with small frequent high calorie meals in conjunction with changes in feeding position, including knees to chest and/or right lateral decubitus positioning. More frequently, a nasojejunal tube is placed past the obstruction to provide consistent high-calorie nutritional supplementation.

A recent review of 18 patients reported the mean duration of medical treatment was 45 days with a range of 18 - 365 days. When enteral nutrition is not tolerated, parenteral nutrition has been utilized. Success of medical management has been documented at over 70% with approximately a 15% re-occurrence rate.

Uncommonly, when medical treatment fails, surgical intervention may be necessary, especially when dilatation and stasis of the proximal small bowel develops. Surgical interventions described include duodenojejunostomy, gastrojejunostomy, and ligation of the ligament of Treitz. One report of 32 cases of SMAS which were all treated surgically demonstrated successful treatment/cure of the disorder with Roux-en-Y side-to-side duodenojejunostomy with amputation of the ligament of Treitz. There were no complications reported or deaths. Surgical success in management has been documented at over 90%.

What are the adverse effects associated with each treatment option?

The primary treatment is nutritional rehabilitation. As such, there are few complications, especially if this can be accomplished without a nasojejunal tube or parenteral nutrition.

If a nasojejunal tube is needed, any associated complication would be similar to complications associated with nasojejunal feeding in general, which would include sinus infections, migration of the tube, and, significantly less common, intestinal perforation or destruction/tearing of the angle of the nares. In the severely malnourished patient, refeeding syndrome can be precipitated by advancing the caloric intake too rapidly.

If parenteral nutrition is required, then central line infections and bacteremia are potential adverse events.

Finally, if surgery is required, complications associated with anesthesia and wound infection must be taken into consideration.

What are the possible outcomes of Superior Mesenteric Artery Syndrome?

SMAS is a medically treatable cause of small bowel obstruction with an overall good prognosis. Conservative medical treatment with nutritional rehabilitation is the least risky of treatment options and is successful in the majority of patients. More than 70% of patients have improvement of symptoms after 6 weeks of treatment.

On rare occasions, surgery may be needed to correct the obstruction and can now be done laparoscopically or even robotically.

What causes this disease and how frequent is it?

The reported incidence of SMAS ranges from 0.013% to 0.3%. It is more common in females than males, and frequently affects individuals with slender builds after acute weight loss. Although there is currently no known genetic mutation associated with SMAS, one case report noted SMAS occurring in 5 out of 8 family members as well as in a set of identical twins.

How do these pathogens/genes/exposures cause the disease?

There are no pathogens or exposures which are directly related to the development of SMAS.

What complications might you expect from the disease or treatment of the disease?

Patients commonly complain of persistent nausea and early satiety even during treatment; however, this gradually improves as the obstruction improves. During nutritional rehabilitation of patients with significant weight loss, refeeding syndrome should be considered as a potential complication with the associated drops in electrolytes, calcium and phosphorus and potentially even the development of pulmonary edema.

How can Superior Mesenteric Artery Syndrome be prevented?

There is no specific means of preventing SMAS. The parents of very slender children can be advised to monitor for symptoms that may be suggestive of SMAS. In addition, slender individuals undergoing orthopedic casting should be considered at increased risk for developing SMAS.

What is the evidence?

Crowther, MA, Webb, PJ, Eyre-Brook, IA. "Superior mesenteric artery syndrome following surgery for scoliosis". Spine (Phila Pa 1976) . vol. 27. 2002. pp. E528-33.

Iko, BO, Monu, JU, Orhue, A. "The superior mesenteric artery syndrome in pregnancy: a case resulting in recurrent pregnancy loss". Eur J Obstet Gynecol Reprod Biol . vol. 21. 1986. pp. 233-6.

Biank, V, Werlin, S. "Superior mesenteric artery syndrome in children: a 20-year experience". J Pediatr Gastroenterol Nutr . vol. 42. 2006. pp. 522-5.

(This series demonstrates the effectiveness of nutritional therapy for SMAS.)

Ozkurt, H, Cenker, MM, Bas, N. "Measurement of the distance and angle between the aorta and superior mesenteric artery: normal values in different BMI categories". Surg Radiol Anat . vol. 29. 2007. pp. 595-9.

Ortiz, C, Cleveland, RH, Blickman, JG. "Familial superior mesenteric artery syndrome". Pediatr Radiol . vol. 20. 1990. pp. 588-59.

Lippl, F, Hannig, C, Weiss, W. "Superior mesenteric artery syndrome: diagnosis and treatment from the gastroenterologist's view". J Gastroenterol . vol. 37. 2002. pp. 640-3.

Lee, TH, Lee, JS, Jo, Y. "Superior Mesenteric Artery Syndrome: where do we stand today?". J Gastrointest Surg . vol. 16. 2012. pp. 2203-11.

Dorph, MH. "The cast syndrome: review of the literature and report of a case". N Engl J Med . vol. 243. 1950. pp. 440-2.

Shiu, JR, Chao, HC, Luo, CC. " Clinical and nutritional outcomes in children with idiopathic superior mesenteric artery syndrome". J Pediatr Gastroenterol Nutr . vol. 51. 2010. pp. 177-82.

(This series demonstrates that an aortomesenteric angle of <200 is present in all children with SMAS.)

Smith, BG, Hakin-Zargar, M, Thomson, JD. "Low body mass index: a risk factor for superior mesenteric artery syndrome in adolescents undergoing spinal fusion for scoliosis". J Spinal Disord Tech . vol. 22. 2009. pp. 144-8.

Lan, M, Liu, Y, Zhou, M. "Diagnosis and treatment of superior mesenteric artery syndrome. (Chinese, English abstract)". J Abdominal Syndrome. 2009.

Mosalli, R, El-Bizre, B, Farooqui, M. "Superior Mesenteric Artery Syndrome: a rare cause of complete intestinal obstruction in neonates". J Pediatr Surg . vol. 46. 2011. pp. e29-31.

Shin, MS, Kim, JY. "Optimal duration of medical treatment in superior mesenteric artery syndrome in children". J Korean Med Sci . vol. 28. 2013. pp. 1220-1225.

Almaami, MY. "Robotic management of superior mesenteric artery syndrome". Surg Laparosc Endosc Percutan Tech. vol. 22. 2012. pp. e144-147.

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