What is the Epidemiology of SMA Syndrome?

Patient Presentation
A 10-year-old female with mental retardation and cerebral palsy came to the emergency room with emesis that had begun 2-3 days ago. She had a history of baseline gastroesophageal reflux and she usually received nutrition by nasojejunal feedings. The emesis was increasing in frequency, volume and forcefulness. The emesis was now dark green in color but without blood. She had no fever and had last stooled 2 days ago. She had no change in her seizure pattern which was 1-3 brief tonic-clonic seizure daily. The past medical history was remarkable for a posterior spinal fusion 8 months previously, and seizures that were controlled by Depakote®(divalproex sodium). Before the spinal surgery she had reflux 1-2 times/day. Since the surgery it was now 3-4 times/day but still of small amounts. The review of systems was otherwise normal.

The pertinent physical exam showed a small patient writhing in pain with a heart rate of 126 beats/minute, blood pressure of 110/80, respiratory rate of 22/minute and she was afebrile. Her growth parameters were a weight of 10 percentile and length of 25%. She had lost 4 kilograms since her surgery. HEENT was non-contributory. Heart and lungs were clear. Abdomen had markedly decreased bowel sounds and was soft but diffusely tender.

The radiological evaluation included an abdominal ultrasound that showed a small amount of ascites in the right lower quadrant and the appendix was thought to be normal, and computed tomography which also showed ascites but could not show an appendix. The laboratory evaluation showed normal electrolytes except for a slightly low potassium at 3.0 mg/dl. BUN was 7 mg/dl and creatinine was 0.4 mg/dl. Her complete blood count showed a hemoglobin of 15 mg/dl, platelets of 533 x 1000/mm2 and white blood cell count of 14.8 x 1000/mm2 without a left shift. AST was 32 U/L and ALT was 17 U/L. Her amylase and lipase were elevated at 426 U/L and 437 U/L respectively.

The diagnosis of possible pancreatitis caused by depakote was made. The patient’s clinical course was that she was treated by being placed NPO with total parenteral nutrition. A gastric tube for drainage was also placed and pain was managed by a small amount of narcotics by family controlled IV administration. She was changed to phenobarbital for her seizures because the suspected pancreatitis. The patient improved with this treatment including her amylase and lipase, but still had emesis. The radiologic evaluation of an upper gastrointestinal study found the barium column to stop at the 3rd part of the duodenum making the diagnosis of superior mesenteric artery syndrome. Over the next 3-4 weeks, with aggressive parental nutrition via a long tube her weight increased and her emesis stopped. At discharge she still had a small amount of spit up about 1 time/day that was consistent with her previous reflux. She was also continued on her phenobarbital.

Case Image

Figure 117 – Axial image from a computed tomography exam of the abdomen performed with intravenous contrast (above) shows the dilated stomach anteriorly in the abdomen and the dilated duodenum posterior to it on the right side of the abdomen that then tapers in diameter as it reaches the superior mesenteric artery in the midline above the spine. The coronal two-dimensional reconstruction of the abdomen from the same exam (below) demonstrates the tremendously dilated nature of the stomach and duodenal bulb.

Superior mesenteric artery syndrome (SMAS) is caused by the compression of the superior mesenteric artery (SMA) against the 3rd part of the duodenum creating a proximal intestinal obstruction. It is relatively rare and can be hard to distinguish from other causes of intestinal obstruction.

Normally the SMA arises from the anterior aorta around the L1 vertebra. It extends anteriorly and caudally into the mesentery of the small bowel. The angle between the SMA and aorta is called the aortomesenteric angle and is usually 38-65°. The distance between the SMA and aorta is usually 10-20 mm. Within the aortomesenteric angle lies the 3rd part of the duodenum and left renal artery along with a fat pad. The fat pad is felt to cushion the other organs and helps maintain the aortomesenteric angle. If the fat in this area is lost, then the angle decreases and compresses the duodenum and if the compression is severe enough then obstruction can occur. The left renal vein can also be compromised. In SMAS the angle is usually 6-25° and the distance between the SMA and aorta is 2-8 mm. Interestingly though, while most patients have a recognizable reason for the SMAS there are also a group of patients who have normal weight. SMAS can also occur after spinal surgeries where the spine is straightened. This causes increased tension on the mesentery and SMA, which again decreases the angle and therefore can cause duodenal compression and/or obstruction.

SMAS usually presents with abdominal pain, nausea, emesis, anorexia, weight loss, postprandial fullness and early satiety. It is easy to see how the cycle of pain, emesis and weight loss, continues the cycle of SMAS.

Diagnosis is usually made with upper gastrointestinal studies, but computed tomography or even angiogram may be necessary. Treatment is usually medical with parental hyperalimentation, nasogastric decompression and postural changes (lying on left side) to help to break the cycle. Additional treatment for symptoms (such as antacids or proton pump inhibitors or prokinetic agents) or co-morbid conditions (see below) are also given. Surgical treatments are usually diversion with duodenojejunostomy being the most common and successful (80-100%).

Learning Point
SMAS can be seen in all ages including newborns and geriatricians. It is more common in the teens-late 30s age groups. Females are more commonly affected than males. In the pediatric age group it is often associated with co-morbid conditions including mental, behavioral, or neurological problems such as depression, anorexia nervosa, brain injuries, mental retardation, seizures, or congenital muscular problems. Infectious diseases that can cause wasting such as tuberculosis and HIV can also be co-morbid conditions. Patients who have had spinal surgeries are also at increased risk of SMAS.

Questions for Further Discussion
1. What causes bilious emesis?
2. What are some signs/symptoms to distinguish ileus from intestinal obstruction?
3. What causes pancreatitis?
4. What are possible complications of spinal surgery?

Related Cases

To Learn More
To view pediatric review articles on this topic from the past year check PubMed.

Evidence-based medicine information on this topic can be found at SearchingPediatrics.com, the National Guideline Clearinghouse and the Cochrane Database of Systematic Reviews.

Information prescriptions for patients can be found at MedlinePlus for these topics: Vascular Diseases and Small Intestine Disorders.

To view current news articles on this topic check Google News.

To view images related to this topic check Google Images.

To view videos related to this topic check YouTube Videos.

Merrett ND, Wilson RB, Cosman P, Biankin AV. Superior mesenteric artery syndrome: diagnosis and treatment strategies. J Gastrointest Surg. 2009 Feb;13(2):287-92.

Lee TH, Lee JS, Jo Y, Park KS, Cheon JH, Kim YS, Jang JY, Kang YW. Superior mesenteric artery syndrome: where do we stand today? J Gastrointest Surg. 2012 Dec;16(12):2203-11.

Lam DJ, Lee JZ, Chua JH, Lee YT, Lim KB. Superior mesenteric artery syndrome following surgery for adolescent idiopathic scoliosis: a case series, review of the literature, and an algorithm for management. J Pediatr Orthop B. 2014 Jul;23(4):312-8.


Donna M. D’Alessandro, MD
Professor of Pediatrics, University of Iowa Children’s Hospital