Superior Mesenteric Artery Syndrome

Etiology

Superior mesenteric artery (SMA) syndrome is a rare disease defined as compression of the third portion of the duodenum between the abdominal aorta and the superior mesenteric artery. Other names for SMA syndrome have included chronic duodenal ileus, Wilkie syndrome, arterio-mesenteric duodenal compression syndrome and cast syndrome. The disease was first reported as a case report in 1842 by Carl Von Rokitansky, and in 1927, Wilkie further detailed the pathophysiology and diagnostic findings of the disease.

Epidemiology

While an accurate prevalence of the disease is unknown, the incidence is estimated at 0.1% to 0.3%. SMA syndrome preferentially occurs in adolescents and young adults with a general age range of 10 to 39 years old but can ultimately occur at any age. It occurs more commonly in females over males with a ratio of 3:2. No ethnic predisposition has been described, but familial cases have been reported.[5][6][7]

Pathophysiology

Duodenal compression is usually due to the loss of the intervening mesenteric fat pad between the aorta and SMA, which in turn, results in a narrower angle between the vessels. The fat pad cushion functions to hold the SMA off the spine and protect it from duodenal compression. A normal aortomesenteric angle is 38 to 65 degrees; however, decreasing the angle less than 25 degrees will decrease the distance to less than 10 mm and cause compression to the third part of the duodenum. Decreases in the aortomesenteric angle can be either congenital or acquired. SMA syndrome is associated with significant weight loss including situations of hypermetabolism (trauma and burns) dietary conditions (anorexia nervosa and malabsorptive diseases) and cachexia causing conditions (AIDS, cancer, paraplegia). Other risk factors include surgical correction of scoliosis, congenitally short or hypertrophic ligament of Treitz, peritoneal adhesions, duodenal malrotation, Ladd's bands, abdominal aortic aneurysm, lumbar hyperlordosis, and mesenteric root neoplasm.

History and Physical

Diagnosis is difficult to make clinically as the signs and symptoms are usually vague and non-specific. Patients typically present with either an acute or gradual course of symptoms. The most common symptoms reported are an epigastric pain, nausea, and vomiting. Other symptoms include abdominal distension, weight loss, early satiety and postprandial epigastric pain which worsens in the supine position.  Symptoms are alleviated with the release of the angle which can be demonstrated in a prone, knee to the chest or left lateral decubitus position. Pain can be intermittent or chronic depending on the severity of obstruction. In the acute phase, severe intestinal obstruction leads to life-threatening dilatation of the stomach. In the chronic state, non-specific and intermittent postprandial pain, nausea, vomiting and weight loss often prevail. The cycle of nausea and vomiting leads to inadequate food intake with results in weight loss and thus, aggravation of the syndrome.

Evaluation

SMA syndrome presents with vague symptoms of bowel obstruction. However, diagnosis is based on interpreting clinical symptoms alongside radiological testing which can confirm its presence. Various imaging modalities that can be used include plain film x-ray, barium x-ray, endoscopy, computed tomography (CT), Doppler ultrasound, and magnetic resonance angiography (MRA). Plain radiographs may reveal a dilated stomach and diminished distal bowel gas. Endoscopy and barium studies can be used but are often nonspecific and not available in an emergency setting. Endoscopy, rather, can be used to investigate complications of the disease including gastric stasis, biliary reflux, gastritis and duodenal ulcers and to rule out other cause of the duodenal compression. CT scan is helpful in diagnostics in that it allows for measurement of aortomesenteric (AO) angle which aids in confirmation of SMA syndrome and has thus replaced MRA as the standard for diagnosis. The normal AO angle is between 38 to 65 degrees and has a distance of 10 to 28 mm. In a study which reviewed 8 cases of SMA syndrome, a reported AO angle cutoff of 22 degrees revealed a 42.8% sensitivity and 100% specificity, and a distance of 8 mm was both 100% sensitive and specific for the condition. Laboratory tests are usually nondiagnostic and it is noted that electrolyte disturbances as well as protein and albumin levels can still be normal despite associated weight loss. While it is rare, SMA syndrome is important to consider because the delay in diagnosis can result in significant morbidity and mortality from malnutrition, dehydration, electrolyte abnormalities, gastric pneumatosis and portal venous gas, gastrointestinal hemorrhage and gastric perforation.[8][9][10]

Treatment / Management

Initial treatment is usually conservative, non-operative medical management. Management in the acute setting includes fluid resuscitation, electrolyte correction, total parenteral nutrition and nasogastric tube insertion for gastric decompression. The patient is encouraged to eat small meals and engage in posture therapy which involves patients lying in the left lateral decubitus position, rather than recombinant, to improve symptoms. Nutritional support through hyperalimentation is of great importance with conservative therapy in an attempt to increase the mesenteric fat pad, thus increasing the AO angle and improving symptoms. Many patients will fail conservative therapy and ultimately require surgical intervention.  Various surgical procedures have been considered for surgical management including gastrojejunostomy, Strong procedure (a division of the ligament of Treitz), transabdominal duodenojejunostomy and laparoscopic duodenojejunostomy. Traditional open bypass surgery was the standard of care until 1998 when the first successful laparoscopic duodenojejunostomy was performed. This technique has since surpassed open bypass as the most common surgical treatment. Laparoscopic duodenojejunostomy has recently replaced open bypass at the standard operative treatment. A study involving laparoscopic duodenojejunostomy as a treatment for failed conservative management was done on 12 patients. This retrospective study revealed improved or eliminated symptoms in 11 of the 12 patients without any postoperative bowel obstruction, wound infection, anastomotic complications or deaths. Most surgeons prefer duodenojejunostomy due to reported success rates of 80% to 100% with reduced postoperative pain shortened hospital stay and reduced risk of incisional herniation.

Differential Diagnosis

• Anorexia bulimia

• Anorexia nervosa

• Chronic idiopathic intestinal pseudo-obstruction

• Collagen vascular conditions

• Diabetes mellitus

• Mega duodenum and duodenal  ileus

• Peptic ulcer disease