Superior mesenteric artery syndrome

Overview

Superior mesenteric artery syndrome (SMAS) is a rare but potentially serious gastrointestinal disorder caused by compression of the third portion of the duodenum between the superior mesenteric artery (SMA) and the aorta. This vascular compression leads to partial or complete obstruction of the duodenum, resulting in symptoms of upper intestinal blockage. SMAS is also known as Wilkie’s syndrome or cast syndrome when associated with external compression.

The condition can cause significant digestive distress and requires timely diagnosis and management to prevent complications.

Causes

SMAS primarily occurs due to a reduced angle between the aorta and the superior mesenteric artery, narrowing the space through which the duodenum passes. Contributing factors include:

• Rapid or excessive weight loss: Loss of the mesenteric fat pad that normally cushions the duodenum.

• Congenital anatomical variations: An abnormally low origin of the SMA or a high insertion of the duodenum.

• Post-surgical changes: Procedures such as scoliosis surgery or abdominal aortic aneurysm repair can alter vascular anatomy.

• External compression: Prolonged use of body casts or braces compressing the abdomen.

• Other causes: Severe catabolic states, eating disorders, trauma, or tumors causing mass effect.

Symptoms

The symptoms of superior mesenteric artery syndrome result from duodenal obstruction and may include:

• Postprandial abdominal pain or fullness

• Nausea and persistent vomiting, often containing bile

• Early satiety and weight loss

• Abdominal bloating and distension

• Reflux or gastroesophageal symptoms

• Symptoms often worsen in the supine position and improve when sitting or lying on the left side

Diagnosis

Diagnosis of SMAS involves a combination of clinical evaluation and imaging studies:

• Medical history and physical exam: Assessing typical symptoms and risk factors such as recent weight loss.

• Upper gastrointestinal series (barium swallow): Shows dilation of the first and second parts of the duodenum with abrupt cutoff at the third portion.

• Computed tomography (CT) angiography: Measures the aortomesenteric angle and distance, visualizing duodenal compression.

• Ultrasound: May assist in assessing vascular anatomy and blood flow.

• Endoscopy: To exclude other causes of obstruction or mucosal disease.

Treatment

Treatment of superior mesenteric artery syndrome depends on symptom severity and underlying cause:

• Conservative management: Initial treatment involves nutritional support to promote weight gain and restore the mesenteric fat pad, including:

  • Small, frequent meals

  • Postural changes to relieve compression (e.g., left lateral decubitus or knee-chest position)

  • Nasogastric decompression if necessary

  • Enteral or parenteral nutrition in severe cases

• Surgical intervention: Considered when conservative therapy fails. Procedures include:

  • Duodenojejunostomy – creating a bypass around the obstruction (most common and effective)

  • Strong’s procedure – division of the ligament of Treitz to mobilize the duodenum

  • Gastrojejunostomy in selected cases

Prognosis

The prognosis of superior mesenteric artery syndrome varies. Many patients respond well to conservative treatment, especially if diagnosed early and nutritional status is improved. Surgical outcomes are generally favorable with high success rates in relieving obstruction and symptoms.

Delayed diagnosis or treatment can lead to chronic malnutrition, electrolyte imbalances, and complications such as gastric perforation. Long-term follow-up is important to ensure nutritional recovery and monitor for recurrence.