Superior mesenteric artery syndrome

Superior mesenteric artery (SMA) syndrome is a rare disorder characterized by compression of the third part of the duodenum between the SMA and the aorta, leading to obstruction. It arises from a reduced aortomesenteric angle due to anatomical factors, significant weight loss, or following certain surgeries (e.g., corrective spinal surgery). Patients typically present with postprandial epigastric pain, nausea, vomiting, and progressive weight loss, which can create a worsening cycle of symptoms. Symptoms are characteristically positional and may improve when lying prone or in a knee‑to‑chest position. Diagnosis is confirmed with imaging, usually contrast‑enhanced CT, which shows duodenal compression and a decreased aortomesenteric angle and distance. Initial management is conservative and includes nutritional support and, when needed, gastroduodenal decompression. Surgical intervention, most commonly duodenojejunostomy, is reserved for patients who do not respond to conservative management.

• Prevalence: rare ^[1]
• Age: Median age is 23 years (range 0–91 years). ^[1]
• Sex: ♀ > ♂ (∼ 3:2) ^[1]

Epidemiological data refers to the US, unless otherwise specified.

SMA syndrome is caused by factors that reduce the aortomesenteric angle, leading to duodenal obstruction. ^[2][3]

• Significant weight loss
  • Eating disorders (e.g., anorexia nervosa)
  • Hypermetabolic states (e.g., burns, trauma)
  • Cachexia (e.g., due to malignancy, tuberculosis)
  • Malabsorption syndromes
  • Bariatric surgery
• Procedures
  • Corrective spinal surgery (e.g., for scoliosis) or application of a body cast
  • Abdominal surgery (e.g., colectomy, ileal pouch-anal anastomosis)
• Anatomical factors
  • Congenitally short or hypertrophic ligament of Treitz
  • Low origin of the SMA
  • High duodenal insertion at the ligament of Treitz
• Other: prolonged bed rest in a supine position

Symptoms may develop acutely (e.g., after major trauma or surgery) or follow a chronic, intermittent course. ^[3][4]

• Nonspecific gastrointestinal symptoms
  • Postprandial epigastric pain
  • Nausea, vomiting
  • Early satiety
  • Heartburn
  • Bloating
  • Weight loss
• Aggravating factors: supine or upright position
• Alleviating factors
  • Prone position
  • Left lateral decubitus position
  • Knee-to-chest position

Anorexia and significant weight loss are common features of SMA syndrome and can trigger a cycle in which weight loss worsens duodenal compression, further intensifying symptoms and promoting additional weight loss. ^[3]

General principles ^[3]

• Diagnosis is suspected based on typical clinical features.
• Gastroenterology should be consulted for upper endoscopy to rule out other causes of upper gastrointestinal obstruction.
• Laboratory studies (e.g., BMP, pancreatic enzymes) may be obtained to assess for complications based on clinical suspicion.
• Diagnosis is supported by imaging, which shows duodenal compression and reduced aortomesenteric parameters.

Imaging ^[3][4][5]

• Contrast-enhanced CT scan
  • Allows for direct visualization of duodenal compression and measurement of aortomesenteric parameters
  • Supportive findings
    • Dilated stomach and proximal duodenum
    • Aortomesenteric angle: ≤ 25° (normal: 38–65°) ^[4]
    • Aortomesenteric distance: ≤ 8 mm (normal: 10–28 mm) ^[4]
• Upper gastrointestinal series: supportive findings include
  • Dilated stomach and proximal duodenum
  • Abrupt, vertical compression of the third part of the duodenum
  • Delayed gastroduodenal transit time (4–6 hours)
  • Relief of the obstruction with postural maneuvers (e.g., left lateral decubitus position)
• Abdominal ultrasound: noninvasive modality to measure aortomesenteric angle and distance

SMA syndrome should be distinguished from nutcracker syndrome, in which the left renal vein is compressed between the SMA and the aorta; the two conditions can co-exist. ^[3]

• Eating disorder (e.g., anorexia nervosa, bulimia nervosa)
• Peptic ulcer disease
• Functional dyspepsia
• Chronic pancreatitis
• Gastric outlet obstruction
• Inflammatory bowel disease (e.g., Crohn disease)
• Celiac disease
• Anatomical duodenal abnormalities (e.g., tumors, diverticula, webs, atresia)
• Nutcracker syndrome
• Median arcuate ligament syndrome
• Gastroparesis

The differential diagnoses listed here are not exhaustive.

General principles ^[3]

• Conservative management is the preferred initial approach. ^[3]
• Early goals of treatment are weight restoration and correction of the underlying cause.
• Surgery is reserved for patients who do not respond to conservative management or present with severe illness.
• Refer patients with eating disorders for psychotherapy.

Conservative management ^[2][3]

• Gastroduodenal decompression (for symptomatic relief)
  • Left lateral decubitus, prone, or knee-to-chest position
  • Nasogastric tube insertion
• Nutritional support
  • Feeding of multiple small portions
  • Enteral feeding via a nasojejunal tube placed distal to the duodenal obstruction
  • Total parenteral nutrition may be used if enteral feeding is not feasible.
• Supportive care (e.g., IV fluids, electrolyte repletion)
• Prokinetic agents (e.g., metoclopramide) to improve gastrointestinal motility

Surgical management ^[3][6]

• Duodenojejunostomy (most common)
  • Creates a bypass around the compressed segment of the duodenum
  • A laparoscopic approach is preferred over an open surgical approach.
• Other procedures include:
  • Gastrojejunostomy
  • Strong procedure
  • Infrarenal transposition of the SMA

• Gastrointestinal complications
  • Mucosal injury (e.g., esophagitis, gastritis, duodenitis)
  • Gastric or duodenal ulcers
  • Gastric or duodenal ischemia, necrosis, or perforation
  • Gastric bezoar
  • Acute pancreatitis
  • Chronic pancreatitis
• Severe malnutrition
• Dehydration and hypovolemia
• Electrolyte abnormalities (e.g., hypokalemia, metabolic alkalosis)
• Acute kidney injury
• Aspiration pneumonia

We list the most important complications. The selection is not exhaustive.