Superior Mesenteric Artery Syndrome

Basics

DESCRIPTION

  • Superior mesenteric artery (SMA) syndrome is the extrinsic compression of the third portion of the duodenum between the SMA and aorta.
  • It is also called Wilkie syndrome, Cast syndrome, or aortomesenteric syndrome.
  • The diagnosis is somewhat controversial because symptoms do not always correlate with radiologic findings and do not always improve following treatment.

EPIDEMIOLOGY

  • Rare
  • More common in adolescents
  • Also seen following corrective scoliosis surgery with a rate of 0.5–2.4%

ETIOLOGY

  • The SMA arises from the abdominal aorta at the L1–L2 vertebral body level and forms an acute downward aortomesenteric angle that is normally between 35 and 65 degrees, due in part to intervening mesenteric fat pad.
  • The third portion of the duodenum lies within the aortomesenteric angle, and narrowing of the angle (<25 degrees) can lead to duodenal compression by the SMA anteriorly and the L3 vertebral body posteriorly.
  • Any factor that narrows the aortomesenteric angle can cause duodenal compression. Common conditions that predispose to narrowing of this angle are as follows:
    • Conditions associated with significant weight loss leading to loss of the mesenteric fat pad:
      • Anorexia nervosa, malignancy, spinal cord injury, trauma, or burns
    • Rapid linear growth in children
    • Increase in lordosis of the back such as from immobilization by body cast, scoliosis surgery, or prolonged bed rest in a supine position
      • Weight percentile for height of <5% is a risk factor for development of SMA syndrome following scoliosis surgery.
    • Variations of the ligament of Treitz: A short/high-anchoring ligament lifts the third or fourth part of the duodenum into the narrower segment in the aortomesenteric angle.
  • If the left renal vein is also compressed, this can lead to microscopic hematuria, also known as nutcracker syndrome.

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