SMA syndrome

Definition

• Extrinsic compression of D3 between SMA and aorta
• Can result in duodenal obstruction

Incidence

• Rare
• F>M
• Young adults

Aetiology

• Congenital (things that close the angle
  • High insertion of duodenum at ligament of Trietz
  • Low SMA origin
• Adhesions
• Rapid weight loss
• Trauma
• Spinal disease, deformity or direct trauma

Pathophysiology

• Normal SMA-aorta angle is approximately 45 degrees
• D3 cross from right to left between SMA and aorta
  • Just caudal of SMA origin
• Left renal vein also within this angle!
• Anything that causes angulation to drop below 25 degrees causes D3 extrinsic compression
• Most common cause is rapid weight loss and reduction in size of mesenteric fat pad between SMA and aorta causes narrowing of the angle

Clinical

• Acute/chronic partial obstruction
• Post prandial pain
• Bilious vomiting
• Weight loss
• Relief of sx with left lateral decubitus positioning?

Investigations

• CTA with sagittal views
• Criteria for SMA
  • Aortomesenteric angle <22 degrees
  • Aortomesenteric distance <10mm
  • OGD to R/O other causes of obstruction
  • Barium swallow - dilated D1 and D2, delayed gastric emptying, antiperistaltic waves

Management

• Acute
  • NGT, resuscitation, IVF, electrolyte replacement
  • Non surgical
    • NJT/TPN
    • Attempt to increase the size of the aortomesenteric fat pad to increase the angle and relieve obstruction
    • 4-6 weeks at least
  • Surgical
    • Indications
      • Failure of non-operative management
    • Options
      • Strong’s procedure
        • DJF flexure mobilisation
        • Division of ligament of Trietz
        • Position duodenum to RIGHT of SMA
        • 25% recurrence rate
        • Does not involve division or bypass of duo
      • Gastrojejunostomy
        • Can get blind loop syndrome or peptic ulceration
      • Duodenojejunostomy +/- division of D4/proximal jejunum
        • Can get blind loop syndrome if D4 divided

Surgical operations for SMA syndrome. A. Strong’s procedure. B. Gastrojejunostomy. C. Duodenojejunostomy is accomplished without division. This is the preferred surgery; or with D. Not recommended as the best option since there is division of the 4th portion of the duodenum