Superior Mesenteric Artery (SMA) Syndrome Workup

Updated: Dec 31, 2018
  • Author: Frederick Merrill Karrer, MD, FACS; Chief Editor: Carmen Cuffari, MD  more...
  • Print
Workup

Imaging Studies

The diagnosis of superior mesenteric artery (SMA) syndrome is difficult. Confirmation usually requires radiographic studies, such as an upper GI series, hypotonic duodenography, and CT scanning.

Fluoroscopic findings suggestive of superior mesenteric artery syndrome include dilation of the first and second portions of the duodenum with an abrupt narrowing at the third portion (see the image below), delayed gastroduodenal emptying, and antiperistaltic waves proximal to the obstruction. Additionally, the obstruction of the duodenum may be relieved by a change in position, especially left lateral decubitus position. [17]

Prompt gastric emptying of residual contrast is pr Prompt gastric emptying of residual contrast is present within the stomach into the second portion of the duodenum. Additional contrast was hand injected through the transpyloric feeding tube to further distend the second portion of the duodenum. The second portion of the duodenum is dilated with very slow transit across the spine into the jejunum. This occurred despite difference in position of the patient. The high-grade partial obstruction at the distal second portion of the duodenum is due to superior mesenteric artery (SMA) syndrome.

A Hayes maneuver (ie, pressure applied below the umbilicus in cephalad and dorsal direction), which elevates the root of small-bowel mesentery, may also relieve the obstruction. In equivocal cases, hypotonic duodenography may depict the site of obstruction and dilation of the proximal duodenum, with antiperistaltic waves within the dilated portion.

CT scanning is useful in the diagnosis of superior mesenteric artery syndrome and can provide diagnostic information, including aorta-superior mesenteric artery distances and duodenal distension. Also, it can be used to assess intra-abdominal and retroperitoneal fat. CT criteria for the diagnosis of superior mesenteric artery syndrome include an aortomesenteric angle of less than 22 degrees and an aortomesenteric distance of less than 8-10 mm. In children, an angle of less than 20° has been correlated with superior mesenteric artery syndrome. [2] CT can also identify problems that may require intervention, like compression of the left renal vein that results in renal vein thrombosis, pneumatosis or portal venous gas, or an abdominal aortic aneurysm. [17]

Upper GI endoscopy may be necessary to exclude mechanical causes of duodenal obstruction. However, the diagnosis of superior mesenteric artery syndrome may be missed with this study.

Abdominal ultrasonography may be helpful in measuring the angle of the superior mesenteric artery and the aortomesenteric distance. When combined with endoscopy, this may offer an alternative way to diagnose superior mesenteric artery syndrome in children to avoid other tests with a risk of radiation exposure. [18]

Manometry may be used to differentiate between the possibility of a myopathic form of chronic intestinal pseudo-obstruction syndrome (hollow visceral myopathy) by demonstrating low-amplitude waves throughout the duodenum, and frequently the stomach, versus an irregular or absent phase III and no postprandial motility changes in a neuropathic form of chronic intestinal pseudoobstruction syndrome. The pattern of increased amplitude of propagated contractions and retrograde contractions should hint or suggest the mechanical obstruction in superior mesenteric artery syndrome.