SMA Syndrome

Published on 19/07/2015 by admin

Filed under Radiology

Last modified 22/04/2025

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 Reformat in sagittal plane to see aorta and SMA

• Antiperistaltic flow of barium proximal to obstruction
• Relief of obstruction in prone, knee-chest, or left lateral decubitus positions

TOP DIFFERENTIAL DIAGNOSES

• Duodenal obstruction (other causes)
• Intestinal scleroderma
• Duodenal stricture

PATHOLOGY

• Predisposing conditions

image Weight loss → depletion of retroperitoneal fat, leading to narrowed aorto-mesenteric angle
image Anatomical and congenital anomalies
image Postoperative states (e.g., scoliosis)

CLINICAL ISSUES

• Postprandial epigastric pain, nausea, vomiting

image Pain relieved in prone, knee-chest, or left lateral decubitus position
• Surgery (bypassing duodenum) indicated when conservative therapy fails

DIAGNOSTIC CHECKLIST

• Can be mimicked by or made worse by other causes of duodenal dilation (e.g., scleroderma)
image
(Left) Supine film from an upper GI series in a woman with recent weight loss and early satiety shows an abrupt, straight-line cut-off image of the 3rd portion of duodenum as it crosses over the midline, with dilation and slow emptying of the proximal duodenum. There is also a duodenal diverticulum image.

image
(Right) Axial CECT shows marked distention of the 2nd portion of the duodenum image and stomach. The 3rd portion of the duodenum image is compressed as it passes between the aorta and the superior mesenteric artery (SMA).
image
(Left) Coronal reformatted CT in the same case shows dilation of the second portion of duodenum image, while the remaining bowel is collapsed. Note this patient’s thin body habitus.

image
(Right) Sagittal-reformatted CT in the same case shows a very narrow angle between the superior mesenteric artery image and the aorta, with compression of the 3rd portion of duodenum image as it passes between these vessels.

TERMINOLOGY

Definitions

• Vascular compression of 3rd portion of duodenum between aorta and superior mesenteric artery (SMA)

IMAGING

General Features

• Best diagnostic clue

image Dilated 1st and 2nd portions of duodenum with abrupt, straight-line transition to collapsed duodenum as it crosses spine

Imaging Recommendations

• Best imaging tool

image Barium upper GI series with CECT
• Protocol advice

image Obtain thin slice CECT with good contrast bolus

– Reformat in sagittal plane to see aorta and SMA

Fluoroscopic Findings

• Dilatation of 1st and 2nd portions of duodenum ± gastric dilatation
• Abrupt narrowing of 3rd portion of duodenum

image Vertical, linear, extrinsic, band-like defect overlying spine
• Antiperistaltic flow of barium proximal to obstruction
• Relief of obstruction in prone, knee-chest, or left lateral decubitus positions

CT Findings

• CECT

image Beak-like compression of 3rd part of duodenum between SMA and aorta
image Aorto-SMA angle < 22-25° in sagittal plane
image Aorto-SMA distance < 8 mm

DIFFERENTIAL DIAGNOSIS

Duodenal Obstruction (Other Causes)

• Gastroduodenoscopy is needed to rule out intraluminal causes
• Other causes of duodenal obstruction (e.g., cancer) can mimic or exacerbate SMA syndrome

Intestinal Scleroderma

• Dilated atonic small bowel with crowded folds and wide-mouthed sacculations
• Check for other small bowel, lung, or skin changes of scleroderma

Duodenal Stricture

• Usually postinflammatory with prior history of ulcer disease
• More common in proximal duodenum

PATHOLOGY

General Features

• Etiology

image Impingement of 3rd duodenum by aorta and SMA
• Predisposing conditions

image Weight loss → depletion of retroperitoneal fat  leads to narrowed aorto-mesenteric angle

– Chronic wasting diseases

image Cancer, paraplegia, cardiac cachexia, drug abuse, body casts
– Anorexia nervosa, malabsorption
– Catabolic states

image Burn, trauma
image Anatomical/congenital anomalies

– High insertion of ligament of Treitz → cephalad dislocation of duodenum
– Intestinal malrotation
– Low origin of SMA → decreased aorto-mesenteric distance
– Lumbar lordosis
image Postoperative states

– Scoliosis surgery
– Bariatric surgery
– Nissen fundoplication
– Aortic aneurysm repair
– Ileoanal pouch anastomosis → mesenteric tension → caudal pull of SMA → ↓ aorto-mesenteric angle

CLINICAL ISSUES

Presentation

• Most common signs/symptoms

image Postprandial epigastric pain, nausea, vomiting
image Pain relieved in prone, knee-chest, or left lateral decubitus position
• Other signs/symptoms

image Anorexia, weight loss

Demographics

• Gender

image More common in women

Natural History & Prognosis

• Good response to medical and surgical treatments

Treatment

• Acute symptoms

image NG tube decompression of stomach
• Medical treatment

image Increase body weight by tube feeding or parenteral nutrition
• Surgery

image Indicated when conservative therapy fails
image Gastrojejunostomy, duodenojejunostomy

DIAGNOSTIC CHECKLIST

Consider

• Can be mimicked by or made worse by other causes of duodenal dilation

 

SELECTED REFERENCES

1. Lam, DJ, et al. Superior mesenteric artery syndrome following surgery for adolescent idiopathic scoliosis: a case series, review of the literature, and an algorithm for management. J Pediatr Orthop B. 2014; 23(4):312–318.

 

Agrawal, GA, et al. Multidetector row CT of superior mesenteric artery syndrome. J Clin Gastroenterol. 2007; 41(1):62–65.

Welsch, T, et al. Recalling superior mesenteric artery syndrome. Dig Surg. 2007; 24(3):149–156.

Unal, B, et al. Superior mesenteric artery syndrome: CT and ultrasonography findings. Diagn Interv Radiol. 2005; 11(2):90–95.

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