Superior mesenteric artery syndrome

Superior mesenteric artery (SMA) syndrome (also known as Wilkie's syndrome) is a rare acquired vascular compression disorder in which acute angulation of superior mesenteric artery (SMA) results in compression of the third part of the duodenum leading to obstruction.

It should not be confused with nutcracker syndrome, also a superior mesenteric artery compression disorder, where the SMA compresses the left renal vein, although some authors use the terms interchangeably. 

Epidemiology

It is an uncommon but well recognized clinical entity. About 400 cases have been described in English literature. Is seen more commonly in females than in males, and usually occurs in older children and adolescents.

Clinical presentation

Patients with SMA syndrome may present acutely, with chronic insidious symptomatology, or with an acute exacerbation of chronic symptoms. 

• acute presentation is usually characterized by signs and symptoms of duodenal obstruction. 
• chronic cases may present with long-standing vague abdominal symptoms, early satiety and anorexia, or recurrent episodes of abdominal pain, associated with vomiting.

Pathophysiology

Normally, fat and lymphatic tissues around the SMA provide protection to the duodenum against compression. Under conditions of severe weight loss, this cushion around the SMA is diminished, causing angulation and reduction in the distance between the aorta and the superior mesenteric artery. This is usually associated with conditions causing significant weight loss such as:

• anorexia nervosa
• malabsorption
• hypercatabolic states (burns, major surgery, malignancy)
• severe congestive heart failure causing cachexia

Other conditions may also precipitate this syndrome: 

• increased spinal lordosis
• application of a body cast
• short ligament of Treitz
• unusually low origin of SMA 

Radiographic features

The diagnosis of SMA syndrome is based on clinical symptoms and radiologic evidence of obstruction. 

Radiography

• plain radiograph demonstrates a dilated, fluid- and gas-filled stomach. 
• Barium radiography shows dilatation of the first and second part of the duodenum, extrinsic compression of the third part, and a collapsed small bowel distal to the crossing of the SMA. 

CTA and MRA

CT-Angiography or magnetic resonance angiography (MRA) enable visualization of vascular compression of the duodenum and measurement of aortomesenteric distance precisely.

• normally, the aortomesenteric angle and aortomesenteric distance is 25° to 60° and 10 to 28 mm, respectively. 
• in SMA syndrome, both parameters are reduced, with values of 6° to 15° and 2 to 8 mm.

Etymology

The SMA syndrome was first described by von Rokitanski in 1861. Later, Wilkie provided a more detailed clinical and pathophysiologic description in a series of 64 patients and suggested treatment approaches.

Treatment and prognosis

Traditionally, treatment has consisted of conservative measures such as:

• nasogastric decompression and hyperalimentation followed by oral feeding with frequent small meals. 
• posturing maneuvers during meals and motility agents may be helpful in some patients. 

Surgery may be considered if conservative treatment fails. 

• duodenojejunostomy is effective in the majority of patients.
• laparoscopic duodenojejunostomy offers a new minimally invasive therapeutic approach to SMA syndrome.
• laparoscopic surgery involving lysis of the ligament of Treitz with mobilization of the duodenum is another minimally invasive approach.