Superior mesenteric artery syndrome (SMA syndrome, also known as Wilkie's syndrome,) is a rare condition first described in 1861, by Rokitansky (1). It occurs when the third (transverse) portion of the duodenum gets entrapped under the superior mesenteric artery. Anatomically, the duodenum passes across the abdominal aorta just below the origin of the SMA. In some cases, various structural anomalies change the angle between the superior mesenteric artery and the aorta (which is normally 45°). This change creates pressure to the duodenum, resulting in to obstruction of its lumen. In the English-language medical literature, there are over 400 cases of SMA syndrome reported, constituting this an unusual cause of upper intestinal obstruction. Some researchers and physicians however still doubt the syndrome's validity (2-6).
The SMA usually forms an angle of approximately 45° (range, 38-56°) with the abdominal aorta, and the third part of the duodenum crosses caudaly to the origin of the SMA, coursing between the SMA and aorta. The SMA usually arises from the anterior aspect of the aorta at the level of the L1 vertebral body. It is enveloped in fatty and lymphatic tissue and extends in a caudal direction at an acute angle into the mesentery. In the majority of patients, the angle between the SMA and the aorta is about 25 to 60 degrees, due in part to the mesenteric fat pad. In the SMA syndrome, the angle is reduced to as low as six degrees due to the loss of the mesenteric fat pad, allowing the SMA to compress the duodenum against the aorta. Any factor that sharply narrows the aortomesenteric angle to approximately 6-25° can cause entrapment and compression of the third part of the duodenum as it passes between the SMA and aorta, resulting in SMA syndrome (7-10).
In addition, the aortomesenteric distance in SMA syndrome is decreased to 2-8 mm (normal 10-20 mm). Alternatively, other causes implicated in SMA syndrome include high insertion of the duodenum at the ligament of Treitz, a low origin of the SMA, and compression of the duodenum due to peritoneal adhesions (11).
Such causes as mentioned above are:
1. Constitutional factors: thin body build, curvature of the spine or laxity of the abdominal walls with a drop in the position of the internal organs,
2. Rapid or severe weight loss in conditions such as cancer or extensive burn injuries, prolonged bedrest, anorexia, or malabsorption syndromes (12-17).
3. Disease deformity, or trauma to the spine or anatomical variants (18-22).
4. Use of a body cast in the surgical treatment of scoliosis or vertebral fractures.
SMA cases after corrective spine surgery, are due to the result of spinal elongation, which decreases the superior mesenteric/aortic angle. Postoperative weight loss is an important factor for the development of SMA syndrome. Although the use of Harrington rods for corrective surgery commonly used in the 1950s and 1960s was an important contributory factor for development of SMA syndrome, newer derotation/translation corrective techniques can also be rarely associated with this disease entity (23-27), as rapid growth without proportional weight gain (particularly in teenagers) (28).
Other rare but recognized causes include trauma or aneurysm of the SMA, and familial predisposition toward SMA syndrome (29,30).
Furthermore anatomic anomalies as abnormally high and fixed position of the ligament of Treitz with an upward displacement of the duodenum or unusually low origin of the SMA.
Also, other unusual causes: traumatic aneurysm of the SMA after a stab wound, familial SMA syndrome and Recurrent SMA syndrome (30-34). Finally, SMA syndrome has also been described in pregnancy, when the gravid uterus reduces in abdominal volume (30).
Physical findings in SMA syndrome are often vague or generalized and the diagnosis of this condition often comes by exclusion. about eight out of ten patients are thin and sickly (asthenic habitus). They often suffer from peptic ulcer disease (25-45%), or hypersecretion of stomach acid (hyperchlorhydria). The presentation can mimic that of subacute small bowel obstruction. Examination can reveal tenderness or pain, fullness, or a succussion splash. Pressure from below the navel upward and toward the back (Hayes maneuver) can lift the SMA, releasing the obstruction and cause relief of both subjective and objective signs. Repositioning during the examination may also afford symptomatic relief.
As it was previously reported the definitive diagnosis of SMA syndrome is difficult. Xray and other imaging studies that may be helpful include (46-51).
Upper GI study with barium contrast - can show dilatation of the first and second portions of the duodenum with a sudden cutoff around the midline.
Computed tomography (CT scan) of the abdomen is useful in the diagnosis of the SMA syndrome and can provide diagnostic information including the aorta-SMA distances and duodenal distension. It can also be used to assess intra-abdominal and retroperitoneal fat. Another diagnostic tool is fluoroscopy with contrast.
Upper GI endoscopy (esophogastroduodenoscopy) may be necessary to exclude mechanical causes of duodenal obstruction. However, the diagnosis of SMA syndrome may be missed with this study.
Finally, abdominal ultrasonography may be helpful in measuring the angle of the SMA and the aortomesenteric distance.