Presentation could be insidious or as an acute exacerbation of the chronic disease. Symptoms are usually reflective of the degree of duodenal obstruction. These include abdominal pain, vomiting which is usually bilious, abdominal distension, postprandial abdominal discomfort, esophageal reflux, and early satiety . SMA syndrome caused by spinal correction surgery usually presents 6 - 12 days after the surgery.
The symptoms of SMA syndrome are typically relieved by lying on the left lateral decubitus or prone position, and by maintaining a knee-chest posture. These positions reduce the tension placed on the small bowel by slightly widening the aorto-mesenteric angle .
Imaging studies are the mainstay for diagnosis of SMA syndrome. Diagnosis also involves exclusion of possible differentials such as duodenal ileus, megaduodenum, duodenal webs, and chronic idiopathic intestinal pseudo-obstruction.
Treatment of SMA syndrome begins with a conservative approach of achieving weight gain to restore the peri-mesenteric fat pad, consequently, widening the aortomesenteric angle and reducing the compression on the duodenum . Conservative management also involves gastric decompression and hyperalimentation .
Feeding may be oral or parenteral and the patients weight is closely monitored. Enteric feeding may be a safer alternative to parenteral feeding and may be achieved by flouroscopy-guided passage of a double-lumen nasojejunal tube distal to the obstruction. However, some cases may require both parenteral and enteral nutrition for optimal caloric provision. Oral feeds are started as liquids then changed to semisolids and solids, depending upon tolerance by the patient.
Metocloramide administration may provide symptomatic relief. The appropriate body posture (prone, left lateral decubitus, or knee-chest positions) is recommended during feedings. Conservative mangement is very successful with a 100% success rate in patients with acute presentation of SMA syndrome as reported by an orthopaedic review.
If this conservative management fails, surgery is advised. Duodenojejunostomy is the surgical procure of choice in treating SMA syndrome and can be performed by laparotomy or laparoscopy. Duodenojejunostomy has a success rate of approximately 90%. An alternative and less invasive procedure is called Strong's procedure which involves lysis of the ligament of treitz after manipulation and proper placement of the duodenum. This procedure, however, has a failure rate of about 25%.
Gastrojejunostomy, which was the preferred surgical treatment for SMA syndrome in the past, has been discontinued because of postoperative complications such as relapses and blind-loop syndrome.
SMA syndrome may cause significant morbidity and high mortality if the syndrome is not diagnosed in time. Complications of this syndrome include dehydration, electrolyte imbalance, malnutrition, duodenal bezoar open link, gastric perforation and massive GI bleeding   . Early diagnosis and treatment, however, provides an excellent outcome.
The causes of SMA syndrome may be genetic or acquired defects in the anatomy of the SMA and arrangement of the abdominal organs. Genetic causes of SMA syndrome include a low insertion point of the superior mesentery artery or a higher terminal of the treitz ligament, moving the duodenum to a higher location. Acquired defects may occur secondary to spinal repair surgeries such as for scoliosis in which the spine becomes elongated displacing the abdominal structures , trauma to the spine, and total proctocolectomy and ileo-anal anastomosis .
A common acquired etiology implicated in SMA syndrome is severe weight loss. Severe weight loss leads to a reduction in the fatty tissue around the SMA, consequently, reducing its ambulation. Common risk factors for such severe weight loss include high metabolic states such as burns , eating disorders , and diseases which cause cachexia such as malignancies and malabsorptive diseases .
Generally, factors which cause narrowing of angle between the aorta and SMA are implied as causes of SMA syndrome. These include thin body build, lumber hyperlordosis, abdominal wall laxity and visceroptosis, severe weight loss as discussed above, spinal surgery, and acquired aneurysms.
Spinal repair techniques used in the past were mostly held responsible as an etiological factor of SMA syndrome. Improvement and advancement in spine correction surgery has reduced this association . Rapid linear growth without a concomitant weight gain is also associated with SMA syndrome, such as in underweight adolescents who had spinal repair surgery for scoliosis .
Rare causes of SMA syndrome include traumatic aneurysm of the SMA, mycotic aortic aneurysms and idiopathic neonatal SMA syndrome   .
SMA syndrome is considered a rare disease. Although its exact incidence rate is not known, it has been suggested to have an incidence of 0.013-0.3% . English literature has described just 400 cases so far.
SMA syndrome mostly affects older children, such as adolescents; the incidence is higher in females as compared to males.Typically it affects individuals between the ages of 20 and 30, as reported by a study. SMA syndrome shows no racial predilections.
In healthy subjects, a cushion of lymphatic tissues and fat around SMA protects duodenum against compression. In cases of severe weight loss, depletion of this cushion leads to change in angulation and distance between aorta and SMA. All other etiological factors such as spinal lordosis and body casts also cause the characteristic anatomic defect of SMA. This anatomic defect is a characteristic narrowing of the angle between the aorta and SMA to less than 25 degrees (normal being 38 degrees - 65 degrees) . There is also a reduction in the aorto-mesenteric distance, by up to 18 mm. The reduction in both the aorto-mesenteric angle and distance results in duodenal obstruction causing SMA syndrome .
Superior mesenteric artery (SMA) is a rare disorder characterized by a reduction of the SMA angle leading to compression of duodenum between SMA and aorta. This results in chronic complete or partial obstruction of the duodenum .
It was first described by Carl Freiherr Von Rokitansky, an Austrian professor, in 1861 after he noted the abnormality during an autopsy session . Afterwards, he provided details on the pathology, pathophysiology and clinical manifestation of the syndrome and posited possible treatment strategies for the syndrome in 64 patients . However, because of the nonspecificity of the symptoms and a wide range of differential diagnoses, other scientists and researchers disagreed with Freiherr's findings and the existence of SMA syndrome. Over the years, following advances in radiological studies, the defect in the SMA and compression of the duodenum have been visualized clearly and the syndrome accepted as an entity for diagnosis .
Although, SMA syndrome may arise from congenital malformation of the SMA, it is commonly due to spine correction surgery for scoliosis and diseases characterized by a high metabolic rate and rapid fat depletion  . Rapid weight loss from eating disorders and malabsorption are, therefore, also implicated in the etiology of this syndrome. Other risk factors of SMA syndrome include laxity of the abdominal wall, lordosis, and use of body casts, hence SMA syndrome is also called cast syndrome.
SMA syndrome is typically a disease of the young and primarily affects older children and adolescents. Symptoms of SMA syndrome are due to duodenal obstruction, and the degree of obstruction. These symptoms include bilious vomiting, nausea, abdominal pain, postprandial discomfort, bloating, and early satiety. Symptoms may be acute manifestations or chronic occurrences and are often relieved when the patient assumes a left lateral decubitus, prone, or knee-chest position .
SMA syndrome is typically a disease of the young.Studies estimate the incidence rate at 0.1-0.3% . However barium studies confirm the diagnosis in 0.013-0.78% of cases  .
The syndrome is mainly diagnosed with imaging studies including fluoroscopy, MRI, and CT scanning to demonstrate the reduce angulation of the SMA and the compression and obstruction of the duodenum. Several researchers maintain that the condition may be over diagnosed because of the long list of possible differential diagnoses.
SMA syndrome is a rare condition arising as a result of compression of a part of duodenum, the upper part of small intestine, between the superior mesenteric artery (SMA) and the aorta. It is more common in females and in persons aged from 10 to 30 years. As the aorta, descends down into the pelvis, it gives off some branches, including the SMA, which supply the small intestine. If the angle at which the SMA leaves the aorta is reduced, it compresses a part of the duodenum which lies between them and causes the SMA syndrome. The result of this compression is a chronic obstruction of duodenum .
SMA syndrome may be caused by genetic abnormalities leading to abnormalities in the structure of the SMA developed during fetal development. However, the most common causes of this syndrome are acquired. Certain conditions such as surgical repair of scoliosis, anus or large intestine affecting the position of the small intestine and diseases which cause rapid weight loss; rapid weight loss reduce the fat pads around the SMA making it easy to compress the duodenum.
The cardinal problem in SMA syndrome is obstruction of the duodenum, such that food can no longer pass through the intestine. This produces symptoms such as vomiting which typically appears green, abdominal pain after eating, abdominal fullness, early satiety, and acid reflux. These symptoms are relieved if the patient lies on his tummy, his left side or sits such that the knees touch the chest.
Whereas early diagnosis and treatment provides a good outcome for the patient, delayed diagnosis may be associated with a myriad of complications including dehydration, malnutrition, perforation of the duodenum, and massive bleeding.
The main diagnostic tools for diagnosis of the syndrome are radiological studies, magnetic resonance imaging and angiography (MRI and MRA), fluoroscopy, CT scan, ultrasound scans are all employed and give details about the narrow space between the aorta and the SMA.
This condition is initially treated medically by increasing feeds to achieve significant weight gain and increasing the fat pads around the SMA. Feeding may be through the mouth, via intravenous or through tubes passed directly into the part of the small intestine beyond the obstruction. If this treatment fails, surgery is the next approach to relieve the compression of the duodenum.