Diagnosis
Our first diagnostic tool is a comprehensive history and physical examination. Once that is complete, many radiologic tests can be used to confirm the anatomic abnormality. The first test ordered is a simple AAS, which may show a “double bubble sign” (Figure 6), indicative of duodenal obstruction.4 There are several other tests, and each facility and surgeon has a preference as to which is considered the “gold standard.” Upper gastrointestinal (GI) barium studies are the simplest and most reliable. The barium test shows foregut anatomy and, to some extent, function. In SMAS patients, one should see duodenal dilatation and failure of the contrast to flow past the third section of the duodenum, along with an abrupt termination of the barium column as the duodenum crosses the vertebrae. This is the traditional method of diagnosis. There is minimal radiation, and the cost is less than that of many other tests, but it can be uncomfortable for the patient.1-4
At some institutions, an upper GI barium study is combined with angiography, which can be used to measure aortomesenteric angle and distance.1,3 Other practitioners prefer computed tomography (CT) with 3-dimensional reconstruction, which allows for measurement of the aortomesenteric angle and distance. In 1 study, CT was found to have an extremely high sensitivity and specificity for these measurements.10 CT angiography also identifies the obstruction with increased sensitivity, but it is rarely necessary and provides more radiation exposure and increased cost.1,6,14,19 Abdominal ultrasound has been used to measure the angle of the SMA and the aortomesenteric distance. When combined with endoscopy, this offers an alternative way to diagnose SMAS and decreases radiation exposure. However, it may require sedation or anesthesia.7,15,17 Overall, 3 criteria are used to define whether a patient has SMAS: duodenal dilatation, an aortomesenteric angle that is less than 25º, and an SMA that is shown to be compressing the third part of the duodenum.5
Treatment
Conservative treatment of SMAS usually starts by removing any precipitating factors present, such as a splint or cast that was applied for scoliosis, or ending activity associated with significant weight loss. Medical management consists of IV hydration, anti-emetics, oral feeding restriction, posture therapy, and placement of an NG tube for decompression. In most cases, patients will need to have an NJ feeding tube passed distal to the site of obstruction. This provides access for enteral feeding, and patients will gradually gain weight, repleting their retroperitoneal fat stores, which pushes the SMA forward and relieves the pressure on the duodenum. Electrolyte balance should be closely monitored along with weight gain. A nutritionist is often consulted to prevent underfeeding, which can produce a slow return to weight gain, poor wound healing, and loss of lean body muscle mass; or overfeeding, which can result in hyperglycemia and respiratory failure. Once patients are stable on enteral feedings, they can begin a slow return to oral intake.2-4,7,12 Total parental nutrition may be needed in some cases, but the risks associated with IV feeding usually outweigh the benefits.4 Almost all cases of acute SMAS can be successfully treated medically if diagnosed in a timely manner and supportive treatment begins promptly.7
Surgical intervention is rarely necessary for acute SMAS, but when conservative measures fail (after a 4- to 6-week trial), or in the presence of peptic ulcer disease or pancreatitis, this may become an appropriate option. In our patient, multiple attempts at passing an NJ feeding tube were unsuccessful, and she needed an operative procedure for insertion of a G-J feeding tube.
Further surgical intervention is usually reserved for those patients with long-standing SMAS for whom medical management has failed or other issues, such as pancreatitis, colitis, or megaduodenum, have arisen. Many operations are described in the literature. A duodenojejunostomy to bypass the site of the obstruction is one option. Another is duodenal derotation (Strong procedure) to alter the aortomesenteric angle and place the third and fourth duodenal portions to the right of the SMA. Other procedures include a Roux-en-Y duodenojejunostomy and duodenal uncrossing. A lateral duodenojejunostomy between the second portion of the duodenum and the jejunum is considered the simplest surgical technique. It achieves successful outcomes in 90% of cases.2-5,14 With regards to SMAS and scoliosis, it is extremely rare that this kind of surgical intervention would be necessary.
Conclusion
When planning operative spinal correction in scoliosis patients (especially females) who have a low BMI at the time of surgery and who have increased thoracic stiffness, be alert for signs and symptoms of SMAS. This rare complication can develop, and timely diagnosis and medical management will decrease morbidity and shorten the length of time needed for nutritional rehabilitation.