April 13, 2022
Years published: 2018, 2022
NORD gratefully acknowledges Domingo T. Alvear, MD, FICS, FACS, Retired Chief of Pediatric Surgery; Medical Advisor, Superior Mesenteric Artery Syndrome Research Awareness and Support, for assistance in the preparation of this report.
Superior mesenteric artery (SMA) syndrome is a rare condition that involves compression of the third portion of the duodenum which is the upper part of the small intestines just past the stomach. This condition occurs when the third part of the duodenum is compressed between two arteries – the main artery of the body called the abdominal aorta (AA) and one of its branches called the SMA. The SMA provides blood supply to the small intestines and the first part of the colon. Compression of the SMA against the AA can prevent duodenal contents from draining into the jejunum (upper small intestine) hence the inability to get proper nutrition leading to weight loss and malnutrition. Pain from the compression can be debilitating, causing “food fear” and aggravating the condition. Nausea and vomiting are manifestations of the compression of the duodenum. When weight loss is persistent, the mesenteric fat pad decreases and causes a decrease in the angle between the SMA and AA hence aggravating the compression and obstruction. Prompt diagnosis and early treatment are essential to avoid significant complications or death.
SMA syndrome is considered extremely uncommon and most consider this as a diagnosis of exclusion i.e., many other more common diagnoses must be ruled out.
The signs and symptoms can vary greatly from one person to another. Sometimes the symptoms are mild and build slowly over time. Without treatment, in some people, symptoms can be severely disabling. Generally, the initial symptoms are nonspecific, which means that symptoms are common ones that can be associated with many different conditions. Sometimes symptoms can come and go (intermittent).
Symptoms can include nausea, vomiting, abdominal pain, indigestion (dyspepsia) and early satiety, in which the person feels full despite having very little food or drink because the stomach is not emptying. The stomach remains full of fluid or food previously ingested hours before. Constipation can occur when there is delay in stomach emptying. Vomiting of undigested food can occur and can become bilious i.e., green or yellow when the blockage becomes severe. Relief can be obtained by lying on the right decubitus or left decubitus (right or left side down) or face down (prone) with both arms and legs up (knee to chest position) after eating or drinking to allow the stomach to empty better. The abdominal pain can be severe after intake of food or drink because the pulsation of the SMA becomes stronger and bounding against the duodenum. Food aversion or food fear follows which aggravates the weight loss and worsens SMA syndrome.
Some affected individuals may also have nutcracker syndrome in which the left renal vein (kidney vein) is compressed by the AA and SMA. Most people affected have no symptoms but those affected will have left flank and pelvic pain and may have blood in the urine (hematuria).
SMA syndrome occurs when the duodenum is compressed by the SMA against the AA to cause blockage and prevent progression of food or fluids into the rest of the small intestine. The small intestine is a long, winding tube that connects the stomach to the large intestine ending in the anus. The small intestine is divided into three sections – duodenum, jejunum and ileum. Each section has a role in digestion and absorption of nutrients that were previously digested in the stomach.
The duodenum is the first part of the small intestine and directly connects to the stomach. It has four parts or sections. The third section can be compressed by the SMA against the AA causing a partial obstruction which manifests as nausea, vomiting and epigastric pain. The mesentery is a double fold that suspends the small intestine and large intestine from the posterior abdominal wall. Loss of the mesenteric fat pad around the SMA and behind the AA has been mentioned in the literature as the most common cause of SMA syndrome secondary to excessive weight loss for any reason like eating disorders, malabsorption, gastric bypass surgery, trauma, malignancies and inflammatory bowel disease (Crohn’s disease or ulcerative colitis). People who had extensive burns can develop SMA syndrome due to fat and muscle wasting seen in this injury.
CT angiography or MRI can measure the angle between the AA and the SMA. The normal angle is 25 – 60 degrees while with SMA syndrome is reduced to 7 – 22 degrees. The distance between the AA and the SMA is normally 10 – 28 mm but with SMA syndrome it is reduced to 2 to 8 mm. Some people with SMA syndrome may be born with this abnormality and diagnosed as infants or preteen children.
The ligament of Treitz is a structure that suspends the junction between the duodenum and the jejunum. A lower origin of the SMA from the AA can be a factor. The ligament of Treitz can be short or thick causing an acute angulation.
A linear growth spurt without accompanying increase in abdominal girth can be a predisposing factor. Patients who had surgical correction for scoliosis can develop SMA syndrome because the angle or the distance between the AA and SMA can decrease when the spine is straightened causing stretching of the AA. Patients who were placed in a body cast after injury or spine surgery have developed SMA syndrome hence the term cast syndrome.
There have been siblings reported to have SMA syndrome.
The prevalence (the number of people with a disease or disorder in a given population at a given time) is unknown. The most frequently quoted estimate is that 0.13 to 0.3% of people in the United States general population have this disorder. SMA syndrome has been reported in greater frequency among teenagers and young adults but can occur at any age including infants and the elderly. It seems to affect more women than men by 3:2 ratio. SMA syndrome can affect individuals of any racial or ethnic heritage hence it is worldwide. It is likely that some people with SMA syndrome have not been diagnosed so the true prevalence may be higher than reported.
A diagnosis of SMA syndrome is based on the identification of characteristic symptoms, a detailed patient history, a thorough clinical evaluation and a variety of specialized tests. A team approach to diagnosis is essential and may include a primary care physician (pediatrician, internist or general practitioner), gastroenterologist, surgeon (pediatric or general), radiologist, nutritionist or dietician, pain specialist, and psychologist or psychiatrist. It is a diagnosis of exclusion hence a period of observation and trial of therapy may be required before a definitive diagnosis is made. Delay in the diagnosis and treatment worsens the condition and can lead to a fatal outcome.
Clinical testing and Workup
A plain radiograph of the abdomen (x-ray) is non-specific or may show an enlarged stomach or bloating. Computed tomography angiography (CTA) or CT scan with intravenous contrast will show the angulation and distance between the AA and SMA as discussed previously. Any radiographic findings must be correlated with the clinical symptoms and response to treatment to be considered important. MRI can be used for patients who are allergic to the IV contrast and will show the same findings.
Hypotonic duodenography was used as the main test for diagnosis prior to CTA. Barium is ingested or injected to the stomach via a tube with fluoroscopy to follow the movement of the barium into the small intestine. If there is delay in gastric emptying, the contrast will remain in the stomach for as long as 6 hours. If there is no delay in gastric emptying, it empties into the duodenum and then to the jejunum without delay. If the patient has SMA syndrome, there will be dilation of the first and second portion of the duodenum and a “to and fro” motion of the contrast in that area. There will be an abrupt cutoff of contrast at the third portion of the duodenum corresponding to the compression of the SMA against the duodenum. When the patient lays on the right side or face down, the contrast will flow into the jejunum. This can be duplicated with a CT scan with oral contrast.
A test called a Doppler ultrasound can be used in the diagnosis of SMA syndrome but is not as sensitive as CTA and is operator dependent. This is more important when there is a suspicion of an associated median arcuate ligament syndrome (MALS) since it can detect the differential velocity of the celiac artery flow during respiration i.e. narrowing occurs during expiration.
The treatment of SMA syndrome is directed toward the specific symptoms that are apparent in each individual. Treatment may require the coordinated efforts of a team of providers including a pediatrician, internist, gastroenterologist, surgeon (pediatric or general), nutritionist or dietician, pain therapist, psychologist, or psychiatrist. Psychosocial support of the entire family may be needed.
Conservative therapy should be tried first before surgery is considered. Frequent small feedings with supplemental high calorie liquid followed by postural therapy are tried first. Insertion of a tube from the nose to the jejunum (naso-jejunal tube) is next. Special formula is used for feeding delivered via a pump for 16 to 20 hours that will deliver adequate calories and fluids needed by the patient. If these methods of feeding fail, high calorie IV feeding (total parenteral nutrition – TPN) maybe needed initially and can supplement tube feedings. Weight gain is the goal to restore the mesenteric fat pad and reverse the loss of angle and decrease the distance between the AA and SMA.
If conservative measures are not working within 6 to 8 weeks and the symptoms worsen, especially if the patient has severe pain and is unable to tolerate GI feeding, surgery becomes indicated.
Gastro-jejunostomy is a procedure where a loop of jejunum is connected to the stomach, but because it is fraught with problems is no longer recommended.
Duodeno-jejunostomy is a procedure where a loop of jejunum is connected to the second portion of the duodenum bypassing the area of obstruction (third portion of duodenum). This can be performed with a small incision (laparoscopically) or with open surgery. This is the most frequently used procedure to relieve the blockage and has a success rate of 70 to 90% according to the literature. Some patients will continue to have pain and symptoms after this procedure.
The Strong procedure divides the ligament of Treitz to allow lowering of the duodeno-jejunal junction which can relieve the compression. If the duodeno-jejunal junction is not sutured to the right abdominal wall, recurrence of the SMA syndrome occurs.
Duodenal derotation is a procedure where the ligament of Treitz is divided and the duodeno-jejunal junction (DJ) is rotated away from the SMA and sutured to the right abdominal wall. If there is a severe kink at the DJ a side-to-side duodeno-jejunostomy is performed at that site. This is a physiologic connection between the duodenum and jejunum and will not have long term complications.
The other procedure is known as infrarenal transposition of the SMA where the SMA is disconnected from the AA and reattached again below the left renal vein and the third portion of the duodenum. This eliminates the compression factor of the SMA.
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