Practice Essentials
Superior mesenteric artery (SMA) syndrome is an uncommon but well recognized clinical entity characterized by compression of the third, or transverse, portion of the duodenum between the aorta and the superior mesenteric artery. This results in chronic, intermittent, or acute complete or partial duodenal obstruction. [1, 2] See the image below. It is linked to severe morbidity and mortality when diagnosis is delayed, making it a crucial differential to consider when there is concern for a bowel obstruction, especially in the setting of recent weight loss. [3]
Prompt gastric emptying of residual contrast is present within the stomach into the second portion of the duodenum. Additional contrast was hand injected through the transpyloric feeding tube to further distend the second portion of the duodenum. The second portion of the duodenum is dilated with very slow transit across the spine into the jejunum. This occurred despite difference in position of the patient. The high-grade partial obstruction at the distal second portion of the duodenum is due to superior mesenteric artery (SMA) syndrome.
SMA syndrome (also known was Wilkie syndrome, cast syndrome, mesenteric root syndrome, chronic duodenal ileus, and intermittent arteriomesenteric occlusion) was first described in 1861 by Von Rokitansky, who proposed that its cause was obstruction of the third part of the duodenum as a result of compression by the superior mesenteric artery anteriorly and the aorta posteriorly. Decreasing the superior mesenteric artery–aorta (SMA-Ao) angle causes compression to the third part of the duodenum.
The major causes of SMA syndrome involve body weight loss and resulting loss of mesenteric fat tissue between the SMA and the aorta, which, in turn, creates a narrower angle between the vessels. [3] See the image below. Some studies report the incidence of SMA syndrome to be 0.1-0.3%. [4] Approximately 0.013-0.78% of barium upper gastrointestinal (GI) studies evaluating for SMA syndrome support the diagnosis. [5, 6]
Anatomy of superior mesenteric artery syndrome showing the relationship between the different anatomical structures involved. Image from Akihiko Oka, MD.
Despite the fact that about 400 cases are described in the English language literature, many have doubted the existence of SMA syndrome as a real entity; indeed, some investigators have suggested that SMA syndrome is overdiagnosed because it is confused with other causes of megaduodenum. Nonetheless, it is a well-known complication of scoliosis surgery, anorexia, and trauma. It often poses a diagnostic dilemma; its diagnosis is frequently one of exclusion.
Signs and symptoms
Patients often present with chronic upper abdominal symptoms such as abdominal pain, nausea, eructation, voluminous vomiting (bilious or partially digested food), postprandial discomfort, early satiety, bloating, and sometimes subacute small bowel obstruction. Its symptoms may mimic anorexia nervosa or functional dyspepsia.
See Presentation for more detail.
Diagnosis
The diagnosis of SMA syndrome is difficult. Confirmation usually requires radiographic studies, such as an upper GI series, hypotonic duodenography, and CT scanning.
See Workup for more detail.
Management
Reversing or removing the precipitating factor is usually successful in a patient with acute SMA syndrome. Conservative initial treatment is recommended for all patients; this includes adequate nutrition, nasogastric decompression, and proper positioning of the patient after eating.
Surgical intervention is indicated when conservative measures are ineffective, particularly in patients with a long history of progressive weight loss, pronounced duodenal dilatation with stasis, and complicating peptic ulcer disease.
See Treatment and Medication for more detail.
Pathophysiology
The superior mesenteric artery usually forms an angle of approximately 45° (range, 38-56°) with the abdominal aorta, and the third part of the duodenum crosses caudal to the origin of the superior mesenteric artery, coursing between the superior mesenteric artery and 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 superior mesenteric artery and aorta, resulting in SMA syndrome. [7] See the image below.
Shown are the (a) normal aortomesenteric relationship and (b) the aortomesenteric relationship in superior mesenteric artery (SMA) syndrome, where the proximal SMA compresses the mid-transverse duodenum against the abdominal aorta. Image from Serina Beydoun, MD.
In addition, the aortomesenteric distance in SMA syndrome is decreased to 2-8 mm (normal is 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 superior mesenteric artery, and compression of the duodenum due to peritoneal adhesions. [8, 9]
Etiology
Important etiologic factors that may precipitate narrowing of the aortomesenteric angle and recurrent mechanical obstruction include the following.
Constitutional factors
Constitutional factors include the following:
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Thin body build
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Exaggerated lumbar lordosis
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Visceroptosis and abdominal wall laxity
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Depletion of the mesenteric fat caused by rapid severe weight loss due to catabolic states such as cancer, surgery, burns, trauma, or psychiatric problems
Severe injuries
Severe injuries, such as head trauma or burns, can lead to prolonged bedrest and malnutrition.
Dietary disorders
Dietary disorders include the following:
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Malabsorption
Spinal disease, deformity, or trauma
Spinal disease, deformity, or trauma (use of body cast in the surgical treatment of scoliosis or vertebral fractures): SMA syndrome cases after corrective spine surgery are due to the result of spinal elongation, which decreases the SMA-Ao angle. Postoperative weight loss is an important factor for development of SMA syndrome. Although the use of Harrington rods for corrective surgery, which was common in the 1950s and 1960s, was an important contributory factor for development of SMA syndrome, newer derotation/translation corrective techniques can also rarely be associated with this disease entity. [11]
Rapid linear growth without compensatory weight gain
Rapid linear growth without compensatory weight gain, particularly in adolescents: Adolescents with low body mass index (< 18 kg/m2) may be at higher risk for developing SMA syndrome after spinal fusion for scoliosis than patients with a higher body mass index. [12]
Anatomic anomalies (rare)
Anatomic anomalies (rare) include the following:
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Abnormally high and fixed position of the ligament of Treitz with an upward displacement of the duodenum
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Unusually low origin of the superior mesenteric artery
Chronic cannabis use
Case reports suggest a possible association between chronic cannabis use and SMA syndrome. Chronic cannabis use, particularly when accompanied by chronic nausea, recurrent episodes of vomiting (as seen in cannabis hyperemesis syndrome), and significant weight loss, may contribute to the development of SMA syndrome. [13]
Unusual causes
Unusual causes include the following:
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Traumatic aneurysm of the superior mesenteric artery after a stab wound
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Abdominal aortic aneurysms and mycotic aortic aneurysms [14]
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Familial SMA syndrome
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Recurrent SMA syndrome
Epidemiology
United States statistics
The precise incidence of this entity is unknown. In a review of the literature, approximately 0.013-0.78% of the findings from upper GI tract barium studies support a diagnosis of SMA syndrome.
Race-, sex-, and age-related demographics
No racial differences have been identified.
More females than males are affected by SMA syndrome. In one large series of 75 patients with SMA syndrome, two thirds of the cases involved women, with an average age of 41 years; one third of cases involved men, with an average age of 38 years.
SMA syndrome usually occurs in older children and adolescents. In one report, 75% of the cases occurred in patients aged 10-30 years.
Prognosis
The outcome is excellent if the entity is diagnosed in a timely fashion and if the patient receives appropriate therapy. In the past, deaths due to progressive dehydration, hypokalemia, and oliguria have been reported; most of these occurred in patients in whom the diagnosis was delayed or missed.
Morbidity/mortality
Delay in the diagnosis of SMA syndrome can result in malnutrition, dehydration, electrolyte abnormalities, gastric pneumatosis and portal venous gas, formation of an obstructing duodenal bezoar, hypovolemia secondary to massive GI hemorrhage, and even death secondary to gastric perforation. [2, 17, 18, 19]
Complications
Complications include the following:
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Electrolyte imbalance (eg, hypokalemia, hypochloremia, metabolic alkalosis)
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Dehydration
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Malnutrition
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Oliguria
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Hypotension
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Peptic ulcer disease
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Aspiration pneumonia
The most frequent complication is gastrointestinal mucosal injury, and the incidence has been reported as 25-59% in patients with SMA syndrome. [3]
Late diagnosis can end in complications, including death because of the imbalance of electrolytes, a perforation of the stomach, gastric pneumatosis, or obstruction caused by duodenum bezoar. [20]
Patient Education
Tell patients that superior mesenteric artery (SMA) syndrome is a rare digestive condition where part of the upper small intestine (duodenum) becomes compressed between two major arteries: the aorta and the SMA. This compression causes a partial blockage of the small intestine, leading to symptoms such as abdominal pain, nausea, and recurrent vomiting.
Inform patients that SMA syndrome usually happens when there is a loss of the fat cushion that normally keeps the arteries apart. Common causes include significant weight loss due to illness, eating disorders, or surgery, as well as rapid growth during adolescence.
Symptoms
Advise patients that the symptoms of SMA syndrome can include the following:
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Nausea and vomiting
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Abdominal pain, especially after eating
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Bloating and a feeling of fullness
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Weight loss
Diagnosis
Inform patients that imaging studies such as a CT scan or an upper GI series are usually needed to confirm compression of the duodenum by the SMA. An upper endoscopy may also be done to rule out other conditions.
Treatment
Conservative management
Tell patients that in many cases, treatment focuses on weight gain and restoring the fat pad between the arteries. This may involve the following:
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Nutritional support (high-calorie meals or feeding tubes)
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Small, frequent meals
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Medications to reduce nausea or acid production
Surgical intervention
Advise patients that if conservative treatment is not effective, surgery may be necessary to bypass the compressed part of the intestine.
Emphasize to patients that early diagnosis and treatment can improve outcomes and help prevent long-term complications. Maintaining a healthy weight and addressing any underlying causes, such as eating disorders, are essential steps in managing SMA syndrome.
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Prompt gastric emptying of residual contrast is present within the stomach into the second portion of the duodenum. Additional contrast was hand injected through the transpyloric feeding tube to further distend the second portion of the duodenum. The second portion of the duodenum is dilated with very slow transit across the spine into the jejunum. This occurred despite difference in position of the patient. The high-grade partial obstruction at the distal second portion of the duodenum is due to superior mesenteric artery (SMA) syndrome.
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Anatomy of superior mesenteric artery syndrome showing the relationship between the different anatomical structures involved. Image from Akihiko Oka, MD.
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Shown are the (a) normal aortomesenteric relationship and (b) the aortomesenteric relationship in superior mesenteric artery (SMA) syndrome, where the proximal SMA compresses the mid-transverse duodenum against the abdominal aorta. Image from Serina Beydoun, MD.
