The typical symptoms of SMAS mimic those of partial duodenal obstruction and include nausea, vomiting, abdominal pain, early satiety, and anorexia that results in weight loss.[6,7,9] Most individuals experience more than one symptom, with the triad of abdominal pain, vomiting, and nausea being the most common. Although weight loss is frequently associated with SMA syndrome SMAS, a low body mass index is not necessarily a prerequisite.
The pain associated with SMA syndrome is classically described as postprandial epigastric pain that is relieved by lying in the prone, knee-chest, or left lateral decubitus position. These all reduce tension of the small-bowel mesentery at the aortomesenteric angle, leading to alleviation of symptoms.[3,7,9]
Duodenal obstruction may also lead to proximal duodenal dilatation (with or without gastric dilatation) along with duodenal stasis and gastric reflux leading to bilious emesis and associated peptic ulcer disease. Case reports of the prevalence of SMAS after scoliosis surgery range from 0.5% to 2.4%. Patients typically experience symptoms within the first postoperative week, and symptoms typically resolve. In contrast, reports of SMAS developing after severe burn injury describe mean burn areas of 48.5% of total body surface area, with a range of 32%-64.5%, indicative of an extreme catabolic state. These patients typically develop symptoms of SMAS after 2 weeks. Once established, the SMAS becomes self-perpetuating, with cyclical vomiting, further weight loss, and exacerbation of symptoms.[7,9]
The differential diagnosis for SMAS includes a wide variety of other causes of abdominal pain. In particular, SMA syndrome should be differentiated from SMA-like syndrome, in which symptoms are caused by generalized duodenal dilatation rather than secondary duodenal compression. The most common causes of SMA-like syndrome are mixed connective tissue disorders (eg, systemic sclerosis, scleroderma) that result in duodenal muscular atrophy, reduced duodenal peristalsis, and development of megaduodenum. Other causes of reduced duodenal peristalsis include diabetes, pancreatitis, dermatomyositis, systemic lupus erythematosus, myxedema, amyloidosis, myotonic dystrophy, and chronic idiopathic intestinal pseudo-obstruction. The differential diagnosis can be further expanded to include irritable bowel syndrome, peptic ulcer disease, gastritis, duodenitis, hiatal hernia, cholelithiasis, obstruction (adhesive, neoplastic), visceral neuropathy, porphyria, and abdominal vessel aneurysm.[6,11] In children, SMA-like syndrome is associated with annular pancreas, duodenal web or stenosis, preduodenal portal vein, duodenal duplication, malrotation, and history of duodenal surgery. Ultimately, diagnosis of SMAS requires high clinical suspicion and is often a diagnosis of exclusion.
Evidence of D3 obstruction with dilatation of D1 and D2, with or without gastric dilatation
Reverse peristalsis in the duodenum proximal to the obstruction
Delayed gastroduodenal transit of 4-6 hours
Position-dependent relief of obstruction (prone, knee-chest, or left lateral decubitus)
Reduced aortosuperior mesenteric artery angle
Reduced aortomesenteric space
Duodenal obstruction can be demonstrated with barium upper gastrointestinal studies. Findings consistent with SMAS include delayed gastroduodenal transit of 4-6 hours, barium retention, proximal duodenal dilatation (> 3 cm), reverse peristalsis in the proximal duodenum, and a characteristic vertical linear extrinsic compression at D3.[3,7,9,13,14] These radiologic features may disappear in the knee-chest or left lateral decubitus position or through the Hayes maneuver, in which direct manual pressure is applied infraumbilical and dorsocephalad in order to elevate the root of the small-bowel mesentery and provide temporary relief of the obstruction.[3,11]
Contrast-enhanced CT or MRI angiography can be performed to evaluate the aortomesenteric anatomy. Patients with SMAS have a mean aortomesenteric angle of 13.5° with a range of 6°-25°, and a mean aortomesenteric distance of 4.4 mm with a range of 2-8 mm. This contrasts with the normal angle and distance of 25°-65° and 10-28 mm, respectively. In general, an angle < 22° and distance < 8 mm is suggestive of SMAS. This is further supported by radiologic evidence of duodenal obstruction with gastric and proximal duodenal dilatation, followed by an abrupt transition point at the level of the SMA.
In some cases, this may cause displacement of the gastric antrum anterosuperiorly into the porta hepatis. Other ancillary findings include left renal vein compression that results in left-sided venous collaterals, isolated left renal vein thrombosis, or left gonadal vein enlargement.
The combination of barium upper gastrointestinal studies and angiography are regarded as definitive diagnostic modalities for SMAS. However, other imaging studies may aid in diagnosis. Plain abdominal radiography may reveal gastric dilatation suggestive of SMAS. Endoscopic examination is nonspecific but may demonstrate signs of stasis and chronic obstruction, with findings of reflux esophagitis and gastritis. The main use of endoscopy is to rule out more common intraluminal pathologies.[9,14,16] Ultrasonography with Doppler imaging may also be used to evaluate the aortomesenteric angle and distance but does not allow three-dimensional angiographic reconstruction.[6,13] Conventional angiography was historically considered the criterion standard but is less commonly performed today, owing to its invasive nature and associated risks and the advent of CT vascular imaging.
The CT scan of this patient showed fluid and contrast distention of the stomach and duodenum to the level of the aorta, and an SMA that suggested SMA compression. The aortomesenteric angle was reduced, at about 15°-19° (normal, 25°-60°), and the distance was reduced to ≤ 4 mm. These findings are suggestive of SMA syndrome (Figure 4).
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Cite this: Saad A. Shebrain, Hailey Chang. Gastro Case Challenge: A Daily Cannabis User With Sharp, Intense Epigastric Pain - Medscape - Jul 11, 2022.