European Journal of Cardiovascular Medicine

Superior mesenteric artery (SMA) syndrome presents a rare but diagnostically challenging cause of small bowel obstruction due to extrinsic compression of the duodenum between the aorta and SMA. This can lead to significant morbidity and mortality if misdiagnosed. First described by Carl Freiherr von Rokitansky in 18421, Wilkie subsequently published a comprehensive series (1927) detailing the pathophysiology and diagnostic features in 75 patients2, further analysed by Barner and Sherman3. The syndrome has been known by various terms, including Cast syndrome, Wilkie syndrome, aorto-mesenteric compass syndrome, mesenteric duodenal obstruction, megaduodenum, and chronic duodenal ileus4. Historically, restrictive casting for scoliosis and hip dysplasia has been implicated in its development5,6. The current medical literature reflects a growing body of evidence, with over 730 articles and approximately 2400 reported cases by 20227.

The SMA usually forms an angle of about 45 degrees (38- 56 degrees) with the aorta. SMA syndrome is presumed to be present if the aortomesenteric angle is less than 25 degrees in adults15. The aortomesenteric distance in SMA syndrome is decreased to 2-8 mm (normal is 10-20 mm).

We have managed seven cases of duodenal obstruction due to SMA syndrome during the time period of June 2015 to January 2023. The study included cases pooled from two tertiary care centres of Andhra Pradesh. The primary evaluation was done by gastroenterologists, psychologists and followed by detailed surgical evaluation. Ultrasonography and upper endoscopy were done for all cases followed by CT scan of the abdomen in all the cases. All the patients had clinical and radiological findings consistent with SMA syndrome. Data collected included patient demographics, clinical presentation, operative data, and outcomes. Data are presented as mean ± standard deviation for continuous variables and as percentages for categorical variables.

The seven patients included 5females and 2 males (female to male ratio was 2.5:1). The mean age of the cases was 21.29 ± 4.15 years (range 13 – 26 years). The Comorbidities identified in these cases included Psychiatric/anxiety (14.29%), anorexia (28.57%), Pancreatitis (14.29%), Mild scoliosis (14.29%), Binge/fasting (14.29%). No clear reason was identified in one case (14.29%) and attributed to fibromyalgia. One patient had previous laparoscopic appendicectomy, but no other patient had any history of abdominal or spinal surgery.

Presentation consistently involved persistent chronic vomiting (100%), nausea (85.71%), oesophageal reflux (85.71%), bloating (71.43%), and epigastric pain (57.14%). The symptoms were chronic with the length of the symptoms ranging from 8 to 96 months (mean 29.14 months) before surgery. One male child of 13 years was having repeated and persistent symptoms on and off since last 5 years. The average period from confirmed diagnosis to surgery was 4.71 months (range 2 – 10 months). All patients had Upper endoscopy (UGIE), Ultrasonography (USG) and Computed tomography (CT) scan.

Figure 1: Upper endoscopy features in SMA syndrome

Figure 2: Ultrasonography findings in SMA syndrome Figure 3: CT image showing the aortomesenteric angle in SMA

Cases having intrinsic obstruction on UGIE were excluded. CT scan findings included dilatation of the first and second parts of the duodenum, with or without gastric dilatation, duodenal obstruction with an abrupt cut off in the third portion and an aortomesenteric artery angle of < 22o.

Surgical management was done after symptoms did not improve after non-operative management by nasogastric decompression, correction of electrolytic imbalances and correction of nutritional status by naos-jejunal tube enteral feeding. The mean preoperative body mass Index (BMI) was 15.31 kg/m2 (range 13.3 – 16.9 kg/m2).

All patients underwent Laparotomic Duodena-Jejunostomy except for one who underwent Strong’s procedure. Dilated stomach and duodenum associated with collapsed small bowel distal to the duodenum was observed in all cases. All patients recovered uneventfully and no complication occurred during the hospital stay. One patient developed a delayed anastomotic stricture with mild leak and had to undergo redo surgery where a loop duodena-jejunostomy was converted to a roux-en-Duodena-jejunostomy.

Table 1: Patient characteristics

Table 2: Patient characteristics (contd.)

  Figure 4: Duodenum exposed                            Figure 5: Duodenojejunostomy

Following surgery, all patients reported improvement in most symptoms. Three patients (42.86%) experienced mildly persistent vomiting, which was managed with medication and resolved within 2-3 months. Six-month follow-up imaging and endoscopy confirmed good stomach and duodenum emptying with no obstruction. The mean weight gain at 6 months duration post-operative was 6.9 kg (range 4.5 – 9.25 kg,p = 0.029*). Mean BMI gain of all patients was 2.91 kg/m2 (range 2.2 – 3.7 kg/m2, p< 0.001*).

SMA syndrome demonstrates a female predominance2, with a reported female-to-male ratio of approximately 3:28. The true prevalence of SMA syndrome in the general population remains elusive. Radiographic studies suggest a range of 0.013% to 0.78%, but limitations exist9-11.  These limitations include potential underdiagnosis or overdiagnosis in clinical practice, along with inherent variability in patient presentations12,13.

SMA syndrome arises from compression of the duodenum's third portion2. This compression is attributed to a narrowed angle between the superior mesenteric artery (SMA) and the abdominal aorta (Ao). The decreased SMA-Ao angle can be congenital or acquired. This narrowing can be caused by factors such as weight loss resulting in loss of mesenteric fat tissue between SMA-Ao (eating disorders, malabsorption, hypermetabolism due to drugs and burns, cachexia due to tuberculosis and malignancy), prolonged bed rest, burns, scoliosis (including its surgical and cast treatments), certain intestinal surgeries (ileal pouch-anal anastomosis, colectomy), and congenital anomalies like a short ligament of Treitz in children.

Aortic artery aneurysm (AAA) can contribute to a clinical picture resembling SMA syndrome, though not a true case. This "pseudo-SMA syndrome" arises from compression of the duodenum by an enlarged aorta near the superior mesenteric artery (SMA) and third portion of the duodenum. Notably, Dr. Osler first described this phenomenon as aorto-duodenal syndrome14.

Figure 1: Anatomy related to the Superior Mesenteric Artery Syndrome7

Superior mesenteric artery (SMA) syndrome presents with non-specific symptoms like nausea, vomiting, epigastric pain, early satiety and post-prandial discomfort, bloating, and weight loss mimicking anorexia nervosa and functional dyspepsia8,16. These can worsen after eating and lying down, but improve when curled forward. Chronic cases cause weight loss due to recurrent vomiting and inadequate food intake, creating a cycle that worsens the condition.

Untreated or severe SMA syndrome can lead to dangerous complications, including shock, aspiration pneumonia, and sudden death even in young patients. The exact cause of sudden death in SMA is not fully understood, but theories point to arrhythmia by severe hypokalaemia, severe compression of the inferior vena cava by dilated duodenum, or severe pulmonary depression induced by alkalosis and increased abdominal pressure. The most recurring complication of SMA is gastrointestinal injury caused by retained or reflexed peptic and bile acid and elevated intraluminal pressure. The raised intraluminal pressure at the second portion of the duodenum can disrupt the normal flow of pancreatic juices, potentially triggering acute pancreatitis. Repeated vomiting can also lead to dehydration, electrolyte abnormalities, severe malnutrition, and aspiration pneumonia. SMA syndrome can sometimes occur alongside other vascular compression conditions. The most common of these, due to its anatomical proximity to the SMA, is nutcracker syndrome. This occurs when the left renal vein is squeezed between the aorta and SMA, leading to symptoms that can mimic SMA syndrome itself17.

Diagnosing SMA syndrome can be challenging due to its non-specific symptoms18. Radiological confirmation of duodenal obstruction is essential for diagnosis. Traditionally,

barium X-ray studies have been used to diagnose SMA syndrome based on specific criteria7. CT is considered the gold standard tool for diagnosing SMA syndrome by visualizing compression of duodenal by SMA along with dilation of the proximal duodenum and stomach19.

The 3D-CT is emerging as a valuable tool in recognizing the anatomy of SMA, aorta and the duodenum20. The normal SMA-Ao angle is between 38 to 65 degrees and has a distance of 10 to 33mm21.The cut-off value was reported as 22 on the SMA-Ao angle and 8 mm distance with 42.8% sensitivity and 100% specificity22. Dynamic Ultrasonography has recently emerged as a valuable technique offering real-time and dynamic evaluation, as well as safe and quick access, as some reports suggest that the optimal position effective in treatment of SMA syndrome may not only be left lateral recumbent position, but could include right recumbent and sitting positions depending on the course of the SMA in relation to the aorta23,24.

While upper endoscopy primarily identifies gastrointestinal complications like mucosal injury, bleeding, or bezoars, it can occasionally reveal extrinsic compression of the duodenum's third portion, potentially suggestive of SMA syndrome. However, upper endoscopy alone is not definitive for diagnosing SMA syndrome.

Linear endoscopic ultrasound (EUS) has emerged as a promising tool for diagnosing SMA syndrome25. It offers a unique advantage: simultaneous endoscopic and ultrasound visualization of the stomach, duodenum, and surrounding structures. This allows for direct visualization of the aortomesenteric angle, crucial for diagnosing SMA syndrome26. Laboratory tests are not diagnostic, but they are necessary to identify the presence of electrolytic complications and pancreato-biliary abnormalities.

In adult patients, non-operative therapy is frequently a in-hospital approach with low success rate ranging from 14%27 to 71%28. In this study the window between diagnosis and surgery was 4.7 months. Existing literature, including case reports and reviews, suggests a significantly longer timeframe between diagnosis of this condition and surgical intervention compared to what is currently observed. This shift in practice may reflect evolving treatment strategies or improved understanding of the urgency associated with this type of duodenal obstruction. Sun Zhuo et al reported a period of 5.8 months29. Several surgical approaches exist for treating this type of duodenal obstruction, as documented in various studies. These techniques include Strong's procedure, gastrojejunostomy, and duodenojejunostomy. Notably, Strong's procedure offers a distinct advantage by preserving the bowel's natural continuity through mobilization of the duodenum via division of the ligament of Treitz. This minimally invasive approach boasts a promising success rate of 75%30. Munene et al. described a 100% success rate for duodenojejunostomy in their case report, along with 13 additional cases identified in the literature31.duodenojejunostomy, despite its reported high success rate, carries a potential risk of blind loop syndrome. Roux-en-Y duodenojejunal bypass offers a potential alternative for SMA syndrome by eliminating the blind loop. It allows for drainage not only from the duodenum proximal to the obstruction, but also from the section of intestine distal to the compression site32. In our study no perioperative complications were identified. One patient developed post operative stricture with leak which required conversion of duodenojejunostomy into Roux-en-Y duodenojejunostomy. All patients experienced weight gain, and mean BMI increased from 15.31 to 18.23 postoperatively. Ylinen P et al. in a series of 16 cases who underwent open duodenojejunostomy and followed for 7 years after surgery reported a gain in weight33.

Several factors limit the generalizability of this study on SMA syndrome. Firstly, the rarity of the condition inherently restricts the sample size, potentially impacting the study's statistical power to draw definitive conclusions. Secondly, the retrospective nature of the study introduces potential bias. The researchers relied on information documented in medical records, which may be incomplete or subjective.  Additionally, the study relies on patient-reported symptom improvement during follow-up, rather than a standardized symptom severity score. This lack of objective measurement weakens the strength of the findings. Finally, the study was conducted in large tertiary hospitals.  While such centres are likely to see a higher volume of complex cases, they may not capture the full picture of SMA diagnosis and treatment.  Patients with milder presentations or those managed medically in general medicine or gastroenterology departments might be missed. This potentially underestimates the overall prevalence of SMA syndrome and the effectiveness of non-surgical approaches.

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