Table of Contents  

Shehadeh, Elwan, and Elfar: Superior mesenteric artery syndrome – a rare diagnosis for common upper gastrointestinal symptoms

Introduction

Superior mesenteric artery (SMA) syndrome, first described by Von Rokitanski in 1861,1 is a rare acquired vascular compression disorder in which acute angulation of the SMA results in the compression of the third part of the duodenum, leading to obstruction.2 The syndrome is typically caused by an angle of 6–25° between the abdominal aorta and the SMA, in comparison with the normal range of 38–56°, as a result of a lack of retroperitoneal visceral fat (mesenteric fat). In addition, the aortomesenteric distance is 2–8 mm as opposed to the typical 10–20 mm.3 It is seen more frequently in females, and usually occurs in older children and adolescents.

Patients often present with chronic upper abdominal symptoms, such as epigastric pain, nausea, eructation, copious vomiting (bilious or partially digested food), postprandial discomfort, early satiety and sometimes subacute small bowel obstruction.4

Diagnosis is very difficult and usually by exclusion of other causes. Standard examinations include abdominal and pelvic computerized tomography (CT) with oral and intravenous contrast, upper gastrointestinal series and, in equivocal cases, hypotonic duodenography. In addition, vascular imaging studies, such as ultrasound and contrast angiography, may reveal increased blood flow velocity through the SMA or a narrowed SMA angle.5,6 Measuring the aortomesenteric distance and angle is the gold standard for the diagnosis of SMA syndrome.

Our patient presented with history of frequent attacks of non-specific abdominal pain over a few years that had been treated symptomatically without a clear diagnosis. However, in the last admission, she presented to our hospital with abdominal pain, vomiting and a frank clinical picture of subacute small bowel obstruction that prompted extensive investigation, including multislice abdominal CT with oral and intravenous contrast administration. This confirmed the diagnosis of SMA syndrome.

Case report

A Bangladeshi girl aged 11 years presented to the emergency room (ER) with a 1-day history of diarrhoea, non-bilious vomiting and abdominal pain. The patient was thin, mildly dehydrated and in moderate pain. Abdominal examination revealed mild periumbilical and epigastric tenderness without distension or organomegaly.

She was admitted to the ER, given i.v. fluid and nil by mouth. A few hours later she was able to tolerate oral feeding without vomiting or abdominal pain, and was discharged home. However, the next day, she again presented with severe epigastric abdominal pain with nausea and non-bilious vomiting, but without diarrhoea, and was admitted to the paediatric ward for observation and to rule out appendicitis.

The patient had a history of three hospital admissions with similar attacks of abdominal pain and vomiting at the ages of 3, 7 and 10 years. All previous investigations were non-conclusive and the diagnosis was non-specific abdominal pain with acute gastritis.

Upon admission to the paediatric ward she vomited bile three times and exhibited mild dehydration (3%). The pain was predominantly epigastric with no signs of peritoneal irritation and no abdominal distension. C-reactive protein was negative and a complete blood count, liver enzymes and function, urea and electrolytes were all normal. The surgeon advised continued observation and abdominal radiography and ultrasonography; both were unrevealing and findings were normal.

The patient’s pain persisted for another 3 days accompanied by vomiting attacks despite the fact that she was receiving only i.v. fluid. As a result a paediatric gastroenterologist was consulted and recommended carrying out a upper gastrointestinal water-soluble oral contrast fluoroscopic follow-through study. However, this was not tolerated by the patient as she continued to vomit even after prescribing antiemetic drugs.

After team discussion, post-intravenous, oral contrast, multislice, abdominal CT revealed a reduced aortomesenteric artery distance, reaching about 5 mm at the level of the duodenal crossing, with a moderately attenuated third part of the duodenum and mild proximal dilatation of the duodenum (Figure 1). Sagittal reformatted images revealed an acute aortomesenteric angle of approximately 23° and the third part of the duodenum crossing posteroinferiorly to the origin of the SMA (Figure 2). These imaging findings confirmed the diagnosis of SMA syndrome.

FIGURE 1

Reduced aortomesenteric distance, reaching about 5 mm at the level of the duodenal crossing, with a moderately attenuated third part of the duodenum and mild proximal dilatation of the duodenum.

HMJ-616-fig1.jpg
FIGURE 2

Sagittal reformatted multislice CT with oral and intravenous contrast revealed that the SMA had an acute aortomesenteric angle of approximately 23°.

HMJ-616-fig2.jpg

Conservative medical management was adopted, and comprised positioning, gradual feeding and proton pump inhibitors. Additionally, a weight gain diet was planned. The patient’s condition gradually improved, especially after positioning and hyperalimentation. Ten days after admission the patient was discharged in a good condition. During follow-up visits in the outpatient clinic she was doing well, compliant with medical management and had started to gain weight.

Discussion

Superior mesenteric artery syndrome is an uncommon but well-recognized clinical entity, seen more commonly in females, and usually occurring in older children and adolescents. The incidence of SMA syndrome is about 0.1–0.3%.7 Approximately 0.013–0.78% of barium upper gastrointestinal radiographs evaluating SMA syndrome support the diagnosis,4,8 making it one of the rarest gastrointestinal disorders known to medical science.9

Superior mesenteric artery syndrome is favoured by particular anatomical conditions, such as a short or hypertrophic ligament of Treitz, a low origin of the SMA, intestinal malrotation, lumbar hyperlordosis and undernutrition or rapid weight loss leading to reduced thickness of the adipose tissue in the aortomesenteric space. Many causes have been identified, including eating disorders (e.g. anorexia nervosa, malabsorption), conditions leading to cachexia (e.g. neoplasia, acquired immunodeficiency syndrome), situations of hypercatabolism (e.g. multiple trauma, burn victims) and surgical causes such as bariatric surgery or correction of spinal malformation. Other reported causes include accelerated growth in adolescents with a rapid increase in height without weight gain or aneurysm of the abdominal aorta. The anatomical condition leads to a vicious cycle of nausea and vomiting, preventing adequate food intake, which in turn favours weight loss and aggravation of the syndrome.10,11

Patients often present with chronic upper abdominal symptoms, such as epigastric pain, extreme ‘stabbing’ postprandial abdominal pain (as a result of both the duodenal compression and the compensatory reversed peristalsis), nausea, eructation, copious vomiting (bilious or partially digested food), postprandial discomfort, early satiety and sometimes subacute small bowel obstruction.10 However, our patient had experienced frequent attacks of abdominal pain over several years, which were treated symptomatically and without a clear diagnosis until she presented to our hospital with a clinical picture of subacute small bowel obstruction, which prompted our further investigations.

Diagnosis is very difficult and is usually by exclusion. SMA syndrome is, thus, considered only after patients have undergone extensive evaluation of their gastrointestinal tract, including upper endoscopy, colonoscopy and evaluation for various malabsorptive, ulcerative and inflammatory intestinal conditions with a higher diagnostic frequency. Diagnosis may follow radiological examination revealing duodenal dilatation followed by abrupt constriction proximal to the overlying SMA, as well as a delay in transit of 4–6 hours through the gastroduodenal region. Standard diagnostic examinations include abdominal CT with oral and i.v. contrast and upper gastrointestinal oral contrast with follow-through series. Furthermore, vascular imaging studies, such as Doppler ultrasound and contrast angiography, may be used to identify increased blood flow velocity through the SMA or a narrowed SMA angle.5,6 Measuring the aortomesenteric distance and angle is the gold standard in the diagnosis of SMA syndrome.

Plain radiographs revealed a dilated, fluid- and gas-filled stomach, while barium radiography revealed dilatation of the first and second parts of the duodenum, extrinsic compression of the third part of the duodenum and a collapsed small bowel distal to the crossing of the SMA.2

Computerized tomography angiography or magnetic resonance angiography enables visualization of vascular compression of the duodenum and precise measurement of aortomesenteric distance and angle.2 Normally, the aortomesenteric angle and aortomesenteric distance are 38–56° and 10–20 mm, respectively, whereas in SMA syndrome both parameters are reduced.3,12

Abdominal ultrasonography may be helpful in measuring the angle of the superior mesenteric artery and the aortomesenteric distance. When combined with endoscopy, it may offer an alternative way to diagnose SMA syndrome in children to avoid other tests with a risk of radiation exposure.13

Our patient was referred for radiological assessment and an upper gastrointestinal water-soluble contrast study with follow-through; however, as a result of persistent vomiting despite antiemetic drugs, the examination was cancelled and post-intravenous, oral contrast, multislice abdominal CT was undertaken instead; this revealed a reduced aortomesenteric artery distance, reaching about 5 mm (see Figure 1). Sagittal reformatted images revealed an acute aortomesenteric angle of about 23°, wheras the SMA normally forms an angle of approximately 45° (see Figure 2).

A delay in the diagnosis of SMA syndrome can result in fatal catabolism (advanced malnutrition), dehydration, electrolyte abnormalities, gastric pneumatosis and portal venous gas, aspiration pneumonia, formation of an obstructing duodenal bezoar, hypovolaemia secondary to massive gastrointestinal haemorrhage, gastric distension, and death secondary to gastric perforation1416 or sudden cardiovascular collapse.3,5

Although research establishing an official mortality rate may not exist, two recent studies of SMA syndrome patients – one published in 2006 looking at 22 cases17 and one in 2012 looking at 80 cases18 – report mortality rates of 0%17 and 6.3%.18 The outcome of treatment is generally expected to be excellent.17

At least 70% of cases of SMA syndrome can be treated medically.1719 Therefore, medical treatment should be attempted first in all cases, unless emergency surgery is necessary upon presentation.17 A 6-week trial of medical treatment is recommended in most paediatric cases.19

The goal of medical treatment for SMA syndrome is resolution of underlying conditions and weight gain. Medical treatment may involve nasogastric tube placement for duodenal and gastric decompression, mobilization into the prone or left lateral decubitus position,20 the reversal or removal of the precipitating factor with proper nutrition and replacement of fluid and electrolytes through a surgically inserted jejunal feeding tube, nasogastric intubation or peripherally inserted central catheter administering total parenteral nutrition. Symptoms typically improve after weight gain,21 unless reverse peristalsis persists, or if fat refuses to accumulate within the mesenteric angle.22 Most patients seem to benefit from nutritional support with hyperalimentation irrespective of disease history.23

The symptoms are typically relieved when the patient is in the left lateral decubitus, prone or knee-to-chest position, and they are often aggravated when the patient is in the supine position. These manoeuvres are thought to reduce the small bowel mesenteric tension at the aortomesenteric angle.24

If medical treatment fails, or is not feasible because of severe illness, surgical intervention is required. The most common operation for SMA syndrome, duodenojejunostomy, was first proposed in 1907 by Bloodgood.4 Performed either as open surgery or laparoscopically, less common surgical treatments for SMA syndrome include Roux-en-Y duodenojejunostomy, gastrojejunostomy, anterior transposition of the third portion of the duodenum, intestinal derotation, division of the ligament of Treitz (Strong’s operation) and transposition of the SMA.25

The possible persistence of symptoms after surgical bypass can be traced to the remaining prominence of reverse peristalsis in contrast to direct peristalsis, although the precipitating factor (the duodenal compression) has been bypassed or relieved. Reverse peristalsis has been shown to respond to duodenal circular drainage; a complex and invasive open surgical procedure originally implemented and performed in China.22

With such conservative procedures, the condition of our patient gradually improved, especially after positioning. The patient was discharged in good condition with appropriate follow-up and recommendations.

Conclusion

Superior mesenteric artery syndrome, although uncommon, deserves consideration in any patient presenting with chronic upper abdominal symptoms, such as epigastric pain, nausea, voluminous vomiting, postprandial discomfort, early satiety or subacute small bowel obstruction. An upper gastrointestinal contrast study is invaluable in evaluating patients with bilious vomiting without abdominal distension and without clear diagnosis; CT with intravenous contrast is a very good alternative when oral contrast is not tolerated.

Finally, the collaboration and case discussion between the different specialties including radiologists, paediatricians, gastroenterologists and surgeons is the key of solving confusing cases when the diagnosis is vague and not straightforward.

References

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