Ultrasound imaging in diagnosis of superior mesenteric artery syndrome


Sergio Neri, Medicina Interna, Policlinico Ed. 29, I piano, Via S. Sofia, 95123 Catania, Italy.
(fax: 0039 095 3782908; e-mail: sergio.neri4@tin.it).


Objectives.  We screened a cohort of subjects affected by various degree of dyspepsia to reveal if they presented a reduction of the aorto-mesenteric angle and to diagnose suspected cases of superior mesenteric artery (SMA) syndrome.

Design.  Controlled, prospective, study.

Setting. Subjects were studied as outpatients.

Subjects.  The study investigated a total of 3622 subjects referred to our department by their general practitioners for dyspepsia and/or abdominal pain.

Interventions.  Abdominal ultrasonography with power colour Doppler, gastroduodenoscopy, hypotonic duodenography, contrast-enhanced spiral computerized tomography were performed.

Main outcome measurement and results.  Color Doppler revealed a significant reduction of the SMA angle in 29 of 950 subjects; gastroscopy showed duodenal compressive pulsation in 14 of 29 patients and X-ray revealed compression of the third segment of the duodenum in 28 of 29 patients. CT confirmed the presence of a reduced angle and various degrees of duodenal compression in all patients. Ultrasonography and CT examinations gave overlapping results (P > 0.05) in diagnosing pathological aorto-mesenteric angle.

Conclusion.  The authors believe that the incidence of reduced aorto-mesenteric angle and SMA syndrome might be underrated.

Ultrasound power colour Doppler imaging is useful in epidemiological screening of reduced aorto-mesenteric angle to diagnose suspected cases of SMA syndrome.


Superior mesenteric artery (SMA) syndrome (or aorto-mesenteric compass syndrome or Wilkie's disease) [1, 2] is a relatively rare condition caused by a short Treitz's ligament, or by an unusually low origin of the SMA causing a reduction of the angle formed by the aorta and the SMA [1–4]. In normal conditions the retroperitoneal, static part of duodenum lies across the SMA and rests on a posterior plane made up of the aorta and the spine, at approximately the level of the L3 vertebra [1–4]. The retroperitoneal fat and lymphatic tissue push the mesenteric artery away from the aorta. It has been reported that conditions reducing the distance and decreasing the angle between the SMA and aorta may compress the horizontal segment of duodenum [1–4]. The syndrome can present itself as acute small bowel obstruction or intermittent compression with chronic symptomatology. The classical presentation is recurrent postprandial pain, nausea, vomiting, bloating, abdominal discomfort or pain and tenderness. The syndrome has been reported in association with pancreatitis, peptic ulcer and intra-abdominal inflammation or cancer [5, 6]. SMA syndrome can affect all age groups but is most common in young patients, especially after rapid weight loss [1–9]. Symptoms can be alleviated by changing position, i.e. lying on the left side and taking up the knee–chest position. With respect to the literature [10–13], surgical treatment is recommended if conservative treatment fails.

Because its appearance in literature SMA syndrome has been widely debated but although many doctors remain sceptical about its existence [14], several reports describe the SMA syndrome. As a distinct clinical entity the syndrome is rare and its incidence is unknown. Estimates of 0.1–0.3% have been put forward but some studies suggested that the incidence is higher [9, 11]. We studied a cohort of subjects affected by various degree of abdominal discomfort in order to detect patients with reduced aorto-mesenteric angle and screen patients with SMA syndrome.

Materials and methods

Our study panel included specialists in hepatology, internal medicine, gastroenterology, angiology and radiology with experience in the ultrasound (US) technique. All the subjects attended our outpatients’ department and were examined by the same medical staff after an overnight fast. Between January 2001 and July 2004 we studied 3622 outpatients referred to our Department of Internal Medicine by their general practitioners for unexplained abdominal discomfort and/or pain, postprandial epigastric fullness, chronic nausea and emesis. We studied these patients during both symptomatic periods and symptom-free intervals in order to diagnose a suspected SMA syndrome that had been indicated by the presence of reduced aorto-mesenteric angle (<25°) and/or duodenal compression. After an overnight fast, US of the abdomen was performed in the entire study cohort and in 50 healthy subjects (control group), followed by echo colour Doppler of the epigastric area (longitudinal scans using a convex 3.5 MHz probe; Acuson Corporation, Mountain View, CA, USA; Mod. 128 xp/10). The mesenteric angle was measured during normal expiration from 2 cm below the beginning of the aorto-mesenteric bifurcation in lateral right, standing and supine positions. In addition, the following examinations were performed in patients with reduced aorto-mesenteric angle and suspected SMA syndrome:

  • Contrast-enhanced spiral computerized tomography (CT) with injection contrast medium, using a General Electric Advantage Plus Scanner.
  • Standardized gastroduodenoscopy.
  • Hypotonic duodenography with barium.

Angiography was performed only in patients with SMA syndrome requiring surgical treatment after conservative therapy was unsuccessful.

The Local Ethical Committee approved the study and informed written consent was obtained from all the subjects studied.

Statistical analysis

All values are expressed as mean. Student's t-test and Pearson's chi-square test were performed. Data analysis was performed using statistical software (stats Homework V.L. Bissonette, south-eastern Louisiana University, Hammond, LA, USA). Values of P < 0.05 were considered significant.


Table 1 reports all the pathologies diagnosed in our 3622 patients. We decided to consider only 950 patients, i.e. patients where US and power colour Doppler had been adequately performed. Conditions that could have jeopardized the results of the examination and the measurement of the angle, such as meteorism, poor patient compliance, nonrespect of fasting, vascular anomalies of the coeliac trunk (for example, the hepatic artery coming directly out of the SMA) were excluded from the study. US detected reduced angles <25° in 29 of the 950 subjects (3.05%). All these 29 patients were young adults aged between 19 and 32 years. Dieting had caused rapid weight loss [mean body mass index (BMI) 18 ± 2 kg m−2] and onset of pain in 10 of 29 (34.5%; all women), whilst 17 of 29 (58.6%; 11 female subjects and 13 male subjects) were tall and underweight (BMI: 17 ± 3 kg m−2). The remaining two patients presented a normal weight/height ratio (BMI: 23 ± 1 kg m−2). US (Table 2) performed in supine patients (Fig. 1) revealed anomalous insertion of the SMA into the aorta (angle <25°) with a mean aorto-mesenteric distance ranging from 2 to 8 mm in 22 of 29 patients; a pathological angle was observed in 26 of 29 patients in the standing position (Fig. 2) and in three of 29 patients in the lateral right position. There was a significant difference (P < 0.05) between the US findings in the supine and lateral positions and between (P < 0.05) the standing and lateral positions. There was no significant difference (P > 0.05) between supine and standing position, the pathological angle was observed during the symptomatic period and symptom-free interval with no significant difference (P > 0.05) between two periods. Gastroscopy showed compressive pulsation on the duodenum in 14 of 29 patients during the symptomatic period and in two of 29 during the symptom-free interval, whereas X-ray with barium (Fig. 3) revealed compression on the third segment of the duodenum in 28 of 29 patients during the symptomatic period and in nine of 29 during the symptom-free interval.

Table 1.  Diseases diagnosed in our study cohort (some diseases were concomitant)
Irritable bowel syndrome33%
Chronic gastritis21%
Gastroduodenal ulcers19%
Hiatus hernia7%
Bowel cancer1.1%
Chronic pancreatitis1.2%
Reduced aorto-mesenteric angle1.2%
Superior mesenteric artery (SMA) syndrome0.9%
Table 2.  Pathological aorto-mesenteric angle observed in our cohort in supine, lateral and standing position
Supine (°, 22)Lateral (°, 3)Standing (°, 26)
Figure 1.

Echo image of patient supine: abdominal pain; major reduction (14°) of the aortic-mesenteric angle (a, aorta; a.c., celiac artery; m, superior mesenteric artery).

Figure 2.

Echo image. Same patient lying down (standing): symptom free; aorto-mesenteric angle 21°.

Figure 3.

Hypotonic duodenography; linear stop of the third portion of duodenum.

Computerized tomography (Fig. 4) confirmed the presence of a reduced angle and various degrees of duodenal compression (SMA syndrome) in all patients during the symptomatic and symptom-free period. Reduced SMA-aorta distance on duodenal stenosis or linear stop of duodenography due to extrinsic compression was not observed in 2672 patients with normal aorto-mesenteric angle where CT (42 cases) and duodenography (eight cases) were performed for other reasons (cancer, peptic ulcer, etc.).

Figure 4.

Contrast-enhanced spiral computerized tomography (CT). Mesenteric-aortic district with aortic-mesenteric angle reduction.

Conservative treatment (nutritional support with hyperalimentation, frequent small meals, postural recommendations during meals, prokinetics) was prescribed for 18 of 29 patients with SMA. They benefit from these treatments with minimization of symptomatology. Surgery was performed in 11 of 28 patients with major degree of duodenal stenosis (duodenojejunostomy in eight of 11; cleavage of the suspensory ligament of Treitz allowing the duodenum to fall away from the apex of the sharpened aorto-mesenteric angle in two of 11; laparoscopic entero-enterostomy in one of 11); surgical treatment significantly improved the patients clinical conditions.


The aorto-mesenteric angle is normally 25–60° [2, 3, 6, 7, 10–12] and the mean aorto-mesenteric distance of 10–28 mm [1–3, 6, 7, 10–12]. Subjects presenting an angle <25° and aorto-mesenteric distance <8–10 mm may be affected by SMA syndrome. This syndrome is characterized by pain caused by compression of the third part of the duodenum between the SMA and the aorta, and it can be attributed to congenital (including anomalies of the origin of the SMA, visceral ptosis, adherences following malrotation during the embryonic period, accentuated lumbar lordosis) and acquired factors (i.e. abdominal muscle hypertrophy, prolonged immobilization, severe burns, anorexia nervosa, severe weight loss, spinal cord injury) [2–4, 7–12]. Patients with SMA syndrome are normally young and can manifest acute small bowel obstruction or chronic postprandial discomfort, abdominal distension, burping, nausea and/or vomiting and duodenal distension [1–3, 6, 7–12]. Differential diagnosis includes irritable bowel syndrome, peptic ulcer, pancreatitis, duodenitis, cholelithiasis, neoplastic obstructions, adhesions, visceral neuropathy, porphyria and aneurysm of the abdominal vessels [6, 11, 12, 15].

According to gastroenterology textbooks [14], radiological or angiography findings of compression of the duodenum are considered conclusive for diagnosis of SMA syndrome [6, 7, 11, 15–18]. X-ray revealing stenotic images of the third and second parts of the duodenum can easily detect SMA syndrome [6, 11, 15–18]. In patients with upper gastrointestinal symptoms, gastroscopy findings of duodenal dilatation, liquid stasis and antiperistaltic waves could be indicative of SMA. It has been reported that contrast-enhanced spiral CT is a useful diagnostic tool [6, 11, 15–18]. Hypotonic duodenography with simultaneous abdominal arteriography or magnetic resonance (MR)-angiography reveal the topological anatomy of the duodenum and SMA [6, 11, 15–18]. Invasive angiography can confirm diagnosis, whilst CT and MR are costly and utilize ionizing radiations and/or iodate contrasts. Noninvasive, low-cost power Doppler can detect reduced aorto-mesenteric angle and may lead to suspected diagnosis of SMA syndrome even in patients where gastroscopy and X-ray with barium do not detect duodenal compression.

In fact, our results showed that US examination performed in the standing position in addition to the standard supine procedure assessed the aorto-mesenteric angle even in the symptomatic-free period when plain hypotonic duodenography and gastroscopy cannot reveal diagnostic findings.

In all our patients affected by pain, US confirmed the presence of a reduced angle; moreover CT, generally speaking gold standard diagnostic investigation, and duodenography confirmed the presence of the compression. CT showed compression and reduced angle both in symptomatic and in asymptomatic period whilst duodenography revealed diagnostic findings during symptomatic period.

Although the very few cases of SMA syndrome reported in the literature hinder statistical analysis, we would like to point out that:

  • 1careful assessment of any painful dyspeptic symptoms in young patients is recommended especially after drastic diets and severe weight loss;
  • 2identification of SMA syndrome can be a diagnostic dilemma and is frequently made by a process of elimination (15);
  • 3SMA syndrome-related symptomatology may vary in severity and expression. This can cause misdiagnosis, especially during a symptom-free interval;
  • 4the incidence of reduced aorto-mesenteric angle and SMA syndrome might be underrated.

It is crucial to diagnose SMA syndrome promptly because effective treatment of the disorder might significantly improve patients’ clinical conditions.

The US enables early diagnosis of reduced aorto-mesenteric angle. This diagnostic procedure is rapid, repeatable, noninvasive, low cost, easy to perform and minimizes exposure to radiation, thus being advantageous especially in young patients. Clearly diagnosis of SMA syndrome is based on clinical symptoms and gold standard diagnostic procedures, especially if performed during the symptomatic period. Our experience showed that US performed both in the supine and standing positions is useful in all patients, especially young ones, presenting inexplicable dyspeptic disorders and/or abdominal pain.

In conclusion, we shown that this method took place even during asymptomatic interval to patients with SMA syndrome by reduced aorto-mesenteric angle and we believe that US are valuable tools for a screening of reduced aorto-mesenteric angle in patients with inexplicable abdominal pain to suspect a SMA syndrome.

Conflict of interest

No conflict of interest was declared.


This study was supported by a grant (60%) from the Italian Ministry of University.