Endoscopic ultrasound (US) is a relatively new technique with rapidly expanding use in the fields of hepatobiliary medicine, pancreatology, and oncology (1). To our knowledge, the role of endoscopic US in the diagnosis of superior mesenteric artery (SMA) syndrome (SMAS) has not been reported in the pediatric literature. SMAS has been reported in children and adults with rapid weight loss resulting in decreased retroperitoneal and mesenteric fat (eg, malabsorption, burns, neoplasia, anorexia nervosa, deformity) and disease or trauma to the spine (2–4). SMAS presents with symptoms of subacute intestinal obstruction resulting from compression of the third part of the duodenum between the superior mesenteric artery and the aorta, where the angle and distance between these vessels decreases with loss of retroperitoneal mesenteric fat (5). Identification of this syndrome can be difficult because it requires a high index of clinical suspicion and diagnostic delay is common (2,6). US has been reported to be a useful diagnostic method for SMAS in adult practice (7), but has not yet been established in children (2). Fluoroscopy has been the most common diagnostic modality, and although it can provide clues to the diagnosis of SMAS, the findings are not specific for SMAS (8). The diagnosis can be established using contrast medium–enhanced spiral computed tomography (CT) and angiography, albeit at the cost of significant irradiation (9). Upper gastrointestinal (GI) endoscopy is not reliably useful in establishing the diagnosis (2,7,10). We report on the use of endoscopic US in establishing the diagnosis of SMAS.
A 15-year-old boy presented with a history of recurrent colicky postprandial abdominal pain, vomiting, and weight loss of 4 kg over a period of 3 months. He had undergone resection of choledochal cyst with biliary diversion at the age of 8 years.
Findings of abdominal US were normal. Barium meal follow-through studies identified 2 areas of narrowing: a stricture at the junction of the first and second part of the duodenum and another area of narrowing in the third part of the duodenum at the point at which the SMA crossed the duodenum. There was dilation proximal to the distal narrowing and the slowing of contrast medium flow at this point was partially alleviated on turning prone. Contrast medium–enhanced CT of the abdomen showed dilation of the first and second parts of the duodenum with narrowing of the third part of the duodenum at the level of the SMA.
This established the diagnosis of SMAS, but upper GI endoscopy was undertaken to evaluate the proximal stricture and a simultaneous endoscopic US study was undertaken. Endoscopy confirmed a stricture at the junction of the first and second parts of the duodenum. A smaller endoscope (EG450HR; Fujinon, Wayne, NJ) was passed through this stricture and a pulsating structure compressing the lumen was noted distally. Endoscopic US was undertaken using a miniprobe (UM-2R; Olympus, London, UK) passed via the endoscopic operating channel. The miniprobe was placed next to the pulsatile structure (Fig. 1). Endoscopic US demonstrated the compression of the duodenum between the aorta and SMA without any preduodenal adipose tissue, confirming the diagnosis of SMAS (Fig. 2). The maximum intervascular aortomesenteric distance measured was reduced to 7 mm (normal range 10–28 mm).
The patient subsequently underwent a laparotomy, which revealed a dilated stomach and proximal duodenum. Two areas of duodenal stenosis were identified: a proximal stricture and distal compression between the aorta and SMA. An acute angle between the SMA and aorta and the absence of retroperitoneal fat was confirmed. Duodenoduodenostomy was performed and his symptoms improved. He gained 4.5 kg weight within 8 weeks of surgery and he remains symptom-free more than 6 months later.
In this case, endoscopic US confirmed the diagnosis of SMAS by demonstrating the vascular nature of the duodenal compression and confirming reduced aortomesenteric distance at the site of narrowing. In our case, the SMAS resulted from weight loss secondary to the proximal duodenal stricture.
The diagnosis of SMAS can be difficult to establish clinically. As in a recently reported large paediatric series of SMAS (2), upper GI contrast study suggested the diagnosis by demonstrating duodenal dilation. These findings are not pathognomonic of SMAS and can occur in other diseases that cause megaduodenum (11). To confirm the diagnosis, direct vascular compression should be confirmed in tandem with the demonstration of the presence of an acute aortomesenteric angle and reduced aortomesenteric distance (2,7,12). The normal aortomesenteric angle is 25° to 60° and the aortomesenteric distance is between 10 and 28 mm in adults (7,10). We and others (2,7,10) have found contrast medium–enhanced CT angiography of the abdomen to be diagnostic; however, fluoroscopy and CT angiography involve considerable radiation exposure in childhood.
Abdominal US with power Doppler imaging has been used to confirm SMAS in adult practice (7). It is often possible to directly confirm the reduced aortomesenteric angle and distance and to visualize duodenal compression. This technique has not been useful in our hands or in a large pediatric series (2), but the reasons for this are not clear. There is no fundamental difference in the pathogenesis of SMAS between adults and children, but the normal aortomesenteric distance is not established in early childhood. In SMAS, US abnormalities may be visible on scans in only the upright position (7), which is not customary in pediatric practice; however, it is likely that US has been underutilized for the diagnosis of SMAS in children. If this entity is clinically suspected, an attempt should be made with US to measure the aortomesenteric angle and distance in the supine and upright positions.
Upper GI endoscopic findings of duodenal dilation, stasis, and antiperistaltic waves may rule out other causes of duodenal obstruction, but the diagnosis of SMAS cannot always be made with certainty. Because there was a clinical indication to undertake endoscopy, we decided to combine this with endoscopic US. To our knowledge, this technique has not been previously described in children. Lippl et al reported the use of endoscopic US to confirm SMAS in 2 adults in whom the findings were similar to ours (10). Endoscopic US can be performed at the same time as GI endoscopy, thereby allowing for early exclusion of other pathological processes that present with features resembling SMAS.
Endoscopic US in combination with endoscopy could be the confirmatory investigation of choice in suspected SMAS. In combination with the greater use of modified abdominal US in suspected cases, it may be possible to confirm the diagnosis of SMAS without the use of any ionizing radiation whatsoever.
The authors thank the Department of Radiology, nursing staff in theaters, and endoscopy suite at Birmingham Children's Hospital for their assistance.
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