Cases Presentation

CT revealed a grossly distended stomach with dilatation of the 1st and 2nd part of duodenum. There was abrupt narrowing of the 3rd part of duodenum between the superior mesenteric artery (SMA) and abdominal aorta. The SMA to aorta angle was decreased and measured 19 degrees (Figures 1 and 2). The aorto-mesenteric distance was also reduced and measured 7 mm. The left renal vein was also compressed between the SMA and aorta.

Figure1: CT contrast sagittal section showing reduced SMA- aorta angle which measures 17.6 degrees

Figure 2: CT contrast axial section showing compression of the third part of the duodenum between the aorta and SMA (arrow)

The head and uncinate process of the pancreas appeared hypodense and poorly enhancing compared to the rest of the pancreatic parenchyma (Figure 3). A small amount of ascites was also noted. Thus, a primary diagnosis of SMA syndrome with pancreatitis was made.

Figure 3: CT contrast axial section showing a hypodense head and uncinate process of the pancreas

The serum amylase and lipase levels were grossly elevated (Ser Amylase 676 U/L (25-125 range) and lipase 1479 U/L (0-60 range) thus corroborating the radiological findings of acute inflammation of pancreas.

The patient was subsequently fed with a naso jejunal tube with calorie specific diet. Symptomatic treatment of anti-emetics, antipyretics, parenteral fluids was given.

The lipase, amylase returned to normal levels after 10 days. Patient was counseled about the dietary restrictions and advised follow up.

A follow up ultrasound done after a fortnight revealed a normal pancreas with a reduced SMA- aorta angle and compression of the left renal vein (Figures 4 and 5).

Figure 4: USG axial section showing compressing of left renal vein between SMA and aorta

Figure 5: Follow up USG (after 15 days) post treatment showing head and neck of pancreas (arrow)

Discussion

Superior mesenteric artery syndrome (SMAS) is a rare condition characterized by vascular compression, wherein the third part of the duodenum is compressed between the aorta and the superior mesenteric artery (SMA)¹. The reported incidence of SMAS in literature ranges from 0.1% to 0.3%².

The normal SMA - aorta angle ranges from 38 to 56° and the aortomesenteric distance is 10 to 20 mm³. In patients with chronic illnesses, low BMI can lead to reduced fat between the vessels causing reduced SMA- aorta angle. Some of these patients may not have any clinical symptoms. Only a reduced angle or reduced aorto-mesenteric distance is not sufficient for diagnosis of SMA syndrome. The patient should have classical symptoms as well. The classic symptoms are post-prandial abdominal pain, nausea, vomiting, early satiety (feeling full quickly) and weight loss⁴.

Pancreatitis is very rarely associated with SMA syndrome, with only a few case reports. The cause of pancreatitis is a secondary occlusive post papillary syndrome causing retrograde reflux of bile into the pancreatic duct due to duodenal compression. This triggers an inflammatory process causing pancreatitis⁵.

Overdistension of stomach can also be seen due to duodenal compression which is the reason why patients usually have multiple vomiting episodes with symptoms suggestive of bowel obstruction as was seen in our case.

The gold standard for diagnosis of SMA syndrome is CT Abdominal Angiography. The accurate angle and distance between the vessels can be calculated which is helpful for clinicians. CT also helps to rule out other coexisting conditions like pancreatitis, gastric necrosis, portal vein gas, etc⁶ 

Abdominal USG plays an important role in evaluating the patient for resolution of pancreatitis since there is no radiation exposure especially in the pediatric age group.

Barium studies can also be done to evaluate the exact site of compression of duodenum. No passage of contrast beyond the narrowed segment or reversal of contrast flow in the dilated proximal segment further aid in diagnosis.

A radiograph of the abdomen can be done to look for small or large bowel obstruction. In our case, radiographs were done to confirm the NJ tube position by the clinicians and not for primary diagnosis

Conclusion
This case shows the rare coexistence of SMA syndrome and pancreatitis. Early diagnosis with radiological modality led to timely intervention by the physician. Proper calorie specific diet will further help to alleviate the symptoms. This case also highlights that timely medicines helped in reversal of pancreatitis which otherwise would have led to severe complications.

References

1.   Karki B, Pun B, Shrestha A, et al. Superior mesenteric artery syndrome. Clin Case Rep 2020;8(11):2295.
2.   Shiu JR, Chao HC, Luo CC, et al. Clinical and nutritional outcomes in children with idiopathic superior mesenteric artery syndrome. J Pediatr Gastroenterol Nutr 2010;51:177-182.
3.  Miyata J, Eshak ES, Yoshioka T, Iso H. Movement of the superior mesenteric artery in patients with superior mesenteric artery syndrome: a case-reference study. Clin Anat 2022;35:891-898.
4.    Van Horne N, Jackson JP. Superior Mesenteric Artery Syndrome. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing 2025.
5.    Sihuay-Diburga DJ, Accarino-Garaventa A, Vilaseca-Montplet J, et al. Acute pancreatitis and superior mesenteric artery syndrome. Rev Esp Enferm Dig 2013;105:626-628.
6.    Oka A, Awoniyi M, Hasegawa N, et al. Superior mesenteric artery syndrome: Diagnosis and management. World J Clin Cases 2023;11(15):3369-3384.