P2.K214: Atypical Congenital Pancreatic Abnormality Causing SMA-like Syndrome in a Pediatric Patient

Introduction: Superior mesenteric artery (SMA) syndrome occurs when the third part of the duodenum is compressed between the aorta and the SMA. SMA syndrome can be idiopathic but typically occurs after weight loss or surgery, as those can result in loss of the mesenteric fat pad that normally protects the duodenum from compression. Patients typically present with symptoms of small bowel obstruction. An annular pancreas is a congenital pancreatic abnormality that can also very rarely result in a duodenal obstruction but of the second part of the duodenum. This abnormality occurs due to failures in rotation and fusion of pancreatic buds during embryogenesis. We present the first case of a pediatric patient with an SMA-like syndrome due to compression of the third part of the duodenum between the aorta and a congenital pancreatic variant posterior to the SMA.

Case Description: Patient is a previously healthy 15 year-old female who presented with sudden onset of nausea, vomiting, epigastric pain, and anorexia for 6 days. Labs included normal CBC, CMP, and lipase. CT abdomen and MRI abdomen showed abrupt caliber change within the mid-third portion of the duodenum concerning for SMA syndrome. However, the patient had a low-normal angle and distance between the abdominal aorta and SMA. Imaging also showed a fingerlike projection of pancreatic tissue arising from the uncinate process extending just posterior to the SMA and SMV contributing to compression (Image 1). Upper GI series showed delayed transit of contrast through the third portion of the duodenum. Conservative nutritional management with nasojejunal tube feeds failed due to vomiting and intolerance of the tube. TPN was started on admission day #8 and patient eventually transitioned to oral feeds and was discharged on a regular diet upon discharge, day #16. Patient follows up in a pediatric GI clinic and has remained asymptomatic with proper nutrition.

Discussion: Despite having compression of the third portion of the duodenum, our patient did not meet diagnostic imaging criteria for SMA syndrome because of her low-normal aortomesenteric angle. We postulate that the atypical pancreatic abnormality created a situation where the aortomesenteric angle did not need to be as acute to cause the compression of SMA syndrome. The particular anatomical pancreatic variant of an uncinate fingerlike projection seen in this case has previously only been documented as an incidental discovery during surgery and post-mortem dissection. This rare pancreatic variant is likely due to abnormal embryogenesis.

Conclusion: To our knowledge, this is the first report of an atypical congenital pancreatic variant contributing to an SMA-like syndrome by compressing the duodenum between it and the aorta. This case emphasizes the importance of recognizing congenital anatomic variations as they can cause clinical symptoms of a syndrome despite not meeting the typical diagnostic criteria.