Diagnostic value of the acute angle between the prestenotic and poststenotic duodenum in neonatal annular pancreas

Objectives To analyze the ability of upper gastrointestinal (GI) saline-contrast ultrasound (US) to detect neonatal annular pancreas. Methods Sixty-two neonates, who presented duodenal obstruction and were examined by upper GI saline-contrast US before treatment, were retrospectively analyzed and categorized into four groups according to their final diagnosis: group A, annular pancreas ( n = 28); group B, duodenal atresia ( n = 2); group C, descending duodenal septum ( n = 25); and group D, normal ( n = 7). The ultrasonic characteristics were analyzed that especially focused on whether the angle between the prestenotic and poststenotic descending duodenum (at or below a derived cutoff) could identify neonatal annular pancreas. Results To detect annular pancreas using the concave contour of the distal prestenotic duodenum, the sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV) were determined at 71.4%, 100%, 100%, and 80.9%, respectively. When using the hyperechogenic band around the constricted duodenum, the sensitivity, specificity, PPV, and NPV were determined at 82.1%, 94.1%, 92%, and 86.5%, respectively. For using the 40.7° acute angle cutoff between prestenotic and poststenotic descending duodenum, the values of sensitivity, specificity, PPV, and NPV were determined at 100%, 97.1%, 96.6%, and 100%, respectively, of which the area under the receiver operating characteristic curve was 0.979. Conclusions Upper GI saline-contrast US has a lower possibility for misdiagnosis of neonatal annular pancreas when considering the acute angle between the prestenotic and poststenotic descending duodenum. Key Points • This study includes the largest series of neonates with annular pancreas of which the characteristics were analyzed using the upper GI saline-contrast US. • Neonatal annular pancreas may be diagnosed by the characteristics—concave contour of the distal prestenotic duodenum; acute angle cutoff of 40.7° between the prestenotic and poststenotic duodenum; the “S” shape formed by the pylorus, the duodenal bulb, and the prestenotic and poststenotic descending duodenum. • The acute angle with the highest diagnostic value can be used to quantitatively diagnose neonatal annular pancreas and avoid potential misdiagnosis caused by sonographers’ subjectivity.