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

• 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.