To investigate the value of multi-slice spiral CT imaging in the differential diagnosis of malignant low level biliary obstructive diseases of different tissue origins.

A retrospective analysis was performed of clinical data of 30 patients with malignant low level biliary obstruction confirmed by surgery or endoscopic retrograde cholangiopancreatography from March 2015 to December 2017 at Children's Hospital of Xinjiang Uygur Autonomous Region. The imaging findings of cholangiocarcinoma, pancreatic head cancer, and ampullary carcinoma diagnosed by multi-slice spiral CT were compared with pathological biopsy results, and the Kappa test was used to judge the consistency of preoperative diagnosis and postoperative pathology.

Multi-slice spiral CT in 30 patients can clearly show the dilatation of the biliary system, thickening of the bile duct wall, and stenosis of the distal obstruction. Cholangiocarcinoma was characterized by moderate-to-severe dilatation of the intrahepatic bile duct, the distal bile duct had a ″cut-off sign″, and the soft tissue density of the obstructed area can grow along the side wall of the bile duct. The common bile duct and pancreatic duct of ampulla cancer patients were expanded, showing a typical "double tube sign". In patients with pancreatic head cancer, the density of tumor was uneven, the boundary was unclear, the enhancement was not obvious, the density was relatively low, and the tail of the pancreas often shrank. Compared with the results of surgery and pathological diagnosis, the accuracy, sensitivity, and specificity of MSCT for diagnosing cholangiocarcinoma, pancreatic head cancer, and ampullary carcinoma were 88.9%, 88.9%, and 83.3%, 75.0%, 85.7%, and 91.3%, and 75.0%, 60.0%, and 96.0%, respectively. MSCT diagnosis and pathological examination had a good consistency (κ=0.70, P<0.01).

MSCT has a great consistency with pathology in preoperative diagnosis of ampullary tumors, and it can be used as a conventional radiographic means for diagnosis of ampullary tumors. CT imaging can clearly display tumor location, size, and the relationship with the surrounding tissue structure.