The role of diffusion-weighted MR imaging for differentiating benign from malignant bile duct strictures

Objectives: To assess the added value of diffusion-weighted imaging (DWI) to conventional magnetic resonance imaging (MRI) for differentiating benign from malignant bile duct strictures. Methods: Twenty-seven patients with a benign stricture and 42 patients with a malignant stricture who had undergone gadoxetic acid-enhanced MRI with DWI were enrolled. Qualitative (signal intensity, dynamic enhancement pattern) and quantitative (wall thickness and length) analyses were performed. Two observers independently reviewed a set of conventional MRI and a combined set of conventional MRI and DWI, and receiver operating characteristic (ROC) curve analysis was assessed. Results: Benign strictures showed isointensity (18.5-70.4 %) and a similar enhancement pattern (22.2 %) to that of normal bile duct more frequently than malignant strictures (0-40.5 % and 0 %) on conventional MRI (P<0.05). Malignant strictures (90.5-92.9 %) showed hypervascularity on arterial and portal venous phase images more frequently than benign strictures (37.0-70.4 %) (P<0.01) On DWI, all malignant strictures showed hyperintensity compared with benign cases (70.4 %) (P<0.001). Malignant strictures were significantly thicker and longer than benign strictures (P<0.001). The diagnostic performance of both observers improved significantly after additional review of DWI. Conclusions: Adding DWI to conventional MRI is more helpful for differentiating benign from malignant bile duct strictures than conventional MRI alone. Key points: • Accurate diagnosis and exclusion of benign strictures of bile duct are important. • Diffusion-weighted MRI helps to distinguish benign from malignant bile duct strictures. • DWI plus conventional MRI provides superior diagnostic accuracy to conventional MRI alone.