Incidentally detected pancreatic duct dilatation on ultrasound and role of MRI

Objective: The clinical significance of incidentally detected pancreatic duct (PD) dilatation at ultrasound (US) without a visualized underlying cause is unclear. We aimed to assess the role of subsequent MRI (including MRCP) and to identify US imaging and laboratory findings predictive of underlying pancreaticobiliary malignancy at the time of initial US.

Materials and methods: Patients with incidentally detected PD dilatation at ultrasound from 2011 to 2019 that had an ensuing MRI were included. Based on MRI results patients were divided into three groups: malignant pancreaticobiliary causes, benign causes and idiopathic PD dilatation. Subsequently the diagnostic ability of MRI was assessed. Initial ultrasound findings and laboratory results were compared between groups to identify predictors of underlying pancreaticobiliary pathology. A p-value < .05 was considered statistically significant.

Results: In 37/59 (63%) patients PD dilatation was confirmed on MRI. MRI demonstrated malignant 7/59 (12%) and benign 10/59 (17%) causes of PD dilatation detected at initial ultrasound. Sensitivity, specificity, negative predictive value, positive predictive value and accuracy of MRI to ascertain the cause of PD dilatation was 89%, 100%, 95%, 100% and 97% respectively. Patients with a larger magnitude of PD dilatation, concomitant CBD dilatation and elevated lipase values were more likely to have underlying pancreaticobiliary malignancy (p < 0.05). No patient with initial negative MRI had pancreaticobiliary malignancy on subsequent work-up.

Conclusion: Incidentally detected PD dilatation on ultrasound is an important finding and should prompt referral to MRI. MRI is an accurate, noninvasive method for identifying the underlying cause of PD dilatation in these patients and in excluding pancreaticobiliary malignancy.