Thread sign in biliary intraductal papillary mucinous neoplasm: a novel specific finding for MRI

Abstract

Objectives: To evaluate thread sign of biliary intraductal papillary mucinous neoplasm (B-IPMN) on magnetic resonance imaging (MRI).

Methods: Thread sign was defined as intraductal linear or curvilinear hypointense striations. Two radiologists independently evaluated the presence and location of thread sign on MR cholangiography (thin-slice, thick-slab and 3D MRC) and axial MR images (T2 TSE, T2 HASTE and DWI) in patients with B-IPMN (n = 38) and in matched control groups with benign (n = 36) or malignant (n = 35) biliary diseases. Sensitivity, specificity, accuracy, positive predictive value (PPV), and negative predictive value (NPV) of thread sign for diagnosing B-IPMN were evaluated.

Results: Thread sign was observed only in patients with B-IPMN on MRC (44.7-52.6 % [17/38-20/38], P < 0.001) and axial MR images (31.6 % [12/38], P < 0.001), except in one patient with recurrent pyogenic cholangitis on MRC (2.8 %, 1/36). The sensitivity, specificity, accuracy, PPV and NPV of thread sign for diagnosing B-IPMN on MRC were 0.53, 0.99, 0.83, 0.95 and 0.80, respectively (reader 1) and 0.45, 1.0, 0.81, 1.0 and 0.77, respectively (reader 2). Thread sign was detected mainly at the extrahepatic bile duct (52.6 %, 20/38).

Conclusion: B-IPMN can manifest thread sign, a novel specific MR finding, mainly at the extrahepatic bile duct on MRI, especially on MRC.

Key points: • Some B-IPMNs manifest thread sign within the bile ducts on MRI. • Thread sign is a highly specific finding for B-IPMN on MRI. • MRC is superior to axial T2WI and DWI for detecting thread sign.

Keywords: Biliary intraductal papillary mucinous neoplasm; Magnetic resonance cholangiography; Magnetic resonance imaging; Mucin; Thread sign.