The Efficacy of Contrast-Enhanced Endoscopic Ultrasound for Differentiating Mural Nodules from Mucus Clots in Branch Duct IPMN

Background/Objectives: The presence of a mural nodule (MN) is one of the findings indicating malignant transformation of an intraductal papillary mucinous neoplasm (IPMN). It is difficult to distinguish true MNs from mucus clots (MCs) by endoscopic ultrasound (EUS) alone. This study aimed to evaluate the efficacy of contrast-enhanced (CE)-EUS for differentiating true MNs from MCs and carcinoma from adenoma. Methods: A total of 104 patients who were diagnosed as having branch duct-type IPMNs with MN-like structures by EUS and underwent CE-EUS between January 2016 and August 2022 were included. MN-like structures without perfusion on CE-EUS were defined as MCs and those with perfusion were defined as true MNs. This was a retrospective study with limited pathological confirmation, and diagnoses in non-surgical cases were based on imaging and follow-up. Results: CE-EUS showed MN-like structures with perfusion in 35 patients and without perfusion in 69 patients. Surgical resection was eventually performed in a total of 28 patients and the diagnostic sensitivity, specificity and accuracy of MNs among them were 100%, 66.7% and 96.4% in CE-EUS; 48%, 66.7% and 50% in CE-CT; and 61.9%, 33.3% and 58.3% in MRCP, respectively. Possible risk factors indicating malignancy were statistically evaluated and presence of an MN was the only significant factor. Among the 35 true MNs, the height of an MN in carcinoma was significantly higher than that of an adenoma. The ROC analysis for detecting carcinoma in true MNs showed an area under the curve of 0.92 with the optimal cut-off value of 7 mm. When this cut-off value was used for diagnosing carcinoma, the sensitivity, specificity, and accuracy were 94.1%, 83.3% and 88.6%, respectively. Conclusions: CE-EUS may be useful for differentiating true MNs from MCs, although diagnostic performance should be interpreted cautiously because most non-surgical cases lacked pathological confirmation.