What is the best imaging modality for Intraductal Papillary Mucinous Neoplasms (IPMNs)?

Best Imaging Modality for Intraductal Papillary Mucinous Neoplasms (IPMNs)

MRI with MRCP (Magnetic Resonance Cholangiopancreatography) is the preferred imaging modality for the diagnosis and surveillance of IPMNs due to its superior soft-tissue contrast and ability to demonstrate ductal communication. 1

Advantages of MRI with MRCP for IPMN Evaluation

• MRI with MRCP has superior sensitivity (96.8%) and specificity (90.8%) compared to CT (80.6% and 86.4% respectively) for distinguishing IPMN from other cystic pancreatic lesions 1
• The reported sensitivity of thin-slice 3-D MRCP acquisitions for demonstrating communication of a cyst with the pancreatic duct is as high as 100%, which is crucial for diagnosing IPMNs 1
• MRI has 91% sensitivity for detecting internal septations, which are important features in characterizing IPMNs 1
• MRI provides superior assessment of mural nodules and internal septations, which are key features for determining malignant potential 1
• MRI/MRCP is very sensitive for identifying whether a patient has single or multiple PCN, with the latter favoring a diagnosis of multifocal side-branch IPMN 1
• MRI avoids radiation exposure, which is particularly important as patients with IPMNs may require lifelong imaging follow-up 1

CT as an Alternative Imaging Option

• CT should be considered in specific clinical scenarios, particularly when identification of calcification is important 1
• When CT is performed, a dual-phase contrast-enhanced pancreatic protocol CT (including late arterial and portal venous phases with multiplanar reformations) is recommended 1
• CT provides excellent spatial resolution and can detect calcifications in both the background parenchyma and within the cyst 1
• The relative sensitivity of pancreatic protocol multidetector CT for detecting internal septations, mural nodules, and communication with the pancreatic duct are 73.9% to 93.6%, 71.4%, and 86%, respectively 1

Role of Endoscopic Ultrasound (EUS)

• EUS is recommended as an adjunct to other imaging modalities, not as the primary diagnostic tool 1
• EUS is helpful for identifying IPMNs with features that should be considered for surgical resection 1
• EUS-FNA (Fine Needle Aspiration) should only be performed when the results are expected to change clinical management 1
• EUS-FNA is not recommended for initial characterization of pancreatic cysts <2.5 cm in size 1
• Contrast harmonic enhanced EUS (CH-EUS) should be considered for further evaluation of mural nodules and is superior to standard EUS and CT for identifying mural nodules 1

Recommended Imaging Protocol for IPMNs

• For initial diagnosis: MRI with MRCP as the first-line imaging modality 1
• No definitive MRI protocol can be recommended due to lack of dedicated comparative studies, but a combination of T2-HASTE (T2-weighted ultrafast spin echo technique) and DWI (diffusion-weighted imaging) has shown similar accuracy to comprehensive contrast-enhanced MRI protocols 1
• For follow-up: MRI with MRCP remains the preferred method 1
• Consider multimodality imaging (adding CT) in cases where identification of calcification is important, for tumor staging, or for diagnosing postoperative recurrent disease 1

Important Features to Assess on Imaging

• Communication between the cyst and the main pancreatic duct (pathognomonic for IPMN) 1
• Presence of mural nodules, which suggest malignant transformation 1
• Main pancreatic duct diameter (>6-10 mm suggests malignancy in main duct IPMNs) 2
• Cyst size (>3 cm in branch duct IPMNs raises concern for malignancy) 2, 3
• Presence of solid components, enhancing walls, or thick septae 1, 2

Common Pitfalls and Caveats

• Communication with the main pancreatic duct can also be seen in pseudocysts, which may lead to misdiagnosis 1
• Interobserver variability in EUS-based diagnoses can be considerable 1
• The accuracy of both MRI and CT remains relatively low for identifying the specific type of pancreatic cystic neoplasm, with reported accuracy between 40-95% for MRI/MRCP and 40-81% for CT 1
• Small cysts may be missed on CT, particularly those <1 cm 2
• When evaluating branch duct IPMNs, ensure adequate assessment of any communication with the main pancreatic duct, as this is crucial for proper classification 4, 5