How to differentiate between main duct and branch duct Intraductal Papillary Mucinous Neoplasm (IPMN)?

From the Guidelines

Main duct intraductal papillary mucinous neoplasms (IPMN) and branch duct IPMN can be differentiated based on their location, appearance on imaging, and clinical significance, with main duct IPMNs involving the main pancreatic duct and carrying a higher risk of malignancy. The distinction between main duct and branch duct IPMN is crucial due to the significant difference in their malignant potential, with main duct IPMNs having a risk of malignant degeneration of approximately 57% to 92% compared to 25% for branch duct IPMN 1. Main duct IPMNs typically appear as segmental or diffuse dilation of the main pancreatic duct measuring ≥5 mm in diameter without other causes of obstruction, and may also show enhancing nodules within the duct on imaging. In contrast, branch duct IPMNs involve the side branches of the pancreatic ductal system, appearing as cystic dilations of branch ducts that communicate with the main pancreatic duct, typically looking like grape-like clusters or cysts ≥5 mm in diameter. Diagnostic evaluation includes cross-sectional imaging, such as MRI, which is preferred over contrast-enhanced CT due to its higher sensitivity and specificity for distinguishing IPMN from other cystic pancreatic lesions 1. Some cases may show mixed features of both types, called mixed-type IPMN, which should be managed as main duct IPMN due to similar malignancy risk. Management decisions, including surveillance versus surgical resection, depend on this classification along with other high-risk features such as jaundice, enhancing mural nodules, or rapid growth, with resection recommended for main duct IPMNs ≥10 mm and for branch-duct IPMNs with high-risk stigmata or symptoms 1. Key points to consider in differentiating between main duct and branch duct IPMN include:

• Location and appearance on imaging
• Clinical significance and malignant potential
• Diagnostic evaluation using cross-sectional imaging and other modalities
• Management decisions based on classification and high-risk features.

From the Research

Differentiation between Main Duct and Branch Duct IPMN

To differentiate between main duct and branch duct intraductal papillary mucinous neoplasms (IPMNs), several factors and diagnostic tools can be considered:

• Imaging techniques: Magnetic resonance imaging (MRI) and endoscopic ultrasound (EUS) are useful for diagnosing IPMNs and detecting main duct involvement 2.
• Tumor size: A larger tumor size is associated with a higher risk of malignancy, and a cutoff of 2 cm may be more sensitive for detecting high-grade/invasive BD-IPMNs than a cutoff of 3 cm 3.
• Mural nodules: The presence of mural nodules on EUS or atypical cells on EUS-fine needle aspiration (EUS-FNA) can indicate high-grade/invasive pathology, even in smaller cysts 3.
• Cyst growth rate and solid components: These factors can also influence the risk of malignancy and the decision to operate or observe 4.
• Sendai criteria: The 2012 Sendai Criteria recommend surgery for main duct IPMNs and mixed-type IPMNs, while branch duct IPMNs without worrisome features or high-risk stigmata may undergo close observation 4, 3.

Diagnostic Accuracy of Preoperative Imaging

The diagnostic accuracy of preoperative imaging for differentiating between branch duct and mixed duct IPMNs is as follows:

• EUS: Sensitivity of 80%, specificity of 78%, and accuracy of 79% 2.
• MRI: Sensitivity of 83%, specificity of 63%, and accuracy of 68% 2.
• Combination of EUS and MRI: Maximum sensitivity but decreased accuracy (sensitivity of 100%, specificity of 64%, and accuracy of 67%) 2.

Management of IPMNs

The management of IPMNs depends on the type and radiological features of the tumor:

• Main duct IPMNs: Surgery is recommended due to the high risk of malignancy 5, 4.
• Branch duct IPMNs: Management involves surgery or surveillance, depending on tumor size, cyst growth rate, solid components, and other factors 4, 3.