What is the next recommended imaging test for evaluating suspected Intraductal Papillary Mucinous Neoplasms (IPMNs) if Magnetic Resonance Imaging (MRI) is not available?

Imaging for Intraductal Papillary Mucinous Neoplasms (IPMNs) When MRI is Unavailable

When MRI with MRCP is unavailable for evaluating suspected IPMNs, a dual-phase contrast-enhanced pancreatic protocol CT is the next best imaging test, as it provides critical diagnostic information about ductal dilation, intralesional septations, mural nodules, and pancreatic duct communication. 1, 2

Diagnostic Performance of CT for IPMNs

CT serves as a valuable alternative to MRI/MRCP with the following characteristics:

• Sensitivity and specificity: 80.6-86.4% for distinguishing IPMN from other cystic pancreatic lesions (compared to 96.8-90.8% for MRI) 1, 2
• Detection capabilities:
  • Internal septations: 73.9-93.6% sensitivity
  • Mural nodules: 71.4% sensitivity
  • Pancreatic duct communication: 86% sensitivity 1, 2

Optimal CT Protocol for IPMN Evaluation

When performing CT in place of MRI, the following protocol should be used:

• Dual-phase contrast-enhanced pancreatic protocol CT including:
  • Late arterial phase
  • Portal venous phase
  • Multiplanar reformations 1
• Intravenous contrast is essential to increase sensitivity for detecting worrisome features and high-risk stigmata 1

Key Features to Assess on CT

When evaluating CT images for IPMNs, pay particular attention to:

1. Main pancreatic duct dilation:

   • 5-9 mm: "worrisome feature" requiring EUS-FNA
   • ≥10 mm: "high-risk stigmata" requiring surgical referral 1, 2

2. Mural nodules: Enhancing mural nodules ≥5 mm have the highest odds ratio (25-29) for predicting malignancy 3

3. Cyst size: Cysts ≥3 cm have a 3-times greater risk of malignancy 1

4. Ductal communication: Communication with the main pancreatic duct suggests IPMN diagnosis 1

5. Calcifications: Both in the background parenchyma and within the cyst 1

Limitations of CT Compared to MRI

Be aware of these limitations when interpreting CT results:

• Lower sensitivity for detecting internal architecture details 1, 2
• Radiation exposure is problematic for long-term surveillance 2
• Less accurate in determining the exact type and extent of IPMN 4
• Underestimates branch duct involvement: CT identified only 46 branch lesions compared to 101 on MRCP in one study 4

When to Consider Additional Testing

Consider endoscopic ultrasound with fine-needle aspiration (EUS-FNA) in the following scenarios:

• Main pancreatic duct dilation between 5-9 mm 1
• Presence of enhancing mural nodules 1, 2
• Cyst size ≥3 cm (even without other worrisome features) 1
• Abrupt main pancreatic duct caliber change 3
• Rapid cyst growth rate (≥5 mm/year) 2, 3

Follow-up Recommendations

For surveillance after initial CT evaluation:

• Follow-up intervals typically range from 6 months to 2 years 1
• Minimum follow-up period of 5-10 years is recommended 1, 2
• Either CT or MRI can be used for follow-up, though modality concordance between baseline and follow-up examinations facilitates comparison 1

Pitfalls to Avoid

• Don't rely solely on CT to exclude multifocal disease, as it may miss small branch duct cysts 4
• Don't overlook main duct involvement on CT, which may overestimate main duct involvement compared to MRCP and surgical pathology 4
• Don't dismiss small cysts (<3 cm) with worrisome features, as they may still contain sufficient fluid for EUS-FNA 1