What is Intraductal Papillary Mucinous Neoplasm (IPMN)?

Intraductal Papillary Mucinous Neoplasm (IPMN)

Intraductal Papillary Mucinous Neoplasm (IPMN) is a mucin-producing neoplasm that arises from the pancreatic ductal epithelium, characterized by papillary growth within the pancreatic ducts, mucin secretion, and ductal dilatation. 1, 2

Definition and Classification

• IPMNs are grossly visible lesions (≥5 mm) that develop within the pancreatic duct system and are characterized by intraductal papillary growth and thick mucin production 3
• Based on anatomical involvement, IPMNs are classified into three types:
  • Main duct type (MD-IPMN): Involves the main pancreatic duct
  • Branch duct type (BD-IPMN): Involves the branch ducts
  • Mixed/combined type: Involves both main and branch ducts 2, 4

Pathological Features

• IPMNs show papillary epithelial proliferation within dilated pancreatic ducts filled with mucin 1
• Histologically, IPMNs are classified into four subtypes based on morphology and mucin expression:
  • Gastric type: Shows simple, short papillae with gastric foveolar epithelium and pyloric-like glands
  • Intestinal type: Exhibits villous growth pattern with pseudostratified columnar cells
  • Pancreatobiliary type: Demonstrates complex arborizing papillae with cuboidal cells
  • Oncocytic type: Shows arborizing papillae with oncocytic cells and intraepithelial lumina 1, 3

Dysplasia Grading

• IPMNs are graded according to cytoarchitectural atypia:
  • Low-grade dysplasia
  • Intermediate-grade dysplasia
  • High-grade dysplasia 3, 5
• The presence of invasive carcinoma significantly impacts prognosis and is reported separately 1

Clinical Significance and Malignant Potential

• The malignancy risk varies by IPMN subtype:
  • Main duct IPMNs: 57-92% risk of malignancy
  • Branch duct IPMNs: 6-46% risk of malignancy 4
• High-risk features that raise concern for malignancy include:
  • Obstructive jaundice with a cystic lesion in the pancreatic head
  • Mass lesion >30 mm
  • Enhanced solid component
  • Main pancreatic duct size ≥10 mm 4
• "Worrisome features" include:
  • Main duct size 5-9 mm
  • Cyst size <3 cm 4

Diagnostic Approach

• Magnetic Resonance Imaging (MRI) with MRCP and Endoscopic Ultrasound (EUS) are the primary diagnostic modalities 2, 4
• Key diagnostic features include:
  • Dilatation of pancreatic ducts without an obstructing lesion
  • Communication between branch duct lesions and main pancreatic duct
  • Presence of mural nodules 2

Management

• Surgical resection is recommended for:
  • Most main duct IPMNs
  • Mixed variant IPMNs
  • Symptomatic branch duct IPMNs
  • Branch duct IPMNs with high-risk features 4
• The extent of pancreatic resection depends on the location and extent of the disease 6
• Regular surveillance is necessary for non-resected lesions and after partial pancreatectomy due to the risk of multifocal disease 5

Prognosis

• 5-year survival rates:
  • 77-100% for non-invasive IPMNs after resection
  • 27-60% for IPMNs with invasive carcinoma 4
• Patients with IPMNs should be monitored for:
  • Disease recurrence after surgery
  • Development of metachronous IPMNs
  • Synchronous or metachronous malignancies in other organs 6, 5

Differential Diagnosis

• IPMNs must be distinguished from:
  • Mucinous cystic neoplasms (which have ovarian-type stroma)
  • Retention cysts and secondary ductal dilatation
  • Intraductal tubular/tubulopapillary neoplasms
  • Large duct type invasive adenocarcinomas
  • Congenital, duplication, and paraduodenal wall cysts 1