Residency · Residency · Diagnostic Radiology

Pancreatic Pathology: Adenocarcinoma, Cystic Lesions, and Pancreatitis

Pancreatic Ductal Adenocarcinoma (PDAC)

Epidemiology

Pancreatic ductal adenocarcinoma is the fourth leading cause of cancer death. The five-year survival rate is approximately 10% overall, improving to 20-40% if the tumor is resectable at diagnosis. Unfortunately, only 15-20% of patients are surgical candidates at presentation. Peak incidence occurs between ages 60 and 80 years.

CT Protocol

Detection of PDAC requires a dedicated pancreatic protocol CT with thin-section imaging at 0.5-1 mm and dual-phase acquisition consisting of a pancreatic parenchymal phase at 40-50 seconds and a portal venous phase at 65-70 seconds after intravenous contrast injection. The pancreatic phase optimizes the contrast difference between the enhancing normal pancreas and the hypoenhancing tumor. Water or low-density oral contrast is used to distend the duodenum, and multiplanar reconstructions in the coronal and sagittal planes are essential for vascular assessment.

CT Findings

The hallmark finding is a hypoattenuating mass relative to the normal pancreas on the pancreatic phase, which is the most sensitive phase for detection. The head and uncinate process are the most common locations, accounting for 60-70% of cases. Pancreatic duct dilation proximal to the mass (upstream duct dilation) is a key secondary sign. The double duct sign, defined as simultaneous dilation of the common bile duct and pancreatic duct, is highly suspicious for a periampullary mass. Abrupt duct cutoff at the level of the mass and pancreatic parenchymal atrophy upstream from the mass are additional findings. Isoattenuating PDAC, which accounts for 5-10% of cases, produces no discernible mass and is detected only by secondary signs such as duct cutoff, atrophy, and vascular encasement.

Resectability Assessment (NCCN Criteria)

A tumor is considered resectable when there is no arterial contact with the celiac axis, SMA, or common hepatic artery, and either no venous contact or 180 degrees or less of SMV or portal vein contact without contour irregularity. Borderline resectable disease shows 180 degrees or less of arterial contact without stenosis or deformity, or greater than 180 degrees of venous contact or venous contour irregularity with a reconstructible vein. Unresectable (locally advanced) disease is characterized by greater than 180 degrees of arterial encasement or aortic invasion, or unreconstructible venous involvement. Metastatic disease includes liver metastases, peritoneal implants, distant lymphadenopathy, and lung metastases.

Vascular Assessment Reporting

The report should specify the degree of contact in degrees of circumference for each major vessel: the SMA, celiac axis, common hepatic artery, SMV, and portal vein. Any vessel deformity, stenosis, occlusion, or thrombus must be documented. Variant arterial anatomy should also be reported, as a replaced right hepatic artery arising from the SMA occurs in approximately 15-20% of patients.

Pancreatic Cystic Lesions

Prevalence

Incidental pancreatic cysts are found in 2-15% of abdominal CT studies and up to 45% of MRI studies. The majority are benign, but the challenge lies in identifying the minority with malignant potential.

Serous Cystadenoma (SCA)

Serous cystadenoma is benign with virtually no malignant potential. The microcystic variant, which is the most common form, consists of multiple small cysts smaller than 2 cm arranged in a honeycomb pattern with a central calcified scar (sunburst calcification) present in 30% of cases. A less common macrocystic variant may mimic a mucinous cystic neoplasm. Serous cystadenoma occurs predominantly in older women and is associated with von Hippel-Lindau disease. Surgical resection is not needed unless the lesion is symptomatic.

Mucinous Cystic Neoplasm (MCN)

MCN is a premalignant lesion with obligate malignant potential. It occurs almost exclusively in women (greater than 95%) and is located in the body or tail of the pancreas. It appears as a unilocular or oligolocular cystic lesion with a thick wall and possible mural nodularity. The key distinguishing feature from IPMN is that MCN does not communicate with the pancreatic duct. Peripheral eggshell calcification may be present. Surgical resection is recommended for all MCNs regardless of size.

Intraductal Papillary Mucinous Neoplasm (IPMN)

Main duct IPMN is characterized by diffuse or segmental dilation of the main pancreatic duct (greater than 5 mm) without an obstructing lesion. It carries a higher malignant potential, with 40-90% harboring high-grade dysplasia or invasive carcinoma. Surgery is generally recommended for main duct dilation exceeding 10 mm, enhancing mural nodules, or obstructive jaundice. Branch duct IPMN presents as a cystic lesion communicating with the main pancreatic duct and has a lower malignant potential at 15-25%. Surveillance follows ACR and AGA guidelines based on size and features. "Worrisome features" include a cyst 3 cm or larger, thickened enhanced cyst wall, main duct 5-9 mm, non-enhancing mural nodule, and lymphadenopathy. "High-risk stigmata" include obstructive jaundice, enhancing mural nodule, and main duct 10 mm or larger. Mixed type IPMN involves both the main duct and branch ducts.

Solid Pseudopapillary Neoplasm (SPN)

SPN is a rare, low-grade malignant tumor that occurs almost exclusively in young women between ages 20 and 30. It presents as a large, well-encapsulated mass with solid and cystic (hemorrhagic and necrotic) components. Peripheral calcification and heterogeneous enhancement of the solid components are characteristic. The prognosis is excellent after resection, with a cure rate exceeding 95%.

Pancreatic Cystic Lesion Comparison

Pancreatic Neuroendocrine Tumor (PNET)

PNETs are hypervascular masses that avidly enhance in the arterial phase, in contrast to the hypoenhancing pattern of PDAC. They are well-circumscribed and may become cystic when large. Functional PNETs include insulinoma (the most common), gastrinoma, glucagonoma, and VIPoma. Non-functional PNETs present with mass effect. On MRI they are T2 hyperintense, show restricted diffusion, and enhance avidly in the arterial phase.

Pancreatitis

Revised Atlanta Classification (2012)

Acute Pancreatitis

Interstitial edematous pancreatitis is characterized by diffuse or localized pancreatic enlargement with peripancreatic fat stranding and possible peripancreatic fluid. On CT the pancreas enhances normally with surrounding inflammatory changes, and the disease is mild and self-limited in most cases. Necrotizing pancreatitis involves necrosis of pancreatic parenchyma and/or peripancreatic tissue. On CT it appears as non-enhancing areas within the pancreas, and intravenous contrast is required for detection. Necrotizing pancreatitis carries higher morbidity with risk of infection and organ failure.

Fluid Collections (Revised Atlanta Terminology)

An acute peripancreatic fluid collection (APFC) occurs within the first 4 weeks, is homogeneous fluid without a wall, and arises in the context of interstitial edematous pancreatitis. A pseudocyst is a fluid collection present for 4 weeks or more that is encapsulated with a defined wall and contains no solid debris, also occurring in interstitial edematous pancreatitis. An acute necrotic collection (ANC) occurs within the first 4 weeks and is a heterogeneous collection containing fluid and solid necrotic debris without a defined wall, arising in necrotizing pancreatitis. Walled-off necrosis (WON) is present at 4 weeks or more and is an encapsulated collection containing both fluid and solid necrotic debris with a defined wall, also occurring in necrotizing pancreatitis.

CT Severity Index (Modified)

The modified CT severity index is based on pancreatic inflammation, necrosis, and extrapancreatic complications. It is used for prognostication, with higher scores correlating with increased morbidity and mortality.

Chronic Pancreatitis

On CT, chronic pancreatitis is characterized by pancreatic calcifications (intraductal), ductal dilation and irregularity (the chain of lakes pattern), and parenchymal atrophy. MRI and MRCP better depict ductal abnormalities and side branch ectasia. Complications include pseudocyst, pseudoaneurysm (most commonly involving the splenic artery), splenic vein thrombosis, and biliary stricture.

<image>A dual-phase CT diagram of pancreatic ductal adenocarcinoma. The left panel shows the pancreatic parenchymal phase with a hypoattenuating mass in the pancreatic head (darker than the avidly enhancing surrounding normal pancreas). The dilated common bile duct and dilated upstream pancreatic duct are labeled (double duct sign). The right panel shows a coronal reconstruction with the mass encasing the superior mesenteric artery to 200 degrees of circumference, indicating unresectable locally advanced disease. Key anatomical structures are labeled: SMA, SMV, portal vein, celiac axis, common hepatic artery. The degree of arterial encasement is annotated.</image>

<image>A comparison panel showing four common pancreatic cystic lesions on CT or MRI. Panel 1 (Serous cystadenoma): microcystic honeycomb pattern with a central calcified scar. Panel 2 (Mucinous cystic neoplasm): macrocystic unilocular lesion in the pancreatic tail with a thick wall and no communication with the pancreatic duct, in a middle-aged woman. Panel 3 (Branch duct IPMN): grape-like cluster of cystic lesions in the uncinate process communicating with the main pancreatic duct (connection demonstrated with an arrow). Panel 4 (Solid pseudopapillary neoplasm): large, well-encapsulated heterogeneous mass with solid and cystic components and peripheral calcification in a young woman. Key features distinguishing each lesion are listed below each panel.</image>

<image>A diagram illustrating the Revised Atlanta Classification of pancreatitis fluid collections. A two-by-two grid with rows labeled "Interstitial edematous" and "Necrotizing" and columns labeled "Less than 4 weeks" and "4 weeks or more." The four resulting boxes show: (1) APFC -- homogeneous fluid, no wall; (2) Pseudocyst -- encapsulated fluid, defined wall, no solid debris; (3) ANC -- heterogeneous fluid with solid necrotic debris, no defined wall; (4) WON -- encapsulated collection with both fluid and solid necrotic debris and a defined wall. Each box contains a small schematic illustration of the collection and a CT image example.</image>

Clinical Pearls

Pancreatic protocol CT with a dedicated pancreatic parenchymal phase is essential for PDAC detection because the hypoenhancing tumor is most conspicuous when the surrounding pancreas is maximally enhanced. Vascular contact should always be reported in degrees of circumference with notation of vessel deformity, as this directly determines surgical resectability. The double duct sign (simultaneous CBD and pancreatic duct dilation) is highly suspicious for a periampullary mass even when no discrete mass is visible. MCNs do not communicate with the pancreatic duct, while IPMNs do, and this distinction on MRCP is the key differentiating feature. The Revised Atlanta terminology should be used when describing pancreatitis complications, as the old terms (phlegmon, pancreatic abscess) are no longer used. In the setting of necrotizing pancreatitis, non-enhancement of the pancreatic parenchyma on contrast-enhanced CT is the diagnostic finding, and CT should be delayed 72-96 hours from symptom onset for accurate assessment of necrosis.

References

• Al-Hawary MM, et al. "Pancreatic Ductal Adenocarcinoma Radiology Reporting Template: Consensus Statement of the SAR and the APA." Radiology, 2014
• Banks PA, et al. "Classification of Acute Pancreatitis -- 2012: Revision of the Atlanta Classification." Gut, 2013
• Tanaka M, et al. "Revisions of International Consensus Fukuoka Guidelines for the Management of IPMN of the Pancreas." Pancreatology, 2017
• Sahani DV, et al. "Pancreatic Cysts: Imaging Features and Management." Radiology, 2013

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