Diagnostic Ultrasound - Abdomen and Pelvis

Cystic Pancreatic Lesion
920
Differential Diagnoses: Pancreas
DIFFERENTIAL DIAGNOSIS
Common
• Pancreatic Pseudocyst
• Serous Cystadenoma of Pancreas
• Mucinous Cystic Neoplasm (MCN)
• Intraductal Papillary Mucinous Neoplasm (IPMN)
Less Common
• Necrotic Pancreatic Ductal Carcinoma
• Solid Pseudopapillary Neoplasm
• Cystic Pancreatic Neuroendocrine Tumor
• Congenital Cyst
• Lymphoepithelial Cyst
• Cystic Metastases
ESSENTIAL INFORMATION
Key Differential Diagnosis Issues
• US can characterize simple or macrocystic pancreatic lesions
○ Most represent pancreatic pseudocysts
• Remaining benign and malignant cystic pancreatic lesions
may appear echogenic due to numerous microcystic
interfaces, soft tissue components, or complex content
• CECT or CEMR is necessary to adequately characterize
internal features that are not well assessed with
transabdominal ultrasound
• Endoscopic ultrasound (EUS) also provides high-resolution
imaging but is invasive and requires conscious sedation
○ Can be used for biopsy or fluid aspiration in
indeterminate cases
• Key features which guide differential diagnosis
○ Location and size
○ Wall thickness
○ Loculation and number of locules
○ Internal septations and septal thickness
○ Presence of solid components and vascularity
○ Central scar
○ Calcification and location
○ Communication with pancreatic duct
○ Fluid characterization/presence of hemorrhage
○ Pancreatic and biliary diameter
○ Upstream pancreatic atrophy
○ Evidence of acute or chronic pancreatitis
○ Locoregional adenopathy and hepatic metastases
• Consider clinical context
○ Patient demographics, pancreatitis, obstructive
symptomatology, familial syndromes
Helpful Clues for Common Diagnoses
• Pancreatic Pseudocyst
○ Common late complication of pancreatitis
– Develops 4-6 weeks after onset of acute pancreatitis
– Evolves over time, whereas neoplastic lesions persist
without change
○ Generally well circumscribed, smooth-walled, unilocular,
anechoic with posterior acoustic enhancement
○ May be complicated
– Multilocular
– Internal echoes with fluid-debris level or septations
– Wall calcification
○ But shows no vascularized soft tissue elements
○ Associated with other findings of acute or chronic
pancreatitis
– Parenchymal atrophy or calcification, fat stranding on
CT, ductal strictures on MR
– Generally not seen with MCN, the primary mimic of
pseudocyst
• Serous Cystadenoma of Pancreas
○ Benign pancreatic tumor
○ Commonly in pancreatic body and tail; 30% occur in
pancreatic head
○ Typically composed of small cystic areas separated by
internal septations
○ Septa coalesce to form central echogenic scar with
"sunburst" calcification
○ Can mimic nonspecific solid and cystic tumor
– Heterogeneous echogenic appearance due to
numerous interfaces
– Intralesional color Doppler flow in fibrovascular septa
○ Characteristic honeycomb appearance on CT, MR, and
endoscopic ultrasound
○ Less commonly, may see oligocystic variant that may be
indistinguishable from MCN by imaging
– EUS-guided cyst aspiration may be helpful in making
diagnosis
○ Usually seen in older women (mean age: 61 years)
• Mucinous Cystic Neoplasm (MCN)
○ Tumors range in grade from benign with malignant
potential to invasive carcinoma
○ More common location: Pancreatic body and tail
○ Anechoic or hypoechoic, thick-walled, cystic mass ±
mildly thickened septa
○ Can demonstrate peripheral calcification
○ May be indistinguishable from pseudocyst
○ Lacks additional findings/history of pancreatitis
○ EUS-guided biopsy may be helpful in making diagnosis
○ Solid components or marked septal thickening suggests
carcinoma
○ Seen almost exclusively in middle-aged women (mean
age: 50 years)
• Intraductal Papillary Mucinous Neoplasm (IPMN)
○ Tumor with varying malignant potential: Branch type
generally benign with low malignant potential; main duct
IPMN thought to be precursor to invasive pancreatic
ductal adenocarcinoma
○ Typically in head of pancreas/uncinate process
○ Main duct type: Marked pancreatic ductal dilatation
– When diffuse, may simulate chronic pancreatitis
□ However, calcification and parenchymal atrophy
are not typically seen
– If segmental, can mimic fluid collection or mucinous
cystic tumor
○ Side branch type: Collections of dilated side branches
– Anechoic or hypoechoic cyst or collection of small
anechoic cysts
– Look for communication with pancreatic duct, which is
a distinguishing feature compared to other cystic
neoplasms
– May be multifocal, whereas serous cystadenoma and
MCN are typically solitary
○ Occur most frequently in older men (mean age: 65 years)