Diagnostic Ultrasound - Abdomen and Pelvis

Pancreatic Pseudocyst
TERMINOLOGY
Definitions
• Collection of pancreatic fluid and inflammatory exudate
encapsulated by nonepithelial fibrous tissue developing > 4
weeks after acute pancreatic fluid collection (APFC)
IMAGING
General Features
• Best diagnostic clue
○ Well-defined unilocular peripancreatic cystic mass in
setting of prior pancreatitis
• Location
○ 2/3 peripancreatic
– Body and tail (85%); head (15%)
○ 1/3 extrapancreatic
– Juxtasplenic, retroperitoneum, intraperitoneal, and
mediastinum
– Intraparenchymal: Left lobe of liver, spleen, kidney
• Size
○ 2-10 cm
• Morphology
○ Spherical or ovoid fluid collection
○ Pancreatic secretions encapsulated by granulation tissue
and fibrous capsule
○ In contrast to true cysts, pseudocysts lack true epithelial
lining
Ultrasonographic Findings
• Grayscale ultrasound
○ Uncomplicated pseudocyst
– Well-circumscribed, smooth-walled, unilocular
anechoic mass with posterior acoustic enhancement
○ Variant/complicated pseudocyst
– Multilocular (approximately 6% of cases)
– Fluid-debris level, internal echoes and septations (due
to hemorrhage/infection)
– Solid or complex in morphology (during initial phase
of cyst formation)
– Wall calcification: May make it difficult to assess
details of pseudocyst
○ Dilated pancreatic duct and common bile duct (CBD)
– Compression by pseudocyst
– Fibrosis/stricture related to chronic pancreatitis
• Color Doppler
○ Absence of internal blood flow
• Endoscopic ultrasound (EUS) may be required for aspiration
and histologic diagnosis
CT Findings
• Round or oval, homogeneous, hypodense lesion with near
water density ("mature" pseudocyst)
• Hemorrhagic, infected pseudocyst: Lobulated,
heterogeneous, mixed density lesion
• Gas within pseudocyst: Infection vs. decompression into
stomach or bowel
• May have imperceptible thin fibrous capsule vs. thick
enhancing wall
• No enhancement of internal contents
• Pseudoaneurysm: Arterial enhancement in cyst wall
MR Findings
• T2WI
○ Hyperintense (fluid)
○ Mixed intensity (fluid + layering debris)
• T1WI C+
○ May show enhancement of fibrous capsule
• MRCP
○ Hyperintense cyst contiguous with dilated pancreatic
duct
Fluoroscopic Findings
• ERCP:Communication of pseudocyst with pancreatic duct
seen in 70% of cases (decreases over time)
Imaging Recommendations
• Best imaging tool
○ CECT, US
• Protocol advice
○ Pseudocyst formation usually requires 6-8 weeks to
mature, which is best time for detection
○ In addition to peripancreatic space, other locations such
as peritoneal space, intraabdominal parenchyma, and
intrathoracic cavity should also be evaluated
○ Follow-up US helps to monitor serial change in size and
to select patients requiring decompression
DIFFERENTIAL DIAGNOSIS
Mucinous Cystic Neoplasm
• Location: Tail of pancreas (more common)
• Multiloculated, thick-walled cystic mass
• Internal solid component/echogenic septa
• May be indistinguishable from pseudocyst by imaging alone
Serous Cystadenoma
• Benign pancreatic tumor (arises from acinar cells)
• Location: Head of pancreas (most common)
• Solid mass with small cystic areas (< 20 mm), usually in
periphery
• Central echogenic scar with calcifications
• Increased vascularity on Doppler examination
Intraductal Papillary Mucinous Neoplasm (IPMN) of
Pancreas
• Low-grade malignancy arising from main pancreatic duct
(MPD) or side branches
• Cystic lesion contiguous with dilated MPD may be
indistinguishable from pseudocyst
• Side branch type usually arises in pancreatic head/uncinate,
resembling cluster of grapes or small tubular cysts
• Main duct type causes dilatation of MPD ± cystic spaces
Cystic Islet Cell Tumor
• Usually nonfunctioning
• Thick-walled cystic mass with minor solid component
○ No pancreatic ductal dilatation
• Angiography/CECT: Hypervascular primary and secondary
True Epithelial Cysts
• Associated with von Hippel-Lindau (VHL) and
• Adult polycystic kidney disease (ADPKD)
• Rare, usually small and multiple nonenhancing cysts
Diagnoses: Pancreas
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