Diagnostic Ultrasound - Abdomen and Pelvis

Acute Pancreatitis
TERMINOLOGY
Abbreviations
• Interstitial edematous pancreatitis (IEP), necrotizing
pancreatitis (NP)
• Acute pancreatic fluid collection (APFC), ±infection
• Acute necrotic collection (ANC), ± infection
Definitions
• Acute inflammatory process of pancreas with variable
involvement of local tissues and remote organ systems
IMAGING
General Features
• Best diagnostic clue
○ Enlarged pancreas with peripancreatic fluid, edema, and
obliteration of fat planes
• Size
○ Focal or diffuse enlargement
Ultrasonographic Findings
• Grayscale ultrasound
○ In mild pancreatitis, US signs may be subtle or absent
○ Enlarged, hypoechoic pancreas: Interstitial edema
○ Blurred pancreatic margin: Pancreatic edema and
peripancreatic exudate
○ Heterogeneous echotexture: Intrapancreatic necrosis or
hemorrhage
○ Pancreatic abscess or infected collections: Difficult to
confirm with US; thick walled, mostly anechoic with
internal echoes and debris
○ Gallstones or biliary intraductal calculi
• Color Doppler
○ Helpful to detect pseudoaneurysm formation and
portosplenic venous thrombosis
CT Findings
• Focal or diffuse enlargement of pancreas with ill-defined
margins, infiltration of peripancreatic fat
• Homogeneous or mildly heterogeneous enhancement
(IEP); focal or diffuse nonenhancement (necrosis)
• Complications
○ Peripancreatic collections (APFC and ANC) do not have
defined wall < 4 weeks after onset
○ Late collections have defined wall with enhancement:
Pseudocyst following APFC; WON (walled-off necrosis)
following ANC
○ Pseudoaneurysm: Cystic vascular lesion, enhances like
adjacent blood vessels
○ Portal/splenic venous thrombosis: Nonenhancement of
thrombosed vein
○ Infection: Presence of gas, unless secondary to fistula to
colon or interventional procedure
MR Findings
• T2WI FS
○ Collections, necrotic areas: Hyperintense
○ Peripancreatic edema, infiltrating fluid: Hyperintense
• T1WI C+
○ Enhancement: Homogeneous or mildly heterogeneous
(IEP) vs. focal or diffuse nonenhancement (necrosis)
○ Vascular occlusions: Filling defects or nonenhancement
of vessel
• MRCP
○ Dilated or normal main pancreatic duct (MPD)
○ Gallstones, choledocholithiasis: Filling defects in
gallbladder or common bile duct
Imaging Recommendations
• Best imaging tool
○ CECT
• Protocol advice
○ US best to evaluate for cholelithiasis in acute pancreatitis
of unknown etiology
○ CECT best in late phase to delineate extent of
inflammation, detect necrosis and complications
○ MR best to detect choledocholithiasis (MRCP) or in
patients unable to undergo CECT
DIFFERENTIAL DIAGNOSIS
Infiltrating Pancreatic Carcinoma
• Irregular, heterogeneous, hypoechoic mass
• Abrupt obstruction & dilatation of pancreatic duct
• Regional nodal metastases: Splenic hilum & porta hepatis
• Contiguous organ invasion: Duodenum, stomach, liver,
mesentery
Lymphoma & Metastases
• Nodular, bulky, enlarged pancreas due to infiltration
• Retroperitoneal adenopathy
• Peripancreatic infiltration (obliteration of fat planes)
Autoimmune Pancreatitis
• Focal or diffuse enlargement
• Narrowed pancreatic duct
• Lack of calcifications or fluid collections
Perforated Duodenal Ulcer
• Penetrating ulcers may infiltrate anterior pararenal space,
simulating pancreatitis
• < 50% of cases have evidence of extraluminal gas or
contrast medium collections
• Pancreatic head may be involved
"Shock" Pancreas
• Infiltration of peripancreatic & mesenteric fat planes
following hypotensive episode (e.g., blunt trauma)
• Pancreas itself looks normal or diffusely enlarged
PATHOLOGY
General Features
• Etiology
○ Alcohol/gallstones/metabolic/infection/trauma/drugs/E
RCP
○ Pathogenesis: Due to reflux of pancreatic enzymes, bile,
duodenal contents, and increased ductal pressure
– MPD or terminal duct blockage
– Edema, spasm; incompetence of sphincter of Oddi
• Genetics
○ Hereditary pancreatitis: Autosomal dominant,
incomplete penetrance
• Associated abnormalities
Diagnoses: Pancreas
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