Acute Pancreatitis and Complications

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 Pancreas typically enlarged and edematous with loss of normal fatty lobulation

image Peripancreatic fat stranding, edema, and free fluid
image Mild edematous pancreatitis can appear normal on CT
• Necrotizing pancreatitis (20-30% of cases): Areas of parenchymal necrosis which are either nonenhancing or severely hypoenhancing 

image Differentiate cases with ≤ 30% necrosis from > 30% necrosis for patient prognosis
image Necrosis may not be present initially, but can develop 3-4 days after symptom onset
• Complications

image Infected pancreatic necrosis: Ectopic gas, in absence of intervention, highly suggestive of infected necrosis
image Central necrosis: Necrosis of central portion of gland/duct with intact pancreas/duct in head and tail
image Pseudoaneurysm: Most common locations are splenic (50%) gastroduodenal (20%), and pancreaticoduodenal (10%) arteries, but any artery can be involved
image Venous thrombosis: Splenic vein most common, but portal veins or SMV can be involved
image Fluid collections: Nomenclature depends on age of collection and edematous vs. necrotizing pancreatitis

PATHOLOGY

• Alcohol and gallstones account for vast majority of cases
• Many other causes, including metabolic disorders, infection, trauma, drugs, anatomic variants, neoplasm, and ERCP

CLINICAL ISSUES

• Overall mortality rate: 5%, with excellent prognosis for interstitial edematous pancreatitis
• Poor prognosis with complications: Mortality of 25% with multiorgan failure or ∼ 30%  for infected necrosis
image
(Left) Axial CECT in an alcoholic patient demonstrates that although the pancreas itself does not appear appreciably enlarged, there is subtle peripancreatic fat stranding image and edema, compatible with mild edematous pancreatitis.

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(Right) Axial CECT in a patient after ERCP with placement of a stent image demonstrates enlargement of the pancreas, edema with loss of normal fatty lobulation, and peripancreatic fat stranding and fluid, compatible with acute edematous pancreatitis.
image
(Left) Axial CECT in a patient with abdominal pain demonstrates enlargement and edema of the pancreas with surrounding fluid and stranding, compatible with acute edematous pancreatitis. The entire gland enhances normally without evidence of necrosis.

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(Right) Transverse ultrasound demonstrates diffuse enlargement of the pancreas image, which appears abnormally hypoechoic, compatible with acute pancreatitis in this patient with a markedly elevated lipase level.

TERMINOLOGY

Definitions

• Acute inflammation of pancreas with variable involvement of other regional tissues or remote organs

IMAGING

General Features

• Best diagnostic clue

image Enlarged, edematous pancreas with peripancreatic fluid, fat stranding, and fluid collections
• Location

image Pancreas and surrounding peripancreatic soft tissues
• Size

image Pancreas usually increased in size (either focal or diffuse)
• Morphology

image 2 subtypes: Interstitial edematous, and necrotizing pancreatitis

CT Findings

• Revised Atlanta classification in 2012 standardized nomenclature used to describe acute pancreatitis
• 2 primary subtypes of acute pancreatitis

image Interstitial edematous pancreatitis (70-80% of cases)

– Pancreas typically enlarged and edematous with loss of normal fatty lobulation
– Peripancreatic fat stranding, edema, and free fluid (with fluid most often localized to lesser sac, anterior pararenal spaces, and paracolic gutters)
– Usually diffuse edema of entire gland, but can rarely be focal and involve just a segment of pancreas
– Normal enhancement of pancreas without necrosis
– Normal appearance of pancreas does not exclude pancreatitis: Mild pancreatitis, usually with minimally elevated lipase levels, can appear normal on imaging
image Necrotizing pancreatitis (20-30% of cases): Areas of parenchymal necrosis which are either nonenhancing or severely hypoenhancing (usually < 30 HU)

– Usually greater degree of peripancreatic fluid and inflammation than edematous pancreatitis
– Differentiate cases with ≤ 30% parenchymal necrosis from > 30% necrosis for patient prognosis
– Necrosis may not be present initially, but can develop 3-4 days after symptom onset

image Early CT can underestimate or miss necrosis
– Revised Atlanta classification system describes 3 subtypes of necrotizing pancreatitis 

image Parenchymal necrosis alone in 5%
image Parenchymal and peripancreatic necrosis in 75%
image Peripancreatic necrosis alone in 20% (exudative pancreatitis)
• Complications

image Infected pancreatic necrosis

– Implies superinfection of necrotic parenchyma and carries very poor prognosis
– Ectopic gas in pancreatic bed, in absence of intervention, virtually diagnostic of infected necrosis
– No other specific findings, although inflammation usually greater in cases with infected necrosis

image May require aspiration for culture in cases with no definitive imaging findings
image Central necrosis (disconnected duct syndrome)

– Necrosis of central portion of gland and pancreatic duct with intact upstream and downstream pancreas/duct in head and tail
– Results in fluid collection in necrotic gland with continual leakage of pancreatic juice into collection
– Diagnosis should be suggested based on distribution of necrosis
– Collection may require either internal drainage or surgery (usually distal pancreatectomy)
image Extrapancreatic fat necrosis

– Due to leakage of pancreatic enzymes into peripancreatic soft tissues resulting in fat necrosis
– Usually low density with heterogeneous fluid and solid components, but can appear nodular and mass-like, mimicking carcinomatosis
– Most often occurs surrounding pancreas, anterior mesentery, or anterior pararenal spaces
– Carries better prognosis than parenchymal necrosis but worse than edematous pancreatitis
image Pseudoaneurysm

– Small contrast-filled outpouching arising next to artery ± adjacent hematoma (due to leak or rupture)
– Most common locations are splenic (50%) gastroduodenal (20%), and pancreaticoduodenal (10%) arteries, but any artery can be involved
– Unexplained hemorrhage in pancreatic bed should prompt careful search for pseudoaneurysm
image Venous thrombosis

– May occur due to either direct intimal injury to vessel from adjacent inflammation and pancreatic enzymes or due to mass effect from adjacent collections
– Splenic vein most often involved, but portal veins or SMV can be involved as well
image Fluid collections

– Acute peripancreatic fluid collection: Fluid collection first 4 weeks after acute edematous pancreatitis

image Simple, nonloculated collection of fluid attenuation with no internal debris or hemorrhage
– Pseudocyst: Fluid collection persisting > 4 weeks after acute edematous pancreatitis

image Loculated collection with a well-defined enhancing wall of granulation tissue most often arising in lesser sac or pararenal spaces
image Can rarely be found in unusual locations distant from pancreas, such as thorax
image Simple collection of fluid attenuation with no internal debris or hemorrhage
– Acute postnecrotic fluid collection: Fluid collection first 4 weeks after acute necrotizing pancreatitis

image Nonloculated, but containing internal necrotic debris and blood products
image Acute complex fluid collection with internal debris and solid material in setting of a normally enhancing gland suggests acute postnecrotic fluid collection due to extrapancreatic necrosis
– Walled-off necrosis: Loculated fluid collection persisting > 4 weeks after necrotizing pancreatitis

image Heterogeneous collection with a well-defined wall and internal necrotic debris/blood products
– “Pancreatic abscess”: Term no longer utilized in revised Atlanta classification
image “Hemorrhagic” pancreatitis:Term not included in Atlanta classification

– Small amounts of blood frequently present in peripancreatic fluid collections and has no direct impact on disease severity

MR Findings

• Pancreas appears enlarged with increased signal on T2WI and abnormally low signal on T1WI due to edema

image Fat suppression very important in highlighting edema and fluid around pancreas on T2WI
• T1WI C+ images similar to CECT in detection of pancreatic necrosis and nonenhancement
• T2WI offers advantage (over CT) of allowing differentiation of simple fluid collections from collections with internal solid debris (i.e., walled off necrosis)
• MRCP can evaluate integrity of pancreatic duct, particularly in patients with suspected central gland necrosis

image May be able to delineate communication between a fluid collection and pancreatic duct
image Can delineate anatomic variants which might predispose to pancreatitis, including pancreatic divisum
image Very sensitive for gallstones and other biliary pathology as cause of pancreatitis
• Acute pancreatitis may be associated with restricted diffusion (lower ADC values than normal pancreas)

Ultrasonographic Findings

• Enlarged, hypoechoic pancreas with adjacent free fluid and blurring of pancreatic margins

image Pancreas may appear normal in mild cases
• Ultrasound often performed at presentation to look for gallstones

Radiographic Findings

• Radiography

image Evidence of localized ileus due to adjacent inflammation, including dilated duodenum or sentinel loop sign (mildly dilated, gas-filled segment of small bowel ± air-fluid levels)
image Colon cutoff sign: Markedly distended air-filled transverse colon with absence of gas distal to splenic flexure due to functional colonic spasm (spread of pancreatic inflammation to proximal descending colon)

Fluoroscopic Findings

• ERCP

image Dilated or normal main pancreatic duct (MPD)
image Communication of pseudocyst with MPD (acutely)
image May show narrowed and tapered distal common bile duct (CBD) with prestenotic biliary dilatation

Angiographic Findings

• Conventional

image Performed when pseudoaneurysm suspected
image Useful when pancreatitis due to vascular cause

– Vasculitis, polyarteritis nodosum, lupus
– Postaortic aneurysm resection

Imaging Recommendations

• Best imaging tool

image Dual-phase (arterial and venous) CECT best initial study
image MR with MRCP helpful problem-solving tool to assess pancreatic duct or composition of fluid collections

DIFFERENTIAL DIAGNOSIS

Infiltrating Pancreatic Carcinoma

• Heterogeneous, hypoenhancing mass with abrupt obstruction of upstream pancreatic duct and upstream pancreatic atrophy
• Pancreatic cancer may present with pancreatitis in ∼ 5% of cases
• Focal pancreatitis can appear mass-like and mimic malignancy
• Presence of dilated pancreatic duct or biliary obstruction should prompt further investigation for underlying mass
• Pancreatic cancer infiltrates dorsally into retroperitoneum, unlike pancreatitis, which infiltrates anteriorly and laterally
• Usually other signs of malignancy, including vascular encasement, metastatic disease (most often liver), etc.
• ERCP of main pancreatic duct (MPD)

image Irregular, nodular, rat-tailed, eccentric obstruction
image Prestenotic (upstream) dilatation
• Angiography: Hypovascular mass encasing vessels

Perforated Duodenal Ulcer

• Can cause fat stranding and edema in anterior pararenal space and mimic pancreatitis
• Pancreatic head may be edematous due to adjacent inflammation
• Inflammation primarily centered around duodenum, not pancreas (often more apparent on coronal reformations)
• < 50% show extraluminal gas or contrast extravasation

“Shock” Pancreas

• “Shock” complex can include infiltration of peripancreatic fat planes with pancreatic edema (similar to pancreatitis)
• Usually associated with clinical history of hypotension and other imaging stigmata of shock, such as “shock bowel”
• Quickly resolves following resuscitation

Lymphoma

• Lymphoma can rarely diffusely infiltrate and enlarge pancreas, superficially mimicking pancreatitis
• Usually associated with regional lymphadenopathy and pancreatic involvement appears mass-like
• No evidence of pancreatic or biliary ductal dilatation
• Vessels encased, but not narrowed or occluded

PATHOLOGY

General Features

• Etiology

image Alcohol (35%) and gallstones (∼ 40%) account for vast majority of cases 

– Larger gallstones more likely to cause pancreatitis as they lodge in sphincter of Oddi
– More common with long history of alcohol, although can occur after single binge drinking episode
image Many other causes, including metabolic disorders (e.g., hypertriglyceridemia, hypercalcemia), infection, trauma, drugs, anatomic variants (e.g., pancreatic divisum, annular pancreas), neoplasm (e.g., pancreatic adenocarcinoma or IPMN), iatrogenic (e.g., ERCP), etc.
image No cause identified for pancreatitis in 1/3 of cases

– Some theorize that many of these cases are attributable to tiny gallstones
image Exact pathogenesis of acute pancreatitis unclear and may vary depending on etiology

– Possibilities include reflux of pancreatic enzymes, bile, and duodenal contents into pancreatic duct, increased ductal pressure due to ampullary obstruction, or activation of intracellular/extracellular homeostatic factors
– Pancreatic enzymes activated and released into surrounding soft tissues causing inflammation and autodigestive injury to pancreas
– 2 phases of acute pancreatitis: Early and late

image Early phase over 1st week and is characterized by systemic inflammatory response syndrome (SIRS)
image Late phase (only seen in severe cases) occurs after 1st week and is characterized by local complications and persistent systemic inflammation
• Genetics

image Hereditary pancreatitis associated with several gene mutations (PRSS1, CFTR, etc.)
• Embryology/anatomy

image Congenital anomalies may cause pancreatitis
image Annular pancreas: Failure of migration of ventral bud to contact dorsal bud
image Pancreas divisum: Ventral and dorsal pancreatic buds fail to fuse; relative obstruction at minor papilla

Staging, Grading, & Classification

• Balthazar CT severity index from 1990 (10 point max)

image A: Normal pancreas (0 point)
image B: Enlarged pancreas (1 point)
image C: Peripancreatic fat stranding and edema (2 points)
image D. Single peripancreatic fluid collection (3 points)
image E: ≥  2 peripancreatic fluid collections or gas (4 points)
image Pancreatic necrosis: None (0 points), ≤ 30% (2 points), 31-50% (4 points), > 50% (6 points)
image Mild pancreatitis: 0-3 points
image Intermediate: 4-6 points
image Severe pancreatitis: 7-10 points
• Modified CT severity index from 2004 (10 point max)

image Normal pancreas (0 points)
image Pancreatic edema and inflammation (2 points)
image Pancreatic or peripancreatic fluid collection or extrapancreatic fat necrosis (4 points)
image Pancreatic necrosis: None (0 points), ≤ 30% (2 points), > 30% (4 points)
image Extrapancreatic complications (pleural effusion, ascites, vascular complication, etc.): 2 points

Gross Pathologic & Surgical Features

• Enlarged pancreas, necrosis, fluid collection, pseudocyst

Microscopic Features

• Interstitial edematous pancreatitis

image Parenchymal edema, hemorrhage, leukocytic infiltration
• Necrotizing pancreatitis

image Pancreatic or peripancreatic tissue destruction, fat necrosis, hemorrhage
• Dilated ducts and protein plugs may be seen

CLINICAL ISSUES

Presentation

• Most common signs/symptoms

image Acute epigastric pain, which often radiates to back
image Abdominal tenderness, abdominal distension, fever, nausea, vomiting

– Symptoms often improve when patient is supine
image Fever and sepsis in setting of necrotizing pancreatitis raises concern for infected necrosis
image Physical examination findings of necrotizing pancreatitis (± hemorrhage)

– Grey Turner sign: Bluish discoloration of flanks
– Cullen sign: Periumbilical discoloration
image 2 of 3 features required to make clinical diagnosis of acute pancreatitis

– Elevated amylase/lipase (3x normal limits)
– Characteristic clinical history
– Characteristic imaging findings
• Clinical profile

image Patient with history of alcoholism, fever, and severe midepigastric pain radiating to back
• Lab data

image ↑ serum amylase and lipase, with lipase more sensitive and specific than amylase
image ↑ ALT suggests biliary etiology (usually gallstones)
image Hyperglycemia, increased lactate dehydrogenase
image Leukocytosis, hypocalcemia (poor prognostic sign)
image Fall in hematocrit, rise in blood urea nitrogen (BUN)

Demographics

• Age

image Can be seen in any age group and varies depending on etiology, but most common in young and middle aged
• Gender

image M > F (more commonly due to alcohol in males, gallstones in females)
• Epidemiology

image Incidence in USA: 0.005-0.01% of general population
image 300,000 per year admitted for acute pancreatitis in USA
image USA: Alcoholic pancreatitis more common in urban and VA hospitals; gallstone pancreatitis more common in suburban and rural settings

Natural History & Prognosis

• Prognosis

image Overall mortality rate of 1-3%, with excellent prognosis for interstitial edematous pancreatitis
image Poor prognosis in setting of complications: Mortality rate: 25% with multiorgan failure or ∼ 30%  for infected necrosis (even with surgical debridement)
image Mortality in early stage of illness due to multiorgan failure, while later mortality mostly due to infection
• Natural evolution of fluid collections

image Acute peripancreatic fluid collections: Develop in first 48 hours and ∼ 50% spontaneously resolve within 2-4 weeks
image Pseudocysts occur in 10-20% of cases and communicate with pancreatic duct in up to 60% of cases

– 50% of pseudocysts are asymptomatic and resolve spontaneously over time
– Only 25% of pseudocysts are symptomatic due to infection, mass effect, pain, gastric outlet obstruction, etc.
• Other Complications

image Pancreas: Fluid collections, pseudocyst, necrosis, abscess
image GI: Hemorrhage, infarction, obstruction, ileus
image Biliary: Obstructive jaundice
image Vascular: Pseudoaneurysm, portosplenic vein thrombosis, hemorrhage
image Disseminated intravascular coagulation (DIC)
image Shock due to pulmonary and renal failure
image Cardiac, central nervous system, and metabolic complications

Treatment

• Initial treatment is conservative, including fluid resuscitation, pain control, n.p.o. (nothing by mouth) with nutritional support until patient can resume oral diet, and antibiotics (only if infection is suspected)

image Early ERCP and sphincterotomy in patients with suspected gallstone pancreatitis only in setting of cholangitis or cholestasis
image Most patients with interstitial edematous pancreatitis will resolve with conservative measures alone
image Severe pancreatitis with necrosis may require intensive care due to high risk of multiorgan failure
• Infected pancreatic necrosis may require surgical debridement (necrosectomy), although surgery typically deferred until 4 weeks after presentation to allow collections to become walled off

image Image-guided fine-needle aspiration may be utilized to distinguish sterile necrosis from infected necrosis if infection suspected and no response to antibiotics
• Asymptomatic fluid collections do not warrant intervention (either drainage, aspiration, or surgery)

image Symptomatic fluid collections (due to mass effect, infection, pain, etc.) may be drained, with walled-off necrosis requiring large-bore catheter or necrosectomy (due to debris and solid components), while simpler fluid collections can be drained with standard catheters
• Angiographic embolization for pseudoaneurysms and anticoagulation for venous thrombosis involving portal vein or SMV

DIAGNOSTIC CHECKLIST

Consider

• Differentiate pancreatitis from other causes of inflammation centered in adjacent structures, such as a perforated duodenal ulcer
• Pancreatic duct obstruction or infiltration posteriorly into retroperitoneum should suggest presence of an underlying mass, rather than routine acute pancreatitis

Image Interpretation Pearls

• Enlarged pancreas with obliteration of peripancreatic fat planes, fluid collections, pseudocyst, &/or abscess formation

Reporting Tips

• Report evidence of renal or respiratory failure

image Another poor prognostic factor in patients with severe acute pancreatitis
image
(Left) Transverse US demonstrates mild diffuse enlargement of the pancreas. The pancreatic duct is normal in size image. The main sign of acute pancreatitis is fluid anterior to the pancreas image as well as fluid anterior to the splenic vein image.

image
(Right) Longitudinal US of the body of the pancreas demonstrates peripancreatic fluid image tracking caudally down the superior mesenteric vein image. There is also fluid noted anterior to the body of the pancreas image, a strong clue to the diagnosis of acute pancreatitis.
image
(Left) Axial T2-weighted MR demonstrates mild diffuse enlargement of the pancreas with linear bands of high signal representing intraparenchymal edema image.

image
(Right) Axial T2-weighted MR at a more cranial level in the same patient shows marked heterogeneity of the pancreas with areas of parenchymal edema image and peripancreatic fluid image consistent with edematous pancreatitis. Fat-suppressed T2WI is the most critical pulse sequence for highlighting changes of acute pancreatitis on MR.
image
(Left) (Left) Supine radiograph shows a dilated transverse colon image with abrupt “cut-off” and narrowing image of the colon at the splenic flexure.

image
(Right) Axial CECT in the same patient shows thickening of the descending colon image as a result of the adjacent pancreatic inflammation, causing the colon cut-off sign. Note the posterior interfascial extension of fluid image with preserved fat in the posterior pararenal space image.
image
(Left) Axial CECT at presentation in a patient with abdominal pain demonstrates findings of acute edematous pancreatitis, with enlargement of the pancreas and significant peripancreatic free fluid.

image
(Right) Axial CECT acquired 3 days later due to the patient’s clinical deterioration demonstrates that the patient now has findings of acute necrotizing pancreatitis, with only a small portion of the pancreatic body image still enhancing. Early CT (< 72 hours) can miss or underestimate pancreatic necrosis.
image
(Left) Axial T2 FS MR demonstrates replacement of the normal pancreas with high T2 fluid signal image due to necrotizing pancreatitis. The more hypointense T2 signal image in the pancreatic bed represents a combination of residual viable pancreatic tissue and necrotic debris.

image
(Right) Axial T1WI C+ MR in the same patient better demonstrates that the patient has severe necrotizing pancreatitis, with only a small portion of the body image still enhancing.
image
(Left) Coronal MRCP in the same patient demonstrates that despite this extensive necrosis, the pancreatic duct image still appears intact, a valuable piece of information for the gastroenterologist. Evaluation of the pancreatic duct is a significant advantage of MR compared to CT.

image
(Right) Axial CECT in a patient with abdominal pain demonstrates that only a small portion of the pancreatic tail image is still normally enhancing, with nonenhancement of the remainder of the pancreas, compatible with necrotizing pancreatitis.
image
(Left) Axial CECT shows extensive pancreatic necrosis with complete lack of enhancement of the body and head of the pancreas image. Note the marked peripancreatic inflammation image and thrombus in the portal vein image.

image
(Right) Axial CECT at a lower plane of section in the same patient shows focal necrosis in the head of the pancreas image. Note the thrombus extending into the superior mesenteric vein image and marked inflammation of the mesentery image. The patient soon expired from multiorgan failure.
image
(Left) Axial CECT in a patient with necrotizing pancreatitis shows an acute postnecrotic fluid collection centered in the pancreatic bed with little remaining enhancing pancreas. The ectopic gas image in the pancreatic bed is virtually diagnostic of infected necrosis, and the patient ultimately underwent necrosectomy.

image
(Right) Axial CECT demonstrates the characteristic findings of infected pancreatic necrosis, with nonenhancement of the entire pancreas and multiple foci of ectopic gas image in the pancreatic bed.
image
(Left) Axial NECT at presentation shows findings of acute interstitial pancreatitis, with infiltration of the peripancreatic fat planes and enlargement of the pancreas.

image
(Right) Axial NECT after 9 days of IV fluid supplementation and bed rest shows the development of gas bubbles image throughout the pancreatic parenchyma. At surgery, extensive infected necrosis of the pancreas was found and a necrosectomy was performed.
image
(Left) Axial NECT in a critically ill patient demonstrates necrosis of the entire pancreas and replacement by necrotic debris and gas bubbles image compatible with infected necrosis. The patient in this case died as a result of his illness.

image
(Right) Axial CECT image demonstrates a high-attenuation pseudoaneurysm image with surrounding hemorrhage image in a patient who suffered a life-threatening bleed from a ruptured pseudoaneurysm of the splenic artery resulting from pancreatitis.
image
(Left) Axial CECT demonstrates a large enhancing pseudoaneurysm image arising within a hemorrhagic pseudocyst in a patient with acute pancreatitis.

image
(Right) Axial CECT demonstrates a large well-defined, loculated fluid collection image several months after a bout of acute edematous pancreatitis. Notice that the collection is simple in appearance without debris or hemorrhage, compatible with a pseudocyst. The large size and mass effect of this pseudocyst necessitated drainage.
image
(Left) Axial CECT performed several months after a bout of pancreatitis demonstrates a large, relatively simple-appearing loculated collection image, with a well-defined wall, occupying the pancreatic bed.

image
(Right) Axial T2 MR in the same patient demonstrates that the collection is actually not simple, but contains significant internal solid debris image, suggesting this represents walled-off necrosis rather than a pseudocyst. Walled-off necrosis, unlike a pseudocyst, often requires either a large bore catheter for drainage, or necrosectomy.
image
(Left) Coronal volume-rendered CECT in a patient several weeks after a bout of necrotizing pancreatitis demonstrates a thick-walled fluid collection image replacing a portion of the pancreatic head, compatible with walled-off necrosis.

image
(Right) Axial T2 MR demonstrates a large chronic post pancreatitis fluid collection. The debris image within the collection suggests that this is walled-off necrosis, not a pseudocyst. Distinguishing these 2 entities is a major advantage of MR compared to CT.
image
(Left) Axial CECT demonstrates a loculated fluid collection image in the lesser sac with a well-defined wall and simple internal contents after a bout of pancreatitis, in keeping with a pseudocyst. An internal drain image has been placed due to this pseudocyst’s mass effect on the stomach.

image
(Right) Axial CECT shows walled-off necrosis image in the body of the pancreas with absence of normally enhancing pancreatic parenchyma in this location. The location of necrosis in this case raises concern for “disconnected duct” syndrome.
image
(Left) Axial T2-weighted MR demonstrates complex fluid image that contains internal debris image representing fat necrosis and hemorrhage. Note the extension of the fluid into the interfascial retroperitoneal space between the perirenal and anterior pararenal spaces and into the muscles of the flank.

image
(Right) Coronal MRCP in the same patient shows multiple distal common duct stones image as the cause of the patient’s acute pancreatitis. Emergent ERCP was performed to remove the common duct stones.
image
(Left) Axial CECT shows heterogeneous enlargement and diminished enhancement of the pancreas image, consistent with severe acute necrotizing pancreatitis.

image
(Right) Axial CECT in the same patient 4 weeks later shows the development of walled-off necrosis image with a well defined, peripherally enhancing wall. Note the multiple nondependent gas bubbles image, indicating infection.
image
(Left) Axial CECT in a patient with abdominal pain and elevated lipase shows multiple low-density hepatic lesions image, consistent with metastases. Note also the lesser sac fluid collection image from acute pancreatitis.

image
(Right) Axial CECT at more caudal level in the same patient shows upstream dilatation of the main pancreatic duct image. Note that the pancreatic duct is obstructed by an isodense mass image. Endoscopic ultrasound biopsy of the mass revealed adenocarcinoma, which presented as pancreatitis.
image
(Left) Axial CECT demonstrates enlargement of the pancreas with peripancreatic edema and stranding compatible with acute pancreatitis. Note, however, the dilated pancreatic duct image, an unusual feature for acute pancreatitis.

image
(Right) Coronal CECT in the same patient demonstrates a hypodense pancreatic adenocarcinoma image obstructing the pancreatic duct image. The presence of a dilated pancreatic duct in acute pancreatitis should always prompt search for an underlying mass.
image
Axial CECT of necrotizing pancreatitis following ERCP shows extensive areas of nonenhancement, indicating necrosis image of the body and tail of the pancreas.

image
Axial CECT at the level of the splenic vein in the same patient shows an acute fluid collection in the anterior pararenal space image with only a small area of a residual, normally enhancing pancreas image.
image
Axial CECT of necrotizing and hemorrhagic pancreatitis complicated by infection shows extensive pancreatic necrosis with an air-fluid level image, indicating a gas-forming infection.
image
Axial CECT at a more caudal level in the same patient reveals high-attenuation fluid (hematoma) image extending into the left anterior pararenal space.
image
Axial CECT shows extensive infiltration of the peripancreatic fat planes. The celiac axis and portal vein image are surrounded, the splenic vein image is occluded, and the gastric wall is thickened.
image
Axial CECT shows extensive peripancreatic infiltration into the perirenal fascia image and ventrally into the mesentery image.
image
Axial CECT shows mild acute pancreatitis. The gland is diffusely enlarged with minimal peripancreatic infiltration image.
image
Axial CECT shows mild acute pancreatitis. Note the enlarged pancreatic head with infiltration of the mesenteric fat image.
image
Axial CECT shows necrotizing pancreatitis. Almost no enhancing viable pancreatic tissue is present, and only fluid and necrotic tissue is seen.
image
Axial CECT shows infected pancreatic necrosis. Note that there is no enhancing parenchyma. The necrotic tissue contains gas bubbles image, which indicate infection.
image
Axial CECT shows central pancreatic necrosis. There is no enhancing viable tissue in the pancreatic tail. The pancreatic body is necrotic, and walled-off necrosis has formed image.
image
Axial CECT shows a viable enhancing pancreatic head and pseudocyst image after pancreatitis.

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