Revised Atlanta Classification - Acute Pancreatitis
Summarized by: Niharika Shahi, M.D.
Reviewed by: Prasaanthan Gopee-Ramanan, M.D.
Original publication details
Authors: Ruedi F. Thoeni
Reference: Thoeni, R. (2012). The Revised Atlanta Classification of Acute Pancreatitis: Its Importance for the Radiologist and Its Effect on Treatment. Radiology, 262(3), 751-764.
Acute pancreatitis (with or without chronic pancreatitis) is clinically defined by A & B +/- C:
A
Abdominal pain suggestive of pancreatitis (typically epigastric pain radiating to back)
&
B
Serum amylase and lipase levels ≥ 3x normal (imaging is to be used if elevated values are < 3x normal)
+/-
C
Characteristic findings on CT, MRI, or transabdominal ultrasound
Early phase
Within 1st week of onset
Progression from early inflammation → variable degrees of peripancreatic edema and ischemia → resolution or permanent necrosis and liquefaction
Late phase
After 1st week of onset; may extend for weeks to months
Characterized by increasing necrosis, infection, and/or persistent multi-organ failure
Role of contrast-enhanced CT in pancreatitis
(ideally > 72 hours after symptom onset to assess complications related to pancreatitis)
CT should be repeated when the clinical picture drastically changes (e.g. sudden onset of fever, decrease in hematocrit, or sepsis)
CT to guide catheter placement for drainage and assess success of treatment in patients who have undergone percutaneous drainage or other interventions
If first episode of pancreatitis in patients > 40 years of age and no identifiable cause for pancreatitis, contrast-enhanced CT should be used to exclude a possible neoplasm
Report considerations
Pancreas or surrounding fat necrosis?
Parenchymal or surrounding collections?
Gallstones?
Biliary dilatation?
Venous (or arterial) thrombosis?
Aneurysms?
Ascites?
GI tract inflammation?
MRI and US reserved for special indications
MRI → detect choledocholithiasis not visualized on contrast-enhanced CT images and to further characterize collections for the presence of non-liquefied material (solid and semisolid components, usually pancreatic and extra-pancreatic debris and necrotic fatty tissue)
Patients with contraindication to contrast-enhanced CT (e.g. allergy to iodinated intravenous contrast agents or pregnancy)
US used to assess presence of stones in gallbladder [higher sensitivity than CT]
*less accurate than contrast-enhanced CT or MR imaging for visualizing distal common bile duct stones and has the disadvantage of being operator dependent
CT features of different types of pancreatitis
Interstitial edematous pancreatitis (IEP)
Localized or diffuse enlargement of the pancreas, with normal homogeneous enhancement or slightly heterogeneous enhancement of pancreatic parenchyma related to edema
Peripancreatic and retroperitoneal tissue may appear normal or with mild inflammatory changes (“mistiness”) with varying amounts of peripancreatic fluid
Contrast-enhanced CT performed 5–7 days after acute onset to definitively characterize as either IEP or ill-defined necrosis
Necrotizing Pancreatitis
Three forms of acute necrotizing pancreatitis, depending on location; all three types can be sterile or infected
Pancreatic parenchymal necrosis alone — < 5% of patients; appears on contrast-enhanced CT as lack of parenchymal enhancement
Peripancreatic necrosis alone — ~ 20% of patients; heterogeneous areas of non-enhancement containing non-liquefied components, commonly located in the retroperitoneum and lesser sac
Pancreatic parenchymal necrosis with peripancreatic necrosis — most common type, seen in 75%–80% of patients with acute necrotizing pancreatitis; may involve main pancreatic duct
Pancreatic and Peripancreatic Collections
Acute peripancreatic fluid collection (APFC)
Absence of necrosis; IEP can be associated with APFC and, over time, with pancreatic pseudocysts
Without non-liquefied components arising in patients with IEP
Caused by pancreatic and peripancreatic inflammation or by rupture of one or more small peripheral pancreatic side duct branches
Conform to the anatomic boundaries of retroperitoneum (especially the anterior pararenal fascia), are usually seen immediately next to the pancreas, and have no discernable wall
Most are reabsorbed spontaneously within few weeks and do not become infected drainage or aspiration of fluid could introduce infection
Pseudocyst
Within 4 weeks from onset of acute IEP, an APFC may gradually transition into a pseudocyst (complication of acute pancreatitis in approximately 10%–20% of cases)
Well-circumscribed, usually round or oval peripancreatic fluid collections of homogeneously low attenuation surrounded by well-defined enhancing wall (capsule consisting of fibrous or granulation tissue)
Infected pseudocyst is diagnosed on CT images by the presence of gas within the pseudocyst or, in absence of gas, by means of fine-needle aspiration (FNA) with Gram staining and culture for bacteria or fungal organisms
A pseudocyst can be treated effectively by draining the fluid in most cases
Acute necrotic collection (ANC)
Presence of necrosis; necrotizing pancreatitis (all three forms) can be associated with ANC and, over time, with walled-off necrosis
All of these collections can be sterile or infected.
Contains both fluid and necrotic material of various amounts (some of which are loculated)
Walled off necrosis (WON)
Over time (usually at or after 4 weeks), the ANC matures and develops a thickened non-epithelialized wall between the necrosis and the adjacent tissue
In contradistinction to a pseudocyst, WON contains necrotic pancreatic parenchyma or necrotic fat
Most non-liquefied components need to be removed by means of a percutaneous image-guided approach, a laparoscopic or endoscopic procedure, or surgery
Complications
All four types of pancreatic fluid collections can be sterile or infected
Collections that contain non-liquefied material are more likely to become infected
Treatments
IEP
Usually self-limited, supportive measures alone suffice
Most APFCs resolve spontaneously or mature into pseudocysts, majority of pseudocysts disappear spontaneously over time and do not require any treatment
Necrotizing Pancreatitis
Necrotizing pancreatitis requires close monitoring, and minimally invasive radiologic procedures or laparoscopic, endoscopic, or surgical techniques are often needed to improve outcome
Sterile Pancreatic Necrosis
CT is performed every 7–10 days to look at evolution of pancreatic necrosis and assess evidence of infection (air bubbles) and complications such as increased peripancreatic necrotic collections or hemorrhage
Patients who have clinical instability (e.g. tachycardia, leukocytosis, fever, organ failure), and do not show radiologic evidence of infection, may benefit from FNA of the necrosis to rule out infected necrosis
Follow-up CT is used to ensure adequate drainage has been achieved, and additional larger catheters may have to be placed in cases of residual necrotic fluid
Infected Pancreatic Necrosis
Generally treated with surgical debridement and antibiotics
Citation
Thoeni, R. (2012). The Revised Atlanta Classification of Acute Pancreatitis: Its Importance for the Radiologist and Its Effect on Treatment. Radiology, 262(3), 751-764.