Acute pancreatitis is a potentially life-threatening condition, characterized morphologically by the interstitial edematous and necrotizing forms. Due to local and systemic complications as well as accompanying organ failure, mild, moderate, and severe courses are differentiated. The classification of severity is based on the revised Atlanta classification.
The Revised Atlanta Classification 2012
Classification and definition of acute pancreatitis were based until a few years ago on the Atlanta classification from 1992 [1], which was fundamentally revised between 2007 and 2012 by 11 international pancreatic expert commissions and published in 2013 [2]. The special feature of the revised classification is the redefinition of local complications and the clear definition of severity.
According to the Atlanta classification 2012, the diagnosis of acute pancreatitis can be made if 2 of the following 3 criteria are met:
1. Abdominal pain typical of the disease (e.g., severe girdle-like upper abdominal pain, often radiating to the back)
2. Elevation of serum lipase (also amylase) > 3 times the upper normal limit
3. Characteristic imaging findings (contrast-enhanced CT, MRI, or ultrasound)
The early and late phases of the disease are distinguished:
Early phase
- First week of the disease, where the systemic response to pancreatitis is predominant.
Late phase
- Persistence of systemic reactions or presence of local complications, which can last weeks to months.
Two forms of acute pancreatitis are distinguished:
1. Interstitial edematous form
- Inflammation is limited to the pancreatic parenchyma and surrounding tissue
- No necrosis
2. Necrotizing form
- Parenchymal necrosis and/or peripancreatic necrosis
Three severity grades of acute pancreatitis are defined:
1. Mild acute pancreatitis
- No organ failure
- No local or systemic complications
2. Moderately severe acute pancreatitis
- Transient organ failure < 48 h
- Local and/or systemic complications (without organ failure)
3. Severe acute pancreatitis
- Persistent organ failure > 48 h (single or multiple organ failure)
- Not necessarily required for definition: local complications (but usually present)
Definition of complications of acute pancreatitis:
1. Local complications
- APFC, acute peripancreatic fluid collection: acute peripancreatic fluid collections in interstitial edematous pancreatitis without necrosis, within the first 4 weeks, no formation of pseudocysts
- Pancreatic pseudocysts; encapsulated fluid with an inflammatory wall without necrosis or at most minimal necrosis formation; arise after the 4th week of edematous interstitial pancreatitis
- ANC, acute necrotic collection: accumulation of fluid and necrosis without capsule in the early phase, affecting pancreatic parenchyma and/or peripancreatic tissue
- WON, walled-off necrosis: encapsulated necrosis; (peri)pancreatic necrosis with a well-defined capsule, which arises no earlier than 4 weeks after the onset of the disease
- Infected necrosis
2. Systemic complications
Exacerbation of pre-existing diseases, e.g., CAD, COPD – does not count as organ failure!
3. Organ failure
Pulmonary, cardiovascular, and renal systems are evaluated according to the modified Marshall score [3].
Fluid collections and necrosis occur within 4 weeks of the onset of acute pancreatitis, while pseudocysts and WON can only be detected > 4 weeks after the onset of pancreatitis. Additionally, up to 50% of cases of necrotizing pancreatitis may develop thrombosis in the splanchnic circulation (portal vein, mesenteric vein, splenic vein) [4].
A study published in 2016 compared the original Atlanta classification from 1992 with the revised version from 2012. The study showed that the original classification performed significantly worse than the revised form, particularly in terms of stratification for the necessity and duration of intensive care treatment as well as for the indication of surgical intervention [5].
Imaging
The onset and time interval of the different stages (early and late phase) are determined by the onset of symptoms, which is why a detailed history is important. If laboratory findings and clinical presentation match the diagnosis of acute pancreatitis, a contrast-enhanced CT is not necessarily required upon patient admission. A contrast-enhanced CT should only be performed upon admission in cases of diagnostic uncertainty (differential diagnosis, e.g., abscess, hollow organ perforation) or if there is already suspicion of local complications at this time (early phase does not mean that no local complications can occur).
CT allows risk stratification by distinguishing between edematous and necrotizing pancreatitis and should be performed no earlier than 72 - 96 hours after symptom onset, but preferably after 5 - 7 days, as the CT is most informative then. It should be noted that the extent of necrosis does not have to be proportional to the severity of the disease. MRI is a diagnostic procedure comparable to CT.
The transabdominal ultrasound examination is the standard procedure in the imaging diagnosis of acute pancreatitis and should be performed on every patient with acute pancreatitis. In addition to visualizing the pancreas itself, other differential diagnoses are usually well delineated, e.g., cholecystitis or nephrolithiasis. Cholecystitis or cholestasis can also provide clues to biliary pancreatitis.
A review compared the need for simple but meaningful scores regarding the severity of acute pancreatitis. The BISAP score (Bedside index of severity in acute pancreatitis) and the HAPS score (Harmless acute pancreatitis score) were considered helpful. However, the modified Marshall score (A definition of organ failure in acute pancreatitis), recommended in the revised version of the Atlanta classification, was not compared [6].
Therapeutic Aspects
In the treatment of acute pancreatitis, an early and late treatment phase can be distinguished in principle. In the early phase, circulatory stabilization, support of organ function, and pain therapy are the focus, while in the late phase, the treatment of infections and the sanitation of necrosis are the focus.
The same criteria that apply to other severe internal diseases are generally suitable for the indication for admission to the intensive care unit. The following scores can be helpful for the decision on intensive care management:
- SIRS = Systemic Inflammatory Response Syndrome
- APACHE II = Estimate mortality in the critically ill
- SOFA = Sequential Organ Failure Assessment
The guidelines of the American College of Gastroenterology contain various patient characteristics that indicate an increased risk for a severe course of acute pancreatitis [7]. The guidelines of the International Association of Pancreatology (IAP)/American Pancreatic Association (APA) recommend intensive care monitoring for every patient with severe acute pancreatitis according to the Atlanta classification [8].
Depending on the etiology of acute pancreatitis, causal therapy must be considered early. If acute biliary pancreatitis with cholangitis is present, an ERCP should be performed within 24 hours to sanitize the infection focus [8, 9], without cholangitis within 72 hours. A cholecystectomy should be performed during the same hospital stay, which is also safe in the context of a necrosectomy [10]. Early cholecystectomy shows no increased risks compared to late elective cholecystectomy [11]. A review from 2012 showed that delayed cholecystectomy led to a higher rate of hospital readmissions [12].
In the late phase of severe acute pancreatitis, pseudocysts or encapsulated necrotic areas may develop. Pseudocysts can compromise adjacent structures such as the duodenum as they grow, they can become infected and bleed. Therefore, if symptoms are present, endosonographic cyst puncture with nasocystic drainage is recommended [13].
Necrosis in the pancreatic and peripancreatic tissue can occur in the early phase as ANC (non-encapsulated necrosis) and in the late phase as WON (necrosis with wall structure). In about 1/3 of cases, necrosis becomes infected, which is associated with increased mortality and therefore requires intervention [14]. Infection of necrosis predominantly occurs only 2 weeks after the onset of the disease [15]. An interventional therapy of infected necrosis should be performed as late as possible, ideally > 4 weeks, when a defined wall structure is distinguishable. Early intervention is both technically more difficult and associated with an increased complication rate (e.g., bleeding, hollow organ perforation) [16]. Therefore, early intervention should only be performed in cases of increasing clinical instability or sepsis. The standard therapy for infected necrosis until the formation of a wall structure is drainage and administration of anti-infectives [16]. Retrospective analyses show that early drainage can reduce the indication for definitive necrosectomy [17].
Intervention in necrosis should generally follow a minimally invasive step-up approach: antibiotics -> drainage -> if necessary, necrosectomy [16]. In about 30% of cases, drainage alone is sufficient; with WON, solid necrotic material is usually present, so additional necrosectomy is required [18]. As an endoscopic maneuver, endosonographic puncture with transgastric or transduodenal placement of a drainage using self-expanding metal stents and subsequent endoscopic necrosectomy through the existing access is considered. The step-up procedure can be performed surgically with sonographically or CT-guided percutaneous drainage placement and subsequent minimally invasive necrosectomy (video-assisted retroperitoneal debridement = VARD).
The minimally invasive step-up procedure causes fewer complications, organ failure, and also costs compared to open necrosectomy [19, 20, 21].
A meta-analysis from 2015 showed that although antibiotic prophylaxis is not generally recommended for acute pancreatitis, mortality in patients with severe acute pancreatitis can be significantly reduced with prophylaxis [22].