Acute pancreatitis is an inflammatory condition of the pancreas that manifests through local and systemic symptoms, which can vary greatly in severity.
It is one of the most common diseases of the gastrointestinal tract and is associated with a great physical, emotional, and financial burden.
The most common causes are gallstones and alcohol consumption, which represent about 95% of the cases. Other rare etiologies include hypertriglyceridemia, anatomical abnormalities of the pancreas, trauma, and others.
In the majority of cases, Acute Pancreatitis will present as a self-limiting, mild disease, with low morbidity. But in approximately 20% of patients, the disease is severe, characterized by pancreatic parenchymal and peripancreatic tissue necrosis.
Overall, the mortality rate associated with pancreatitis is about 27%.
The Atlanta Classification and Definition of Acute Pancreatitis
The first classification of pancreatitis, the Atlanta Classification of Acute Pancreatitis was published in 1992 with the goal of standardizing the definition of pancreatitis and its severity grading. Twenty years later, the Atlanta Classification was revised, and an update in the definition and classification of Acute Pancreatitis was proposed, considering the information acquired from studies and publications in between, with the goals of improving the clinical assessment of severity, enabling standardized reporting of data, and facilitating communication between peers.
It defines Acute Pancreatitis as a condition presenting with at least 2 of 3 criteria:
- Abdominal pain, typical of AP
- Laboratory findings – amylase and lipase values 3 times higher than the normal range
- Imaging findings
It also subdivides Acute Pancreatitis into two types – Edematous vs Necrotizing – and into three grade presentations – Mild, Moderately Severe and Severe.
Necrosis in acute pancreatitis can be parenchymal, peripancreatic or both. It usually evolves over several days and can be underestimated in early CT.
Patients with necrosis have increased morbidity and mortality rates, specially in the case of infection.
The natural history of necrosis is variable, from its state (solid or liquid) to its duration (persistent or auto-limited) and infection.
It can evolve to form collections, whose name depend on the time of evolution since the onset. Collections within the first 4 weeks are termed acute necrotic collections or ANC. Over 4 weeks, the collection becomes encapsulated and is termed walled-off necrosis or WON. These collections may contain fluid and/or solid necrosis.
Infected Pancreatic Necrosis
Diagnosis of infected necrosis relies mainly on clinical changes in the patient’s course of treatment. Signs and symptoms of shock or persistence of organ failure, despite adequate management, in a patient with local complications, may indicate it.
Nevertheless, radiologic imaging exams will help confirm diagnosis.
Of these, CECT is the most common and the standard choice. It is not usually required on admission, but only when diagnosis was not made clear by the history and laboratory findings. It is ideally performed after 72h. Features like the presence of gas and perfusion changes will help in the diagnosis. CT should be repeated as necessary to evaluate the evolution of pancreatic collections.
Acute necrotic collections, whether they are infected or not, should not be the object of intervention, unless overly symptomatic. Early intervention is associated with high rates of morbidity and mortality.
After 4 weeks, when the collection is encapsulated and becomes a walled-off necrosis, infection requires intervention, usually radiologic or endoscopic drainage.
The Step-Up Approach consists of minimal invasive treatment followed by a gradually more invasive procedure, if the previous treatment fails to resolve the problem.
The goal is to treat the infected necrotic collections with as less stress as possible.
This approach proved its superiority in the PANTER trial, which randomly assigned patients to open necrosectomy and to the step-up approach. Superiority was found in morbidity, new-onset organ failure and new-onset diabetes, and was revalidated with the long-term results published this year.
The first step of the approach consists in drainage, either percutaneous or endoscopic, followed, or not, by the second step – necrosectomy.
About 35% of patients experience resolution with antibiotics and drainage, and with no need for further intervention.
The approach can be surgical or endoscopic, depending on the technique used for the necrosectomy.