What Is the Difference Between a Pancreatic Pseudocyst and Walled-Off Necrosis?

How are these collections classified?

Under the revised Atlanta classification, collections that follow pancreatitis are named by both content and duration. In the first four weeks, an acute peripancreatic fluid collection occurs without necrosis, while an acute necrotic collection occurs when necrosis is present. After four weeks, once a wall has formed around the collection, it is called a pseudocyst if there is no necrosis, or walled-off necrosis if necrotic tissue is present.

Why does content matter?

• Pseudocyst: mostly fluid; generally responds well to drainage with a thin catheter
• Walled-off necrosis: fluid together with solid necrotic tissue; catheter drainage alone can be inadequate due to clogging
• WON often requires wide-caliber endoscopic drainage and, when needed, staged removal of necrotic tissue

Telling them apart on imaging

On CT, both can appear as well-defined collections and may look similar to each other. MRI is generally more sensitive for showing solid components within the collection, and endoscopic ultrasound provides detailed information as well, particularly when drainage is being planned. This is why, whenever a report mentions a 'cyst,' the content should always be properly assessed.

Not to be confused with pancreatic cysts or IPMN

Pseudocysts and walled-off necrosis are the result of a prior episode of pancreatitis. IPMN and other cystic tumors, by contrast, arise from the pancreatic tissue itself and require a different kind of follow-up and risk assessment. In a patient with no history of pancreatitis who is found to have a cystic lesion, the priority is making this distinction correctly — otherwise the follow-up plan may be set up incorrectly.

When is intervention needed?

A collection causing no symptoms is not drained simply because it is large. Size alone is not a criterion for intervention; many collections shrink or resolve on their own over time.

• Inability to eat due to pressure on the stomach or intestine, persistent nausea or vomiting
• Pressure on the bile duct causing jaundice
• Signs of infection: fever, rising inflammatory markers, worsening overall condition
• Persistent pain and weight loss
• Rare complications such as bleeding

Options for intervention

In suitable cases, internal drainage can be performed by placing a stent from the stomach or duodenum wall into the collection under endoscopic ultrasound guidance. Percutaneous catheter drainage is preferred especially where endoscopic access is not suitable given the location. In walled-off necrosis, staged removal of necrotic tissue using endoscopic or minimally invasive methods may be needed; surgery is reserved for selected cases.

The method chosen depends on the location and content of the collection, the patient's overall condition, and the center's experience.

How is follow-up planned?

For patients who do not need intervention, periodic imaging and clinical review are carried out. Maintaining nutrition, tracking weight, and monitoring the course of pain are all part of the plan. New fever, vomiting, or jaundice should prompt a visit without waiting for the scheduled follow-up.