Complications of Acute Pancreatitis, Pseudocyst and Necrosis
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Direct answer
Pancreatic pseudocyst and necrosis are local complications of acute pancreatitis, classified under the revised Atlanta system by their content and timing. A pseudocyst is a fluid collection with a fibrous wall and no epithelial lining that forms after four weeks, while necrosis involves non-viable pancreatic tissue that can become infected. Infected necrosis is managed step-up style, with antibiotics for proven infection and drainage delayed until the wall matures.
What you must remember
- Acute peripancreatic fluid collection: an early, non-encapsulated, non-necrotic collection that often resolves without any intervention.
- Acute necrotic collection: a collection containing solid and fluid necrotic material within four weeks of onset, which may resolve or organise.
- Pseudocyst: an encapsulated fluid collection without necrosis, forming after four weeks, with a wall of granulation or fibrous tissue rather than epithelium.
- Walled-off necrosis: an encapsulated collection that contains necrotic debris, drained only when infected or symptomatic.
- Infected necrosis: suspected from fever, rising inflammatory markers and gas bubbles within a collection on CT, and confirmed by culture of fluid.
- Drainage indications for pseudocyst: symptoms, infection, rupture or bleeding; older textbooks add size above about 6 cm or persistence beyond six weeks, but an asymptomatic pseudocyst needs no drainage.
- Haemorrhage: pseudoaneurysm bleeding is a dangerous late complication, treated by CT angiography and angioembolisation.
- Other complications: pancreatic ascites, splenic vein thrombosis, left pleural effusion and ARDS can complicate the course.
A step-up approach to collections and necrosis
Contrast CT is best timed after the first few days, because it underestimates necrosis early, and drainage is delayed until the collection has matured, as early drainage often causes harm. The intervention then escalates only as far as the patient's condition requires.
- Classify the collection: Use CT features and timing, with repeat imaging at about four weeks, to decide whether the collection is an acute collection, a pseudocyst or walled-off necrosis, since the wall defines the next step.
- Look for infection: Gas within a collection, fever or sepsis, and rising markers point to infected necrosis, and fluid culture confirms it.
- Give antibiotics only when infected: Carbapenems are preferred, or a quinolone with metronidazole, and prophylaxis is not given for sterile necrosis.
- Drain minimally first: Endoscopic transmural or percutaneous drainage is the first intervention for infected or symptomatic collections with a mature wall.
- Escalate if needed: Necrosectomy is reserved for patients who do not improve after drainage, with minimally invasive approaches favoured over open surgery.
- Manage haemorrhage and leaks: CT angiography and angioembolisation treat pseudoaneurysm bleeding, while a persistent leak may need a stent or surgery.
Where the exam tries to catch you
The exam tests whether you time interventions correctly and avoid treating sterile collections as infected.
- Trap: draining every peripancreatic collection on day three Correct: acute collections often resolve, and early drainage is reserved for infected or symptomatic collections.
- Trap: calling a fluid collection a pseudocyst before four weeks Correct: before four weeks it lacks a mature wall and is an acute peripancreatic fluid collection.
- Trap: giving prophylactic antibiotics for sterile necrosis Correct: antibiotics are for proven or strongly suspected infection only.
- Trap: ignoring a sudden fall in haemoglobin in a patient with a known pseudocyst Correct: pseudoaneurysm rupture needs urgent CT angiography and embolisation.
Frequently asked questions
What is the difference between a pseudocyst and walled-off necrosis?
A pseudocyst is an encapsulated collection of fluid without significant necrosis, whereas walled-off necrosis contains necrotic debris within its wall. Both form after about four weeks, so cross-sectional imaging is needed to distinguish solid debris from fluid.
When should a pancreatic pseudocyst be drained?
Pancreatic pseudocysts are drained when they are symptomatic, infected, rupturing or bleeding. Older textbooks add size above about 6 cm or persistence beyond six weeks, though an asymptomatic pseudocyst needs no drainage. Endoscopic transmural drainage is often the first choice when the wall is mature.
How is infected pancreatic necrosis treated?
Infected pancreatic necrosis is treated with targeted antibiotics, such as a carbapenem, and a step-up approach of drainage first. Necrosectomy is reserved for patients who do not improve after drainage.
Why is sudden bleeding in a pseudocyst a concern?
Sudden bleeding in a patient with a pseudocyst suggests a pseudoaneurysm of a peripancreatic artery, which can be life-threatening. CT angiography to localise it and angioembolisation to stop it are the standard treatments.