Pancreatic necrosis, collections and pseudocyst

01OverviewDefinition, clinical context and the essential points that orientate the chapter.

Collection names combine content and time. During the first four weeks, interstitial oedematous pancreatitis can produce a homogeneous acute peripancreatic fluid collection without a definable wall; necrotising pancreatitis can produce a heterogeneous acute necrotic collection containing liquid and devitalised tissue. After roughly four weeks, a mature wall may form. A homogeneous fluid collection without necrosis becomes a pseudocyst, whereas an encapsulated collection with necrotic material is walled-off necrosis. Calendar age helps but imaging content and capsule maturity decide treatment.

Many collections resolve without intervention. Size by itself is not infection, pressure or cancer. A mature asymptomatic pseudocyst may be observed when follow-up is reliable; a large collection causing early satiety, vomiting, pain, biliary compression, fistula or vascular complication needs specialist action. Sterile necrosis may look alarming and generate systemic inflammation without bacteria. Conversely, infected necrosis can lack intralesional gas. Deterioration should prompt cultures and imaging, while avoiding reflex fine-needle aspiration when the MDT can make a clinical diagnosis and drainage will obtain material.

Treatment follows anatomy and physiology. When infected necrosis can be reached through stomach or duodenum, endoscopic ultrasound-guided drainage may provide source control; percutaneous access is valuable for lateral or pelvic extension and unstable patients. Direct endoscopic necrosectomy, minimally invasive surgery or open surgery is added only when drainage and antibiotics are insufficient or complications demand it. Delay until encapsulation is generally safer if the patient can be stabilised. Pseudoaneurysm embolisation, perforation surgery and compartment decompression remain emergency exceptions.

Key points

Use revised Atlanta terminology: acute peripancreatic fluid collection and pseudocyst contain fluid without necrotic debris; acute necrotic collection and walled-off necrosis contain variable solid necrosis.
Collections younger than about four weeks usually lack a mature capsule; after maturation, a pseudocyst follows interstitial disease and walled-off necrosis follows necrotising pancreatitis.
Do not call every post-pancreatitis collection a pseudocyst, because solid debris changes drainage technique, stent choice, infection risk and the possible need for necrosectomy.
Stable sterile necrosis does not require prophylactic antimicrobials or automatic intervention; management includes nutrition, analgesia, organ support and purposeful follow-up imaging.
Suspect infected necrosis with gas in the collection, positive culture, new sepsis or deterioration after initial improvement, while also searching for line, lung, urine and biliary sources.
NICE recommends an endoscopic approach for infected or suspected infected necrosis when anatomically possible; drainage-first step-up care and delayed debridement need an expert pancreatic MDT.
Pseudocyst intervention depends on symptoms and complications such as infection, gastric or biliary obstruction, bleeding, rupture or troublesome enlargement, not on diameter alone.
Sudden pain, haemodynamic collapse or falling haemoglobin can indicate pseudoaneurysm bleeding into a collection; activate major-haemorrhage care and urgent CT angiography or interventional radiology.

02AetiologyUnderlying causes, associations and risk factors, with why each one matters.

Necrotising acute pancreatitis

Severe pancreatic inflammation can destroy pancreatic and peripancreatic tissue, generating acute necrotic collections that later become walled off.

Duct disruption and fluid leakage

Interstitial pancreatitis, trauma, surgery or duct disruption releases enzyme-rich fluid, forming acute peripancreatic collections or a mature pseudocyst.

Secondary infection

Gut organisms may seed devitalised tissue during the disease course, converting sterile necrosis into infected necrosis and systemic sepsis.

03PathophysiologyThe causal sequence from the underlying abnormality to symptoms and harm.

1
Enzymatic and vascular tissue death
Activated enzymes, inflammation and microvascular failure cause fat necrosis and non-viable pancreatic or surrounding tissue during severe pancreatitis.
2
Collection organisation
Fluid and debris initially lack a mature wall, then gradually develop a capsule as pseudocyst or walled-off necrosis depending on contents.
3
Infection or mass effect
Bacterial invasion or enlargement produces sepsis, pain, gastric or biliary compression, fistulation and vascular erosion after collection maturation.

04Clinical features and red flagsSymptoms, examination findings, patterns of presentation and time-critical warnings.

Uncomplicated maturing collection

A clinically improving patient with a well-defined or resolving collection, stable haemoglobin and no infection or obstruction often needs observation rather than drainage.

Infected necrosisRed flag

New fever, rising support, bacteraemia, gas within necrotic material or decline after initial recovery raises infection and needs urgent pancreatic-MDT management.

Gastric or biliary compression

Early satiety, persistent vomiting, inability to feed, recurrent jaundice or worsening cholestasis may result from a mature collection compressing stomach, duodenum or duct.

Pseudoaneurysm haemorrhageRed flag

Abrupt severe pain, gastrointestinal bleeding, bruising, hypotension or an otherwise unexplained haemoglobin drop is a vascular emergency until excluded.

Disconnected duct syndrome

Persistent high-output external fistula, recurrent fluid after apparently successful drainage or viable upstream pancreas separated by necrosis suggests duct disruption needing specialist planning.

05InvestigationsWhat to request, why it matters and how to interpret it.

Investigation order

Read from the initial assessment onwards. Tests may run in parallel in urgent care; first-line, preferred, confirmatory, definitive and gold-standard labels appear only when the chapter explicitly states them.

01
Pancreatic-protocol contrast CTFirst step
Why
Define necrosis, collection content, gas, wall maturity, extension, mass effect, vessels and procedural access routes.
Interpretation and limitations
Heterogeneous non-liquid material indicates necrosis rather than a simple pseudocyst; imaging timing and clinical change determine whether another scan is useful.
02
MRI with MRCP
Why
Characterise solid debris and pancreatic duct anatomy when CT is insufficient or repeated radiation is undesirable.
Interpretation and limitations
Demonstrated duct communication or disconnection affects recurrence and stent strategy, but unstable patients need faster source-control planning.
03
FBC, CRP, renal and liver profiles
Why
Monitor inflammation, anaemia, organ function and biliary compression before and after intervention.
Interpretation and limitations
A falling haemoglobin can indicate occult bleeding; inflammatory markers alone cannot reliably separate sterile from infected necrosis.
04
Blood and drainage cultures
Why
Identify infection and narrow antimicrobials when systemic sepsis or drainage provides a safely obtained specimen.
Interpretation and limitations
Collection organisms can be polymicrobial or healthcare-associated; prior antibiotics reduce yield and colonised drains complicate later interpretation.
05
CT angiography
Why
Detect active bleeding or pseudoaneurysm when haemoglobin falls, haemodynamic instability develops or blood appears in a drain.
Interpretation and limitations
A splenic, gastroduodenal or other arterial lesion requires urgent interventional-radiology or surgical management, even if bleeding is intermittent.
06
Endoscopic ultrasound assessment
Why
Evaluate wall apposition, intervening vessels, debris burden and suitability for transmural drainage.
Interpretation and limitations
Doppler reduces vascular injury risk; drainage device and need for later necrosectomy are specialist choices based on content and anatomy.

06Differential diagnosisRealistic alternatives and the features that help distinguish them.

Pseudocyst versus walled-off necrosis

A pseudocyst contains fluid after interstitial pancreatitis, whereas solid necrotic debris defines walled-off necrosis and changes drainage planning.

Pancreatic cystic neoplasm

No pancreatitis history, internal septa, mural nodules or ductal features raise a neoplastic cyst rather than a post-inflammatory collection.

Haemorrhage or pseudoaneurysm

Sudden pain, falling haemoglobin or enhancing vascular focus within a collection indicates bleeding requiring urgent interventional assessment.

07ManagementImmediate care, first-line treatment, alternatives and escalation.

01ObserveStable sterile collectionFirst stepThe patient is improving without sepsis, bleeding, obstruction, uncontrolled pain or nutritional compromise.

1Use accurate Atlanta terminology, record collection age and content, and establish whether the pancreatic duct or surrounding vessels are involved.
2Continue oral or enteral nutrition, analgesia, rehabilitation and cause-directed pancreatitis care without prophylactic antibiotics.
3Repeat imaging only at a clinically meaningful interval or for new symptoms, not simply to document every small dimensional change.
4Provide written warning signs and a named pancreatic follow-up route, because infection or obstruction can develop after discharge.

02InfectedNecrosis step-up treatmentClinical, microbiological or radiological evidence supports infected or probably infected pancreatic necrosis.

1Resuscitate sepsis, obtain cultures when promptly available and start a microbiology-guided antibiotic regimen with adequate pancreatic-tissue relevance.
2Refer to a centre combining interventional endoscopy, radiology, pancreatic surgery and critical care; agree whether endoscopic or percutaneous drainage offers safest access.
3Drain first and reassess physiology, nutrition and residual solid burden before adding direct endoscopic, minimally invasive or open necrosectomy.
4Delay debridement until walled-off maturation when the patient can be stabilised, but intervene earlier for uncontrolled sepsis or another life-threatening complication.

03EmergencyBleeding or ruptureCollapse, peritonism, gastrointestinal haemorrhage, bloody drain output or abrupt haemoglobin decline suggests vascular or visceral catastrophe.

1Activate ABCDE and major-haemorrhage protocols, secure blood products and involve senior surgery, interventional radiology and critical care immediately.
2Obtain urgent CT angiography if physiology allows, while avoiding blind endoscopic puncture or drain manipulation near a possible pseudoaneurysm.
3Use angiographic embolisation when feasible for arterial bleeding, with operative treatment for failed control, perforation or other surgical pathology.
4After haemostasis, reassess collection infection, duct integrity, nutrition and future drainage because the underlying pancreatic process remains.

Key medicines and prescribing safety3 treatments · regimens, roles and cautions

Treats bacterial infection while endoscopic or radiological drainage and possible debridement achieve source control.

Antibiotics for infected pancreatic necrosis

Choose a current microbiology and BNF-directed intravenous regimen, adjusted to cultures, renal function, prior exposure and local resistance surveillance.

Do not use for sterile collections; prolonged broad therapy selects resistant and fungal infection, and pharmacology cannot remove avascular devitalised tissue.

Supports breathing, mobility, sleep and nutrition while the collection matures or definitive treatment is planned.

Analgesia for collection-related pain

Use a personalised multimodal regimen from the current BNF and acute-pain service, titrating any opioid with regular functional review.

Increasing requirements can signal infection, obstruction or bleeding; monitor constipation, ileus, cognition, respiration and dependence risk.

Provides gastric acid suppression in selected patients but does not treat a pancreatic collection itself.

Proton-pump inhibitor when specifically indicated

Use a standard BNF adult regimen only for a recognised acid-related, bleeding-risk or post-intervention indication and set a review date.

Avoid routine indefinite use; consider enteric infection, hypomagnesaemia and medicine interaction, and never substitute it for vascular bleeding assessment.

08ComplicationsImportant consequences, why they occur and why they matter clinically.

Infected necrosis and sepsis

Colonised devitalised tissue drives persistent fever, organ failure and a need for delayed multidisciplinary step-up source control when feasible.

Pseudoaneurysm haemorrhage

Pancreatic enzymes erode nearby arteries, causing concealed or gastrointestinal bleeding that can be rapidly fatal without embolisation or surgery.

Obstruction, fistula and duct disconnection

Large collections compress stomach or bile duct, rupture into adjacent organs or persist because viable upstream pancreas remains disconnected.

09Monitoring and follow-upTreatment response, safety checks and longer-term review.

Track temperature, organ support, pain, feeding tolerance, weight and functional progress rather than using collection diameter as the sole outcome.
After drainage, record device type, route, output, flushing plan, cultures and who decides removal, exchange or necrosectomy.
Repeat haemoglobin and haemodynamic assessment urgently when drain character changes or gastrointestinal bleeding occurs.
Review antibiotics against culture results and achieved source control, watching for line infection, Clostridioides difficile and fungal disease.
Assess for recurrent fluid, external fistula and disconnected duct after drain removal, especially when upstream pancreas remains viable.

10Special situationsVariants, exceptions and circumstances that change the usual approach.

Content beats size

Solid necrotic debris determines procedural complexity far more than a single maximum collection diameter.

Four weeks is approximate

Encapsulation develops biologically rather than at midnight on day twenty-eight; imaging must confirm a safe mature wall.

Gas is persuasive

Intralesional gas strongly suggests infection unless introduced by prior instrumentation or a fistula, but its absence does not exclude sepsis.

Drainage is diagnostic too

A therapeutic procedure can provide cultures and reveal debris, reducing the need for separate diagnostic needle aspiration.

Blood may be intermittent

Pseudoaneurysm haemorrhage can temporarily stop, so transient haemodynamic improvement must not cancel angiographic assessment.

11Common pitfallsFrequent interpretation and management errors.

01
Calling heterogeneous walled-off necrosis a simple pancreatic pseudocyst.
02
Draining an asymptomatic collection solely because it appears large.
03
Using antibiotics for sterile necrosis without evidence of bacterial infection.
04
Performing early debridement before a wall forms when stabilisation is possible.
05
Puncturing a collection without excluding intervening vessels or pseudoaneurysm.
06
Removing a drain without considering pancreatic duct disconnection and recurrence.