Acute Pancreatitis

Description

Pancreatitis refers to the inflammatory condition of the pancreas. It is characterised by activation of pancreatic enzymes within the pancreas, leading to autodigestion and inflammation. Acute pancreatitis, is a potentially life-threatening condition that requires immediate medical attention.

Pathogenesis

Acute pancreatitis is typically a result of premature activation of pancreatic enzymes within the pancreas rather than the bowel, leading to inflammation and possible self-digestion of pancreatic tissues. As the pancreas lacks a fibrous capsule, the inflammatory process may spread to multiple anatomic compartments, leading to further complications.

It can be caused by gallstones, alcohol consumption, certain medications, high calcium levels, high triglyceride levels, infection, injury to the abdomen, and certain inherited genetic mutations.

Subtypes

There are two subtypes as described in the Revised Atlanta Classification:

Interstitial Oedematous Pancreatitis (90-95% of cases): Often referred to simply as “acute pancreatitis” or “uncomplicated pancreatitis”.
Necrotising Pancreatitis: Necrosis develops within the pancreas or peripancreatic tissue.

Epidemiology, Risk Factors & Associations

Pancreatitis is relatively common with an incidence rate of 4.9 to 35 per 100,000 people worldwide. It’s often associated with metabolic disorders such as obesity and type 2 diabetes mellitus due to shared risk factors. Risk factors of acute pancreatitis:

Gallstone passage/impaction: Most common cause of acute pancreatitis, responsible for up to 15% of cases.
Idiopathic causes: In around 20% (10-30%) of cases, no definitive cause is identified, though there may be associations with congenital duct abnormalities.
Alcohol abuse: This is the most common cause of chronic pancreatitis. A non-linear dose-response relationship is seen, with a 1.2x risk with ~40 g/day alcohol consumption and a 4x risk with ~100 g/day.
Metabolic disorders: Hypertriglyceridaemia-induced pancreatitis accounts for 1-4% of cases and is the most common cause during pregnancy. Other metabolic disorders include hypercalcaemia.
Trauma: Blunt abdominal trauma causing disruption of the pancreatic duct is a common cause in paediatric patients (cholelithiasis is likely the most common). Non-accidental injury is an important consideration for pancreatic injury.¹
Malignancy: Pancreatic adenocarcinoma and lymphoma can lead to pancreatitis.
Hereditary pancreatitis: Mutations in the SPINK1 gene, which follows an autosomal dominant inheritance pattern, have been implicated in hereditary pancreatitis.

Clinical Features

Typically, the onset of acute pancreatitis is marked by persistent, severe epigastric pain that may radiate to the back in 50% of patients. This pain tends to be poorly localised, with an exacerbation in supine positioning.
Signs of haemorrhage, although rare, can be detected during physical examination and may include periumbilical bruising (Cullen sign) or flank bruising (Grey-Turner sign). Hypotension and features of shock may be present.
Other common symptoms include: Nausea and vomiting, fever, tachycardia, hypotension and shock.

Complications

Potential complications from pancreatitis include pancreatic necrosis, infection, pancreatic abscess, and pseudocyst formation. Chronic pancreatitis can result in malabsorption and diabetes.

pancreatic fluid collections (defined by the presence or absence of necrosis), liquefactive necrosis of pancreatic parenchyma, vascular complications like hemorrhage and pseudoaneurysm, fistula formation, and abdominal compartment syndrome.

Complications from acute pancreatitis can be severe and life-threatening.

Infected pancreatic necrosis implies superinfection of necrotic parenchyma, leading to sepsis and carries a very poor prognosis.
Central necrosis (disconnected duct syndrome) is necrosis of the central portion of the gland and pancreatic duct with intact upstream and downstream pancreas/duct in the head and tail.
Extrapancreatic fat necrosis occurs due to leakage of pancreatic enzymes into peripancreatic soft tissues resulting in fat necrosis.
Pseudoaneurysm: Often of the splenic artery (50%), gastroduodenal artery (20%), pancreaticoduodenal artery (10%). Presents as a small, contrast-filled outpouching next to an artery. May rupture.
Venous thrombosis can occur due to either direct intimal injury to a vessel from adjacent inflammation and pancreatic enzymes or due to mass effect from adjacent collections. Splenic vein most commonly involved, however, can also involve portal and superior mesenteric vein.
Pancreatic fluid collections: These can be acute peripancreatic fluid collections (APFCs), pseudocysts (encapsulated fluid collections), acute necrotic collections (ANCs), or walled-off necrosis (WON), with varying levels of severity and clinical significance. These collections can also be complicated by infection.

Extrapancreatic and systemic complications can also occur:

Systemic inflammatory response syndrome (SIRS): This can lead to multi-organ dysfunction syndrome (MODS), particularly in necrotising pancreatitis, leading to a high mortality rate.
Pulmonary complications: These can include pleural effusion (most commonly left side, though can be bilateral), atelectasis, acute respiratory distress syndrome (ARDS), and pneumonia.
Cardiovascular complications: Hypotension and shock can occur due to the release of inflammatory mediators.
Renal complications: Acute kidney injury.
Gastrointestinal complications: Ileus, gastric outlet obstruction, and gastrointestinal bleeding.

Pathological Features

Histopathology

Acute pancreatitis: The key histopathological features include acute inflammation and cell death (necrosis), and infiltration by neutrophils, macrophages, and lymphocytes.
- Pseudocyst walls are formed by fibrous tissue and lack an epithelial lining.
Chronic pancreatitis: Characterised by progressive fibrosis and destruction of pancreatic parenchyma.
Autoimmune pancreatitis: Characterised by lymphoplasmacytic infiltrate rich in IgG4-positive plasma cells and fibrosis.
Hereditary pancreatitis: Histopathologic findings can be variable and may include features of acute or chronic pancreatitis.

Biochemistry

Elevation of serum amylase and lipase is 90-95% specific.
A normal amylase level, particularly in cases of chronic pancreatitis, and a normal lipase level, although extremely rare, do not rule out pancreatitis.

Genetics

Hereditary pancreatitis: Can be due to mutations in several genes, including PRSS1, SPINK1, and CFTR.

Radiological Features

Imaging Recommendations

If the diagnosis of acute pancreatitis is established by abdominal pain and by increases in the serum pancreatic enzyme activities, a CECT is not usually required for diagnosis.

Ultrasound

May appear normal in early or mild pancreatitis (i.e. equal or slightly increased echogenicity relative to liver).
Enlargement of the pancreas as well as hypoechoic or heterogeneous echotexture is caused by associated interstitial oedema,
Main pancreatic duct dilatation (> 3 mm at the head, > 2 mm at the body and tail)
Fluid may dissect along vessels and along the portosplenic confluence and superior mesenteric vein – perivascular cloaking.²
Peripancreatic fuid may accumulate in the anterior pararenal and perirenal spaces bilaterally.
There may be evidence of gallstones or biliary dilatation if biliary obstruction is the cause.
Colour Doppler: Conventional grayscale and colour Doppler imaging techniques are less sensitive in detecting parenchymal necrosis.

CT

Interstitial Oedematous Pancreatitis (70-80% of cases)

Pancreas may appear normal in mild pancreatitis with minimally elevated lipase levels
Diffuse, segmental or focal pancreatic oedema causing enlargement with loss of normal fatty lobulation.
Peripancreatic fat stranding/haziness, oedema, and free fluid, often localised to the lesser sac, anterior pararenal spaces, and paracolic gutters.
In the absence of necrosis, the pancreas demonstrates normal homogenous enhancement.
Associated collections:
- Acute peripancreatic fluid collections (APFCs) can develop within the first 4 weeks and can spontaneously resolve.
  - Homogenous collection of fluid density with no definable capsule/wall, confined by normal peripancreatic fascial planes with no intrapancreatic extension
- Pseudocysts, which are encapsulated fluid collections, may occur after 4 weeks.
  - Well-circumscribed, round/oval collection of homogenous fluid density with a well-defined wall/capsule. May involve pancreas.

Necrotising Pancreatitis (20-30% of cases)

Characterised by areas of parenchymal necrosis, either non-enhancing or severely hypoenhancing (usually < 30 HU). Necrosis may not be initially present but can develop 3-4 days after symptom onset.
Typically presents with a greater degree of peripancreatic fluid and inflammation than interstitial oedematous pancreatitis.
Three subtypes of necrotising pancreatitis according to the Revised Atlanta classification system:
- Parenchymal necrosis alone: 5%
- Parenchymal and peripancreatic necrosis: 75%
- Peripancreatic necrosis alone (exudative pancreatitis): 20%
Associated collections:
- Acute necrotic collections (ANCs) can form in the first 4 weeks.
  - Heterogenous non-liquid density with intra- or extrapancreatic involvement and no definable wall.
- Walled-off necrosis (WON), or encapsulated collections, can occur after 4 weeks.
  - Heterogenous fluid loculations of varying liquid and non-liquid density with well-defined walls and intra- or extrapancreatic involvement.
- Infected necrosis
  - Suspected by the presence of gas within collection.

MRI

In acute pancreatitis, the pancreas may appear enlarged with increased signal on T2WI and abnormally low signal on T1WI due to edema.
MRCP can evaluate the integrity of the pancreatic duct, particularly in patients with suspected central gland necrosis.
Acute pancreatitis may be associated with restricted diffusion (lower ADC values than the normal pancreas).

Grading and Staging

The severity of acute pancreatitis can be graded according to the revised Atlanta classification, which includes mild, moderate and severe, based on the presence of local complications and organ failure.

Mild acute pancreatitis is characterised by the absence of organ failure and the absence of local or systemic complications.
Moderately severe acute pancreatitis is characterised by the presence of transient organ failure or local or systemic complications in the absence of persistent organ failure
Severe acute pancreatitis is characterised by persistent organ failure.

Diagnosis

The diagnosis of acute pancreatitis requires two of the following three features³:

Abdominal pain consistent with acute pancreatitis (acute onset of a persistent, severe, epigastric pain often radiating to the back)
Serum lipase activity (or amylase activity) at least three times greater than the upper limit of normal
Characteristic imaging findings of acute pancreatitis.

Differential Diagnosis

Imaging-based

Pancreatic Adenocarcinoma: Focal pancreatitis (which frequently involves the pancreatic head and neck can be difficult to distinguish from pancreatic adenocarcinoma. Short-term follow-up to ensure resolution may help.

Clinically-based

Acute cholecystitis: Can also present with upper abdominal pain. Ultrasound or CT would show gallbladder inflammation or stones.
Perforated peptic ulcer: Severe abdominal pain may be due to a perforated ulcer. Plain radiography or CT may show free air under the diaphragm.

Management

Management involves pain control, fluid resuscitation and supportive care. Severe cases may require admission to the intensive care unit.
Patients with gallstone pancreatitis may require endoscopic retrograde cholangiopancreatography (ERCP) or cholecystectomy.
Patients should be referred to a gastroenterologist for ongoing care.

References

Updated on 23 July 2024

Tagged: Category 1 Key Condition Paediatrics

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