ACUTE PANCREATITIS ULTRASOUND
Category: Diagnostic Radiology
Abstract : Acute pancreatitis - clinical features Acute inflammation of the pancreas has a number of possible causes, but is most commonly associated with gallstones or alcoholism. Clinically it presents with severe epigastric pain, abdominal distension and nausea or vomiting. In milder cases, the patient may recover spontaneously. If allowed to progress untreated, peritonitis and other complications may
Acute pancreatitis - clinical features
Acute inflammation of the pancreas has a number of possible causes, but is most commonly associated with gallstones or alcoholism. Clinically it presents with severe epigastric pain, abdominal distension and nausea or vomiting. In milder cases, the patient may recover spontaneously. If allowed to progress untreated, peritonitis and other complications may occur.
Biochemically, raised levels of amylase and lipase (the pancreatic enzymes responsible for the digestion of starch and lipids) are present in the blood and urine. Acute inflammation causes the pancreatic tissue to become necrosed, releasing the pancreatic enzymes which can further destroy the pancreatic tissue and also the capillary walls, entering the blood stream.
Ultrasound appearances
Mild acute pancreatitis may have no demonstrable features on ultrasound, especially if the scan is performed after the acute episode has settled. In more severe cases the pancreas is enlarged and hypoechoic due to oedema. The main duct may be dilated or prominent.
As the condition progresses, digestive enzymes leak out, forming collections or pseudocysts. These are most frequently found in the lesser sac, near the tail of the pancreas, but can occur anywhere in the abdomen —within the pancreatic tissue itself, anywhere in the peritoneal or retroperitoneal space or even tracking up the fissures into the liver— so a full abdominal ultrasound survey is essential on each attendance.
Pseudocysts are so called because they do not have a capsule of epithelium like most cysts, but are merely collections of fluid surrounded by adjacent tissues. A pseudocyst may appear to have a capsule on ultrasound if it lies within a fold of peritoneum. Pseudocysts may be echo-free, but generally contain echoes from tissue debris and may be loculated. In a small percentage of cases, a pseudocyst or necrotic area of pancreatic tissue may become infected, forming a pancreatic abscess.
Although acute pancreatitis usually affects the entire organ, it may occur focally. This presents a diagnostic dilemma for ultrasound, as the appearances are indistinguishable from tumour. The clinical history may help to differentiate; suspicion of focal pancreatitis should be raised in patients with previous history of chronic pancreatitis, a history of alcoholism and normal CA 19–9 levels4 (a tumour marker for pancreatic carcinoma). The enlargement of the pancreas in acute pancreatitis may have other consequences, for example the enlarged pancreatic head may obstruct the common bile duct, causing biliary dilatation. Doppler ultrasound is useful in assessing associated vascular complications. Prolonged and repeated attacks of acute pancreatitis may cause the splenic vein to become encased and compressed, causing splenic and/or portal vein thrombosis, with all its attendant sequelae.
Although ultrasound is used to assess the pancreas in cases of suspected acute pancreatitis, its main role is in demonstrating the cause of the pancreatitis, for example biliary calculi, in order to plan further management. The ultrasound finding of microlithiasis or sludge in the gallbladder is highly significant in cases of suspected pancreatitis, and has been implicated in the cause of recurrent ciated with pancreatitis, due to the reflux of bile into the pancreatic duct. ERCP, which is more invasive and subject to potential complications, is generally reserved for circumstances which require the removal of stones, alleviating the need for surgery, and in the placement of stents in the case of strictures.
Pancreatitis can be difficult to treat, and management consists of alleviating the symptoms and removing the cause where possible. Patients with gallstone pancreatitis do well after cholecystectomy, but if the gallbladder is not removed recurrent attacks of increasingly severe inflammation occur in up to a third of patients. Pseudocysts which do not resolve spontaneously may be drained percutaneously under ultrasound or CT guidance, or, depending on the site of the collection, a drain may be positioned endoscopically from the cyst into the stomach. Pseudocyst formation may cause thrombosis of the splenic vein, spreading to the portal and mesenteric veins in some cases. Other vascular complications include splenic artery aneurysm, which may form as a result of damage to the artery by the pseudocyst. Surgery to remove necrotized or haemorrhagic areas of pancreatic tissue may be undertaken in severe cases.
Management of acute pancreatitis
While ultrasound is useful in demonstrating associated gallstones, biliary sludge and fluid collections, CT or MRI demonstrates the complications of acute pancreatitis with greater sensitivity and specificity. Localized areas of necrotic pancreatic tissue can be demonstrated on contrast-enhanced CT, together with vascular complications, such as thrombosis.
MRCP or CT is used to demonstrate the main
pancreatic duct and its point of insertion into the common bile duct. Anomalous insertions are associated with pancreatitis, due to the reflux of bile into the pancreatic duct. ERCP, which is more invasive and subject to potential complications, is generally reserved for circumstances which require the removal of stones, alleviating the need for surgery, and in the placement of stents in the case of strictures.
Pancreatitis can be difficult to treat, and management consists of alleviating the symptoms and removing the cause where possible. Patients with gallstone pancreatitis do well after cholecystectomy, but if the gallbladder is not removed recurrent attacks of increasingly severe inflammation occur in up to a third of patients. Pseudocysts which do not resolve spontaneously may be drained percutaneously under ultrasound or CT guidance, or, depending on the site of the collection, a drain may be positioned endoscopically from the cyst into the stomach. Pseudocyst formation may cause thrombosis of the splenic vein, spreading to the portal and mesenteric veins in some cases. Other vascular complications include splenic artery aneurysm, which may form as a result of damage to the artery by the pseudocyst. Surgery to remove necrotized or haemorrhagic areas of pancreatic tissue may be undertaken in severe cases.
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