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In this essay, I will define pancreatitis as a hepatobiliary disease and explain its progression in detail. I will also discuss which imaging modalities are best to diagnose and detect pancreatitis and compare and contrast those modalities to each other, as well as pointing out how the images appear on these imaging modalities. Patient issues and safety aspects of the imaging will be discussed within the management of the disease, and treatment will be considered to specify outcome of the disease. In this essay, I will also discuss new developments and techniques in this area and their importance in research and treatment.
Pancreatitis and its progression
Pancreatitis is the inflammation of the pancreas which is a gland located behind the stomach and secretes digestive juices or enzymes by a pancreatic duct (National Institutes of Health, 2008). According to research by the Division of Surgery and Oncology, University of Liverpool (2007), every year, 6000 people develop pancreatitis in the UK and 1 in 10 cases end in death. Gallstones and alcohol are the common causes of pancreatitis; pancreatitis can occur as a result of long-term alcohol intake and gallstones which occur in the gall bladder may obstruct the pancreatic duct, allowing digestive juices to enter the pancreas. Trauma, tumour, infections, genetic factors, ERCP, abdominal surgery, heart and lung by-pass surgery, medications such as oral contraceptive pills, steroids and thiazides, and high calcium-fat levels in the blood are other causes of the pancreatitis. Pancreatitis may be acute or chronic. Acute pancreatitis is an acute and sudden inflammation of the pancreas in which patients usually complain of vomiting, fatigue, high temperature, jaundice, feeling sick, abdominal pain, lethargy, irritability and headache (Dubagunta, Still and Komar, 2001). On the other hand, chronic pancreatitis is the irretrievable and scarring damage of the gland. In chronic pancreatitis, pancreatic parenchyma and loss of exocrine occurs as a result of the inflammation of the pancreas and usually happens after an attack of acute pancreatitis. Patients with chronic pancreatitis have less pain but lose weight, have bleeding, jaundice and liver problems and they are not able to produce insulin and digest food (Dubagunta et al., 2001).
Acute pancreatitis progresses from mild to severe, going from organ failure to sepsis and ending in death. In acute pancreatitis, the serum amylase level increases in five to ten days, possibly as a result of common bile duct obstruction, increased bilirubin and alkaline phosphatise(Carroll, Herrick & Gipson, 2007). The progress of the disease occurs in a short time: patients may have several attacks even though the patient gets well after each attack. Mild acute pancreatitis does not lead to organ failure but leads to interstitial oedema, whereas severe acute pancreatitis leads to organ failure, renal failure, necrosis and pseudocyst formation as well as GI haemorrhage and metabolic abnormalities (Carroll et al., 2007).
Chronic pancreatitis does not have much progression except the gallstones through the ampulla of Vater and cannulation at endoscopic retrograde cholongiopancreatogram (ERCP) but proteolytic enzymes need to be activated. Nearly one third of the cases progress very quickly because pancreatic necrosis affects the fat and spreads through the retroperitoneal space behind the large bowel and then goes into the small bowel mesentery, therefore necrotic tissue may be infected (Carroll et al., 2007).
New developments and imaging techniques
Multiple imaging modalities are used to diagnose and evaluate pancreatitis. Plain abdomen and chest x-ray, computed tomography (CT) and ultrasound (US) are used to diagnose acute pancreatitis and abdomen x-ray, CT, ultrasound, endoscopic ultrasound, endoscopic retrograde cholangiopancreatography (ERCP) and magnetic resonance cholangiopancreatography (MRCP) are used to detect chronic pancreatitis (Saokar, Rabinowitz, Sahani, 2007; Carroll et al., 2007).
Traditional imaging techniques include plain film radiography, abdominal sonography, CT scans and ERCP. Endoscopic ultrasonography and MRCP secretin stimulation are the new options and all help early diagnosis of chronic pancreatitis (Siddiqi & Miller, 2007; Choueiri, Balci, Alkaade and Burton, 2010). Technological improvements in imaging modalities have provided a revolution for the management of acute pancreatitis. In particular, advances in imaging modalities such as contrast-enhanced sonography, which assesses vascularisation in the pancreas and diagnoses pancreatic necrosis and parenchymal necrosis more quickly and easily than conventional ultrasound. It also evaluates the parenchymal necrosis like CT and MRI. Some research suggests that percutaneous conventional ultrasound is the preferred initial technique for evaluation of acute pancreatitis (Rickes and Uhle, 2009). On the other hand, according to Kwon and Scheiman (2006), spectroscopy, which is a new development in pancreatic imaging, is an important technique because it distinguishes well chronic pancreatitis from malignancy and multidetector row CT provides high quality and accurate images. These new developments provide better diagnosis and give accurate staging of pancreatitis.
The severity of pancreatitis is measured better by the CT, which evaluates any possible complications. Contrast-enhanced CT shows pancreatic necrosis but is not very effective for showing abnormality in mild pancreatitis. Spiral CT is useful to evaluate pancreatitis because it scans the entire pancreas in a single breath hold and evaluates parenchymal and vascular enhancement. Contrast-enhanced CT is also useful in cases of acute pancreatitis, having a high degree of accuracy in showing small gas bubbles, calcifications, fluid collections, dilatation of the pancreatic duct and parenchyma (Matos et al., 2005). In addition, while unenhanced CT scan is essential for evaluating any recent haemorrhage, contrast-enhanced CT scan diagnoses pancreatitis at an early stage. According to Elmas (2001), dual-phased spiral acquisition should be performed and first phase is performed at 25s for the arterial, second phase at 50s for portal venous, and the rate of contrast medium injection is 4ml/s. An initial scan during the arterial phase of enhancement is performed to detect arterial pseudoaneurysms (Bolek, Baker and Walsh, 2006). However, according to UK guidelines, CT protocol, spiral or multislice CT are essential to assess acute pancreatitis because speed is an advantage in CT in detecting acute pancreatitis as it occurs suddenly and there is a need of action immediately for very ill patients. UK guidelines suggest that 500ml of contrast should be given by oral or a nasogastric tube and contrast to Elmas (2001), post contrast series should be performed after IV injection of 100ml of non-ionic contrast which is obtained at 3ml/s. Thin collimation at less than 5mm should be obtained at 40 seconds after injection starts. A second image should be taken at 65 seconds after injection. It also provides soft tissue reconstruction with 300-400 window width and between 0 to 50 window levels.
The CT severity index provides highly effective diagnosis of the staging of pancreatic complications. It shows the classification of the pancreatitis, according to which patients from grade A to C are classified as having mild pancreatitis, A demonstrates normal pancreatic appearance, B demonstrates focal or diffuse enlargement of the pancreas, C is pancreatic abnormalities and peripancreatic inflammation, grade D indicates peripancreatic fluid collection and Grade E shows gas in the pancreas, which is an indication of prolonged morbidity as well as abscess and a high mortality rate (Elmas, 2001; Weissleder, Wittenberg, Harisinghani and Chen, 2007).
In chronic pancreatitis, unenhanced CT identifies stones more easily and is superior to location of the calcifications inside the pancreatic gland because stones appear in hyperdense formations (Graziani et al., 2005). According to Manfredi (2001), chronic pancreatitis is well seen by CT with 74% sensitivity and 85% specificity. In mild form, pancreatic fatty planes show high density and in severe form, acute fluid collections show low attenuation. CT demonstrates normal appearance of the pancreas in mild pancreatitis without peripancreatic abnormality hence it will be difficult to detect diffuse enlargement of the gland. On the other hand, in severe pancreatitis CT shows fewer enhancements in the pancreas but it has priority for staging the severity of the pancreatitis. Contrast-enhanced CT and MRI have similar diagnostic value (Koo, Chinogureyi and Shaw, 2010).
If a patient is allergic to iodinated contrast media or has poor renal function, then MRI will be helpful for the upper abdomen with gadolinium diethylenetriamine pentaacetic acid enhancement (DTPA), rather than a CT scan (Koo, Chinogureyi and Shaw, 2010). .
MRI gives more detailed information about the pancreatitis and also has no ionising radiation and gadolinium, with lower toxicity, which makes MRI preferable when assessing the disease, but longer scan time, limited availability and cost are the disadvantages of it. MRI is used to determine the extent of any fluid collections in the pancreas, and by using gadolinium it rules out necrosis in severe acute pancreatitis. Fat suppression sequences and fast spin echo with phased array coils provide excellent contrast resolution and reliable imaging details in the pancreatic tissue. T2 weighted images and gadolinium-enhanced T1 sequences are quite useful to assess acute pancreatitis. T2 weighted spin echo imaging is more effective than CT because it is very sensitive to fluid collections and is more reliable at showing internal structure. Contrast enhancement is essential to assess any pancreatic parenchymal perfusion and necrosis as well as the location, extent and size of the fluid collections around the gland (Robinson and Sheridon, 2000).
MRI is vital for staging the severity of acute pancreatitis but it may be contraindicated for patients with severe pancreatitis because they may be too ill to be able to cooperate with the breath hold sequences. Breath hold sequences are important because they reduce motion artefacts. In addition, they are contraindicated if there is any pacemaker and intracranial aneurysm clip. One of the most useful sequences for pancreatic evaluation is the T1 weighted gradient echo, which is good to evaluate pancreatitis with fat suppression and dynamic imaging after gadolinium is given and T1 weighted with fat suppression has high signal intensity (Balci et al., 2009). However, the T2 weighted sequence is good to detect any abnormality in the pancreatic duct and biliary tract as well as fluid collections, gallstones and pseudocyts (Miller et al., 2004).
Plain x-ray does not have many functions for diagnosing acute pancreatitis but if a patient has non-specific abdominal pain then abdomen and erect chest x-ray will be performed to rule out any possible perforation and obstruction (Royal College of Radiologists, 2007). Plain x-ray will demonstrate the small loop of dilated small bowel in acute pancreatitis. However, in chronic pancreatitis, abdomen x-rays may help us to see any pancreatic calcification with alcohol related pancreatitis and exclude any calcified gallstones (Dubagunta et al., 2001).
In acute pancreatitis, conventional ultrasound has a restricted role in diagnosing the disease because parenchymal necrosis is hardly detected and organ perfusion may not be assessed. Nevertheless, ultrasound is the first line imaging modality to evaluate acute pancreatitis and a very sensitive imaging technique to visualise the pancreas as well as the biliary tract for ductal dilation, calcifications and fluid collections. It is crucial to detect any changes in parenchymal structure and pancreas volume. Colour Doppler ultrasound and harmonic imaging are useful to show any possible vascular complications. Sensitivity is from 60% to 70% while specifity is 80% to 90% (Manfredi, 2001). Contrast-enhanced sonography provides high accuracy in the staging of acute pancreatitis and is the best imaging technique to assess the severity of the disease if contrast agent is contraindicated (Rickes and Uhle, 2009). Ultrasound also demonstrates any swelling in the pancreas as well as showing the gall bladder stones as common bile dilatation. Endoscopic ultrasound (EUS) is quite a new technique, and offers very accurate images to detect or evaluate tumours and stones. Even though EUS has not been used very often if compared to ERCP, it provides more accuracy than ERCP (GUT-UK guidelines). The biggest advantage of endoscopic ultrasound is that it may be used for obese patients, as well as assisting abscess drainage (Carroll et al., 2007).
In acute pancreatitis, the pancreas is enlarged and becomes hypoechoic; the outer margings of the pancreas are irregular and poorly defined. It is not an indication for EUS; on the other hand, pancreatic pseudocysts are visualised on EUS (Dancygier & Lightdale, 1999). EUS shows inflammatory changes in patients when ERCP suggests it is a chronic pancreatitis. In contrast to some research, Halligan and Fenlon (2004) believe EUS is more sensitive than the ERCP in early chronic pancreatitis.
ERCP and MRCP
ERCP as a gold standard is a very sensitive technique and superior for detecting chronic pancreatitis, showing pancreatic ductal changes, and is also quite useful for detecting mild pancreatitis. The radiographic appearance of ERCP in chronic pancreatitis is that the main ducts and side branches seem diffuse and irregularly dilated and contain filling defects which are calcified and cause duct obstruction (Baillie, 1997). ERCP classifies normal, mild, moderate and severe pancreatitis, according to Cambridge classifications. On the other hand, ERCP is a very invasive technique with possible complications after the procedure and has no ability to detect pancreatic exocrine function. However, MRCP provides similar images to ERCP and has advantages over ERCP as a less invasive technique. It is one of the best imaging modality to detect chronic pancreatitis. It is sensitive to severe pancreatitis and secretin stimulated MRCP improves accuracy in diagnosis of pancreatitis (Sugiyama, Haradome and Atomi, 2007).
Within MRCP, it is easy to see the distal to the side of the obstruction and in severe pancreatitis MRCP shows morphological changes as well as dilation, stricture, filing defects, branch dilation, pseudocysts and upstream pancreatic duct, but it may miss branches that are less than 1mm in width. It is difficult to detect mild pancreatitis in MRCP because it has lower spatial resolution and cause pancreatic duct to collapse but secretin stimulated MRCP (S-MRCP) improves the quality of images in the pancreatic ducts because secretin, which is injected into the patient, raises the flow of the pancreatic juices and therefore it helps to dilate the pancreatic ducts, so that main ducts and side branches are seen well. A new technique, secretin simulated diffusion weighted MRI assesses function by detecting changes of water in pancreatic parenchyma because it shows water molecules. This technique may be useful for detecting mild pancreatitis (Sugiyama, Haradome and Atomi, 2007). S-MRCP also shows any functional abnormalities. For example, the T2 weighted sequence is more effective than CT to show fluid collections or haemorrhage, while S-MRCP shows the connection between pseudocyst and a main pancreatic duct. T1 weighted sequences demonstrate peripancreatic fat with high signal (Balci et al., 2009).
Management and treatment of pancreatitis
The first and correct diagnosis for acute pancreatitis should be made within 48 hours of admission (Rickes and Uhle, 2009). All patients should have enough oxygen and fluids to protect themselves from organ failure. Fluids should be given to patients intravenously and continuously monitored. Patients with severe pancreatitis should be hospitalised in a high dependency unit or intensive care unit to provide full monitoring (GUT-UK guidelines). Abdominal pain and increasing of pancreatic enzymes (lipase and amylase) are the clinical features for diagnosis of acute pancreatitis but may not provide diagnostic accuracy. Blood tests, faeces sample test and urine tests will be done as a first step (Rickes and Uhle, 2009).
In mild pancreatitis, patients need to stay in hospital and should be given IV crystalloid fluids and analgesia. They must not take anything by mouth and most patients need opiate analgesia even though it causes spasms in the sphincter of Oddi. If the patient vomits, then a nasogastric tube should be given. Most patients recover in 48 hours to 72 hours. Resuscitation after hypovolaemic shock is the key point of the management, because the patient needs a large volume of fluids in the first 48 hours (Beckingham, 2001).
Alternatively, Ranson and APACHE II are grading system which measure the severity of pancreatitis. APACHE II (Acute Physiology and Chronic Health Evaluation) is one of the best systems to monitor patientsââ‚¬â„¢ response to treatment. After two days their score is compared with the Ranson system to detect pancreatitis from mild to severe with 80% diagnostic accuracy (Rickes and Uhle, 2009).
Pain relief such as pethidine or tramadol may be given to patients to reduce the pain. Close monitoring of volume statuses and complications for acute pancreatitis are essential for the treatment as well as nutritional support and antibiotics to prevent any possible infection. Antibiotics are important and should be used because pancreatic necrosis may occur as a late complication for severe pancreatitis so those antibiotics such as cefuroxine may help to reduce or stop infections. They should be taken up to 14 days. However, as a non-surgical treatment, an intravenous drip will be used to reduce dehydration. If the patient is asked not to eat anything, then a tube will be provided from nose to the small bowel to give nutrients.
ERCP should be performed to detect any possible gallstones and obstructive jaundice. Urgent ERCP is used to evaluate the risk of severe pancreatitis with biliary obstruction, increased bilirubin, jaundice and worsening pain in abnormal ultrasound examination because these patients need more immediate surgical intervention. Therefore, urgent ERCP reduces mortality and morbidity rates (Carroll et al., 2007). This urgent ERCP should be obtained within 72 hours after the onset of pain but if that patient has gallstone pancreatitis then they should undergo endoscopic sphincterotomy (GUT-UK guidelines). Ultrasound can be used as a treatment of pancreatitis with percutaneous guided drainage of an abscess or pseudocyts (Rickes and Uhle, 2009).
After a CT scan has been performed, the radiologist then decides whether a further CT scan is necessary for the patient. Usually if the patient is scanned in less than 7 days after an acute attack and the patientââ‚¬â„¢s condition still does not change over the period of time, then surgeon and radiologist decide whether further scan is needed. Surgery may be needed if the patient is acutely ill, so the surgeon will be informed if there may be need of necrosectomy and aspiration after CT scan (Beckingham, 2001).
If a patient has pancreatic necrosis, then surgery may be needed to remove that part of the pancreas which has been damaged or it can be done by inserting a tube through the skin. In addition, if acute pancreatitis is caused by gallstones then it should be removed by ERCP or a surgical operation. Patients should eat a low fat diet, avoid alcohol and certain medicines to prevent acute attacks and reduce the risks of acute and chronic pancreatitis. For chronic pancreatitis, patients should stop drinking alcohol if their condition is caused by alcohol and are advised to have a high protein, low fat diet and vitamin supplement as a supporter for the metabolism (Beckingham, 2001).
Rapid diagnosis plays a vital role in pancreatitis. The patient with pancreatitis can avoid the disease by preventing the causes, with low fat diet, no alcohol intake and avoidance of certain medications. Blood tests, a sample of faeces and urine tests will be performed before plain x-ray, US, CT scan, ERCP and MRCP. Imaging modalities are important to diagnose pancreatitis. Even though CT has an important role in diagnosing and staging in early acute pancreatitis, as it is more accessible and less expensive than MRI and is more sensitive to calcifications, ultrasound is still the first line imaging technique for follow up. However, it can be said that EUS has an important role in the early stages and is a commonly preferred method of detecting any tumours and stones (Koo, Chinogureyi and Shaw, 2010).