Chronic pancreatitis is a long-term inflammation of the pancreas that progressively damages the organ. It can lead to permanent damage and impairment of endocrine and exocrine function. Patients typically present with abdominal pain and other symptoms related to maldigestion. Diagnosis of chronic pancreatitis relies on a combination of clinical presentation, laboratory tests, and imaging studies. Computed tomography (CT) scanning is one of the key imaging modalities used to help diagnose and monitor chronic pancreatitis.
What is chronic pancreatitis?
Chronic pancreatitis refers to persistent inflammation of the pancreas that results in irreversible morphological changes and damage to the organ. It is characterized by progressive and permanent destruction of the pancreatic parenchyma leading to exocrine and endocrine insufficiency. This is in contrast to acute pancreatitis, which involves sudden inflammation of the pancreas that may resolve after the inciting factor is treated.
The key features of chronic pancreatitis include:
– Recurrent or persistent abdominal pain, typically epigastric in location and often radiating to the back. The pain can range from mild discomfort to severe pain.
– Exocrine insufficiency leading to maldigestion and malabsorption of nutrients like fat, protein, and carbohydrates. This manifests as steatorrhea, weight loss, and vitamin deficiencies.
– Endocrine insufficiency resulting in diabetes mellitus due to the loss of insulin-producing beta cells.
– Morphological changes and damage to the pancreas that can be seen on imaging like CT scan. These include calcifications, dilated pancreatic duct, pseudocysts, gland atrophy, and fibrosis.
– Increased risk of pancreatic cancer.
What causes chronic pancreatitis?
There are several potential causes and risk factors for developing chronic pancreatitis:
– Chronic alcohol consumption – This is the most common cause in adults, accounting for up to 70% of cases in the Western world. Chronic heavy alcohol use (>80 g/day for men and >50 g/day for women over many years) leads to toxin-mediated pancreatic injury.
– Genetic mutations – Hereditary factors account for about 25% of cases. Mutations in genes like PRSS1, CFTR, SPINK1, and CTRC can predispose to chronic pancreatitis.
– Autoimmune disease – This accounts for about 6% of chronic pancreatitis cases. It occurs when immune cells start attacking pancreatic tissue, mistaking it for a harmful substance.
– Obstructive causes – Pancreatic duct obstruction due to factors like pancreas divisum, pancreatic tumors, or pseudocysts can obstruct outflow leading to increased pancreatic pressure and injury.
– Other causes – These include pancreatic trauma, vascular disease, hypercalcemia, hypertriglyceridemia, and certain medications.
Pathophysiology and progression
The pathophysiology of chronic pancreatitis involves:
– Recurrent acute inflammatory events, often subclinical, that cause progressive architectural damage to the pancreas over time. This recurrent acute on chronic inflammation leads to permanent changes.
– Pancreatic stellate cell activation – These cells mediate pancreatic fibrosis. Chronic inflammation activates these cells to lay down collagen and other extracellular matrix proteins, leading to fibrosis and scarring.
– Oxidative stress and toxins like alcohol generate free radicals that damage pancreatic cells.
– Obstruction of pancreatic ducts leads to increased pressure and parenchymal injury.
– Eventually, the normal lobular morphology of the pancreas is lost and replaced by fibrotic tissue. This impairs exocrine and endocrine function.
– Continued inflammation, fibrosis, calcifications, and loss of pancreatic tissue over many years lead to severe glandular atrophy and insufficiency. But even early pathological changes can cause symptoms.
– Progression is variable, with periods of acute flare-ups followed by smoldering inflammation. But over 5-10 years, most patients develop end stage chronic pancreatitis.
Signs and symptoms
The clinical presentation of chronic pancreatitis may include:
– **Abdominal pain** – The most common symptom, occurring in 80-90% of patients. Typically, a constant dull ache in the upper abdomen radiating to the back. Pain can fluctuate in severity.
– **Maldigestion** – Due to reduced production of pancreatic enzymes. Steatorrhea, weight loss, and vitamin deficiencies may occur.
– **Diabetes** – Develops in 50% of patients as a result of impaired insulin production.
– **Jaundice** – May occur from blockage of bile drainage from swollen inflamed pancreatic head.
– **Vomiting** – In some cases, chronic inflammation leads to gastric outlet obstruction.
– **Exocrine gland enlargement** – A palpable, nodular, and enlarged pancreas may be felt if extensive inflammation and fibrosis occurs.
– **GI bleeding** – Due to splenic vein thrombosis or pseudocyst erosion into vessels.
– **Pseudocysts** – Fluid-filled cystic lesions that may develop near the pancreas. These occur in about 20-40% of cases.
Diagnosis
Diagnosing chronic pancreatitis requires:
– **Medical history** – Symptoms of long-standing abdominal pain and maldigestion, risk factors such as alcohol use.
– **Lab tests** – Fecal elastase levels decreased; serum amylase and lipase may be elevated, especially during flare-ups.
– **Imaging** – CT scan, MRI, MRCP, EUS are used to visualize pancreatic structural changes.
– **Pancreatic function testing** – Direct testing of exocrine and endocrine function may be done in some cases.
There are no definitive clinical criteria. Diagnosis requires a combination of characteristic clinical features, lab abnormalities, and morphological changes on imaging that point towards chronic pancreatitis. A stepwise approach is followed, with more advanced tests done if initial evaluation is inconclusive.
Does chronic pancreatitis show up on CT scans?
Yes, CT imaging can detect many of the features of chronic pancreatitis. CT has become the primary initial cross-sectional imaging modality used for diagnosing chronic pancreatitis.
Some CT scan findings in chronic pancreatitis include:
Pancreatic calcifications
– Pancreatic calcifications visible on CT are considered pathognomonic for chronic pancreatitis.
– Are seen in 30-90% of patients, though more commonly in advanced disease.
– Occur due to dystrophic calcification in areas of necrosis and fibrosis.
– Can appear as punctate, nodular, or branching calcifications scattered through pancreas.
– Size and pattern can help gauge severity and progression.
Pancreatic duct abnormalities
– Main pancreatic duct dilation >3 mm.
– Irregularity and dilatation of side branches.
– Intraductal calculi may be seen as filling defects.
– Strictures and obstructions caused by fibrosis and scarring.
Parenchymal atrophy
– Pancreatic tissue loss and atrophy.
– Results in a small, irregular gland.
Morphological changes
– Fatty replacement of pancreas.
– Focal pancreatic enlargement.
– Pseudocyst formation.
– Peripancreatic fluid collections.
Other features
– Splenic vein dilation, varices due to stenosis.
– Biliary ductal dilatation.
– Inflammatory fat stranding around pancreas.
Thus, CT imaging provides both direct visualization of damaged pancreas and indirect signs of chronic inflammation. These typical findings allow radiologists to distinguish chronic pancreatitis from acute pancreatitis or normal pancreatic anatomy.
Advantages of CT scans in chronic pancreatitis
Some benefits of using CT scans for diagnosis include:
– Readily available and fast. CT scanners are widely available.
– Non-invasive imaging technique compared to tests like ERCP.
– Sensitive for detecting fat infiltration, atrophy, fibrosis and calcifications – changes that occur earlier in chronic pancreatitis.
– Useful for assessing complications like pseudocysts and bile/vascular obstruction.
– Allow clear visualization of pancreatic duct anatomy.
– Help distinguish mass-forming chronic pancreatitis from pancreatic cancer in certain cases.
– Allow monitoring of disease progression or treatment response during follow-up. New or evolving changes can be detected in the pancreas.
– Can be used when MRI/MRCP is contraindicated or unavailable.
– Pancreatic protocol CT is considered one of the best initial studies for suspected chronic pancreatitis.
Thus, CT imaging is invaluable for confirming the diagnosis, excluding other conditions, and monitoring structural progression in chronic pancreatitis.
Limitations of CT scan for chronic pancreatitis diagnosis
However, CT scans do have some limitations including:
– Radiation exposure risk during repeated follow-up scans.
– May miss early or subtle changes of chronic pancreatitis.
– Less sensitive than MRI/MRCP for detecting subtle duct abnormalities and early parenchymal changes.
– Cannot reliably assess pancreatic exocrine functional impairment.
– Difficult to differentiate inflammatory mass from pancreatic cancer in some cases.
– Calcifications only develop in 30-90% of patients and may be absent early on.
– Morphological findings can be seen with other conditions like acute pancreatitis or pancreatic cancer.
Thus, normal CT findings do not completely exclude chronic pancreatitis. Early changes may be better visualized on MRI/MRCP. And CT may not be able to differentiate mass-forming chronic pancreatitis from cancer in all cases.
Comparison to MRI and endoscopic ultrasongraphy
Though CT scan is the usual first-line imaging test, other modalities like MRI or endoscopic ultrasound may be better for certain aspects:
**MRI and MRCP**
– More sensitive than CT for detecting subtle structural and morphological changes early in disease.
– Better visualization of main pancreatic duct and side branches.
– MRCP can help differentiate chronic pancreatitis and cancer in indeterminate cases.
– No radiation exposure.
**Endoscopic ultrasound**
– Provides high resolution images of pancreas.
– Can detect subtle parenchymal and duct changes missed on CT.
– Allows targeted biopsy of abnormal areas to distinguish mass-forming chronic pancreatitis from cancer.
– Can assess for early chronic pancreatitis.
Guidelines for diagnosing chronic pancreatitis on CT
Several criteria and guidelines exist for diagnosing chronic pancreatitis on CT scan:
– **Cambridge classification** – Diagnosis requires either (a) Calcifications alone OR (b) Pancreatic duct dilatation to >3mm and at least 3 of 9 other features including parenchymal atrophy, duct irregularity, duct strictures, stones, enlarged gland, cysts, or obstruction of bile duct/duodenum/vessels.
– **Modified Cambridge classification** – Less strict criteria requires either calcifications or ductal dilatation/irregularity along with just one other feature. Improves sensitivity for early disease.
– **Asian consensus criteria** – Requires pancreatic duct dilatation (>3 mm) along with hypodense gland, fibrotic strands, calcifications, or cysts/pseudocysts.
– **Mayo Clinic diagnostic criteria** – Requires 1 of 3 following features: Multiple intraductal calcifications (>3), Pancreatic ductal dilatation and beading, Fibrosis/enlargement of pancreas.
No single criteria has very high accuracy. Diagnosis should be based on clinical context along with morphologic changes on high-quality pancreas protocol CT scan. The cambridge criteria are most widely used.
Typical CT protocol and technique for chronic pancreatitis
– **Pancreatic protocol CT** is optimized to evaluate pancreas. Important considerations include:
– Non-contrast CT to detect pancreatic calcifications
– Pancreatic parenchymal phase – Imaging 45-50 seconds after contrast
– Delayed phase at 90 seconds to assess late enhancement
– Negative oral contrast (water)
– Thin slices 1-2 mm with multiplanar reconstructions
– High spatial resolution, adequate contrast enhancement and pancreatic parenchymal timing is key.
– Radiologist expertise in interpreting chronic pancreatitis changes is important for identifying subtle findings.
– Comparison with prior exams when available helps discern progressive changes.
When should CT scan be done for suspected chronic pancreatitis?
CT scanning should be considered if chronic pancreatitis is suspected based on risk factors, symptoms, or abnormal blood tests. CT is most helpful in certain scenarios:
– As initial test in new-onset suspected chronic pancreatitis with classic symptoms of pain and maldigestion.
– For evaluating complications like pseudocysts, bile/vascular compression in known chronic pancreatitis.
– Detection of calcifications is important to establish diagnosis when other tests are equivocal.
– To exclude or confirm pancreatic cancer in patients with obstructive jaundice or a pancreatic mass concerning for malignancy.
– When onset of diabetes occurs in middle age or later.
CT assessment is also commonly done:
– During acute exacerbations or flare-ups in patients with known chronic pancreatitis.
– As follow-up to monitor progression and development of new complications in established disease.
– When other imaging like MRI is inconclusive.
– Before planned interventions such as surgery or endoscopic procedures to evaluate suitability.
The decision of when to utilize CT scan should be individualized based on clinical judgment and multidisciplinary input.
Conclusion
In summary, CT imaging plays an important role in the diagnosis and monitoring of chronic pancreatitis. CT scans can detect features of chronic pancreatitis including pancreatic calcifications, duct dilatation and strictures, gland atrophy and enlargement, pseudocysts, fat infiltration, and vascular complications. While CT findings alone are not sufficient to make the diagnosis, pancreatic protocol CT showing characteristic morphological changes in the appropriate clinical context is supportive of chronic pancreatitis and can help exclude alternative diagnoses. CT has advantages of wide availability, rapid acquisition, and ability to assess complications. However, MRI and MRCP may be more sensitive in certain settings and endoscopic ultrasound allows biopsy of masses. Diagnosis requires integrating clinical, laboratory, and imaging findings with multidisciplinary input.