The Pancreas

Chapter 14 The Pancreas



Ivan Damjanov, MD, PhD




1 List the most important diseases of the enzymes produced by the exocrine pancreas


Pancreatic acini secrete more than 20 digestive enzymes. These enzymes are released in response to stimulation, which may be neurogenic or hormonal with polypeptide hormones such as cholecystokinin. The most important enzyme disorders are:


image Developmental disorders

image Acute and chronic pancreatitis

image Tumors

image Diabetes



Key Points: The Pancreas



1. The pancreas is an exocrine gland attached to the duodenum that also contains endocrine cells producing insulin, glucagon, and several other polypeptide hormones.

2. The three most important diseases of the pancreas are pancreatitis, pancreatic carcinoma, and diabetes.


DEVELOPMENTAL DISORDERS



2 Describe annular pancreas


In this anomaly, the head of the pancreas encircles the duodenum. An abnormally shaped pancreas may narrow the duodenum and interfere with the passage of food.



3 What is pancreas divisum?


In this anomaly, there are two separate pancreases, each of which is attached to the duodenum by a separate duct. This anomaly results from incomplete fusion of the two fetal pancreatic anlagen.



4 Where is aberrant pancreatic tissue most often found?


Pancreatic acini and islets may be found anywhere in the other parts of the gastrointestinal tract in 2% of normal people. Most often, such choristomas are found in the duodenum and the stomach. These lesions are usually accidentally discovered during histologic examination of gastrointestinal organs resected or biopsied for an unrelated reason. Larger masses may be mistaken for tumors.



INFLAMMATION



5 What is acute pancreatitis?


Acute pancreatitis is in most instances a sterile (noninfectious) chemically mediated inflammation of the pancreas resulting from injury of the exocrine pancreas. It occurs in two forms:


image Interstitial or edematous pancreatitis: This mild inflammation is characterized by edema and widening of interstitial spaces that contain scattered inflammatory cells. There is no or only minor necrosis of acinar cells. Interstitial pancreatitis occurs relatively often in severely sick people, in various forms of shock, and after prolonged operations. It may be recognized by mild elevation of pancreatic enzymes in blood. It requires no treatment and heals spontaneously.

image Acute hemorrhagic pancreatitis: This is a severe and life-threatening condition, which is not common.


6 Describe the pathogenesis of acute hemorrhagic pancreatitis


Acute hemorrhagic pancreatitis is an acute inflammatory process caused by enzyme-mediated destruction of pancreatic and peripancreatic tissue. The key event is the inappropriate activation of pancreatic digestive enzymes inside the ducts and acini of the exocrine pancreas. Activated enzymes act on the pancreatic cells, which leads to additional release of digestive enzymes into the interstitial and peripancreatic tissues and blood vessels.



7 Describe the sequence of a hypothetical event leading to acute pancreatitis


The inappropriate activation of enzymes inside the pancreas leading to autodigestion is thought to occur in the following sequence (Fig. 14-1):


image Obstruction of the terminal portions of the choledochopancreatic duct

image Reflux of bile into the pancreatic ducts

image Increased pressure inside the excretory portion of the pancreas that reverses the flow of bicarbonate-rich pancreatic juices backward into the acini

image Activation of pancreatic lytic enzymes in the small ducts and acini

image Rupture of damaged acinar cells leading to a release of digestive enzymes into the interstitial spaces and peripancreatic tissue

image Autodigestion of proteins, lipids, and carbohydrate moieties of cells forming the pancreas, peripancreatic fat tissue, and blood vessels

image

Figure 14-1 Acute pancreatitis. Most of the pathologic findings are related to the action of enzymes released from injured pancreatic acini and ducts. DIC, disseminated intravascular coagulation.



8 List the most common causes of acute pancreatitis


Most cases of acute hemorrhagic pancreatitis (>80%) are related to biliary tract disease and alcohol abuse. Bile stones are known to obstruct the common choledochopancreatic duct and thus cause reflux of bile into the pancreas. Alcohol is thought to cause a spasm of the sphincter of Oddi that may also lead to reflux.



9 List other exogenous causes of acute pancreatitis



image Drugs (More than 100 drugs are known to cause pancreatitis, but most often it occurs in patients taking azathioprine and mercaptopurine (2% of patients may have mild pancreatitis). Corticosteroids and high doses of estrogens are also associated with higher incidence of pancreatitis.)

image Trauma (e.g., seatbelt injury)

image Surgery (Surgeons refrain from operating on or palpating the pancreas unless it is essential for the treatment.)

image Diagnostic procedures (Endoscopic retrograde cholangiopancreatography [ERCP] used to visualize pancreatic ducts and obtain cytologic samples may damage the pancreas. Note that it is not advisable to perform diagnostic fine needle aspiration biopsies of the pancreas.)

image Sepsis

image Hypotension (e.g., shock following massive bleeding)

image Viruses (mumps virus, cytomegalovirus—especially in acquired immune deficiency syndrome [AIDS])


10 List endogenous causes of acute pancreatitis



image Hyperlipidemia: Obesity is a known risk factor, but the exact mechanism of pancreatic injury is not completely understood. It is thought that fatty acids may injure acinar cells. Endogenous hyperlipidemia (especially type V) is also associated with an increased incidence of acute pancreatitis.

image Hypercalcemia: Calcium is thought to activate trypsin in the pancreas.

image Familial pancreatitis: The cause of this disease is not known.

image Idiopathic pancreatitis: This can occur without any obvious cause and accounts for 10% of cases; it is the most common cause of pancreatitis (after alcohol and biliary disease).


11 What are the gross pathologic features of acute hemorrhagic pancreatitis?



image Enlargement of the pancreas that is focally hemorrhagic or necrotic is seen.

image Necrosis of fat tissue around the pancreas or omentum: Fat necrosis leads to the formation of fat soaps. These foci appear white, resembling chalk.

image Ascites is found in severe cases. The fluid is turbid, brownish yellow, or blood tinged.


12 Describe the histologic findings in acute pancreatitis



image Necrosis of pancreatic acini, ducts, and blood vessels: In these anatomic sites, the component cells lose their outlines and nuclei.

image Fat necrosis: Fat cells become indistinct and lose their internal structure. The entire field appears bluish because of the deposition of calcium salts. Specks of calcium soaps appear like dark blue aggregates or amorphous material.

image Hemorrhage: Blood infiltrates the tissues.

image Acute inflammation: Neutrophils invade the necrotic tissue. In later stages, neutrophils are replaced by macrophages and the entire area undergoes fibrosis.


13 What are the most important local complications of acute hemorrhagic pancreatitis?



image Pseudocyst: Massive necrosis leads to liquefactive necrosis of the tissue, which becomes enclosed by granulation tissue. The granulation tissue transforms into a fibrous scar that contains the fluid full of pancreatic enzymes.

image Abscess: Infection superimposed on pancreatic necrosis leads to abscess formation. It is associated with high mortality.

image Hemorrhagic ascites: Bleeding occurs from enzymatically damaged blood vessels.


14 What are the systemic (distant) complications of acute hemorrhagic pancreatitis?



image Shock: It is multifactorial but mostly due to increased vascular permeability caused by the action of pancreatic enzyme.

image Disseminated intravascular coagulation: Endothelial injury caused by pancreatic enzymes in circulation leads to the formation of platelet and fibrin thrombi in small vessels.

image Adult respiratory distress syndrome: It is a manifestation of shock, but it also evolves because of enzymatic injury of the alveolar–capillary units in the lungs. Alveolar–capillary injury is accompanied by facilitated passage of fluids into the alveoli (pulmonary edema) and the formation of hyaline membranes.

image Renal failure: It is mostly a consequence of shock and other complications.

image Subcutaneous fat necrosis: Foci of fat necrosis develop unpredictably and are related to the action of lipolytic enzymes that have entered the circulation.


15 What are typical symptoms and signs of acute hemorrhagic pancreatitis?



image Sudden onset of severe abdominal pain

image Pain more prominent in the left upper quadrant of the abdomen; may radiate into the back

image Nausea and vomiting, aggravated by eating

image General distress with fever, sweating, tachypnea, and tachycardia


16 Which enzymes appear in high concentration in blood during an attack of acute hemorrhagic pancreatitis?



image Amylase: It is a sensitive marker of acute pancreatitis, especially if the elevation is 4 times above normal values. Amylase appears in blood within hours of the onset of pancreatic injury. However, hyperamylasemia is not specific for acute pancreatitis, and it may be of extrapancreatic origin. For example, after cardiac surgery 30% of patients have hyperamylasemia, 50% of which is of salivary gland origin. The fallopian tubes also contain amylase, and it may be elevated in extrauterine pregnancy.

image Lipase: It appears slightly later in blood, but it is more specific than amylase.

image Trypsin: This enzyme has the highest specificity and sensitivity for pancreatic injury, but the measurement requires the use of a radioimmunoassay, which is not available in all hospitals.


17 Which other tests give abnormal results in acute pancreatitis?



image Leukocytosis: This is self-evident because pancreatitis is associated with a mobilization of neutrophils that infiltrate the necrotic tissue.
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Jul 23, 2016 | Posted by in PATHOLOGY & LABORATORY MEDICINE | Comments Off on The Pancreas
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