The pancreas is a key regulator of digestion and metabolism through both endocrine and exocrine functions. Disorders of surgical importance include acute pancreatitis, chronic pancreatitis, and pancreatic cancer.
EMBRYOLOGY
Formation of the pancreas begins during the first few weeks of gestation, with the development of the ventral and dorsal pancreatic buds. Clockwise migration of the ventral bud allows fusion with the larger dorsal bud, creating the duct of Wirsung, which is the main pancreatic duct. Failure of this process results in pancreas divisum, wherein the duct of Santorini drains a portion of the exocrine pancreas through a separate minor duodenal papilla (Fig. 9-1). This anatomic variant is associated with pancreatitis. Annular pancreas occurs when the ventral bud fails to rotate, resulting in pancreatic tissue completely or partially encircling the second portion of the duodenum. This situation may result in duodenal obstruction, requiring duodenojejunostomy or gastrojejunostomy in some cases.
|
Figure 9-1 • Pancreas divisum. Instead of draining through a common pancreatic duct, the ducts of Wirsung (major duct) and Santorini (minor duct) enter the duodenum separately. |
ANATOMY AND PHYSIOLOGY
The pancreas is a retroperitoneal structure located posterior to the stomach and anterior to the inferior vena cava and aorta. This yellowish, multilobed gland is divided into four portions: head, which includes the uncinate process; neck; body; and tail (Fig. 9-2). It lies in a transverse orientation, with the pancreatic head in intimate association with the C loop of the duodenum, the body draped over the spine, and the tail nestled in the splenic hilum.
|
Figure 9-2 • Regional anatomy of the pancreas. |
The arterial blood supply to the pancreatic head is derived from the anterior and posterior pancreaticoduodenal arteries (Fig. 9-3). These arteries arise from the superior pancreaticoduodenal artery, which is a continuation of the gastroduodenal artery, and from the inferior pancreaticoduodenal artery, which arises from the superior mesenteric artery. The body and tail are supplied from branches of the splenic and left gastroepiploic arteries. Venous drainage follows arterial anatomy and enters the portal circulation.
|
Figure 9-3 • Blood supply of the pancreas. The celiac axis gives rise to the common hepatic artery and splenic artery. The common hepatic artery gives rise to the gastroduodenal artery, which supplies the head of the pancreas, and the splenic artery gives rise the pancreatic magna and many small branches into the body and tail. In addition, the superior mesenteric artery gives rise to the inferior pancreaticoduodenals arteries, which supply the head and the uncinate process. |
Sympathetic innervation is responsible for transmitting pain of pancreatic origin, whereas efferent postganglionic parasympathetic fibers innervate islet, acini, and ductal systems. In patients with intractable pain from chronic pancreatitis who have failed operative drainage or resection, splanchnicectomy (sympathectomy) can be performed to interrupt sympathetic nerve fibers.
The functional units of the endocrine pancreas are the islets of Langerhans, which are multiple small endocrine glands scattered throughout the pancreas that make up only 1% to 2% of the total pancreatic cell mass. The bulk of the pancreatic parenchyma is exocrine tissue. Four islet cell types have been identified: A cells (alpha), B cells (beta), D cells (delta), and F cells (pancreatic polypeptide [PP] cells).
Alpha cells produce glucagon, which is secreted in response to stimulation by amino acids, cholecystokinin, gastrin, catecholamines, and sympathetic and parasympathetic nerves. The role of alpha cells is to ensure an ample supply of circulating nutritional fuel during periods of fasting. It promotes hepatic gluconeogenesis and glycogenolysis and inhibits gastrointestinal motility and gastric acid secretion.
P.70
The largest percentage of islet volume is occupied by the insulin-producing beta cells. The main function of insulin is to promote the storage of ingested nutrients. Insulin is released into the portal circulation in response to glucose, amino acids, and vagal stimulation. Insulin has both local and distant anabolic and anticatabolic activity. Local paracrine function is the inhibition of glucagon secretion by alpha cells. In the liver, insulin inhibits gluconeogenesis, promotes the synthesis and storage of glycogen, and prevents glycogen breakdown. In adipose tissue, insulin increases glucose uptake by adipocytes, promotes triglyceride storage, and inhibits lipolysis. In muscle, it promotes the synthesis of glycogen and protein.
Somatostatin is secreted by islet delta cells in response to the same stimuli that promote insulin release. Pancreatic somatostatin slows the movement of nutrients from the intestine into the circulation by decreasing pancreatic exocrine function, reducing splanchnic blood flow, decreasing gastrin and gastric acid production, and reducing gastric emptying time. Somatostatin also has paracrine-inhibitory effects on insulin, glucagon, and PP secretion.
F cells secrete PP after ingestion of a mixed meal. The function of PP is unknown; however, it may be important in priming hepatocytes for gluconeogenesis. Patients with pancreatic endocrine tumors have been noted to have elevated levels of circulating PP.
The basic functional unit of the exocrine pancreas is the acinus. Acinar cells contain zymogen granules in the apical region of the cytoplasm. Acini are drained by a converging ductal system that terminates in the main pancreatic excretory duct. The centroacinar cells of individual acini form the origins of the ducts, with intercalated duct cells lining the remainder.
P.71
Exocrine pancreatic secretions are products of both ductal and acinar cells. Ductal cells contribute a clear, basic-pH, isotonic solution of water and electrolytes, rich in bicarbonate ions. Secretion of pancreatic fluid is principally controlled by secretin, a hormone produced in the mucosal S cells of the crypts of Lieberkühn in the proximal small bowel. The presence of intraluminal acid and bile stimulates secretin release, which binds pancreatic ductal cell receptors, causing fluid secretion.
Pancreatic digestive enzymes are synthesized by and excreted from acinar cells after stimulation by secretagogues (cholecystokinin, acetylcholine). Excreted enzymes include endopeptidases (trypsinogen, chymotrypsinogen, and proelastase) and exopeptidases (procarboxypeptidase A and B). Other enzymes produced are amylase, lipase, and colipase. All peptidases are excreted into the ductal system as inactive precursors. Once in the duodenum, trypsinogen is converted to the active form, trypsin, by interaction with duodenal mucosal enterokinase. Trypsin, in turn, serves to activate the other excreted peptidases. In contrast to the peptidases, the enzymes amylase and lipase are excreted into the ductal system in their active forms.
ACUTE PANCREATITIS
PATHOGENESIS
Acute pancreatitis is a disease of glandular enzymatic autodigestion that has varying presentations, ranging from mild parenchymal edema to life-threatening hemorrhagic pancreatitis. Multiple causes have been identified, with alcoholism and gallstone disease accounting for 80% to 90% of cases among Western populations. The remaining cases are attributed to hyperlipidemia, hypercalcemia, trauma, infection, ischemia, trauma from endoscopic retrograde cholangiopancreatography (ERCP), and cardiopulmonary bypass (Table 9-1). The exact pathogenesis of acute pancreatitis remains unclear. One possibility is that obstruction of the ampulla of Vater by gallstones, spasm, or edema causes elevated intraductal pressure and bile reflux into the pancreatic duct. Activation and extravasation of intraparenchymal enzymes results in tissue destruction and ischemic necrosis of the pancreas and retroperitoneal tissues.
|
TABLE 9-1 Causes of Acute Pancreatitis |
|||||||||||
|
History
Because of the different degrees of pancreatic tissue destruction seen in cases of pancreatitis, the presentation of acute disease is varied, and diagnosis may be difficult. Important past medical history includes information regarding prior episodes of pancreatitis, alcoholism, and biliary colic. Patients present with upper abdominal pain (often radiating to the back), nausea, vomiting, and a low-grade fever. A severe attack of pancreatitis is manifested by hypotension, sepsis, and multiorgan failure. Patients with an alcoholic cause usually experience pain 12 to 48 hours after alcohol ingestion.
PHYSICAL EXAMINATION
Patients have upper abdominal tenderness, usually without peritoneal signs. The abdomen may be slightly distended secondary to a paralytic ileus. Low-grade fever and tachycardia are common.
DIFFERENTIAL DIAGNOSIS
Acute pancreatitis is often difficult to differentiate from other causes of upper abdominal pain. The clinical presentation may mimic that of a perforated peptic ulcer or acute biliary tract disease. Other conditions that may have similar presentations are acute intestinal obstruction, acute mesenteric thrombosis, and a leaking abdominal aortic aneurysm.
DIAGNOSTIC EVALUATION
More than 90% of patients who present with acute pancreatitis have an elevated serum amylase. However,
P.72
amylase levels are relatively nonspecific, because many other intra-abdominal conditions, including intestinal obstruction and perforated peptic ulcer, may cause amylase elevation. If the diagnosis is unclear, a lipase level should also be measured, because it is solely of pancreatic origin.
Leukocytosis >10,000/mL is common, and hemoconcentration with azotemia may also be present because of intravascular depletion secondary to significant third-space fluid sequestration. Hyperglycemia frequently occurs as a result of hypoinsulinemia, and hypocalcemia occurs from calcium deposition in areas of fat necrosis.
Routine chest x-ray may reveal a left pleural effusion, known as a sympathetic effusion, secondary to peripancreatic inflammation. Air under the diaphragm indicates perforation of a hollow viscus, such as a perforated peptic ulcer.
The classic radiographic finding on abdominal x-ray is a sentinel loop of dilated mid- to distal duodenum or proximal jejunum located in the left upper quadrant, adjacent to the inflamed pancreas. In cases of gallstone pancreatitis, radiopaque densities (gallstones) may be seen in the right upper quadrant.
Ultrasonography is the preferred modality for imaging the gallbladder and biliary ductal system, because it is more sensitive as compared with computed tomography (CT) scan. Ultrasound is the study of choice for the detection of cholelithiasis during the workup of gallstone pancreatitis.
CT is the most sensitive radiologic study for confirming the diagnosis of acute pancreatitis. Virtually all patients show evidence of either parenchymal or peripancreatic edema and inflammation. CT is also valuable in defining parenchymal changes associated with pancreatitis, such as pancreatic necrosis and pseudocyst formation. For severe cases, CT scanning with intravenous contrast is important for determining the percentage of pancreatic necrosis, which is a predictor of infectious complications. CT-guided interventional techniques can also be performed to tap peripancreatic fluid collections to rule out infection.
ERCP is useful for imaging the biliary ductal system and can be a diagnostic, as well as a therapeutic, modality. In the case of gallstone pancreatitis, the presence of common bile duct stones (choledocholithiasis) can be confirmed and the stones extracted endoscopically. Magnetic resonance cholangiopancreatography is a newer noninvasive technique that is a diagnostic, but not therapeutic, modality.
DISEASE SEVERITY SCORES
Because the clinical course of pancreatitis can vary from mild inflammation to fatal hemorrhagic disease, prompt identification of patients at risk for development of complications may improve final outcomes. The Ranson criteria are well-known prognostic signs used for predicting the severity of disease on the basis of clinical and laboratory results (Table 9-2). The ability to predict a patient's risk of infectious complications and mortality at the time of admission and during the initial 48 hours allows appropriate therapy to be instituted early in hospitalization. Mortality is correlated with the number of criteria present at admission and during the initial 48 hours after admission: 0 to two criteria, 1% mortality; three to four criteria, 16%; five to six criteria, 40%; and seven to eight criteria, 100%. Since the publication of the Ranson criteria in 1974, newer severity scores have been developed (Acute Physiology and Chronic Health Evaluation II score) to estimate mortality risk in critically ill patients. This calculation uses 12 variables in intensive care unit patients to predict mortality.
|
TABLE 9-2 Ranson Criteria for Acute Pancreatitis |
||||||||||||||||
|
||||||||||||||||
TREATMENT
Medical treatment of pancreatitis involves supportive care of the patient and treatment of complications as they arise. No effective agent exists to reverse the inflammatory response initiated by the activated zymogens. With adequate care, however, most cases are self-limited and resolve spontaneously.
P.73
Hydration is the most important early intervention in treating acute pancreatitis, because significant third-spacing occurs secondary to parenchymal and retroperitoneal inflammation. Hypovolemia must be avoided because pancreatic ischemia may quickly develop secondary to inadequate splanchnic blood flow.
Traditional treatment calls for putting the pancreas "to rest" by not feeding the patient (NPO). The goal is to decrease pancreatic stimulation, thereby suppressing pancreatic exocrine function. Nasogastric suction can be instituted to treat symptoms of nausea and vomiting.
Antibiotics should be initiated if there is infected pancreatic necrosis, as confirmed by biopsy. In the absence of this, antibiotics are widely used for pancreatitis, but their efficacy is controversial.
If the severity of disease necessitates a prolonged period of remaining NPO, an alternative method of administering nutrition must be instituted. Intravenous nutrition (total parenteral nutrition/hyperalimentation) is commonly initiated. Once pancreatic inflammation resolves, gradual advancement of oral intake proceeds, beginning with low-fat, high-carbohydrate liquids to avoid pancreatic stimulation.
Oxygen therapy may be necessary for treatment of hypoxia, which often occurs secondary to pulmonary changes thought to be due to circulating mediators. Evidence of atelectasis, pleural effusion, pulmonary edema, and adult respiratory distress syndrome may be seen on chest radiograph.
Surgical treatment of acute pancreatitis is directed at complications that develop secondary to the underlying disease process. During the early phase of pancreatitis, areas of necrosis may form because of tissue ischemia from enzyme activation, inflammation, and edema. Necrotic areas eventually liquefy and may become infected if they are unable to reabsorb and heal. CT scanning with intravenous contrast is the key test for defining the extent of pancreatic necrosis. Nonenhancement of 50% or more of the pancreas on CT scan is a strong predictor for the development of infectious complications. Infected collections require surgical debridement and drainage to avoid fatal septic complications.
Initially, collections around the pancreas during episodes of pancreatitis are termed acute pancreatic fluid collections. Peripancreatic collections that persist after the inflammatory phase has subsided may develop a thickened wall, or "rind." Such collections are called pancreatic pseudocysts. To alleviate symptoms or prevent major complications, surgical drainage is usually required for cysts >6 cm in diameter that have persisted for more than 6 weeks. Standard therapy is internal drainage into the stomach, duodenum, or small intestine.
During the later stage of disease, abscess formation may occur. The pathogenesis is a progression: an ischemic parenchyma progresses to necrosis and is seeded by bacteria, with eventual abscess formation. Most bacteria are of enteric origin, and standard antibiotic therapy is insufficient treatment. If surgical drainage and debridement are not performed, the mortality nears 100%. Percutaneous drainage is usually inadequate, because only the fluid component is removed and the necrotic infected tissue remains. These patients are often remarkably sick. Multiple debridements may be required when the episode is severe. It is not uncommon for anasarca to result from massive volume resuscitation, and it may be difficult to close the abdomen. In this case, a temporary closure should be used. Definitive closure is performed as early as possible after the infection is controlled and the edema has improved. Operations to remove infected pancreatic tissue can be extremely bloody and adequate access and blood should be available.
Hemorrhage secondary to erosion of blood vessels by activated proteases can be a life-threatening complication. Often it is the main hepatic, gastroduodenal, or splenic artery that bleeds. All efforts should be made to control this with angiography, because it can be exceedingly difficult to control this lesion in the operating room.
CHRONIC PANCREATITIS
Of patients with acute pancreatitis, a small number progress to chronic pancreatitis. The chronic form of disease is characterized by persistent inflammation that causes destructive fibrosis of the gland. The clinical picture is of recurring or persistent upper abdominal pain with evidence of malabsorption, steatorrhea, and diabetes.
PATHOGENESIS
Chronic pancreatitis can be categorized into two forms: calcific pancreatitis, usually associated with persistent alcohol abuse, and obstructive pancreatitis, secondary to pancreatic duct obstruction. Alcohol-induced calcific pancreatitis is the most common form of disease in Western populations. Proposed mechanisms of disease include ductal plugging and occlusion by protein and mineral precipitates. The resulting inflammation and patchy fibrosis
P.74
subsequently lead to parenchymal destruction and eventual atrophy of the gland. Obstructive chronic pancreatitis is due to ductal blockage secondary to scarring from acute pancreatitis or trauma, papillary stenosis, pseudocyst, or tumor. This blockage results in upstream duct dilatation and inflammation.
HISTORY
Abdominal pain is the principal presenting complaint and the most frequent indication for surgery. The pain is upper abdominal, is either intermittent or persistent, and frequently radiates to the back. Patients are often addicted to narcotic pain relievers. Other symptoms result from exocrine insufficiency (malabsorption) and endocrine insufficiency (diabetes mellitus).
DIAGNOSTIC EVALUATION
Given the functional reserve of the pancreas, the diagnosis of chronic pancreatitis is best made using imaging techniques that detect pancreatic morphologic changes rather than tests of glandular function. Exocrine function may be evaluated by the secretin cholecystokinin test, which is now rarely used.
The radiologic signs of chronic pancreatitis include a heterogeneously inflamed or atrophied gland, a dilated and strictured pancreatic duct, and the presence of calculi. Ultrasonography and CT are useful initial imaging procedures; however, ERCP is the most accurate means of diagnosing chronic pancreatitis, because it clearly defines the pathologic changes of the pancreatic ductal system and the biliary tree.
P.75
TREATMENT
Effective treatment of chronic abdominal pain is often the focus of care for patients with chronic pancreatitis. Opiates are useful for controlling visceral pain; however, many patients become opiate depen-dent over the long term. Alcohol nerve blocks of the celiac plexus have only moderate success.
Pancreatic exocrine insufficiency is treated with oral pancreatic enzymes, and insulin is used to treat diabetes mellitus. Ethanol intake by the patient must cease.
Surgical intervention is undertaken only if medical therapy has proved unsuccessful in relieving chronic intractable pain. Functional drainage of the pancreatic duct and the resection of diseased tissue are the goals of any procedure. Given ERCP and CT findings, the correct operation can be planned.
For patients with a "chain of lakes"–appearing pancreatic duct, caused by sequential ductal scarring and dilatation, a longitudinal pancreaticojejunostomy (Puestow procedure) is indicated to achieve adequate drainage. A Roux-en-Y segment of proximal jejunum is anastomosed side-to-side with the opened pancreatic duct, facilitating drainage (Fig. 9-4). Distal pancreatic duct obstruction causing localized distal parenchymal disease is best treated by performing a distal pancreatectomy.
|
Figure 9-4 • Longitudinal pancreaticojejunostomy used in the treatment of chronic pancreatitis. |
ADENOCARCINOMA OF THE PANCREAS
EPIDEMIOLOGY
Pancreatic adenocarcinoma is a leading cause of cancer death, trailing other cancers such as lung and colon. Men are affected more than women by a two-to-one ratio. Risk factors for development of pancreatic cancer are increasing age and cigarette smoking. The peak incidence is in the fifth and sixth decades. Ductal adenocarcinoma accounts for 80% of the cancer types and is usually found in the head of the gland. Local spread to contiguous structures occurs early, and metastases to regional lymph nodes and liver follow.
HISTORY
The signs and symptoms of carcinoma of the head of the pancreas are intrinsically related to the regional anatomy of the gland. Patients classically complain of obstructive jaundice, weight loss, and constant deep abdominal pain owing to peripancreatic tumor infiltration. Patients may present with jaundice and a palpable nontender gallbladder, indicating tumor obstruction of the distal common bile duct (Courvoisier sign). Pruritus often accompanies the development of jaundice.
DIFFERENTIAL DIAGNOSIS
The differential diagnosis of malignant obstructive jaundice includes carcinomas of the ampulla of Vater, pancreatic head, distal common bile duct, or duodenum.
DIAGNOSTIC EVALUATION
The most common laboratory abnormalities are elevated alkaline phosphatase and direct bilirubin levels, indicating obstructive jaundice. The average bilirubin level in neoplastic obstruction is typically higher than that seen in bile duct obstruction from gallstone disease.
CT and ERCP are the modalities of choice for evaluating pancreatic cancer. CT reveals the location of the mass, the extent of tumor invasion or metastasis, and the degree of ductal dilatation (Fig. 9-5). ERCP defines
P.76
the ductal anatomy and the extent of ductal obstruction and provides biopsy specimens for tissue diagnosis. Drainage stents can be placed into the common bile duct during ERCP for biliary tree decompression. Imaging information suggesting unresectability includes local tumor extension, contiguous organ invasion, superior mesenteric vein or portal vein invasion, ascites, and distant metastases.
|
Figure 9-5 • Pancreatic adenocarcinoma. Computed tomography image demonstrates an endoscopically placed biliary stent (curved arrow), passing through a mass (M) in the head of the pancreas. The pancreatic adenocarcinoma has almost obliterated the superior mesenteric vein (arrowhead) and abuts the superior mesenteric artery (open arrow). A retrocaval lymph node is noted (thick arrow). From Kelsen DP, Daly JM, Kern SE, et al. Gastrointestinal Oncology: Principles and Practice. Philadelphia: Lippincott Williams & Wilkins, 2002. |
TREATMENT
The operation for resectable tumors in the head of the pancreas is pancreaticoduodenectomy (Whipple procedure; Fig. 9-6). This major operation entails the en bloc resection of the antrum, duodenum, proximal jejunum, head of pancreas, gallbladder, and distal common bile duct.
|
Figure 9-6 • Pancreaticoduodenectomy (Whipple procedure). Preoperative anatomic relationships (A) and postoperative reconstruction (B). |
PROGNOSIS
Long-term survival for pancreatic cancer remains dismal, and most patients die within 1 year of diagnosis. The 5-year survival rate for all patients with tumors of the head of the pancreas is approximately 3%. For individuals with tumors amenable to Whipple resection, the 5-year survival rate is only 10% to 20%. Tumors of the body and tail are invariably fatal, because diagnosis is usually made at a more advanced stage as a result of the lack of early obstructive findings.
OTHER PANCREATIC NEOPLASMS
Approximately 20% of all pancreatic cystic lesions will not be pseudocysts. These lesions may be benign or malignant, but even the malignant ones carry better prognosis than adenocarcinoma. Simple cysts are usually congenital. When they appear in children, no treatment is necessary. In patients with polycystic kidney disease, 10% will also have pancreatic cysts. They do not require treatment.
More complicated cystic disease of the pancreas includes serous cystadenoma and mucinous cystic neoplasms. Serous cystadenomas most often occur in women between 30 and 50 years of age. They are generally asymptomatic. Ultrasound reveals a complex low-density mass with fine septae. The fluid is generally clear. Resection is generally curative. Mucinous cystic neoplasms have malignant potential and should be resected with a margin, usually requiring formal partial pancreatectomy. Survival is excellent at 5 years at approximately 70%.
Solid and cystic papillary neoplasms tend to present as large lesions in young women. Resection is often curative.
Intraductal papillary mucinous neoplasms are distinguished from the other cystic lesions of the pancreas in that the pancreatic duct is enlarged because of mucin deposition. ERCP demonstrates mucin in the duct. These lesions have malignant potential and require resection. Long-term prognosis is excellent with resection.
P.77
FUNCTIONAL TUMORS OF THE PANCREAS
INSULINOMA
This is the most common tumor of pancreatic islet cells. It is more common in women than men and commonly affects middle-aged patients. Hypersecretion of insulin causes symptoms. Diagnosis is made from the classic Whipple triad of low fasting blood sugars (less than 45 mg/dL); symptoms of hypoglycemia, including palpitations, tachycardia, and shaking; and resolution by administration of exogenous glucose. Patients can lose consciousness or experience seizures. Although most are sporadic, any patient with this syndrome should be suspected of having multiple endocrine neoplasia (MEN) type I, especially if the lesions are multiple. Patients will have an immunoreactive insulin-to-glucose ratio of greater than 0.3 and elevated proinsulin and C-peptide levels. These lesions may be difficult to find because of their small size. Workup includes CT or magnetic resonance imaging to localize the lesion and determine whether metastases are present. Somatostatin receptor scintigraphy may be useful but often fails to localize the lesion. Even if the lesion is not localized, surgical exploration is indicated to try to locate and resect the tumor. Intraoperative ultrasound should be used in this case. Even when metastatic disease is present, resection may be indicated for symptomatic relief.
Gastrinoma
This tumor is defined by gastrin hypersecretion, causing the severe peptic ulcer disease of Zollinger-Ellison syndrome. The syndrome is slightly more common in men than in women and generally affects patients in middle age. Eighty percent of cases are sporadic, whereas 20% will occur in association with MEN type I. These lesions most commonly occur in the pancreas or duodenum, but can also occur in other areas. Patients present with symptoms of acid hypersecretion, ulcers, and secretory diarrhea. This lesion accounts for less than 1% of all ulcer disease. Patients will have elevated gastrin levels and basal acid output. Secretin stimulation test is used to confirm the diagnosis. CT, magnetic resonance imaging, and ultrasound all have some utility in localizing the tumor, but somatostatin scintigraphy is the test of choice. In sporadic cases not associated with MEN type I, treatment is medical management of gastric hypersecretion and then resection, given the malignant potential of the lesion. In patients with MEN type I, management must be coordinated with treatment of the other abnormalities.
OTHER TUMORS
Other, rarer types of neuroendocrine tumors that may affect the pancreas may elaborate vasoactive intestinal peptide, pancreatic polypeptide, adrenocorticotropic hormone, and growth hormone–releasing factor.
Key Points