Section 4.4: Pancreatic Pathology

Section 4.4: Pancreatic Pathology

Pancreatic Anatomy and Normal Values

Evaluation of the pancreas is a highly technical aspect of the ARDMS Abdomen exam. The normal pancreas is isoechoic or hyperechoic relative to the normal liver. In pediatric patients, the pancreas can be slightly hypoechoic. With age, the gland undergoes fatty infiltration and fibrotic changes, leading to decreased size (atrophy) and increased echogenicity. The main pancreatic duct (duct of Wirsung) should be measured in the body of the gland and is considered normal when it is 2 mm or less in diameter. The pancreas is retroperitoneal, and visualization is often obscured by gas in the overlying stomach and duodenum. Utilizing the left lobe of the liver as an acoustic window, applying graded compression, or having the patient drink water to fill the stomach can improve visualization.

Acute Pancreatitis

Acute pancreatitis is an acute inflammatory process of the pancreas. The most common etiologies are biliary tract disease (gallstones obstructing the ampulla of Vater) and alcohol abuse.

• Sonographic Findings:
  • Diffuse Enlargement: The gland is enlarged, swollen, and edematous.
  • Hypoechoic Echotexture: The pancreas appears hypoechoic relative to the liver. This occurs because interstitial fluid, inflammatory exudate, and cellular swelling reduce the scattering of ultrasound waves.
  • Vascular Compression: The swollen pancreas can compress the adjacent splenic vein, which runs along its posterior border.
  • Focal Pancreatitis (Phlegmon): An inflammatory mass that can mimic pancreatic cancer. It appears as a localized hypoechoic area, typically in the pancreatic head.
  • Fluid Collections: Sonographers must search for peripancreatic fluid, which commonly accumulates in the lesser sac (between the stomach and pancreas) and the anterior pararenal space.
• Laboratory Findings: Serum amylase rises within 24 hours of onset, while serum lipase rises within 72 hours and remains elevated longer. Lipase is more specific for pancreatitis.

Chronic Pancreatitis

Chronic pancreatitis is characterized by progressive, irreversible destruction of the pancreatic parenchyma, leading to fibrosis, atrophy, and loss of endocrine and exocrine function. It is most commonly caused by chronic alcoholism.

• Sonographic Findings:
  • Atrophy: The gland is shrunken and small.
  • Coarse, Hyperechoic Echotexture: The parenchyma is heterogeneous and hyperechoic due to extensive fibrosis and fatty replacement.
  • Pancreatic Calcifications: Multiple, bright echogenic foci scattered throughout the parenchyma, representing intraductal calculi. This is the hallmark diagnostic feature.
  • Pancreatic Duct Dilation: The main pancreatic duct is dilated (> 2 mm) and tortuous, displaying a beaded appearance due to strictures and stone obstruction.

Pancreatic Pseudocysts

A pancreatic pseudocyst is an encapsulated collection of pancreatic secretions, blood, and necrotic debris. Unlike a true cyst, its wall is composed of fibrous tissue and inflammatory membranes rather than an epithelial lining.

• Clinical Context: Typically develops 4–6 weeks after an episode of acute pancreatitis or pancreatic trauma.
• Sonographic Appearance: A well-defined, round or oval mass, most commonly located in the lesser sac. It is usually anechoic but can contain internal debris, septations, or gas bubbles. It demonstrates posterior acoustic enhancement.
• Complications: Pseudocysts can rupture into the peritoneal cavity, cause biliary obstruction, or erode into adjacent vessels, leading to a life-threatening pseudoaneurysm.

Pancreatic Adenocarcinoma and the Courvoisier Gallbladder

Pancreatic adenocarcinoma is the most common primary pancreatic malignancy, accounting for 95% of cases. It arises from the ductal epithelium, occurs more frequently in elderly males, and carries an extremely low survival rate.

• Clinical Presentation: Painless jaundice (due to CBD compression), weight loss, and epigastric pain radiating to the back.
• Sonographic Findings:
  • Hypoechoic Mass: A poorly defined, homogeneous, hypoechoic solid mass, most commonly located in the pancreatic head (70% of cases).
  • Double Duct Sign: Concurrent dilation of the common bile duct and the main pancreatic duct. This occurs when a pancreatic head tumor obstructs both ducts at the ampulla of Vater.
  • Courvoisier Gallbladder: A palpably enlarged, distended, non-tender gallbladder filled with bile. This is caused by mechanical obstruction of the distal CBD, typically by a pancreatic head mass.
  • Vascular Invasion: The mass can encase or invade the superior mesenteric vein (SMV), portal vein, splenic vein, or superior mesenteric artery (SMA). Evaluation of vascular patency is critical for staging.

Pancreatic Cystadenomas: Serous vs. Mucinous

Cystic neoplasms of the pancreas are divided into two main categories based on malignancy potential:

1. Serous Cystadenoma (Microcystic): A benign lesion most common in elderly women. Sonographically, it appears as a cluster of multiple tiny cysts (< 2 cm). Because the cysts are so small, the multiple acoustic interfaces can cause the mass to appear solid and hyperechoic. A central stellate scar with calcification is highly specific.
2. Mucinous Cystadenoma / Cystadenocarcinoma (Macrocystic): A premalignant or malignant lesion, most commonly occurring in the body or tail of the pancreas in middle-aged women ("mother tumor"). Sonographically, it presents as a large, multilocular cystic mass (> 2 cm) with thick septations, internal debris, papillary projections, or mural nodules.