Pancreas Anatomy and Sonography

Pancreas Anatomy and Physiology

• The pancreas is a non-encapsulated organ located in the retroperitoneal space, between the duodenal loop and splenic hilum.
• It's divided into head, uncinate process, neck, body, and tail, each with distinct dimensions.
• The head lies anterior to the inferior vena cava (IVC) and medial to the second part of the duodenum.
• The uncinate process extends posterior and medial from the head, behind the superior mesenteric vein (SMV) and portal vein (PV) confluence.
• The neck is anterior to the IVC and SMV/PV confluence, and to the right and more inferior than the body/tail.
• The body is anterior to the abdominal aorta, superior mesenteric artery (SMA), and left renal vein (LRV). The stomach is anterior to the body, and the left kidney is lateral to it.
• The tail is anterior and medial to the splenic hilum, potentially obscured by stomach gas.

Sonographic Evaluation of the Pancreas

• Indications for evaluation include epigastric/abdominal pain, abdominal distension, jaundice, and abnormal amylase/lipase levels.
• Patient preparation involves an 8-12 hour NPO period. Gastroscopic exams within 6 hours are contraindicated due to introduced air.
• Breathing techniques to optimize imaging include using the left lobe of the liver as an acoustic window, positioning the patient supine or right lateral decubitus, and allowing water in the stomach to serve as a window.
• Pancreas shapes can be horseshoe, dumbbell, comma, or tadpole.
• Echogenicity is typically equal to or slightly hyperechoic to the liver. Age and body habitus influence echogenicity; in children, the pancreas is often hypoechoic, while in adults, hypoechoic pancreas is often abnormal.

Pancreatic Physiology

• Exocrine function involves secretion of digestive enzymes (trypsin, chymotrypsinogen, lipase, amylase) into the ductal system, essential for digestion and absorption. The pancreas can secrete up to 4 liters of exocrine fluid daily.
• Endocrine function involves hormone production secreted into the blood or tissues, via the Islets of Langerhans.
• Alpha cells secrete glucagon, which converts stored glycogen to glucose.
• Beta cells secrete insulin, regulating glucose uptake by liver, muscle, and fat tissue. Low insulin can lead to diabetes.
• Delta cells secrete somatostatin, which regulates glucagon and insulin release.

Pancreatic Ducts

• The common bile duct (CBD) runs posterior to the first part of the duodenum and the head of the pancreas.
• The CBD and the main pancreatic duct (duct of Wirsung) join to form the hepatopancreatic ampulla (ampulla of Vater), opening into the second part of the duodenum at the major papilla.
• The normal measurement for the main pancreatic duct is 2mm or less.
• The accessory pancreatic duct (duct of Santorini) opens into the second part of the duodenum at the minor papilla, roughly 2cm superior to the ampulla of Vater.
• Around 50% of the population has a complete regression of the duct of Santorini.

Congenital Pancreatic Pathology

• Pancreas divisum: Failure of the dorsal and ventral pancreatic ductal systems to fuse, resulting in a smaller Santorini's duct draining the head, and a larger dorsal duct draining the rest of the gland. This isn't usually problematic but may lead to insufficient pancreatic enzyme drainage.
• Annular pancreas: The ventral pancreas or pancreatic head encircles the second portion of the duodenum, potentially presenting with a double-bubble sign. More common in males and often associated with complete or partial duodenal atresia.
• Ectopic pancreas: Pancreas tissue grows in other organs (stomach, duodenum, intestines).
• Agenesis: An extremely rare condition with complete or partial dorsal agenesis.

Pancreatic Pathology (Non-neoplastic)

• Cystic Fibrosis: An exocrine gland disorder causing viscous secretions, hindering pancreatic function and leading to recurrent pancreatitis. Sonographic findings may include increased echogenicity, gland atrophy, fibrosis, and fatty replacement.
• Polycystic Disease: Autosomal dominant disorder causing multiple cysts in kidneys, liver, and less commonly (10%) in the pancreas.
• Von Hippel-Lindau Disease: Autosomal dominant disorder associated with pancreatic abnormalities (adenomas, islet cell tumors).

Pancreatic Pathology (Inflammatory)

• Acute Pancreatitis: Inflammation of the pancreas, often with sudden onset, severe epigastric or RUQ pain, nausea/vomiting, and mild fever. Early imaging may be unremarkable but eventually shows an enlarged, hypoechoic gland and possible ductal dilation. A significant cause is biliary tract disease (gallstones).
• Chronic Pancreatitis: Irreversible destruction of pancreatic tissue due to repeated inflammation. Symptoms include persistent epigastric pain, nausea/vomiting, flatulence, and weight loss. Common causes include alcohol abuse, autoimmune pancreatitis, and hereditary pancreatitis. Imaging findings include a small echogenic gland, calcifications, and ductal dilation.

Pancreatic Pathology (Neoplastic)

• Pancreatic Adenocarcinoma: A significant cause of cancer-related death, most frequently arising from the pancreatic head. Symptoms, initially non-specific, can include abdominal pain, painless jaundice, and weight loss. Risk factors include smoking, high-fat diet, and chronic pancreatitis. Imaging findings include a solid, hypoechoic mass, and possible bile duct obstruction.
• Cystic Neoplastic Lesions: Include benign serous cystadenomas (microcystic adenomas), and malignant mucinous cystic adenomas (macrocystic cystadenomas or cystadenocarcinomas). These are less common, with serous cystadenomas showing small cysts and possible calcifications. Mucinous cysts are larger, have multiple septations and debris, and may be pre-malignant or malignant.
• Islet Cell Tumors: Uncommon, functioning tumors often difficult to localize by ultrasound. Common types include insulinomas, gastrinomas, and glucagonomas.

Whipple Procedure

• Also known as pancreaticoduodenectomy, performed for cancer of the pancreatic head. Removes a portion of the head of the pancreas, bile duct, gallbladder, and duodenum.

Other Key Points

• Labs: Amylase and lipase are significantly elevated in acute pancreatitis and other conditions, like pancreatic malignancy obstructing pancreatic or biliary ducts.
• Pancreatic Pseudocysts: Fluid-filled collections of pancreatic enzymes and debris, typically walled off by the retroperitoneum. Develop due to acute pancreatitis, chronic pancreatitis, pancreatic trauma, etc.
• Multiple Endocrine Neoplasia (MEN): An inherited endocrine disorder with involvement of parathyroids, pancreatic islet cells, pituitary glands, and adrenal glands, often leading to cancer.
• Liver Transplants: The most common reason is end-stage liver disease. Post-operative complications include vascular complications like hepatic artery/portal vein/IVC thrombosis or stenosis. Complications include rejection and infection.