current pancreas

Pancreatic Location and Gross Anatomy

Anatomy and location of the pancreas in the retroperitoneum

Anatomic Location:
- Situated within the epigastric region of the retroperitoneum.
- Positioned anterior to the abdominal aorta and inferior vena cava (IVC).
- Located posterior to the stomach, which frequently covers the organ with overlying bowel gas.
- The pancreatic head is positioned within the C-loop of the duodenum.
- The pancreatic tail rests medial to the splenic hilum.

Gross Anatomical Structure:
- Divided into five main anatomical sections: head, uncinate process, neck, body, and tail.
- The head is typically located more caudally compared to the body and tail.
- Characterized as a soft, lobulated organ that lacks a true connective tissue capsule.
Dimensions and Size Variations:
- Average organ length ranges from $12\text{ cm}$ to $15\text{ cm}$ .
- Size correlates with sex assigned at birth, with male pancreases being larger on average than female pancreases.

Pancreatic Ducts and Measurements

Pancreatic ductal system and entry into the duodenum

Main Pancreatic Duct (Duct of Wirsung):
- Traverses the main body of the gland.
- Merges with the common bile duct (CBD) at the ampulla of Vater.
- Empties into the second portion of the duodenum through the sphincter of Oddi at the major duodenal papilla.
Accessory Pancreatic Duct (Duct of Santorini):
- A smaller secondary duct branch.
- Empties separately into the duodenum at the minor duodenal papilla.
Normal Duct Caliber Measurements:
- The main pancreatic duct averages approximately $2\text{ mm}$ in overall lumen caliber.
- Clinical Sonography Rule: If the pancreatic duct is visualized during an ultrasound examination, it must be measured.

Relationships to Surrounding Vasculature and Structures

Pancreatic Head:
- Situated right lateral to the superior mesenteric vein (SMV) / portal confluence.
- Positioned directly anterior to the IVC.
- Located inferior to the main portal vein (MPV).
- Contains two distinct circular vessel cross-sections in ultrasound views:
  - Anterior aspect: Gastroduodenal artery (GDA).
  - Posterior aspect: Common bile duct (CBD).
Uncinate Process:
- Extends posterior to the superior mesenteric vein (SMV).
- Lies directly anterior to the IVC.
Pancreatic Neck:
- Situated directly anterior to the portal confluence and superior mesenteric vein (SMV).
- Hamburger Sign (Sagittal View): Formed by the anatomical sandwich of the pancreatic neck (anterior bun), SMV (meat/middle structure), and uncinate process/IVC (posterior bun).
Pancreatic Body:
- Positioned anterior to the splenic vein, superior mesenteric artery (SMA), and abdominal aorta.
- Lies anterior to the origins of the celiac trunk and SMA.
Pancreatic Tail:
- Positioned lateral and anterior to the splenic vein.
- Extends toward the medial side of the splenic hilum.
- The splenic vein and splenic artery dive posteriorly along the medial side of the pancreatic tail, often appearing in cross-section at its posterior boundary when imaged in oblique or transverse planes.

Congenital Anatomic Variants

Diagnostic Overview:
- Transabdominal ultrasound plays a minimal role in diagnosing congenital pancreatic variants.
- Variants are generally asymptomatic, have minimal clinical significance, and are typically discovered incidentally on CT, MRI, or endoscopic procedures.
Pancreatic Divisum:
- Occurs in approximately $10\%$ of the general population.
- Develops prenatally due to the failure of the embryonic dorsal and ventral pancreatic bud ducts to fuse.
- Classic Anatomy: The small ventral duct (duct of Wirsung) drains only the ventral head via the major papilla, while the larger dorsal duct (duct of Santorini) drains the majority of the gland via the minor papilla.
- Clinical Impact: Usually benign, but may predispose individuals to recurrent pancreatitis or complicate cases of pancreatic cancer that do not involve the main duct. On routine abdominal ultrasound, it can occasionally mimic a solid mass; definitive evaluation requires Endoscopic Ultrasound (EUS) or CT/MRCP.

Diagram of Annular Pancreas surrounding the duodenum

Annular Pancreas:
- A rare congenital anomaly where a ring of ectopic pancreatic parenchyma surrounds the first portion (C-loop) of the duodenum.
- Can cause extrinsic duodenal obstruction resulting in symptoms such as abdominal pain, abdominal distention, and persistent vomiting.
- On ultrasound, it presents as pancreatic tissue encircling or appearing within the duodenal wall area adjacent to the IVC and right kidney.

Agenesis of the dorsal pancreas with dependent stomach sign

Partial Agenesis / Agenesis of Dorsal Pancreas (ADP):
- An extremely rare congenital anomaly.
- Characterized by the partial or complete absence of the pancreatic body and tail.
- Imaging Sign: The "dependent stomach sign" or "dependent intestine sign," wherein the empty distal pancreatic bed is filled by the stomach or bowel loops abutting the anterior border of the splenic vein.

Pancreatic Physiology: Endocrine and Exocrine Functions

Dual Functional Roles:
- Functions as both an endocrine gland (releasing hormones directly into the vascular system) and an exocrine gland (secreting digestive juice into ductal systems entering the gastrointestinal tract).

Histology and architecture of pancreatic islets and acini

Endocrine Function (Islets of Langerhans):
- Islet cells are vascularly interspersed microscopic clusters arranged around capillaries, located in their highest concentration within the pancreatic tail.
- Alpha Cells:
  - Secrete Glucagon in response to low blood glucose levels (hypoglycemia).
  - Stimulates glycogenolysis (breakdown of stored glycogen into glucose in hepatocytes).
  - Stimulates gluconeogenesis (formation of new glucose from lactic acid and amino acids).
  - Inhibited by hyperglycemia.
- Beta Cells:
  - Secrete Insulin in response to high blood glucose levels (hyperglycemia).
  - Facilitates cellular glucose uptake and carbohydrate metabolism.
  - Promotes glycogenesis (conversion and storage of glucose as glycogen).
  - Increases amino acid uptake, protein synthesis, and fatty acid synthesis (lipogenesis).
  - Slows down glycogenolysis and gluconeogenesis.
  - Hormonal imbalance or deficiency results in Diabetes Mellitus.
- Delta Cells:
  - Secrete Somatostatin.
  - Acts locally to inhibit the secretion of both insulin and glucagon.
  - Inhibits the release of growth hormone (GH) and thyroid-stimulating hormone (TSH) from the anterior pituitary gland.
Exocrine Function (Acinar Cells):
- Exocrine cells are arranged in grape-like clusters termed acini.
- Synthesize, package, and secrete digestive proenzymes and alkaline fluids into intercalated ducts leading to the main pancreatic duct.
- Bicarbonate Ion Production:

Regulation of Pancreatic Secretions and Digestive Hormones

Neural Regulation:
- Mediated by the Vagus Nerve (Cranial Nerve X) via the Parasympathetic Nervous System ("rest and digest").
- Triggers early secretion of a modest volume of water, electrolytes, and digestive enzymes upon sensory perception or consumption of food.
Hormonal Regulation:
- Cholecystokinin (CCK):
  - Synthesized and released by duodenal mucosal cells in response to the arrival of fatty acids and partially digested proteins.
  - Stimulates acinar cells to produce and release enzyme-rich pancreatic juice.
  - Induces gallbladder contraction and relaxation of the sphincter of Oddi.
  - Increases hepatic bile acid synthesis and slows gastric emptying.
- Secretin:
  - Produced by duodenal epithelial cells in response to acidic chyme ( $\text{pH} < 4.5$ ) entering from the stomach.
  - Stimulates ductal cells to produce water and bicarbonate-rich fluid.
  - Inhibits gastric acid secretion, reduces stomach and intestinal peristalsis, and promotes liver bile secretion.
- Gastrin: Secreted by the
  stomach
  • Stimulates acid
  secretion by the
  stomach and
  enzymes secretion
  by the pancreatic
  cells.
  Gastrin hormone Function. Gastrointestinal hormone that affects Gastric acid secretion in sto
  mach, aids in bile production in liver,

Diagnostic Laboratory Tests and Imaging Modalities

Laboratory Diagnostic Tests:
FASTING BLOOD GLUCOSE
• GLUCOSE TOLERANCE
• AMYLASE
• LIPASE
• CALCIUM
• Fecal Fats

Sonographic Evaluation and Clinical Guidelines

Sonographic Appearance:
- Normal adult pancreatic parenchyma is homogeneous and mildly hyperechoic relative to the adjacent liver parenchyma due to retroperitoneal fat deposition.
- May appear isoechoic or hypoechoic in younger patients or thin individuals with low body fat stores.
- The portosplenic confluence and splenic vein form the primary posterior anatomical landmark marking the back border of the pancreatic body and tail in transverse planes.
Patient Preparation and Techniques:
- NPO Status: Patient should be fasting for $6\text{ to }8\text{ hours}$ prior to the exam to minimize interference from overlying stomach and bowel gas.
- Patient Positioning: Utilize supine, semi-erect, fully erect, or right lateral decubitus (RLD) positions.
Essential Clinical History Questions:
- History of acute or chronic pancreatitis?
- Prior abdominal surgeries (e.g., cholecystectomy, pancreatic resection)?
- Presence of epigastric pain radiating to the back?
- Nausea, vomiting, or fever?
- Personal or family history of gallstones?
- Diagnosis of Type 1 or Type 2 Diabetes?
- Unexplained weight loss (including exact amount and timeframe)?
Standard Sonographic Protocol Routine:
- Transverse View: Head and Uncinate process
- Transverse View: Body
- Transverse View: Tail
- Sagittal View: Head
- Sagittal View: Neck and Uncinate process
- Sagittal View: Body
- Sagittal View: Tail (approached from midline or left intercostal position)