The Pancreas

ANATOMY OF THE PANCREAS

Overview of the Pancreas

  • The pancreas lies anterior to the first and second lumbar bodies. It is located deep within the epigastrium (upper central region of the abdomen) and left hypochondrium (upper left section of the abdomen) and is positioned behind the lesser omental sac.

  • Major posterior vascular landmarks include the aorta and inferior vena cava, contributing to its anatomical positioning.

  • The pancreas extends in a horizontal oblique fashion from the second portion of the duodenum (first part of the small intestine) to the splenic hilum (the entry point for blood vessels to the spleen).

  • Variations of the lie of the pancreas include:

    • Transverse

    • Horseshoe

    • Sigmoid

    • L-shaped

    • Inverted V

Structural Components of the Abdomen Related to the Pancreas

  • The pancreas is surrounded by important anatomical features:

    • Stomach: anterior to the body and tail of the gland

    • Vessels: Aorta and inferior vena cava, superior mesenteric artery and vein are posterior to the pancreas.

    • Liver: Located above the pancreas, with additional connections through various ligaments and spaces (right and left hypochondrium spaces, colic flexure, and kidneys).

Coronary Spatial Relationships

  • Majority of the pancreas is situated in the retroperitoneal cavity.

    • Head: Surrounded by peritoneum

    • Anterior Pararenal Space: Occupied by the pancreas

Pancreatic Relationships

a. Borders

  • Superior Border: Stomach, duodenum, and transverse colon define its boundaries.

  • Inferior Border: Lies superior to the connective prevertebral tissues, portal-splenic confluence, superior mesenteric vessels, aorta, inferior vena cava, and lower border of the diaphragm.

Four Divisions of the Pancreas

  • Head: Most inferior portion.

  • Neck: Lies anterior to the portal-splenic confluence.

  • Body: Largest section of the pancreas.

  • Tail: Extends towards the splenic hilum.

Anatomy in Context: Ductal Relationships
Pancreatic Ducts

  • Duct of Wirsung: Primary duct; it extends along the entire length of the pancreas, entering the duodenum with the common bile duct at the ampulla of Vater, regulated by the sphincter of Oddi.

  • Duct of Santorini: Accessory duct draining the upper anterior head of the pancreas.

Characteristics of the Normal Pancreas
Size Regulations

  • On ultrasound, the anteroposterior dimensions are typically:

    • Head: Normally 2−32-3 cm. Abnormal if >33 cm.

    • Neck: Normally 1.5−2.51.5-2.5 cm. Abnormal if >2.52.5 cm.

    • Body: Normally 2−2.52-2.5 cm. Abnormal if >2.52.5 cm.

    • Tail: Normally 1−21-2 cm. Abnormal if >22 cm.

  • The main pancreatic duct (Duct of Wirsung) usually measures <22 mm in diameter.

Echogenicity

  • The normal pancreas should have echogenicity greater than that of the liver but less than that of the spleen, depending on the fatty/fibrous texture. In older individuals, it may appear more echogenic due to fatty infiltration.

Echotexture and Surface

  • The pancreas has a homogeneous echotexture with a smooth to slightly lobulated surface (notably due to the islets of Langerhans).

Vascular Supply
Arterial Supply

  • Anterior and Inferior Pancreaticoduodenal Arteries: Supply the pancreas head and part of the duodenum.

  • Splenic Artery: Supplies body and tail of the pancreas via four branches which include:

    • Suprapancreatic (rising from the celiac axis and splenic artery)

    • Pancreatic

    • Prepancreatic (before the pancreas)

    • Prehilar (before leaving the spleen)

  • Additional Arteries: Inferior pancreaticoduodenal arteries (part of superior mesenteric artery).

Venous Drainage

  • The pancreas's venous drainage occurs through the tributaries of the splenic and superior mesenteric veins, which form the portal venous system at the posterior border of the pancreas. These vessels are important sonographic landmarks for localizing the pancreas.

Congenital Anomalies of the Pancreas
Examples

  • Agenesis: Complete absence of the pancreas. Sonographically, absence of pancreatic tissue in the normal location.

  • Pancreas Divisum: Dorsal pancreas drains through the minor papilla, while the ventral part drains through the major papilla. Sonographically, may show a dilated dorsal pancreatic duct and a normal or small ventral duct, but often difficult to diagnose with ultrasound alone.

  • Ectopic Pancreatic Tissue: Presence of pancreatic tissue outside the normal anatomic location. Sonographically, a small, well-defined mass with echogenicity similar to the pancreas, located in unusual sites like the stomach or duodenum.

  • Annular Pancreas: Occurs when the ventral bud does not rotate properly during development, surrounding the duodenum, and possibly causing duodenal obstruction. Sonographically, may show duodenal obstruction (double bubble sign) and pancreatic tissue encircling the duodenum, though often obscured by bowel gas.

Pancreatic Functions
Exocrine Functions

  • Includes the secretion of enzymes for digestion, such as:

    • Lipase: Digests fats

    • Amylase: Digests carbohydrates

    • Proteolytic Enzymes (Trypsin, Chymotrypsin, Carboxypeptidase): Digests proteins

    • Nucleases: Digests nucleic acids

Endocrine Functions

  • The pancreatic cell types and their respective hormones include:

    • Beta Cells: Secrete Insulin, converting glucose into glycogen.

    • Alpha Cells: Secrete Glucagon, converting glycogen into glucose.

    • Delta Cells: Secrete Somatostatin, acting as an inhibitor of alpha and beta cells.

Laboratory Tests
Common Tests to Evaluate Function

  • Amylase Tests: Elevated levels may indicate pancreatic issues.

  • Lipase Tests: More specific for pancreatic inflammation.

  • Glucose Tests: Levels indicate endocrine function effects.

Sonographic Evaluation of the Pancreas
Stepping Stones for Visualization

Sonographic scans require identifying critical structures for accurate evaluation:

  • Landmarks: Superior mesenteric artery (SMA), gastroduodenal artery, portal vein, inferior vena cava, common bile duct, pancreatic duct (Duct of Wirsung), and antrum of stomach when assessing pancreas and its vascular supply. The common bile duct usually runs posterior to the head of the pancreas.

Imaging Process

  • Pancreatic structure visualization depends on patient positioning (e.g., left lateral decubitus position, erect position to move bowel gas). The stomach's position relative to the pancreas forms essential landmarks; fluid in the stomach can serve as an acoustic window.

Pathology of the Pancreas
Pancreatitis

  • It is inflammation of the pancreas categorized as:

    • Acute and Chronic

    • Severity: Ranges from mild to severe.

    • Caused by duct blockage and damage; tissues may be digested by their enzymes.

Acute Pancreatitis

  • Characterized by interstitial edema with minimal peripancreatic inflammation.

  • Sonographic Findings: Pancreas may appear diffusely enlarged and hypoechoic due to edema. Often, the borders are ill-defined. Peripancreatic fluid collections (often anechoic or hypoechoic) may be seen, particularly in the lesser sac, paracolic gutters, or around the kidneys.

  • Extra Pancreatic Fluid Collections and Edema: Visible as anechoic or hypoechoic fluid collections, potentially with internal echoes if complicated (e.g., hemorrhage, infection). Diffuse edema appears as hypoechoic infiltration of fat.

  • Complications: Spontaneous rupture of pseudocysts, hemorrhagic pancreatitis, phlegmonous pancreatitis, and pancreatic abscess formation.

Hemorrhagic Pancreatitis

  • A severe form characterized by extensive necrosis of the pancreas with associated bleeding.

  • Sonographic Findings: Pancreas appears heterogeneous with areas of increased echogenicity (from hemorrhage) and decreased echogenicity (from necrosis). Fluid collections may be complex, containing both anechoic and solid or echogenic components.

Phlegmonous Pancreatitis

  • A diffuse inflammatory edema of the soft tissues, often involving the pancreas and peripancreatic tissues, typically without necrosis.

  • Sonographic Findings: Ill-defined, hypoechoic, often solid-appearing mass reflecting the inflammatory process in and around the pancreas, without a distinct capsule.

Pancreatic Abscess

  • A localized collection of pus within or adjacent to the pancreas, usually a complication of severe pancreatitis.

  • Sonographic Findings: Complex fluid collection with thick, irregular walls, internal septations, and debris. Gas bubbles may be seen as highly echogenic foci with posterior shadowing, indicating infection.

Chronic Pancreatitis

  • Develops through repeated acute episodes leading to permanent structural damage (fibrosis, atrophy).

  • Symptoms include abdominal pain, weight loss, and exocrine/endocrine insufficiency.

  • Associated with risk of pancreatic malignancies.

  • Sonographic Findings: Pancreas may be normal in size, atrophic, or focally enlarged. Highly echogenic due to fibrosis and calcifications (seen as bright foci with posterior shadowing). The main pancreatic duct may be irregularly dilated (exceeding 22 mm), and strictures or calculi within the duct may be present. Irregular or lobulated contour.

Pseudocysts

  • Formation: Results from escaped enzymes leading to sterile abscess formation due to inflammation or ductal obstruction; common complications include spontaneous rupture.

  • An internal fluid collection may manifest in various abdominal locations.

  • Locations: Most commonly in the lesser sac, but can be found in the retroperitoneum, mediastinum, or groin.

  • Typical Sonographic Patterns: Usually anechoic, well-defined, smooth-walled, round or oval mass with strong posterior acoustic enhancement. May contain internal debris, septa, or fluid-fluid levels if complicated (e.g., hemorrhage, infection).

  • Spontaneous Rupture of a Pseudocyst: Leads to diffuse fluid collection (ascites) and signs of peritonitis.

Cystic Lesions of the Pancreas

  • Diverse group of lesions ranging from benign cysts to malignant neoplasms.

    • Cystic Fibrosis of the Pancreas: Leads to ductal obstruction, atrophy, and fatty replacement of the pancreas, often with multiple small cysts.

    • Sonographic Findings: Increased echogenicity of the entire gland due to fibrosis and fatty infiltration, often with numerous small, anechoic cysts (<11 cm), and possible pancreatic atrophy.

    • Von Hippel-Lindau Syndrome: Genetic disorder associated with pancreatic cysts and neuroendocrine tumors.

    • Sonographic Findings: Multiple simple pancreatic cysts, which are typically anechoic with thin walls. May also identify solid, hypervascular neuroendocrine tumors.

    • Solid Pseudopapillary Neoplasms: Rare lesions with mixed solid and cystic components, typically seen in young women.

    • Sonographic Findings: Large, well-encapsulated, heterogeneous mass with both solid (hypoechoic) and cystic (anechoic) areas, hemorrhage, and calcifications. Often located in the tail of the pancreas.

Pancreatic Neoplasms

  • Adenocarcinoma: Most common malignant pancreatic neoplasm, generally poor prognosis with high mortality.

    • Clinical Features: Symptoms often include jaundice, weight loss, and pain.

    • Sonographic Findings: Typically appears as a hypoechoic, irregular, ill-defined mass, often in the head of the pancreas. May cause dilation of the pancreatic duct (double duct sign with dilated common bile duct) and often involves adjacent vessels (e.g., superior mesenteric vein, portal vein) showing loss of a clear interface or direct invasion.

Cystic Pancreatic Neoplasms

  • Serous Cystadenoma: Benign tumor composed of numerous small cysts, often with a central stellate scar; typically anechoic with posterior enhancement.

    • Sonographic Findings: Well-circumscribed mass, often lobulated, composed of multiple tiny (<<22 cm) anechoic cysts giving it a

ANATOMY OF THE PANCREAS
Overview of the Pancreas

  • The pancreas lies anterior to the first and second lumbar bodies. It is located deep within the epigastrium (upper central region of the abdomen) and left hypochondrium (upper left section of the abdomen) and is positioned behind the lesser omental sac.

  • Major posterior vascular landmarks include the aorta and inferior vena cava, contributing to its anatomical positioning.

  • The pancreas extends in a horizontal oblique fashion from the second portion of the duodenum (first part of the small intestine) to the splenic hilum (the entry point for blood vessels to the spleen).

  • Variations of the lie of the pancreas include:

    • Transverse

    • Horseshoe

    • Sigmoid

    • L-shaped

    • Inverted V

Structural Components of the Abdomen Related to the Pancreas

  • The pancreas is surrounded by important anatomical features:

    • Stomach: anterior to the body and tail of the gland

    • Vessels: Aorta and inferior vena cava, superior mesenteric artery and vein are posterior to the pancreas.

    • Liver: Located above the pancreas, with additional connections through various ligaments and spaces (right and left hypochondrium spaces, colic flexure, and kidneys).

Coronary Spatial Relationships

  • Majority of the pancreas is situated in the retroperitoneal cavity.

  • Head: Surrounded by peritoneum

  • Anterior Pararenal Space: Occupied by the pancreas

Pancreatic Relationships

a. Borders

  • Superior Border: Stomach, duodenum, and transverse colon define its boundaries.

  • Inferior Border: Lies superior to the connective prevertebral tissues, portal-splenic confluence, superior mesenteric vessels, aorta, inferior vena cava, and lower border of the diaphragm.

Four Divisions of the Pancreas

  • Head: Most inferior portion.

  • Neck: Lies anterior to the portal-splenic confluence.

  • Body: Largest section of the pancreas.

  • Tail: Extends towards the splenic hilum.

Anatomy in Context: Ductal Relationships
Pancreatic Ducts

  • Duct of Wirsung: Primary duct; it extends along the entire length of the pancreas, entering the duodenum with the common bile duct at the ampulla of Vater, regulated by the sphincter of Oddi.

  • Duct of Santorini: Accessory duct draining the upper anterior head of the pancreas.

Characteristics of the Normal Pancreas

Size Regulations

  • On ultrasound, the anteroposterior dimensions are typically:

    • Head: Normally 2−32-3 cm. Abnormal if >33 cm.

    • Neck: Normally 1.5−2.51.5-2.5 cm. Abnormal if >2.52.5 cm.

    • Body: Normally 2−2.52-2.5 cm. Abnormal if >2.52.5 cm.

    • Tail: Normally 1−21-2 cm. Abnormal if >22 cm.

  • The main pancreatic duct (Duct of Wirsung) usually measures <22 mm in diameter.

Echogenicity

  • The normal pancreas should have echogenicity greater than that of the liver but less than that of the spleen, depending on the fatty/fibrous texture. In older individuals, it may appear more echogenic due to fatty infiltration.

Echotexture and Surface

  • The pancreas has a homogeneous echotexture with a smooth to slightly lobulated surface (notably due to the islets of Langerhans).

Vascular Supply
Arterial Supply

  • Anterior and Inferior Pancreaticoduodenal Arteries: Supply the pancreas head and part of the duodenum.

  • Splenic Artery: Supplies body and tail of the pancreas via four branches which include:

    • Suprapancreatic (rising from the celiac axis and splenic artery)

    • Pancreatic

    • Prepancreatic (before the pancreas)

    • Prehilar (before leaving the spleen)

  • Additional Arteries: Inferior pancreaticoduodenal arteries (part of superior mesenteric artery).

Venous Drainage

  • The pancreas's venous drainage occurs through the tributaries of the splenic and superior mesenteric veins, which form the portal venous system at the posterior border of the pancreas. These vessels are important sonographic landmarks for localizing the pancreas.

Congenital Anomalies of the Pancreas
Examples

  • Agenesis: Complete absence of the pancreas. Sonographically, absence of pancreatic tissue in the normal location.

  • Pancreas Divisum: Dorsal pancreas drains through the minor papilla, while the ventral part drains through the major papilla. Sonographically, may show a dilated dorsal pancreatic duct and a normal or small ventral duct, but often difficult to diagnose with ultrasound alone.

  • Ectopic Pancreatic Tissue: Presence of pancreatic tissue outside the normal anatomic location. Sonographically, a small, well-defined mass with echogenicity similar to the pancreas, located in unusual sites like the stomach or duodenum.

  • Annular Pancreas: Occurs when the ventral bud does not rotate properly during development, surrounding the duodenum, and possibly causing duodenal obstruction. Sonographically, may show duodenal obstruction (double bubble sign) and pancreatic tissue encircling the duodenum, though often obscured by bowel gas.

Pancreatic Functions
Exocrine Functions

  • Includes the secretion of enzymes for digestion, such as:

    • Lipase: Digests fats

    • Amylase: Digests carbohydrates

    • Proteolytic Enzymes (Trypsin, Chymotrypsin, Carboxypeptidase): Digests proteins

    • Nucleases: Digests nucleic acids

Endocrine Functions

  • The pancreatic cell types and their respective hormones include:

    • Beta Cells: Secrete Insulin, converting glucose into glycogen.

    • Alpha Cells: Secrete Glucagon, converting glycogen into glucose.

    • Delta Cells: Secrete Somatostatin, acting as an inhibitor of alpha and beta cells.

Laboratory Tests
Common Tests to Evaluate Function

  • Amylase Tests: Elevated levels may indicate pancreatic issues.

  • Lipase Tests: More specific for pancreatic inflammation.

  • Glucose Tests: Levels indicate endocrine function effects.

Sonographic Evaluation of the Pancreas
Stepping Stones for Visualization

Sonographic scans require identifying critical structures for accurate evaluation:

  • Landmarks: Superior mesenteric artery (SMA), gastroduodenal artery, portal vein, inferior vena cava, common bile duct, pancreatic duct (Duct of Wirsung), and antrum of stomach when assessing pancreas and its vascular supply. The common bile duct usually runs posterior to the head of the pancreas.

Imaging Process

  • Pancreatic structure visualization depends on patient positioning (e.g., left lateral decubitus position, erect position to move bowel gas). The stomach's position relative to the pancreas forms essential landmarks; fluid in the stomach can serve as an acoustic window.

Pathology of the Pancreas
Pancreatitis

  • It is inflammation of the pancreas categorized as:

    • Acute and Chronic

    • Severity: Ranges from mild to severe.

    • Caused by duct blockage and damage; tissues may be digested by their enzymes.

Acute Pancreatitis

  • Characterized by interstitial edema with minimal peripancreatic inflammation.

  • Sonographic Findings: Pancreas may appear diffusely enlarged and hypoechoic due to edema. Often, the borders are ill-defined. Peripancreatic fluid collections (often anechoic or hypoechoic) may be seen, particularly in the lesser sac, paracolic gutters, or around the kidneys.

  • Extra Pancreatic Fluid Collections and Edema: Visible as anechoic or hypoechoic fluid collections, potentially with internal echoes if complicated (e.g., hemorrhage, infection). Diffuse edema appears as hypoechoic infiltration of fat. Parapancreatic inflammation and fluid: Beyond direct pancreatic involvement, inflammation can spread to the surrounding retroperitoneal tissues. Fluid collections in the parapancreatic spaces (e.g., lesser sac, left anterior pararenal space, around the spleen and kidneys) are common findings. These collections may be sterile or infected, ranging from simple anechoic fluid to complex collections with debris and septations.

  • Complications: Spontaneous rupture of pseudocysts, hemorrhagic pancreatitis, phlegmonous pancreatitis, and pancreatic abscess formation.

Hemorrhagic Pancreatitis

  • A severe form characterized by extensive necrosis of the pancreas with associated bleeding.

  • Sonographic Findings: Pancreas appears heterogeneous with areas of increased echogenicity (from hemorrhage) and decreased echogenicity (from necrosis). Fluid collections may be complex, containing both anechoic and solid or echogenic components.

Phlegmonous Pancreatitis

  • A diffuse inflammatory edema of the soft tissues, often involving the pancreas and peripancreatic tissues, typically without necrosis.

  • Sonographic Findings: Ill-defined, hypoechoic, often solid-appearing mass reflecting the inflammatory process in and around the pancreas, without a distinct capsule.

Pancreatic Abscess

  • A localized collection of pus within or adjacent to the pancreas, usually a complication of severe pancreatitis.

  • Sonographic Findings: Complex fluid collection with thick, irregular walls, internal septations, and debris. Gas bubbles may be seen as highly echogenic foci with posterior shadowing, indicating infection.

Chronic Pancreatitis

  • Develops through repeated acute episodes leading to permanent structural damage (fibrosis, atrophy).

  • Symptoms include abdominal pain, weight loss, and exocrine/endocrine insufficiency.

  • Associated with risk of pancreatic malignancies.

  • Sonographic Findings: Pancreas may be normal in size, atrophic, or focally enlarged. Highly echogenic due to fibrosis and calcifications (seen as bright foci with posterior shadowing). The main pancreatic duct may be irregularly dilated (exceeding 22 mm), and strictures or calculi within the duct may be present. Irregular or lobulated contour.

Pseudocysts

  • Formation: Results from escaped enzymes leading to sterile abscess formation due to inflammation or ductal obstruction; common complications include spontaneous rupture.

  • An internal fluid collection may manifest in various abdominal locations.

  • Locations: Most commonly in the lesser sac, but can be found in the retroperitoneum, mediastinum, or groin.

  • Typical Sonographic Patterns: Usually anechoic, well-defined, smooth-walled, round or oval mass with strong posterior acoustic enhancement. May contain internal debris, septa, or fluid-fluid levels if complicated (e.g., hemorrhage, infection).

  • Spontaneous Rupture of a Pseudocyst: Leads to diffuse fluid collection (ascites) and signs of peritonitis.

Cystic Lesions of the Pancreas

  • Diverse group of lesions ranging from benign cysts to malignant neoplasms.

  • Cystic Fibrosis of the Pancreas: Leads to ductal obstruction, atrophy, and fatty replacement of the pancreas, often with multiple small cysts.

  • Sonographic Findings: Increased echogenicity of the entire gland due to fibrosis and fatty infiltration, often with numerous small, anechoic cysts (<11 cm), and possible pancreatic atrophy.

  • Von Hippel-Lindau Syndrome: Genetic disorder associated with cysts neuroendocrine tumors. Sonographic Findings: Multiple simple cysts, which are typically anechoic thin walls. May also identify solid, hypervascular Solid Pseudopapillary Neoplasms: Rare lesions mixed solid cystic components, seen in young women. Large, well-encapsulated, heterogeneous mass both (hypoechoic) (anechoic) areas, hemorrhage, calcifications. Often located the tail of pancreas.

Pancreatic Neoplasms

  • Adenocarcinoma: Most common malignant pancreatic neoplasm, generally poor prognosis with high mortality.

  • Clinical Features: Symptoms often include jaundice, weight loss, and pain.

  • Sonographic Findings: Typically appears as a hypoechoic, irregular, ill-defined mass, often in the head of the pancreas. May cause dilation of the pancreatic duct (double duct sign with dilated common bile duct) and often involves adjacent vessels (e.g., superior mesenteric vein, portal vein) showing loss of a clear interface or direct invasion.

Cystic Pancreatic Neoplasms

  • Serous Cystadenoma: Benign tumor composed of numerous small cysts, often with a central stellate scar; typically anechoic with posterior enhancement.

  • Sonographic Findings: Well-circumscribed mass, often lobulated, composed of multiple tiny (<<22 cm) anechoic cysts giving it a microcystic appearance.

Lymphoma of the Pancreas

  • Primary Pancreatic Lymphoma: Rare form of pancreatic malignancy, accounting for a small percentage of pancreatic tumors. It typically presents as a localized mass arising from the pancreas.

  • Secondary Pancreatic Involvement: More common, occurring as part of disseminated lymphoma affecting regional lymph nodes (e.g., peripancreatic, retroperitoneal) that may compress or infiltrate the pancreas.

  • Clinical Features: Nonspecific symptoms like abdominal pain, weight loss, and obstructive jaundice. Fever and night sweats may also be present.

  • Sonographic Findings: Often appears as a hypoechoic, well-defined or ill-defined solid mass. It can be heterogeneous and may show increased vascularity. Involvement of peripancreatic and retroperitoneal lymph nodes is a common finding, appearing as enlarged, hypoechoic masses. The pancreatic duct may be dilated if there is obstruction.