"Liver, biliary system, pancreas and spleen"
Liver, biliary system, pancreas and spleen Long Nguyen Embryology of the digestive glands Liver, gallbladder and pancreas develop from endodermal diverticulae that bud from the duodenum in the 4th to 6th weeks Liver sprouts first and expands in ventral mesentery Cystic diverticulum also in ventral mesentery Pancreas arises from a dorsal and ventral bud. Ventral pancreatic bud migrates posteriorly to fuse with the dorsal bud. Main duct of ventral bud becomes the main pancreatic duct. Liver - exam questions Write short notes on the segmental anatomy of the liver. (9/07, 9/05, 4/05, 9/04, 9/02) Write short notes on the arterial supply to the liver and its normal variants. (9/08, 10/01) Liver Lies in right upper quadrant. Underlies the thoracic cage. Conforms to right dome of diaphragm Connected to the diaphragm by the falciform and coronary ligaments Liver - relations Surfaces separated by inferior border of liver and coronary ligament posteriorly Bare area between the reflections of coronary ligaments in direct contact with diaphragm and not covered by peritoneum Diaphragmatic surface Smooth and convex Separated from diaphragm by subphrenic recess Liver – relations (2) Visceral (posteroinferior) surface Lies in contact with oesophagus, stomach and lesser omentum on the left Duodenum in midline Right kidney, adrenal and hepatic flexure of the colon on the right H-shaped arrangement of structures Crossbar formed by porta hepatis (portal vein, hepatic artery, hepatic ducts, nerve plexus and lymph vessels Left: ligamentum teres (remnant of left umbilical v.) and ligamentum venosum (remnant of ductus venosum) Liver - old lobar anatomy Right and left lobes divided by plane through the IVC and gallbladder fossa on (Moore) Caudate lobe Lies posteriorly between lig. venosum and IVC fossa Porta hepatis inferiorly Tail-like caudate process connects to right lobe and separates portal vein from IVC Quadrate lobe Anteroinferior between GB bed and lig. teres Porta hepatis superiorly Caudate and quadrate lobe considered to be part of left lobe Reidel’s lobe (not a true lobe) Lower border of the right lobe lateral to the GB may project downwards for a considerable distance as a broad or bulbous process Occurs in 5-10% of females and rarely in males Liver - vascular anatomy Double blood supply from hepatic artery (30%) and portal vein (70%) Arterial supply by common hepatic artery branch of coeliac artery. Gives off right gastric and gastroduodenal arteries before reaching the liver in the free edge of the lesser omentum. Divides into left and right hepatic arteries before entering the liver at the porta. Variants of right hepatic artery below Portal vein formed posterior to neck of pancreas by union of SMV and splenic vein Liver - vascular anatomy (2) Right and left lobes functionally independent and defined by arterial distribution Each supplied by left and right portal v., left or right hepatic arteries and drained by left or right hepatic duct (portal triad) Quadrate lobe supplied by left hepatic artery Caudate lobe supplied by both Liver - hepatic veins Hepatic veins are intersegmental and do not run with the structures of the portal triad Right, middle and left hepatic veins drain corresponding thirds of the liver Middle hepatic vein lies in the principal plane between right and left lobes Left hepatic vein lies between medial and lateral segments of the left lobe Right hepatic vein lies between anterior and posterior segments of the right lobe All drain into the IVC without an extrahepatic course Inferior group of small veins from right lobe also drains into IVC Liver - segmental anatomy (Couinaud system) Knowledge of segments important in the assessment of location and extent of hepatic pathology as surgery is performed in segmental fashion and distribution of disease determines whether lesions are resectable. The hepatic veins divide the liver into 4 divisions A horizontal plane through the portal vein divides the 4 divisions into superior and inferior segments Segments numbered in clockwise direction starting at caudate lobe (segment 1) Liver – Lymph drainage and innervation Lymph drainage Superficial and most deep lymph vessels converge at the porta and end in the hepatic lymph nodes (eg. Cystic LN near GB neck or LN of omental foramen) Hepatic LN’s drain into coeliac LN’s around the coeliac trunk, then thoracic duct Some deep lymph vessels follow hepatic veins to IVC foramen in diaphragm and end in middle phrenic LN’s Innervation Sympathetic and parasympathetic supply from the hepatic plexus, a derivative of coeliac plexus (formed from fibres of left and right vagus and right phrenic nerves) Gallbladder and biliary tree – exam questions Write short notes on the anatomy of the gall bladder (9/04) Write short notes on the anatomy of the biliary tree (excluding the gallbladder) and normal variations (4/08, 9/07, 4/05) Gallbladder and cystic duct Pear shaped sac lies to the right of the quadrate lobe in GB fossa on the visceral surface of liver Concentrates and stores bile secreted by the liver Cholecystokinin produced by intestinal mucosa during digestion, passes to GB and causes it to contract and release bile Fundus, body and neck Mucosal membrane arranged into spiral folds (valves of Heister) at GB neck and cystic duct Gallbladder - relations Anterosuperiorly GB fossa of liver Fundus projects from inferior border of liver, located at tip of 9th costal cartilage in MCL where lateral edge of rectus abdominis meets costal margin Posteroinferiorly Neck: lesser omentum. Omental (epiploic) foramen lies immediately to the left. Body: D1 Fundus: transverse colon Gallbladder – blood supply Arterial supply cystic artery Venous drainage directly into liver or via a cystic vein Biliary Tree Bile is secreted by hepatocytes into bile canuliculi which drain into interlobular bile ducts. Progressively larger ducts formed. Left and right hepatic ducts emerge from porta and merge to form common hepatic duct (4cm) Joined on the right by the cystic duct from the GB to form the common bile duct (8- 10cm long, 5-6mm diameter) Runs in free edge of lesser omentum, passes posterior to D1 and head of pancreas Comes in contact with pancreatic duct on the left side of D2 Usually unite in the duodenal wall to form hepatopancreatic ampulla (of Vater) Ampulla opens into descending part of duodenum at summit of major duodenal papilla, 8-10cam from pylorus Biliary Duct – blood supply Arterial supply Proximally: cystic artery Middle: right hepatic artery Distally: posterior superior pancreaticduodenal a. Venous drainage Proximally: drainage directly into liver Distally: posterior superior pancreaticduodenal v. Lymph drainage Cystic LN, node of omental foramen, hepatic LN’s Biliary Tree - variants Accessory hepatic ducts may arise in the liver and join the right hepatic duct, common hepatic duct, common bile duct, cystic duct or GB Right and left hepatic ducts may fail to unite giving a double duct Cystic duct Absent Joins common hepatic duct on the left rather than the right Joins the right hepatic duct or an accessory duct Joins the common hepatic duct anywhere between the porta and the duodenum (low and high union) Variants in union of CBD and pancreatic duct Pancreas – exam questions Write short notes on the anatomy of the pancreatic ducts and variations. (9/08) Make brief notes on the embryology of the pancreas. (10/00) What sonographic landmarks are useful in identifying the pancreas? (10/00) Describe the sonographic appearance of a normal pancreas. Pancreas Retroperitoneal organ lies transversely and slightly obliquely at L1-L2 level Transverse mesocolon attached to anterior margin Exocrine (pancreatic enzymes) and endocrine functions (glucagon and insulin) Head, neck, body and tail Pancreas - Relations Head Lies in curvature of duodenum Anterior to IVC, aorta, right renal vessels and left renal vein Uncinate process projects posteriorly and to the left and lies posterior to superior mesenteric vessels CBD passes posteriorly in a groove or embedded within Neck Anterior to the union of splenic vein and SMV to form the portal vein Body Curves over vertebrae and great vessels Anterior to the aorta and lies between the coeliac trunk and the SMA Splenic vein passes posterior Tail lies in the splenorenal ligament Usually contacts the hilum of the spleen Pancreas - Embryology Arises from the junction of the primitive foregut and midgut as a larger dorsal division and a smaller ventral bud Ventral bud swings posteriorly to unite with the inferior aspect of the dorsal bud trapping the superior mesenteric between divisions Ventral bud forms the uncinate process Duct of the ventral bud forms the proximal end of the main pancreatic duct; the distal end of the dorsal pancreatic duct forms the remainder. Pancreas - variations Pancreas – blood supply Arterial supply Head: superior pancreaticoduodenal a. (from gastroduodenal artery) and inferior pancreaticoduodenal a. (from SMA) Body and tail: branches from splenic artery Venous drainage Mostly splenic v., but also portal v. and SMV Spleen Large soft vascular lymphatic organ in the left upper quadrant Up to 12cm with long axis in line with 10th rib Arises from mass of mesenchymal cells located between layers of dorsal mesogastrium. Spleen - relations Posterior to stomach. Connected to greater curvature by gastrosplenic ligament Anterior to superior part of left kidney. Connected by splenorenal ligament Laterally: diaphragm, 9th-11th left ribs Tail of pancreas lies at splenic hilum Spleen – blood supply Arterial supply Splenic artery divides into end arteries as it enters the spleen No anastamoses, hence obstruction of one end artery results in area of splenic infarction Venous drainage Splenic vein Lymph drainage Pancreaticopsplenic LN’s