venous drainage of thorax and abdomen including portal system

inferior vena cava, azygous and portal system of veins

1. Venous drainage of thorax and abdomen By Dr. Soran M Kareem Total of 2 lectures

2. Lecture outline Superior vena cava + tributaries Azygos system + tributaries Inferior vena cava + tributaries Portal system of veins + tributaries Portosystemic anastomosis Clinical notes; Portal hypertension/ consequences Varicose veins CABG & the great saphenous veins Important Mnemonics

3. Further readings! Anatomical basis of dentistry ; by Bernard Liebgott 3 rd edition chapters 3 & 4 pages; 82-84/ 1-103/ 116 Figures; 3-32 & 4-14/ 4-28

4. SVC The  superior vena cava  (SVC) is a large, valve-less vein that conveys venous blood from the upper half of the body and returns it to the right atrium . The  superior vena cava  is classified as a large vein, with a wide diameter of up to 2cm and a length of approximately 7cm. It arises from the union of the  left  and  right brachiocephalic veins , posterior to the first right costal cartilage. It descends vertically through the superior mediastinum, behind the intercostal spaces and to the right of the aorta and trachea. At the level of the second costal cartilage, the SVC enters the  middle mediastinum  and becomes surrounded by the fibrous pericardium. It terminates by emptying into the superior aspect of the right atrium at the level of the third costal cartilage.

5. Reviw of som important 1 st sems notes!

6. Tributaries of SVC The   superior vena cava  contains venous blood from the head, neck, both upper limbs and from structures within the thorax It is formed by the union of the right and left  brachiocephalic veins  – which provide venous drainage of the head, neck, and upper limbs. At the level of T4, the superior vena cava receives the azygous vein , which drains the upper lumbar region and thoracic wall. The SVC receives tributaries from several minor vein groups: Mediastinal veins Oesophageal veins Pericardial veins

7. Azygos system/ vein The azygos venous system is located on either side of the  vertebral column  and drains the viscera within the  mediastinum , as well as the  back  and thoracoabdominal walls. This system consists of the azygos vein and its two main tributaries: the  hemiazygos vein  and the accessory hemiazygos vein.

8. The azygos vein usually arises either from the lumbar azygos vein or from the posterior side of  inferior vena cava  around the level of  renal veins . It passes through the  diaphragm , reaches the mediastinum and finally drains into the  superior vena cava . The azygos venous system has many anastomoses with inferior vena cava and vertebral venous plexuses. This makes it an important connection between the two venae cavae which allows alternate drainage route in case of inferior vena cava obstruction,

9. Clinical Relevance: Superior Vena Cava Obstruction The superior vena cava is a thin-walled, low pressure vessel which makes it vulnerable to  compression . Superior vena cava obstruction can occur either due to external compression or from an occlusion within the vessel lumen itself. The most common cause of SVC obstruction is  malignancy , typically from lung cancer, lymphoma, or metastatic disease. Vessel obstruction interrupts venous return and can lead to swelling in the neck, face, and upper limbs. Clinical features include shortness of breath and distension of the veins of the face and upper limb. SVC obstruction can be assessed clinically by performing  Pemberton’s test . The patient is asked to raise both arms above their head – a positive test is indicated if facial oedema or cyanosis occurs after approximately 1 minute.

10. IVC It conveys most of the blood from body below diaphragm to right atrium It is formed by union of common iliac veins behind right common iliac artery at level of L5. It ascends on right side of aorta, pierces central tendon of diaphragm at level of T8, & drains into right atrium. Right sympathetic trunk lies behind its right margin & right ureter lies close to its right border. Tributaries : 2 Anterior visceral tributaries: right and left hepatic veins 3 Lateral visceral tributaries: right suprarenal vein, renal veins, and right testicular or ovarian vein. 5 Lateral abdominal wall tributaries: inferior phrenic & 4 lumbar veins 3 Veins of origin: 2 common iliac veins & median sacral veins.

11. Portal system/ portal vein Venous drainage of most of GIT and its accessory organs is drained into liver by portal venous system. Proximal tributaries drain directly into portal vein, but distal tributaries correspond to branches of celiac artery and superior and inferior mesenteric arteries . Portal Vein : It drains blood from abdominal part of GIT from lower third of esophagus to halfway down anal canal; it also drains blood from spleen , pancreas & gallbladder. Portal is short and formed behind neck of pancreas by union of superior mesenteric & splenic veins . It ascends to the right, behind 1st part of duodenum , and enters lesser omentum . It then runs upward in front of opening into lesser sac to porta hepatis , where it divides into right and left terminal branches.

12. Tributaries of Portal Vein Splenic vein: begins at hilum of spleen by union of several veins & is joined by short gastric & left gastroepiploic veins. It unites with superior mesenteric vein behind neck of pancreas to form portal vein . Inferior mesenteric vein: ascends on posterior abdominal wall and joins splenic vein behind body of pancreas. It receives superior rectal veins, sigmoid veins, and left colic vein. Superior mesenteric vein: ascends in root of mesentery of small intestine. It passes in front of 3rd part of duodenum & joins splenic vein behind neck of pancreas. It receives jejunal , ileal , ileocolic, right colic, middle colic, inferior Pancreaticoduodenal & right gastroepiploic veins. Left gastric vein: drains left portion of lesser curvature of stomach & distal part of esophagus. Right gastric vein: drains right portion of lesser curvature of stomach. Cystic veins: either drain gallbladder directly into liver or join portal vein.

13. Portal hypertension results mainly from increased resistance to blood flow in the portal vein. A common cause of this resistance is  disease within the liver ; uncommon causes include blockage of the splenic or portal vein and impaired hepatic venous outflow.