ANATOMY OF THE PORTAL VENOUS SYSTEM

 

ANATOMY OF THE PORTAL VENOUS SYSTEM

 

• The portal system includes all veins which carry blood from the abdominal

  part of the alimentary tract, the spleen, pancreas and gall bladder.

• The portal vein is formed by the union of the superior mesenteric vein and

   the splenic vein just posterior to the head of the pancreas.

• It extends for a distance of 6-8 cm to reach the porta hepatis where is enters

   the liver in two main branches, one to each lobe.

• The portal vein has a segmental intrahepatic distribution.

PORTAL HYPERTENSION

• The portal pressure is normally less than 5mm Hg.

• Patients develop clinical features or complications of portal hypertension

   when it is above 10 mm Hg.

AETIOLOGY

According to the site of obstruction, portal hypertension is classified into:

I.      Pre-Sinusoidal:

        A. Infra-Hepatic Causes:

Obstruction of the portal vein, before entering the liver due to:

1. Umbilical infection in neonates: Infection may pass via the

     para-umbilical vein to the portal vein causes the thrombosis.

2.     Congenital narrowing of the portal vein.

3.     Increased blood viscosity e.g. dehydration.

4.     Retarded circulation e.g. Polycythaemia.

5.     Abdominal infections and septicemia, leading to roughness of the     

    wall of the portal vein & thrombosis.

6.     Invasion by malignancy e.g. pancreatic or HCC.

B. Intra-Hepatic Causes:

Obstruction of the portal vein branches inside the liver due to:

1.     Schistosomiasis: There is peri-portal fibrosis.

2.     Hodgkin’s disease, leukemias and sarcoidosis:

There is infiltration of the portal tracts by the abnormal cells.

3.     Congenital fibrosis of portal tracts (rare).

4.     Toxins e.g arsenic (rare).

II. Sinusoidal and Post-Sinusoidal:

A.         Intra-Hepatic Causes:

Obstruction of the sinusoids and the hepatic veins in the liver due to:

1.  Liver cirrhosis.

2.  Veno-occlusive disease.

B.   Supra-Hepatic Causes:

Obstruction of the blood flow coming from the liver to the right ventricle due to:

1.     Budd-Chiari syndrome.

2.     High I.V.C. obstruction.

3.     Constrictive pericarditis and pericardial effusion.

4.     R.V.F. and T.I.

Most of the cases of portal hypertension in adults are due to liver cirrhosis & schistosomal hepatic fibrosis.

Porto-Systemic shunts

When portal hypertension occurs, the body tries to decrease the portal pressure through opening of porto-systemic shunts.

1-    Oesophageal & gastric varices:

• These are dilated veins located at the lower part of the oesophagus

   (oesophageal varices) which may have gastric extension or associated with

    dilated veins in the fundus of the stomach (gastric varices).

• They develop as anastomosis between left & short gastric veins (Portal)

   and azygos vein (systemic).

·        Varices may rupture causing haematemesis or melaena.

·        They may bleed mildly & repeatedly causing anaemia.

·        They may be asymptomatic and these have to be searched for in 

every case of cirrhosis or hepatic schistosomiasis in order to take       prophylactic measures to prevent their first bleeding.

2-          Rectal varices:

          Due to anastomosis between superior haemorrhoidal vein (Portal)

          and middle & inferior haemorroidal veins (systemic).

3-          Recanalisation of the para-umbilical vein:

         • The para-umbilical vein is present in the round ligament of the liver.

         • It connects the left portal with the superior & inferior epigastric veins.

         • Opening of this anastomosis will lead to the development of dilated

           veins radiating from the umbilicus “Caput medusa” and on auscultation

           between the umbilicus and xiphisternum a soft murmur may be heard

           due to passage of blood in the para-umbilical vein “venous hum”.

4-           Others: detected by ultrasonography or during operation.

·        Between the liver (Portal) and diaphragm (systemic).

·        Between the spleen (Portal) and diaphragm or Kidney (systemic).

·        Between duodenum & colon (Portal) and abd. wall (systemic).

Complications of Portal hypertension

1-     Variceal bleeding: haematemesis, melaena & anaemia.

2-     Congestive gastropathy: haematemesis, melaena & anaemia.

3-     Ascites: if there is associated hypoalbuminaemia.

4-     Hepatic encephalopathy: due to passage of toxins through porto-systemic shunts, so by-pass the liver.

5-     Hypersplenism: thrombocytopenia, less commonly leucopenia and rarely anaemia.

Factors predisposing to bleeding from varices are

1-     High portal pressure.

2-     Large size of the varices.

3-     Signs of impending rupture.

4-     Child-pugh grade C.

5-     NSAIDS & corticosteriods.

CLINICAL PICTURE:

Symptoms

·        Dyspepsia: due to gastric congestion.

·        Abdominal distention after meals: due to intestinal congestion.

·        Haematemesis and melaena: due to rupture varices, congestive 

     gastropathy or gastric erosions.

·        Dragging pain in the left hypochondrium: due to big spleen.

·        Abdominal enlargement: due to huge spleen or ascites.

·        Symptoms of liver failure or history of schistosomiasis:

     may be  present as liver cirrhosis & hepatic schistosomiasis are the 

     commonest causes for portal hypertension.

Physical Signs

1.The Liver:

·        In hepatic causes (mainly cirrhosis and schistosomiasis):
   The liver is shrunken, firm, with sharp border.

·        In supra hepatic causes: The liver is enlarged, soft and tender.

·        In infra hepatic causes: The liver is usually normal.

2. The Spleen:

·        Is enlarged due to portal hypertension and R.E. hyperplasia.

·        Splenomegaly may be associated with hypersplenism.

2.     Ascites:

If portal hypertension is associated with hypoalbuminaemia.

4. Caput medusa and venous hum:

May be present

5. Signs of liver failure:

May be present.

INVESTIGATIONS:

I. Detection of Oesophageal & Gastric Varices:

• Varices indicate the presence of portal hypertension.

• They are detected by endoscopy or barium swallow.

• Endoscopy is superior to barium swallow for the following reasons:

               1. It detects early varices.

2.     It grades the varices.

3.     It can detect signs of impending rupture.

4.     It detects gastric varices.

5.     It detects active bleeding and its site.

6.     It can be used for sclerotherapy or banding of varices.

II.      Visualization of the Portal System:

Dilatation of the portal vein or the presence of shunts will indicate portal hypertension. This is visualized by:

          1. Ultrasonography & computerized tomography.

          2. Spleno-portography:

            A radio-opaque material is injected via the spleen into the portal

            circulation.

III.           Estimation of Portal Pressure:

 1. Percutaneous Intrasplenic Pressure:

• The pressure is estimated through a needle introduced into the spleen. • • It is increased in pre and post sinusoidal causes.

• It can be used for cirrhosis & schistosomiasis.

2. Wedged Hepatic Pressure:

• A catheter is introduced through an arm vein into the SVC, IVC,

   hepatic veins and pushed till it is wedged in hepatic sinusoids.

• This method measures the sinusoidal pressure.

• The portal pressure measured by this method is increased in

   post-sinusoidal and decreased in pre-sinusoidal causes.

IV. Evaluation of the Liver Condition:

               1. Liver function tests.

               2. Liver biopsy.

TREATMENT OF PORTAL HYPERTENSION AND VARICES:

I. Preventing the first bleeding (Primary Prophylaxis)

1. b adrenergic blockers:

• Propranolol is the standard method for primary prophylaxis.

• It significantly decreases the incidence of bleeding varices

   through lowering the portal pressure by:

  - Decreasing the cardiac output.

  - Blocking the vasodilator receptors on the splanchnic arterioles. • • The dose is 80-160 mg /day.

2. Band ligation:

• This is done if b blockers can not be used.

•  As in hypotension and bronchial asthma.

II. Management of Bleeding Varices

                   A. General Measures for Haematemesis:

1.     Hospitalization.

2.     I.V line.

3.     Wide bore gastric tube & washing.

4.     Blood transfusion:

• Given if Hb is less than 8 gm/100 ml or if there is shock.

 • Blood must be fresh:

   - To contain coagulation factors

   - To have little ammonia to prevent encephalopathy.

5.     Vit. K  I.V.

6.     PPIs or H₂ blockers by injection.

7.     Sedatives are better avoided.

- If necessary, use oxazepam (excreted by the Kidney).

- Don’t use morphia (metabolized in the liver).

8.     Endoscopy: To define the site of haemorrhage.

B.   Pharmacological treatment:

This is used till sclerotherapy or banding are available or in combination with them or after their failure.

1-     Vasopressin (Pitressin):

Action: Vasoconstriction of visceral arterioles will lead to diminished portal pressure and so will decrease haemorrhage.

Administration: 20 U in 100 ml glucose 5% I.V. over 10 minutes.

Side effects: Blanching, colic, vomiting & diarrhoea.

Contraindications:

7.     Ischaemic heart: As it causes spasm of the coronaries.

8.     Pregnancy : As it cause contraction of the uterus.

9.       Hypertension: As it increases peripheral resistance.

Associated drug: nitroglycerine to protect the heart.

2-     Terlipressin (Glypressin):

• A synthetic derivative with the same action of vasopressin.

• It is given 2 mg/6 hours intravenously, better with nitroglycerine.

3-     Synthetic Somatostatin (Sandostatin)

• This is a synthetic growth hormone release Inhibiting factor

   (GH-RIF), called octeriotide.

• It has the same effect of terilpressin but with no side effects.

• The dose is 50 mg/hour by infusion.

C. Balloon temponade:

This is used if sclerotherapy or banding are not available or after failure of sclerotherapy, banding or pharmacological treatment. The varices are compressed using Sungestaken-Blackemor tube:

- This is a 3 lumen tube, one for gastric aspiration or feeding, the second  for inflating gastric balloon (by 100 ml water) & the third for aspirating fluids in the oesophagus to prevent aspiration.

- The tube is put for a maximum of 48 hours.

- Complications:

·     Oesophageal ulceration.

·     Pneumonia, lung abscess & asphyxia.

D. Injection Sclerotherapy:

-Intra or perivariceal injection of sclerosing material through an endoscope can stop bleeding in 90% of cases.

-The currently used sclerosant is ethanolamine oleate.

E. Injection of Tissue Adhesive (Glue):

-         This is a material that sticks to the tissues & so prevents bleeding.

-         It is used for injection of gastric varices & big oesophageal varices.

-         The used material is called “Histoacryl blue”

F. Band Ligation:

- A special device & rubber bands are used to strangulate the varices.

- This stops bleeding & causes variceal necrosis & fibrosis.

- It is difficult to use it if there is excess bleeding.

G.  Transjugular Intrahepatic Portal-Systemic Shunt (TIPS):

- A special device is introduced through the jugular vein to the liver to

  put a stent connecting the hepatic with the portal vein.

- This decreases the portal pressure & stops bleeding.

- It has the same complications as shunt operations.

- It is done after failure of the previous measures to stop bleeding.

H.   Emergency Surgery: (rarely used)

1-     Ligation of bleeding varices.

2-     Oesophageal transection using the staple gun.

3-     Portal– caval shunt.

I.    Measures to Prevent Encephalopathy:

    See liver failure.

III. Management of the Patient after Bleeding are

A. Local treatment of the Varices:

1. Band ligation: the best method

    - It needs fewer settings.

    - It causes fewer side effects than sclerotherapy.

2-     Sclerotherapy:

- Injection is repeated weekly till varices disappear.

- Then follow up & re-injection at wider intervals.

3-     Tissue adhesives:

      For gastric varices & large oesophageal varices.

4-     Vasoligation. (rarely used)

B.   Porto-systemic shunt to lower the portal pressure:

1. Porta - caval shunt. (rarely used).

2. Distal spleno – renal shunt (rarely used).

3. TIPSS.

C.   Propranolol (Inderal):

Its role in secondary prophylaxis is still debatable.