The common association between abnormal liver function, splenomegaly, and anaemia was recognized nearly a century ago, and was attributed to portal hypertension.

Long-standing elevated portal pressure, whether caused by intrahepatic or extrahepatic factors, invariably leads to congestive splenomegaly. Although the most common underlying factor is hepatic cirrhosis, portal hypertension also occurs in conditions associated with more or less normal hepatic morphology, such as malaria, and schistosomiasis. Whatever its cause, splenomegaly increases blood flow through the red pulp. This is especially evident in congestive splenomegaly, in which the increased volume of perfusing blood increases the filtering capacity of the spleen. When blood cells are sequestered and haematological parameters are altered, the condition is known as hypersplenism.

The term hypersplenism carries no aetiological implications, but merely signifies the presence of pancytopenia, with cellular elements affected in different degrees, accompanied by splenomegaly. Since bone marrow function is usually normal, splenectomy usually results in complete or partial correction of the pancytopenia.

The cytopenias which result from congestive splenomegaly are of variable severity. They are also influenced by the factors causing the portal hypertension. Anaemia is usually mild to moderate, the haematocrit rarely being below 25 per cent and stable in the absence of complications such as bleeding or nutritional deficiencies. The anaemia is due to several factors, including blood dilution secondary to increased plasma volume and splenic pooling of red cells, which can trap up to 25 per cent of the total circulating red cell mass, depending upon the size of the spleen. Red cell survival is also decreased, by up to 50 per cent, and this is also proportional to spleen size. This haemolysis is a result of repeated metabolic insults to red cells caused by splenic pooling. The consequent red cell changes become irreversible, and damaged cells are eventually phagocytosed by splenic reticuloendothelial cells. Depending upon the underlying aetiology of the portal hypertension, there may be an added element of inadequate bone marrow response to anaemia, as occurs in cirrhosis.

Splenic pooling of up to 35 per cent of circulating platelets occurs normally. Splenomegaly accentuates this phenomenon and leads to thrombocytopenia of variable severity. Commonly, there is a direct inverse correlation between spleen size and platelet count. Platelets in the spleen survive normally and some or most of them become available to the general circulation at times of stress. In hypersplenic patients, the total platelet mass is normal.

Finally, leucopenia is common, but is usually mild and mainly due to an absolute diminution of the granulocyte count. In one study, six patients with leucopenia and splenomegaly secondary to cirrhosis were studied with the DF ³²P lifespan technique. Five had shortened red cell survival, even though granulocyte production was normal. Although leucopenia may be due to the existence of a large splenic pool, there is normally no significant splenic pooling of granulocytes. This finding is further supported by a correlation between leucopenia and splenic size.

Splenectomy has long been advocated to correct the pancytopenias which result from the hypersplenism associated with portal hypertension. Even though this intervention may correct the haematological picture, it rarely changes the course of the underlying disease and it can give rise to serious septicaemia. A retrospective study of 563 patients concluded that splenectomy may be less satisfactory in correcting hypersplenism than is a distal splenorenal shunt, which often improves cytopenias and controls variceal bleeding. The efficacy of the distal splenorenal renal shunt has recently been challenged, however.

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