Splenic vascular disturbances mainly affect the red pulp and can involve the venous or arterial blood flow. The venous blood flow may be impaired by congestion and morphologically shows dilated splenic sinuses. Disturbances of the arterial blood flow may occur in connection with anomalies of the erythrocyte membrane or in immune haemolysis and usually are characterized by narrow splenic sinuses. Infarction of the spleen is usually caused by arterial embolism.