Scanning electron microscopy (SEM) studies of the spleen--normal and pathological.

This paper reviews the SEM observations on normal and pathological human spleens. The findings reported by other research groups are briefly introduced. The white pulp is supported by a network of trabecules which may be partly hollow inside and represent a hitherto unknown channel system of highly variable calibers. The marginal zone or the perifollicular red pulp receives much arterial blood from the follicular arteries. The spongy spaces of the marginal zone also contain many lymphocytes. The arterioles in the red pulp open into free spaces in the cords of Billroth. Red cells which have lost plasticity as the result of aging or by taking the shape of stomatocytes and spherocytes in such hematological diseases as hereditary spherocytosis (HS), are interrupted by the narrow slits on the sinus wall, and phagocytosed by patrolling macrophages more easily than normally. SEM images support the view that the particulate matters in blood cells, like intracellular parasites, may be squeezed through the sinus slits ("pitting function") while the cells transit from the cord into the sinus. The sinus rod cells are normally connected with each other by their side processes leaving spindle-shaped slits in between. These rods are adhered together in different pathological conditions, i.e., in hepatosplenic diseases such as hepatic cirrhosis and portal hypertension and in such hematological diseases as HS and idiopathic thrombocytopenic purpura (ITP). Increased thread-like projections of the rods are noticed in these diseases. SEM observations indicate that macrophages are cells which are independent of both reticular and endothelial cells. In most pathological spleens, macrophages are observed to be elevated in phagocytotic activity. They take up erythrocytes vigorously in the spleens of HS and incorporate numerous blood platelets in the cases of ITP.