Structural characteristic of splenic sinuses in idiopathic portal hypertension

Splenic sinuses in idiopathic portal hypertension (IPH; 8 patients), liver cirrhosis (LC; 14 patients) and in regenerating autotransplanted spleens from 25 rats were compared with each other by scanning electron microscopy (SEM) and immunohistochemistry using antibodies against proliferating cell nuclear antigen (PCNA). Spleens obtained from six patients with gastric carcinoma and from five untreated adult rats were examined as controls. SEM of the sinuses showed that in IPH endothelial cells became irregular in shape, and the interendothelial slits of sinuses were irregularly enlarged. Sinus endothelial processes traversing the sinusal lumen were also found. The same changes were observed in the proliferating sinuses during regeneration of splenic tissue after autotransplantation in rats, but disappeared when the regeneration was completed. Irregular endothelial cells were few in LC. PCNA-positive sinus endothelial cells were increased in number in IPH as compared with those in LC; the mean number of PCNA-positive ones per cm2 was 45.4 in IPH and 8.2 in LC. It was suggested that, from SEM observation of sinus endothelial cells and counting PCNA-positive sinus endothelial cells, the sinuses of the spleen in IPH consist of proliferating endothelial cells or are in the state of increased proliferation. In conclusion, splenomegaly in IPH was presumed to be caused by proliferation of sinus endothelial cells, and by the increased splenic blood flow in the irregularly widened interendothelial slits of the sinuses.