Distinguishing periportal fibrosis from portal fibrosis in hepatic schistosomiasis.

Abstract

Schistosomiasis is an important disease in humans and various domestic animals in many parts of the world. The main clinical symptoms of schistosomiasis include serious hepatic lesions induced by the ova of schistosomes. Although the majority of ova deposited in the mesenteric veins are supposed to reach the intestinal lumen, a considerable number of ova are carried by the portal blood flow to the liver, where they are lodged in the small blood vessels of the portal tracts. Indeed, many investigators have tried to elucidate the characteristics of hepatic fibrosis induced by these ova. The pioneering work of Symmers in 1904 [1] described the hepatic lesions in humans caused by ova of Bilharzia haematobia. Symmers reported that the liver surface displayed a pronounced increase in the perivascular connective tissue, and the cross-sections were dominated by an enormous increase of fibrous tissue (Glisson’s capsule) which normally surrounds the portal canals, forming a pattern reminiscent of white clay-pipe-stems. Symmers’ work remains as a kind of creed or paradigm for investigators of hepatic schistosomiasis, but it has also initiated a persisting confusion as to the correct terminology of fibrosis in relation to the portal tracts. Symmers described the liver changes as a new form of liver cirrhosis and this description might have contributed to the terminological confusion because these changes do not meet the qualifications for cirrhosis according to current pathology textbooks. The confusion is centred on the crucial question: should fibrosis of the portal tracts, and particularly around branches of the portal vein, be called periportal fibrosis or portal fibrosis? There is a general agreement among anatomists, histologists and pathologists to use the terminology portal area, portal tract, portal canal or portal triad to describe the accumulation of connective tissue, which normally supports branches of the hepatic artery and portal vein, the bile ducts and lymphatic vessels. In addition, changes within these areas are described as portal and changes in the adjacent parenchyma outside these areas are described as periportal (see, for example, Refs [2–4]). Unfortunately, this terminology does not seem to have communicated itself to researchers of hepatic schistosomiasis among whom a difference of opinion has prevailed (Table 1). The difference, however, appears to be limited to the choice of terminology and is not based on a difference of opinion among the authors as to the nature of the fibrosis, which is generally described as an increase of connective tissue in the portal tracts. It is correct that fibrosis around a bile duct in a portal area is sometimes designated peribiliary fibrosis (or biliary fibrosis), but this does not warrant the designation of fibrosis around a portal vein in a portal area as periportal fibrosis. The consequence of this is that fibrosis around a branch of the hepatic artery would be designated perihepatic fibrosis. To avoid misunderstandings and misinterpretations in the future, we encourage researchers to coordinate their terminology in accordance with the terms generally applied by anatomists, histologists and pathologists. Fibrosis within a portal tract should be called portal fibrosis, and fibrosis of the parenchyma adjacent to a portal tract should be called periportal fibrosis. These are the logical and correct terms to apply to fibrosis in relation to the portal tracts and their immediate surroundings.