There are other vascular changes in schistosomiasis, not directly related to the eggs and occurring without the granulomatous reaction which surrounds the egg. There are two varieties: arteritis and hyaline thrombi. The arteritis results from a fibroid necrosis of the vessel wall, with disruption of the elastic fibers, and is very similar to the arteritis of collagen disease. It is thought to be a local allergic reaction. The changes can be so severe that this form of arteritis can also disturb the pulmonary circulation and contribute to the pulmonary hypertension.Hyaline thrombi may be found in many arteries, arterioles and venules. Microscopically there are hyaline, polypoid masses beneath the vascular endothelium. These hyaline thrombi are multiple and found throughout the lungs and are yet another factor contributing to the pulmonary hypertension. It is possible that these hyaline masses are the result of embolization of eggs or even worms.

Much less common is the finding of a Bilharzia granuloma, the bilharzioma. This is a solitary lesion, which can occur anywhere in the lungs or heart, and may persist unchanged for some years or may shrink or increase in size. Pathologically it is a granuloma around an egg (or occasionally a worm), which has penetrated the vessel wall with minimal damage. Radiologically, it can be difficult to distinguish from any other granuloma, or even a small neoplasm.

The most common histological finding, the bilharzial "tubercle", 0.1-0.5 cm in size, is the least common radiological presentation and the most difficult to recognize (Figs. 2.58, 2.59). The tubercle is formed when the egg provokes a granuloma surrounded by histiocytes within the lung parenchyma and the inflammatory reaction becomes chronic, with the granuloma resolving to a focus of fibrosis and scarring. These small granulomas are always related to the bronchioles or alveoli. In some patients the alveoli fill with a serofibrinous exudate which may progress to become patchy consolidation characteristic of bronchopneumonia. The live adult schistosome in the lung is harmless; an exactly similar granulomatous lesion may develop around a dead worm, forming either a small tubercle or the much larger bilharzial granuloma. These "bilharziomas" do not contribute to the pulmonary hypertension.

These granulomatous-fibrotic changes must be differentiated from the acute reaction which occurs during treatment or the fleeting reaction during the stage of acute infection (the Katayama syndrome). Although it is difficult to obtain histopathological material at this phase, because it is transient and heals completely both clinically and radiologically, it is probable that there are no significant residual histological changes and no permanent damage. These reactions are probably allergic.

4. The liver, spleen and portal system. Unfortunately, the story of schistosomiasis in the human body does not end with involvement of the gastrointestinal and genitourinary tracts or the lungs. Not all the eggs shed by the female worms in the mesenteric venules are trapped in the colon, small bowel, bladder, ureters and/or lungs, or are passed to the outside in feces and urine to perpetuate the life cycle of the parasite. Many eggs and worms are forced back into the portal veins from mesenteric venules. Here they penetrate the walls of the small portal veins and lodge in the periportal connective tissue, where they incite an inflammatory cell reaction, eventually leading to multiple granulomas in the liver followed by fibrous tissue formation (Figs. 2.42-2.45). These lesions obstruct the small portal veins before they enter the hepatic sinusoids, causing a presinusoidal pattern of cirrhosis, known as Symmers' fibrosis. Initially, the fibrous tissue is confined to the portal tracts, with hepatic cells being uninvolved. Therefore, portal hypertension occurs long before there are measurable changes in liver function, in direct contrast to Laennec's (postsinusoidal) cirrhosis.

There are three types of intrahepatic vascular lesions in schistosomiasis; (1) substitution by granulomas; (2) sclerosis and narrowing of portal venules; and (3) intrahepatic thrombophlebitis. Newly developed sleeve-like capillary networks surround the portal vein and probably form intrahepatic shunts between the portal and systemic circulations. There may also be extensive development of portal systemic collaterals outside the liver that help to lower the portal pressure with resultant esophageal, gastric and mesenteric varices which can be quite dramatic in their size and number (Figs. 2.54-2.58). There is an increase in blood flow through the hepatic artery to compensate for the decreased portal flow. Late in the disease, hepatic fibrosis becomes more generalized, the liver decreases in size, and there is less distinction between presinusoidal and postsinusoidal cirrhosis.