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Schistosomiasis japonica

The initial infection with S. japonicum can cause the Katayama reaction and is more likely to give rise to CNS symptoms than the other varieties of schistosomiasis at this stage.

Schistsoma japonicum can produce 3,000 eggs per worm per day, and the eggs are smaller than those of other schistosomes. It has been suggested that this may account for the somewhat different characteristics of schistosomiasis japonica. Others have disputed this but there is no doubt that the radiological findings are different.

The S. japonicum worms live in mesenteric veins and their eggs are deposited predominantly within small bowel venules and in the mesentery. CT has shown that in some patients the heaviest load is in the colon rather than in the small bowel. All the eggs are within the submucosal and subserosal layers of the intestine, and only a few are in the muscularis. They may also be found in the same layers in the appendix. In the later stages, fibrosis and constriction of the mesentery may occur, so that the loops of bowel, particularly the duodenum, may be deformed by adhesions as well as by the intrinsic granulomas.

Small Bowel

The mucosa of the duodenum and the upper jejunum becomes edematous, coarse and irregular; motility is decreased and there may be some dilatation. There is excess mucus secretion and flocculation of barium can occur. The terminal ileum may show similar changes (Fig. 2.36).

Colon and Rectum

Schistsoma japonicum infection produces changes very similar to those seen in schistosomiasis mansoni. The early changes include edema and spiculation of the mucosa; polyps are not uncommon: there may be a cobblestone appearance in the mucosa, in both the large and small bowel, with less tendency to form large and multiple polyps. CT has shown that when the eggs calcify there can be either a curvilinear or nodular pattern of calcification: in the sigmoid colon the calcification has been heavy enough to cause parallel lines. However, although the calcification may be more marked than in S. mansoni, there is usually less distortion of the colon (Fig. 2.33).

Retroperitoneum

Granulomas located in the retroperitoneal space may become large enough to resemble malignant disease. Although CT, and occasionally ultrasound, can demonstrate multiple eggs, the exact differential diagnosis may only be possible by biopsy. Because such schistosomal granulomas are inflammatory, they have increased vascularity with many new vessels forming as collaterals bypass arterioles which have been obliterated. Ultrasound, MRI, and even angiography can show that these are highly vascular masses. The response to appropriate antischistosomal therapy may be one way to make the correct diagnosis, but there are no specific features shown by any method of imaging.

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Copyright: Palmer and Reeder