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Imaging Diagnosis of Acute Schistosomiasis ( The Katayama Syndrome)

The chest radiograph is either normal or shows increased vascular and interstitial markings and minimal enlargement of the hilar lymph nodes. Miliary tuberculosis in its early stages or a simple virus infection may be suspected. The changes are not specific but, in conjunction with a significant history and eosinophilia, they may help to confirm the diagnosis. Skin tests are variable; the complement fixation test is usually positive. The chest radiograph returns to normal with or without treatment. In the abdomen there are three sonographic (and CT) findings which contribute to the diagnosis of the Katayama stage of acute schistosomiasis.

There may be a nonspecific hepatosplenomegaly (splenomegaly was particularly noted in series from Brazil). The left lobe of the liver may be more enlarged than the right. The liver is sonographically homogeneous or, in a few cases, hyperechoic. Liver enzymes may be slightly abnormal. At the same time there may be periportal and juxtapancreatic lymphadenopathy, particularly in children. The lymph nodes are sharply outlined and round or oval, with a thin surrounding hypoechoic halo.

Ultrasonography may also show multiple small nodules throughout the liver parenchyma. In schistosomiasis mansoni they have been described as hypoechoic, but in schistosomiasis japonicum they are hyperechoic. There are not many reports of these findings and the different echogenicity is more likely to reflect a different clinical pattern than an intrinsic difference in the reaction of the two species. The histopathology has not been described (1999), and it is not known whether such findings are always present. Differences will not be surprising because there are many variations in response, even to the same species of schistosome. These nodules may persist in spite of adequate therapy: they may be 4-5 mm in diameter and are well shown on CT scanning, being hypodense with delayed contrast enhancement. Even with a second course of treatment, it may take 20 weeks before the liver in sonographically normal although the patient's clinical condition will have improved long before this. These natural history without treatment has not been described (1999). In subacute schistosomiasis, echogenic lesions in the liver are thought to be due to portal vein branches (in cross-section). It probably takes from 3 to 5 years to develop stage one periportal (Symmers) fibrosis when patients have a high-intensity infection. With low infection rates, it may take much longer. There is no evidence of portal hypertension during the Katayama stage. It should be emphasized again that the diagnosis is only reliably made when correlated with the clinical findings, a raised eosinophilia, and preferably, the findings of eggs in the feces or on biopsy.

The acute phase of S. japonicum infection results in central nervous system involvement in about 2% of patients, possibly because the eggs of S. japonicum are the smallest of the more common species. There is a focal pattern of egg distribution in the brain, resulting in a wide variety of symptoms, not only headache but speech impairment, disorientation, memory loss, visual disturbances, seizures and coma; in a few patients there may be spasticity, cranial nerve findings and various patterns of paralysis. CT scans of the brain may show edema around low-density inflammatory foci, which are often multiple and contrast-enhancing with edema. In some cases there may be a mass effect , causing shift with pressure on any part of the ventricular system. The CSF pressure may be slightly raised, but all the findings will be very variable, depending on the distribution and the number of eggs. In most cases there has not been a clear correlation between the parasite load and the possibility of CNS involvement or its extent. The diagnosis will be made in the usual way, by serology or recognition of the ova in stool. If treated appropriately, and with steroids, complete resolution can be expected within about eight weeks, matched by an improvement of clinical symptoms and signs.

This pattern of CNS involvement must be distinguished from the mass effect which is found in chronic cerebral schistosomiasis affecting patients who have been previously and often repeatedly infected.

Imaging changes other than in the acute state are different with each type of infection and will be discussed separately.

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Copyright: Palmer and Reeder