Tropical Medicine Mission Index of Diseases About Tropical Medicine Tropical Medicine Home Page Tropical Medicine Staff

Next Page

Schistosomiasis Haematobium

There is no doubt that ultrasonography has added significantly to the understanding of urinary tract schistosomiasis, by permitting surveys of children and adults and providing accurate information on the results of treatment. However, there are conflicting results in various reports, which again shows how much individual variation there is between populations, even villages, seemingly infected with the same schistosome to the same extent. Anyone working in a particular country or locality must determine the effect of schistosomiasis in their own patients, but it is possible to give a general review.

Many different studies have been made to assess the value of the various imaging methods in suspected or proven schistosomiasis haematobium. Ultrasound, which is noninvasive, radiation free and inexpensive, is an excellent way to assess morbidity. It is the most widely available method for studying the liver and spleen size, and for detecting liver disease (periportal fibrosis and portal hypertension). In the early stages of liver disease there is some observer variation: as the disease progresses, the results become more consistent. Ultrasound is also an excellent way of detecting hydronephrosis and thickening of the bladder wall; it can demonstrate early malignant change in the bladder and can assess residual urine. It is not so accurate in finding ureteric lesions (hydroureter, calcified ureteric granulomas) or bladder wall calcification and is less accurate with renal or bladder calculi. It is quite unreliable in the detection of mesenteric or other abdominal calcification, including calcification of the liver.

Intravenous urography is excellent in demonstrating the whole urinary tract, particularly ureteric lesions (stenosis, dilatation, poor peristalsis), bladder wall calcification, and bladder capacity.

Plain radiography of the abdomen is of little assistance unless there is bladder or ureteric calcification, when it becomes a very useful investigation. It can also show calcification in the seminal vesicles. Plain radiography can also detect moderate or advanced intestinal or non-visceral calcification but, in the earlier stages, does not show calcification as clearly as CT which is excellent for the demonstration of calcification in any site or organ, including pelvic tissue: it is also excellent for recognizing other lesions in the urinary tract. CT can demonstrate CNS lesions (which are rare in schistosomiasis haematobium, being more common in S. mansoni and S. japonicum infections). Myelography is useful for spinal schistosomiasis, but not as accurate as CT or magnetic resonance imaging (MRI).

Magnetic resonance imaging is most important in the CNS, particularly for imaging the brain and spinal cord in schistosomiasis mansoni or japonicum. While it can demonstrate urinary tract and other intra-abdominal schistosomiasis, it has little advantage over ultrasound or CT. It is much less accurate in the demonstration of any calcification.

Wherever schistosomiasis haematobium is endemic, 60-70% of children aged 4-14 years will have bladder lesions; about 20% of boys and 2-5% of girls in this age group will have hydronephrosis. Ureteric lesions will usually be bilateral, but not symmetrical. Between 10 and 15% of these children will have ureteric lesions only, which may reflect the stage of the infection. The vast majority of ureteric lesions, over 90%, will be in the lower third of the ureters. In adults in the same endemic areas, about 50-60% of men and 20-30% of women will have bladder lesions, but only about 15% of men and less than 10% of women will have hydronephrosis. This is less than among the children. In some series there is a positive relationship between the severity of the bladder lesions and the egg count. In other series there is no correlation.

In areas where the infection occurs but is not known to be endemic, the prevalence is much less. Surveys show that in supposedly schistosome-free areas, 10% of children and 16% of adult men and perhaps 5-10% of adult women may have active infections. In these non-endemic areas, hydronephrosis is very uncommon at any age, unless there is bladder calcification. Once there is bladder calcification, visible on imaging, hydronephrosis becomes twice as common as it is in patients who have no visible calcification. Bladder calcification, even when quite heavy, makes little difference to bladder function because the ova are predominantly in the mucosa and submucosa, not in muscle. Difficulty in micturation in patients with schistosomiasis is likely to be evidence of cystitis or bladder neck thickening.

Ultrasonography

In the urinary tract, ultrasonography can detect hypertrophy of the bladder mucosa, thickening of the bladder wall (which is normally less than 5 mm when the bladder is distended), and bladder calcification. If the ureters are easily demonstrated by ultrasound, they are probably thickened and abnormal; in some patients calcification will be seen, but ultrasound is not a reliable way to demonstrate early ureteric changes. Dilatation of the renal collecting system can be detected very early, and represents the result of significant ureteric dysfunction. (Increased proteinuria, more than one gram per liter in mid-day urine, strongly suggests that there is urinary tract stasis and may suggest the need for imaging.)

Because of the strong association between schistosomiasis haematobium and squamous cell carcinoma of the bladder, particular care should be taken during ultrasonography to accurately record bladder wall thickening. Repeat ultrasonography is advisable after treatment; about 70% of schistosomal bladder lesions will regress significantly in less than 12 months (after treatment with praziquantel). If a bladder lesion does not improve, long-term follow-up is required to exclude malignancy. Over 90% of patients who have schistosomal carcinoma of the bladder will have ureteric obstruction; in a non-schistosomal (transitional cell) bladder carcinoma less than 25% will have ureteric obstruction.

There are authorities who believe that the liver is not affected by S. haematobium; however, there are others, equally eminent, who state that all schistosomes cause similar liver pathology, some more commonly than others. An International Expert Committee, convened by the World Health Organization (together with UNDP and the World Bank), met in Cairo, Egypt in 1991 to draw up criteria for assessing the extent of schistosomal infections as demonstrated by ultrasonography. This very experienced committee provided separate guidelines for S. haematobium, S. mansoni, and S. japonicum. Module 4 for S. haematobium (Annex B, p. 24 of the report) is "The record sheet for S. haematobium pathology-ultrasound findings: Liver Pathology", which leaves no doubt that this group was convinced that S. haematobium does indeed affect the liver. There is, nevertheless, no question that liver pathology occurs more frequently and perhaps more severely with S. mansoni infections: the description of the ultrasonographic findings is therefore provided in that section. The practicing radiologist will more often be concerned with the extent of the changes rather than the specific schistosome, and certainly will not be able to distinguish between the schistosomes by hepatic ultrasonography.

Radiography

Plain radiography of the abdomen is of no assistance until calcification has developed in the bladder and ureters, although in severe infections calcified eggs may also be seen in the soft tissues. ( Early calcification is much more clearly seen by CT.) Intravenous (contrast) urography will provide very useful diagnostic information. All the early findings will be in the ureters and bladder; the kidneys remain normal until later in the disease.

Back to the Table of Contents

Copyright: Palmer and Reeder