Ultrasonography

Ultrasonography of the liver is very important in schistosomiasis, and especially in S. mansoni, given its particular association with liver pathology. The earliest evidence of infection is loss of the normal smooth liver outline. In the left lobe, the surface becomes wavy, the posterior margin convex or straight, and the caudal margin rounded instead of concave. At some stages the caudal margin will become sharp. Measurements of liver size must be established within each locality; there is too much geographical variation to provide reliable standards.

An early change in the liver is thickening around the portal vein and its main branches. These become highly echogenic, especially around the porta hepatis. There may be enlargement of the splenic veins also and, when portal hypertension develops, there is usually splenomegaly. As portal hypertension increases, multiple varicosities and collateral veins will develop, including short gastric , paraumbilical, coronary, and esophageal veins. Visualization of any collateral veins is abnormal.

There are standard WHO criteria allowing the grading of the pathology due to S. haematobium (and for other schistosomes also). These are useful to permit accurate comparison in epidemiological surveys in different countries. In the liver, criteria are based on the width of the periportal echogenic bands. As with the bladder, there is considerable variation in the extent of the disease in different regions of the tropics.

When surgery is considered for severe liver disease, the diameters and blood flow velocity of the portal vein and hepatic artery can be measured using a Doppler duplex technique. Pre- and post surgical studies allow accurate assessment for treatment. When successful, there should be a decrease in the venous portal blood flow to the liver and an increase in the arterial hepatic blood flow. Probably the best vein to use for the diagnosis of portal hypertension is the splenic vein, although some authorities prefer the portal vein.

A few patients with chronic persistent hepatitis will show early periportal fibrosis and this must be differentiated from early schistosomiasis. If there is no periportal fibrosis on ultrasound, there is unlikely to be hepatosplenomegaly.

The direct detection of esophageal varices with ultrasound can be very difficult. With careful scanning it may be possible to show some of the dilated vessels around the cardia. An alternative is to use an ultrasonographic scoring system, rating periportal fibrosis, portal vein diameter, spleen size, and portal-systemic anastomoses. With experience this can provide a fairly accurate, non-invasive means of screening for esophageal varices. It correlates strongly with prior gastrointestinal hemorrhage.

Apart from the liver changes, in 80% of patients who show periportal fibrosis there will be thickening of the wall of the gallbladder. There will usually be omental thickening also. The findings on hepatic ultrasonography are so accurate and reliable that they should replace the liver biopsy as a method of confirming the diagnosis of schistosomiasis.

The World Health Organization staging, to record the severity of hepatic disease in schistosomiasis by ultrasonography, is based on the following criteria. All measurements for hepatomegaly assume that there is no other reason, such as cardiac failure, or leishmaniasis.

A. Liver outline. This is normally smooth (grade 0).
Grade (1) is slightly irregular.
Grade (2) is grossly irregular.

B. Measurements, taken in longitudinal cross-section with the transducer above the aorta, from the upper to the caudal margin of the left lobe, provide standards which must be reassessed locally in endemic countries, and with allowance for the height of the individual.

Left lobe in adults:
Normal (0) is 70 mm or less
Enlarged (1) is more than 70 mm

Right lobe in adults is measured in the right midaxillary view:
Normal (0) is more than 140 mm
Small, shrunken (1) is 140 mm or less

Another sign of abnormality in adults (not in children) is the finding of echogenic "spots" in the liver parenchyma which are not part of the portal system.

C. Periportal veins. The inner diameter of the portal vein, measured midway between the porta hepatis and the bifurcation, is normally 12 mm or less. If over 12 mm, it is abnormal.

Periportal echogenicity is assessed by the average of three outer to outer measurements (maximum transverse outer diameter) of the increased width of echodensity around branches of the portal vein, measured between the first and third branches.

Normal (0) equals less than 3 mm
Grade (1), 3-5 mm
Grade (2) greater than 5-7 mm
Grade (3) greater than 7 mm.

D. The gallbladder must be assessed when full, i.e. when the patient has been fasting (no food, only water to drink for six hours or more). If the gallbladder is not full, the wall will show on ultrasound scans as a double line. All measurements are of the anterior wall on the longitudinal view of the full gallbladder; the thickness of the wall should be less than 5 mm. When the wall thickness is 5 mm or more, this is abnormal (grade 1).
(It must be noted that many ultrasonographers use 3 mm as the maximum thickness of a normal full gallbladder wall in the fasting patient. Less than 5 mm is therefore a safe margin to allow for variation between observers. The gallbladder wall may thicken for other reasons, such as cardiac failure or dengue fever.)

E. The spleen should not be more than 120 mm (12 cm) in length, measured in the midaxillary line. It may, of course, be larger due to causes other than schistosomiasis such as malaria or leishmaniasis.

F. Collateral veins are almost always abnormal. If there are none, this is normal (0). If the observer is not certain, this is grade (1); if veins are definitely present, this is grade (2). If there are collateral veins, the record should include which veins have been seen, the coronary, paraumbilical, or short gastric.

G. Ascites is abnormal (excluding other causes); if there is none this is (0), if the observer is undecided this is grade (1) and if definitely present, this is grade (2). There are minimally different criteria for grading schistosomiasis japonica.

Portal Hypertension

For many years splenoportography and splenic manometry have been used to assess portal-hypertension in schistosomiasis. Ultrasound, with duplex Doppler, can effectively replace these invasive methods and is also an excellent method to assess postoperative improvement. Many studies from different countries confirm the close correlation between the ultrasound grading levels and the level of portal hypertension. The best index and correlation may be of the diameter of the splenic vein, measured at the hilus (normally less than 9 mm), but the size of the portal vein and superior mesenteric vein must also be measured. There is direct and accurate correlation between the diameter of the splenic vein and the intrasplenic pressure.

The mean velocity of the blood flow in the splenic vein may be normal, in spite of the increased diameter; it is likely to exceed that of the superior mesenteric vein. The blood flow in hepatic veins may not be increased. The grading of periportal fibrosis correlates well with the risk of bleeding. If worse than grade (1) and if the spleen is more than 11 cm in length, there is a significant risk of bleeding. A palpable liver and the portal vein diameter do not give a good correlation with the risk of hemorrhage.

Following successful surgery, there is usually a decrease in the size of the portal vein and an increase in the size of the hepatic artery. Mean blood velocity in the portal vein will be decreased but there will be no change in the blood flow velocity in the hepatic artery. It should be noted that preoperatively, splenic vein thrombosis is not uncommon, which will invalidate some of the usual measurements. As expected, there is a difference depending on the type of surgery, when devascularization is compared with a distal splenorenal shunt. After devascularization, the portal blood flow velocity is usually decreased, whereas it is increased following splenorenal shunt.