Hepatic schistosomiasis, predominantly seen in individuals from endemic areas like Africa and the Middle East, is characterised by parasitic infection by Schistosoma species causing periportal fibrosis, portal hypertension, and the pathognomonic pipestem fibrosis on liver biopsy, with characteristic calcified schistosome eggs visible on abdominal imaging.
Description
Hepatic schistosomiasis is a parasitic infection of the liver caused by trematode worms of the genus Schistosoma. It’s a significant public health issue in endemic regions and can result in chronic liver disease, with complications such as liver fibrosis, portal hypertension, and hepatosplenic disease. It is the most common cause of hepatic fibrosis in the world.
Pathogenesis
The disease process starts when the cercariae of Schistosoma species, predominantly S. mansoni, S. japonicum, and S. mekongi, penetrate human skin in contaminated water. These then mature into schistosomula, enter the bloodstream, and migrate to the liver where they mature into adult worms. These worms lay eggs which are released into the bile ducts and intestines to be excreted in faeces. The eggs that do not get excreted become lodged in the liver tissues, triggering an immune response that results in granuloma formation and progressive fibrosis.
Epidemiology, Risk Factors & Associations
Schistosomiasis affects over 200 million people worldwide, predominantly in Africa, South America, the Middle East, and Asia. Risk factors include poor sanitation, farming, and fishing in endemic areas. Schistosomiasis is associated with bladder cancer in cases of infection with S. haematobium, though this subtype does not typically cause liver disease.
Clinical Features
- Most infected individuals are asymptomatic.
- During the acute phase (Katayama fever), individuals may experience fever, fatigue, hepato-splenomegaly, and eosinophilia.
- Chronic hepatic schistosomiasis presents with signs of portal hypertension, such as ascites, variceal bleeding, and splenomegaly.
Complications
The main complications of hepatic schistosomiasis include liver fibrosis, portal hypertension, ascites, oesophageal varices, and hepatosplenomegaly. Chronic infection can lead to hepatocellular carcinoma, though this is relatively rare.
Pathological Features
Histologically, liver biopsy reveals granulomas surrounding Schistosoma eggs. The granulomas consist of a mixture of immune cells, predominantly eosinophils. With time, these granulomas can lead to periportal fibrosis (‘pipestem fibrosis’), particularly in S. mansoni and S. japonicum infections. Portal tract expansion with fibrosis is a key feature.
Radiological Features
On imaging, hepatic schistosomiasis has several characteristic features, although these can vary depending on the stage and severity of the disease.
US
May show periportal fibrosis, irregular liver surface, splenomegaly, and ascites. Doppler may reveal portal vein changes suggestive of portal hypertension.
CT
May show an enlarged liver with periportal tracking (pipestem fibrosis), splenomegaly, and ascites. Active disease may present with multiple small, low-attenuating lesions throughout the liver parenchyma.
MRI
May show similar findings to CT, with periportal fibrosis appearing as low-signal intensity on T2-weighted images. Active disease can appear as small hyperintense foci on T2-weighted images, representing granulomas.
Grading and Staging
There’s no universally accepted grading or staging system for hepatic schistosomiasis. However, the severity of disease can be inferred from the extent of liver fibrosis and the presence of complications such as portal hypertension and ascites.
Differential Diagnosis
- Cirrhosis of other etiologies: Can present with similar clinical and radiological features, but history, regional prevalence, and serological testing can help distinguish.
- Hepatic Hydatid Disease: Cysts may be seen on imaging, but the lack of calcification and characteristic imaging findings, along with serological testing, can help distinguish it from schistosomiasis.
- Hepatic tuberculosis: Can present with granulomas on histopathology, but the involvement of other organs, imaging findings, and positive tuberculosis tests can help in differentiation.
Management
Management primarily involves antiparasitic therapy with praziquantel. Regular ultrasound surveillance is recommended in individuals with established hepatic schistosomiasis to monitor for progression of liver disease. In cases of portal hypertension, management is similar to that for other causes of portal hypertension, including the use of non-selective beta-blockers and endoscopic management of varices. In severe cases, liver transplantation may be required.