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Case Report
 
Nerve Infiltrating Echinococcus Multilocularis (Alveolar Hydatid Disease) Masquerading as Malignancy
Keywords :
Nalini Bansal1, Vivek Vij2, Manav Wadhawan3
1Department of  Histopathology, SRL Ltd Fortis Escorts Heart Institute, Okhla, New Delhi 
2Department of Liver Transplant and Hepatobiliary Surgery, Fortis Escorts Heart Institute, Okhla, New Delhi 
3Department of  Hepatology, Fortis Escorts Heart Institute, Okhla, New Delhi 


Corresponding Author
:
Dr Nalini Bansal
Email: drnalinibansal@yahoo.com


DOI: http://dx.doi.org/10.7869/tg.462

Echinococcus Multilocularis (EM) causes Alveolar Hydatid disease. Humans are accidental hosts of the parasite. The parasite always affects the liver and forms large masses mimicking malignancy. These masses are however slow growing and well marginated. Involvement of vascular structures has been reported. We herein report the first known case of EM causing nerve infiltration.

Case Report

We report a case of a 24 year old female resident of Kyrgyzstan who was a known case of hydatid liver disease involving both lobes of the liver and vascular structures. Abdominal Multislice Spiral CT performed in her native country revealed lesions in the right and left liver lobes with involvement of the right and left hepatic arteries,  hepatic veins, portal vein and hepatic segment of the inferior venacava.  Portal hypertension was noted.
She underwent laparotomy for the same.However, due to extensive involvement of vessels and the inferior venacava, the mass was deemed inoperable and the patient was referred for liver transplantation
She underwent living donor liver transplant, and the native liver was sent for histopathological examination.
Grossly the explantedliver weighed 1659 gm, measuring 22x17x11 cm. The liver was soft in consistency with the external surface being a smooth brown color. The left lobe capsule appears thickened and whitish. Serial slicingof the specimen revealed two large lesionsone in each lobe of the liver with a creamy yellow cut surface. The right measured  11x11x7 cm and the left,  8x5.6x5.5 cm. (Figure 1a,b) The firm cream coloured lesion showed central areas of cystic change filled with browngrumous debris. The lesion in the right lobe was seen extending upto the porta hepatis. The gall bladder was adherent to the liver bedmeasuring 5x2 cm.
Light microscopy of the section examined from the firm cream colored mass with adjacent liver interface showed abundant granulomatous reaction around the laminated Periodic acid-Schiff (PAS) positive parasitic membranes. The granulomatous reaction was seen creeping into adjacent liver tissue and destroying the hepatocytes. The inflammatory infiltrate was  predominantly comprised of eosinophils, lymphocytes and epithelioid cells. Only periphery of the lesion showed viable inflammatory cells. The remaining central area of the  mass showed coagulative necrosis with interspersed laminated membranes. Foci of calcification were noted. Section from the porta hepatis showed infiltration by similar granulomatous reaction.There was a prominent peri and intraneural inflammatory infiltrate at the porta (Figure 1c). Section from adherent gall bladder showed necrosis and parasitic remnants in wall tissue (Figure 1d). Immunohistochemistry of the nerve infiltration stainedpositive  for S100, CD56 and calretinin (Figure 2). The parasitic membranes were  PAS positive andcaid fastnegative, with Masson’s trichrome stain showing two tone appearance (Figure 3)
The patient  was diagnosed to have had alveolar hydatid disease with parasitic infiltration of the liver and gall bladder demonstrating mass effect along with involvement of the portal vein and nerve bundles at the porta hepatis.







Discussion

Alveolar hydatid disease is a disease of the Northern Hemisphere commonly seen  in Russia, Central Asia, China, Northern Japan, Central-Western Europe, Eastern Europe, Turkey, and Alaska.The disease is caused by Echinococcus multilocularis. Foxes, and occasionally dogs and cats are the definitive hosts with rodents and other small mammals serving as intermediate hosts.  The eggs produced by the adult parasite are released into the environment by the fox and the cycle continues with digestion of contaminated food by the intermediate host. The eggs penetrate the bowel wall and invade the lymphatic and portal systems, and from there they spread to multiple organs. The parasite matures into its metacestode stage in natural intermediate hosts and in humans who are accidental hosts.1-3. The metacestode stage almost always occurs in the liver. Within the liver they cause formation of infiltrative mass lesions with no distinct demarcation from adjacent hepatic parenchymal tissue. Over time these masses undergo diffuse fibrosis with calcific foci and necrotic areas. Rarely the parasite can undergo lymphovascular invasion and is disseminated to other intra-abdominal organs.4-6 However, to our knowledge there has been no reported case of nerve infiltration by Echinococcus multilocularis.
Most cases are seen between the age of 50 and 70 years. The natural course of the disease consists of approximately 5-15 years of an asymptomatic incubation period followed by a chronic period.1,2 Clinical features are non specific including pain, abdominal lump, fever, jaundice or portal hypertension.
Radiologically, features may mimic a primary or metastatic liver tumour. CT is the best imaging modality for diagnosis. Imaging shows a heterogeneous non enhancing well marginated lesion with both central & peripheral calcification.7
Hepatic lobectomy witha prolonged course of chemotherapy is suggested. Liver transplantation is the final resort for incurable symptomatic billiary alveloar hydatid disease cases.8,9 In conclusion, alveolar echinococcus forms a slow growing infiltrative solid cystic lesion in the liver with the potential to cause obstruction of the bile duct, portal vein, hepatic vein or inferior vena cava. The disease is highly fatal if left untreated and can cause lymphovascular dissemination with delayed recurrence. This feature of vascular dissemination and widespread infiltration, including nerves, shows resemblance to a malignant tumour.

References
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