Type:
Educational Exhibit
Keywords:
Performed at one institution, Diagnostic or prognostic study, Retrospective, Parasites, Cysts, Diagnostic procedure, MR-Diffusion/Perfusion, Abdomen, Abdominal Viscera
Authors:
E. Salman Yalniz, A. Yalnız; KOCAELİ/TR
DOI:
10.26044/ecr2020/C-06122
Background
Echinococcosis is a parasitic disease caused by larval forms of echinococci. There are four main species of the genus Echinococcus; E. granulosus, E. multilocularis, E. oligarthrus and E.vogeli (1). In humans, the E. granulosus cestodes causes cystic echinococcosis (CE), E. multilocularis cestodes causes alveolar echinococcosis (AE), and E. vogeli and E. oligarthrus cause polycystic echinococcosis. Although CE is common worldwide, AE is seen only in the northern hemisphere (Fig. 1). The exposure to Echinococcus eggs is affected by occupational and environmental factors. The incidence of CE is most common in sheep breeding areas, while AE increases in groups of people who spend more time in the wild (2).
The definite hosts are foxes, whereas rodents are intermediate hosts in the life cycle of E. multilocularis. 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 (Fig. 2). The eggs penetrate the intestinal wall and from there spread to other organs through the lymphatic and portal system. The parasite goes into a metacestode stage in natural intermediate hosts and in humans who are accidental hosts (1,3,4). The disease is most commonly seen in the liver. Unilocular cystic form, also known as hydatid cyst caused by E. granulosus, is easily diagnosed due to its typical radiological features and serological tests. Alveolar echinococcus caused by E. multilocularis; it can be confused with liver malignancies due to its infiltrative appearance, increase in size and distant metastasis, and biopsy is often required for definitive diagnosis.
A diagnosis of AE is based on the presence of at least two of the following findings (5):
- A lesion or lesions with the typical appearance, detected at cross-sectional imaging
- Echinococcus species–specific serum antibodies detected in blood tests with high diagnostic sensitivity and confirmed in immunoassays with high specificity
- Histopathologic features suggestive of E. multilocularis
- Nucleic acid of E. multilocularis detected in a clinical specimen.
The World Health Organization Informal Working Group on Echinococcosis developed a clinical classification termed as the PNM system, which is based on imaging findings. The PNM classification system describes the presence of a hepatic parasitic mass (P), involvement of adjacent organs (N), and distant metastasis (M) (Fig. 4). The aim of PNM classification is to develop the quality of treatment and to standardize the evaluation of outcomes between health institutions. Following the identification of PNM categories, the patient is staged as I, II, IIIA, IIIB or IV (Fig. 5).