Magnetic resonance appearance of cerebral cystic echinococcosis: World Health Organization (WHO) classification

Cystic echinococcosis (CE) of the brain is an uncommon parasitic infestation. The World Health Organization (WHO) recently published a classification of hepatic CE based upon ultrasonographic findings.

To evaluate whether the new WHO classification of hepatic CE can be used in the classification of cerebral CE.

The magnetic resonance (MR) imaging findings of 17 patients (14 male, three female), aged 10-24 years (mean age 16 years), with pathologically proved cerebral CE, and who underwent pre- and postcontrast MR imaging, were retrospectively evaluated. The cysts were classified according to the new WHO classification and their clinical stages. The MR imaging findings were correlated to the histopathologic findings.

The fertile active cysts (n=12) that showed protoscoleces appeared as unilocular cysts with no visible wall (cystic lesions; CL), unilocular spherical cysts with a clear visible wall (CE1), or as a unilocular mother cyst with multiple vesicles arranged peripherally along the cyst wall (CE2). The transitional form (CE3) (n=2) containing scoleces showed multiple daughter cysts entirely filling the maternal cyst. The inactive cysts (n=3) that had lost their fertility appeared as a "ball of wool" with collapsed membrane or had detached membrane with water-lily sign (CE4) and calcified lesions (CE5).

The WHO classification of hepatic CE can be used in the classification of cerebral CE when evaluated by MRI, as it can differentiate fertile active cysts from the transitional and inactive forms of cerebral cystic echinococcosis. This information is essential for treatment planning.