Diagnostic difficulties with central nervous system actinomycosis.

When faced with expanding brain lesions of unknown origin showing a ring-shaped enhancement on post-contrast imaging, we use definite criteria to direct further investigation and distinguish among a number of possible diagnostic hypotheses. However, a correct diagnosis may be difficult in some cases, especially when dealing with less frequent conditions. This is the case of actinomycosis, a highly treatable but insidious infection for which nowadays there may be a low level of attention. Brain localization is associated with a significant morbidity and may represent a true diagnostic pitfall. Here we report the difficulties encountered with a case of central nervous system actinomycosis.