Infections of the central nervous system caused by atypical bacteria are becoming more common. Borrelia burgdorferi and Rickettsia conorii are microorganisms transmitted by ticks; infection with these bacteria result in a wide spectrum of manifestations on imaging. In areas where these tick-borne microorganisms are endemic, including Spain, these infections must be included in the differential diagnosis of patients with a variety of systemic and neurologic symptoms. The clinical presentation of these infections is nonspecific, and CT is normally the initial imaging technique, although MRI is more sensitive to early changes. On MRI, these infections can manifest as small lesions in the deep supratentorial white matter that are hyperintense on T2-weighted/FLAIR sequences. It is fundamental to know the imaging characteristics of the different atypical bacterial infections and their differential diagnoses. Good history taking combined with complementary tests (blood tests and CSF analysis) and the neuroimaging findings can help reach the right diagnosis and enable appropriate treatment, thereby preventing possible neurological sequelae.
