Cytomegalovirus is a herpes virus that causes cytomegalic inclusion disease (big cells with inclusion bodies). This can be a congenital (intrauterine) infection, or may be seen in immune compromised hosts. In the CNS, CMV may cause a meningitis, encephalitis, or an ependymitis. CMV encephalitis may not always produce abnormalities on CT and/or MRI. CMV ependymitis may cause linear periventricular enhancement. This appearance must be distinguished from CNS lymphoma, which is also commonly periventricular. Infectious ependymitis usually causes thinner and more linear periventricular enhancement. CNS lymphoma usually causes thicker and more irregular periventricular enhancement - and, is usually hyperattenuating on a plain CT.