CNS infections : a case-based review

Abstract

Understand the correlation between pathologie features and imaging findings of the broad spectrum of infections involving the central nervous System. Recognize the three basic patterns of disease : meningeal enhancement, focal parenchymal lesions and masses, and diffuse white matter involvement. Identify imaging manifestations of complications of these diseases. Leptomeningeal (pia-subarachnoid) enhancement is characteristic of most clinical cases of meningitis while pachymenin-gitis is much less commonly seen and usually secondary to tuberculosis. Empyema is a serious complication of meningeal infection and characterized by intense enhancement of the surrounding membrane. Imaging findings correlate with pathologie stages of cerebritis and abscess formation with maximal edema noted in the late cerebritis stage and well-developed ring enhancement seen in the early abscess stage. Most acute encephalitis is secondary to HSV infection as a hemorrhagic meningoencephalitis with a predilection for the temporal lobes and limbic System in older children and adults. Subacute encephalitis, typified by HIV encephalitis and progressive multifocal leukoencephalopathy, are less prevalent in the highly active anti-retroviral therapy era. Creutzfeldt-Jakob disease is characterized by involvement of the caudate head, lenticular nuclei, thalamuss, and cortical regions with restricted water diffusion. Cysticercosis is the most common CNS infection and most common cause of epilepsy Worldwide. Five forms of CNS tuberculosis are recognized : leptomeningitis, cerebritis, tuberculoma, abscess, and encephalopathy. Toxoplasmosis is the most common cause of an intracranial mass in an adult immunocompromised patient. Cryptococcosis is the most common CNS fungal infection and has three imaging manifestations : cryptococcoma, dilated perivascular spaces, and nodular masses. Fungal infections are usually secondary to aspergillosis and mucormycosis and typically involve the basai ganglia with masses that have increased protein content. Imaging findings of central nervous System (CNS) infections parallel the great spectrum of gross pathologie presentations of these diseases. Three basic patterns are seen : meningeal enhancement, focal parenchymal lesions and masses, and diffuse white matter involvement. In most circumstances, the imaging appearance will provide confirmation of a morphologie abnormality suspected clini-cally but, with rare exception, will not implicate a specifie offending organism. As a generai rule, magnetic resonance imaging (MRI) is superior to computed tomography (CT), especially when contrast-enhanced studies are utilized. Fluid-attenuated inversion recovery (FLAIR) sequences and contrast-enhanced fat-suppressed sequences may increase detection of abnormalities. MR spectroscopy, diffusion-weighted imaging, and metabolic imaging (positron emission tomography and single-photon emission computed tomography) may be useful in further refining the differential diagnosis.