Cerebritis

Infant with
sepsis. Axial (left) and coronal (right) T1 MRI with contrast of the brain show diffuse meningeal enhancement along with a large variably enhancing solid right occipital lesion that has surrounding edema.The diagnosis was meningitis and cerebritis due to Group B streptococcus.
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Cerebritis is a term that represents inflammation of the brain in the setting of infection, before the development of a cerebral abscess.

Terminology

Cerebritis is essentially the same as encephalitis except that it is used to denote brain parenchymal inflammation secondary to infection with bacteria or other non-viral pathogens. In contrast, encephalitis usually is assumed to denote inflammation due to a virus or paraneoplastic/autoimmune process .

Pathology

Cerebritis is divided into early and late phases and lasts typically 10-14 days depending on the virulence of the pathogen .

Early cerebritis

Early cerebritis is usually a relatively short-lived phenomenon (2-3 days), representing edema, vascular congestion and coagulative necrosis .

Late cerebritis

Late cerebritis represents progressive infection, such that areas of the brain undergo liquefactive necrosis. It occurs at approximately 1 week from initial infection.

Late cerebritis may progress and organize to form a cerebral abscess, where a capsule of granulation tissue lines a cavity containing purulent material . This may occur approximately 2 weeks from initial infection.

Radiographic features

CT
  • early cerebritis
    • may appear normal by CT
    • poorly marginated cortical or subcortical hypodensity with mass effect, corresponding to edema
    • little or absence of enhancement
    • +/- small areas of hemorrhage
  • late cerebritis
    • more defined, but still irregular, rim-enhancing lesion with a hypodense center
MRI

MRI is more sensitive to the early changes of cerebritis and will demonstrate the signal changes expected for an area of inflammation :

  • early cerebritis
    • T1: iso- to hypointense
    • T2/FLAIR: increased signal with surrounding vasogenic edema
    • T1 C+: no or minimal heterogeneous enhancement
    • DWI/ADC: restricted diffusion, may be patchy
  • late cerebritis
    • progressive, especially peripheral, enhancement (not well-defined vs abscess)
    • progressive restricted diffusion

Treatment and prognosis

In most cases cerebritis has progressed to cerebral abscess by the time the diagnosis is made; however, if detected early enough, medical management with antibiotics can successfully treat cerebritis .