Clinical and Radiologic Features of Cerebritis
Cerebritis is a term used to describe an acute inflammatory reaction in the brain, with altered
permeability of blood vessels, but not angiogenesis. Cerebritis is the earliest form of brain
infection that may then progress to abscess formation, as previously noted. Cerebritis alone can
be managed nonsurgically with antibiotics (30).
The appearance of early cerebritis on T1-weighted MR imaging is a hypointense or
isointense area with minimal mass effect and little to no enhancement after IV contrast
administration. The affected area is hyperintense on T2-weighted images and FLAIR images
and may demonstrate restricted diffusion on diffusion-weighted imaging; this has been
attributed to increased cellularity (from infiltrating neutrophils), ischemia, and cytotoxic
edema (28).
Mimic of Cerebritis
As opposed to infectious cerebritis, autoimmune cerebritis occurs with systemic lupus
erythematosus (SLE). CNS involvement in SLE typically occurs within three years of diagnosis
and may even precipitate full-blown SLE presentation. On CT, there is cerebral atrophy and
possible focal infarcts or calcification as well as extensive, potentially reversible white matter
changes (28).
MRI is superior for demonstrating active lesions that appear as hyperintense white
matter spots on FLAIR imaging, with restricted diffusion and IV contrast enhancement.
Differentiating old lesions from infectious cerebritis may be difficult as both are bright on
T2-weighted imaging, and neither entity enhances with IV contrast administration. MR
spectroscopy (MRS) and PET imaging can be utilized to further evaluate for suspected lupus
cerebritis in difficult cases. MRS findings, though nonspecific, include a decreasedN-acetyl
aspartate peak and increased choline and lactate peaks. PET imaging demonstrates parieto-
occipital hypometabolism, even in MR-negative cases (28).
Clinical and Radiologic Diagnosis of Meningitis
Meningitis is an inflammatory infiltration of the pia mater, the arachnoid, and the CSF. The
disease can have an infectious or noninfectious etiology. Early in the course of disease, the
initial diagnosis is made on clinical evaluation, including lumbar puncture, as imaging
findings are often normal. On CT, there may be hydrocephalus with enlargement of the
subarachnoid space and effacement of the basal cisterns. There is enhancement within the sulci
and cisterns after IV contrast administration, secondary to breakdown in the blood–brain
barrier, as well as areas of low attenuation from altered perfusion patterns. On MR, exudate in
the subarachnoid space is isointense on T1-weighted images and hyperintense on T2-weighted
images. Again, there is leptomeningeal enhancement after IV contrast administration, which is
typically smooth and linear (Fig. 17). Diffusion-weighted imaging findings depend on altered
perfusion and the presence of vascular complications such as arterial occlusion (28,30).
Mimic of Meningitis
Carcinomatous meningitis occurs from both secondary and primary brain tumors. The most
common distant primary tumors include breast and lung cancer. Glioblastoma multiforme,
pineal tumors, and choroid plexus tumors can also extend along the leptomeninges. The
enhancement pattern of carcinomatous meningitis is often thicker and irregular compared
with that which is seen with infectious meningitis, although thin and linear enhancement
can also occur. In such cases, clinical information, including presence of a primary
malignancy, and CSF analysis may be needed to definitively differentiate between the two
entities (28,30).
Clinical and Radiologic Diagnosis of Encephalitis
Encephalitis is an inflammation of the brain parenchyma that may be focal or diffuse and is
most commonly associated with viral infection (rather than cerebritis, which is associated with
bacterial infection). Potential agents include eastern and western equine, herpes simplex,
Epstein–Barr, and varicella viruses as well as cytomegalovirus (CMV). Herpes encephalitis, to
which the elderly are particularly vulnerable, is a dangerous form of the disease with high
90 Luongo et al.