mortality rates if therapy is not promptly initiated. CT is often negative in these patients.
Abnormal findings on MR and nuclear imaging studies depend on the specific virus. Herpes
typically involves the medial temporal and inferior frontal lobes (Fig. 18A), whereas Japanese
encephalitis affects the thalami, brain stem, cerebellum, spinal cord, and cerebral cortex.
Abnormal high-intensity lesions can be demonstrated on T2-weighted and FLAIR sequences
(Fig. 18B). Contrast enhancement may range from none to intense (28,30,35).
Figure 18 (A) Contrast-enhanced axial CT image of the brain in a patient with herpes encephalitis demonstrates
low attenuation in the left temporal lobe (arrow). (B) A corresponding T2-weighted axial MR image from the same
patient demonstrates high signal intensity in both medial temporal lobes (arrows) consistent with the diagnosis of
herpes encephalitis.
Figure 17 Contrast-enhanced sagittal MR
image of the brain demonstrates mild leptome-
ningeal enhancement, most pronounced in the
posterior fossa (arrow), in a 53-year-old male
with cryptococcal meningitis on CSF analysis.Radiology of Infectious Diseases and Their Mimics in Critical Care 91