The concentration of glutamate and glycine in CSF is significantly increased in encephalitis (21). These observations suggest an excitotoxic mechanism may play a role in neuronal damage in herpes encephalitis. Neonatal herpes simplex type 2 encephalitis involves the cortex and white matter extensively. Herpes simplex type 1 encephalitis in older children and adults usually involves the medial temporal lobe, inferior frontal lobes and insula. Widespread brain lesions in neonatal herpes encephalopathy are presumably related to the vulnerability to excitatory amines in the neonatal brain.
In neonatal herpes encephalitis, MRI/DWI shows widespread, asymmetric lesions in both hemispheres including the basal ganglia and thalami (Figure 7). MRS shows increased lactate and glutamate/glutamine peaks.
Figure 7. A 2-week-old female with herpes simplex type 2 encephalitis
A. T2WI shows asymmetric hyperintense lesions in the thalami.
B,C. DWI shows asymmetric but extensive hyperintense lesions with decreased ADC in the thalamus and gray and white matter of both hemispheres. This extensive distribution seems to be related to vulnerability to excitotoxic injury during the post-natal period.
D. MRS (TE 144 ms, PRESS) shows inverted lactate peaks, an increased glutamate/glutamine (Glx) peak and decreased NAA peak.
E. MRS (TE 35 ms, PRESS) shows lactate peaks and an increased glutamate/glutamine (Glx) peaks.