Herpes simplex encephalitis

Case contribution: Dr Radhiana Hassan


  • A 12 years old girl with underlying ASD (atrial septal defect)
  • Presented with fever and altered behaviour one week after COVID-19 vaccination
  • CT scan brain done revealed cerebral oedema with impending internal herniation
  • Urgent craniotomy and EVD insertion was done
  • She was referred for further management from other hospital
  • MRI brain was performed
MRI brain in axial planes


MRI brain in coronal plane, T1-weighted images post contrast
MRI brain in coronal plane, T2-weighted images


MRI findings:

  • Extensive abnormal signal intensity is seen in the temporal lobes,  inferolateral frontal lobes and insula cortex
  • Involvement is bilateral but asymmetrical, worse on the right side
  • It is hypointense on T1, hyperintense on T2 and FLAIR with minimal contrast enhancement post contrast
  • Sparing of basal ganglia is seen
  • Craniectomy defect and post operative changes are also seen
  • No hydrocephalus on current images (previous CT scan images were not available)

Diagnosis: Herpes simplex encephalitis

Progress of patient:

  • Patient responded well with treatment


  • Herpes simplex encephalitis is the most common cause of fatal sporadic necrotizing viral encephalitis
  • In adolescent/adult type, it is commonly caused by Type 1 herpes simplex virus (>95% of cases).
  • MRI shows abnormality involving the cortical and subcortical regions of bilateral temporal, frontal lobes and insula region. Involvement of extratemporal regions, cingulate gyrus can also be seen.
  • Involvement is bilateral and asymmetrical
  • Basal ganglia is usually spared, an important feature to differentiate with MCA infarction.
  • There may be associated with restricted diffusion, gyral swelling, loss of gray-white matter interface with mild or no enhancement.
Author: radhianahassan