Pediatric Herpes Simplex Virus-1 Encephalitis

  • Etiology: Necrotizing hemorrhagic encephalitis that is localized in limbic system
  • Imaging:
    — Lesions typically in temporal lobe and are medial before lateral in location with extra-temporal regions in 40% of children
    — Asymmetric brain damage – unilateral or bilateral
    — Gray matter usually before white matter
    — Extension to insula and orbital surface of frontal lobes and cingulate gyrus and thalamic lesions: children with parietal or opercular lesions (probably related to the existence of numerous thalmo-cortical connections)
  • Imaging CT:
    — Often normal in first 2-3 days
    — Later see diffuse mild edema and swelling
  • Imaging MRI:
    — Shows gyral edema
    — May be hemorrhagic
    — T1WI post enhancement: With or without enhancement in early stage
    — T2WI: Temporal lobe hyperintense
    — FLAIR: Temporal lobe hyperintense
  • DDX:
  • Complications:
  • Treatment:
  • Clinical: In older child or adult

Radiology Cases of Herpes Simplex Virus-1 Encephalitis

MRI of pediatric herpes simplex virus-1 encephalitis
Axial T1 MRI (above left) shows along the left medial temporal lobe low signal intensity and blurring of the gray matter-white matter junction which demonstrates high signal intensity on axial T2 (above right) and axial FLAIR (below left) while the area shows mild restricted diffusion on axial DWI (below right).
US of HSV-1 / herpes simplex virus-1 encephaliti
Coronal US of the brain (above) shows a round echogenic lesion in the left fronto-parietal region. Axial CT without contrast of the brain (below) shows the lesion to be high density with surrounding low density edema and felt to represent intraparenchymal hemorrhage.