Mass effect and herniation syndromes

Classically thought to be shifts in brain tissue across rigid landmarks causing compression, but some now consider herniations to be an epiphenomenon – i.e. correlation not causation. Either way, useful to consider the syndromes:

Taken from Radiopaedia

Central transtentorial herniation

  • Usually chronic causes (tumour in cortex)
  • Diencephalon (i.e. thalamus area) forced downwards
  • Shearing of pituitary stalk >> DI
  • Trapping of PCAs >> cortical blindness
  • Early brainstem compression >> coma
  • Rupture of basilar paramedian vessels causing Duret haemorrhages
Stage of compressionRespsPupilsOcculomotorMotor
DiencephalonYawning, occasional pausesSmall, responsiveDoll's eyes +ve
Upgaze palsy (Parinaud)
Localises to pain, Babinski +ve
MidbrainCheyne-stokesMod-dilated, fixedDoll's eyes -veDecorticate >> Decerebrate, Babinski +ve
Lower ponsRegular, shallow, rapidMod-dilated, fixedDoll's eyes -veFlaccid, Babinski +ve
MedullaSlow, irregularDilated, fixed

Uncal herniation

  • Usually acute, expanding haemorrhage
  • Uncus and hippocampal gyrus forced over tentorium
  • Ipsilateral CN III compression >> dilated, fixed pupil
  • PCA compression
  • Rapid progression to brainstem compression
  • Order of signs differentiate from central

Cingulate herniation (subfalcine)

  • Usually asymptomatic initially
  • Progresses to ACA compression
  • Hemiplegia (LL>Face>UL)
  • Progresses to central herniation syndrome

Cerebellar tonsillar herniation (“coning”)

  • Tonsils forced downwards through foramen magnum
  • Rapid medullary compression >> respiratory arrest