Fact-sheet: CHANTER syndrome - Cerebellar Hippocampal and Basal Nuclei Edema with Restricted diffusion


Updated on 12/10/2025 at 9:45 AM

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Definition

Severe form of neurotoxicity related to opioid intoxication, most commonly fentanyl.

CHANTER syndrome (Cerebellar Hippocampal and Basal Nuclei Edema with Restricted diffusion) is characterized on imaging by bilateral cytotoxic edema of the hippocampi and cerebellar cortex, and sometimes of the basal ganglia.

CHANTER syndrome encompasses:

  • POUNCE syndrome = Pediatric Opioid Use-associated Neurotoxicity with Cerebellar Edema
  • opioid-associated amnestic syndrome involving only the hippocampi

Clinical features

Impaired consciousness and memory impairment.

MRI

  • Cytotoxic edema of the cerebellar cortex and hippocampi, showing diffusion hyperintensity with restricted ADC.
  • Asymmetric cytotoxic edema of the basal ganglia.
  • The edema may cause a mass effect and result in obstructive hydrocephalus.
  • Rarely, cortical occipital cytotoxic edema and subcortical white matter involvement.

Management

Neurosurgical consultation for:

  • ventricular drainage
  • posterior fossa decompression

Medical treatment: mannitol and/or hypertonic saline

Differential diagnosis

  • Anoxic encephalopathy
  • Reversible posterior leukoencephalopathy syndrome - PRES
  • Heroin-induced spongiform leukoencephalopathy