Cerebellar, hippocampal, and basal nuclei transient edema with restricted diffusion (CHANTER) syndrome

Cerebellar, hippocampal, and basal nuclei transient edema with restricted diffusion (CHANTER) syndrome describes a constellation of imaging findings in adults with opioid neurotoxicity. It is characterized by cytotoxic edema in the bilateral hippocampi and cerebellar cortices, and variably in the basal ganglia ¹.

This entity likely falls within a pathophysiologic spectrum with pediatric opioid use‐associated neurotoxicity with cerebellar edema (POUNCE) syndrome (which occurs in children), and opioid-associated amnestic syndrome (which involves the hippocampi alone). It is probably distinct from chasing the dragon leukoencephalopathy, which predominantly affects white matter and occurs after inhalational heroin use.

Clinical presentation

Patients present with a decreased level of consciousness ^1,2.

Radiographic features

Imaging shows cerebellar edema, which may progress to cause hydrocephalus ². MRI demonstrates bilateral, symmetric restricted diffusion in the grey matter of the cerebellum and hippocampi, as well as asymmetric involvement of the basal ganglia ^1,2. The cerebral cortex is spared ¹.

History and etymology

The syndrome was first described by an American group of clinicians in a seminal case series in 2019 ¹.

Differential diagnosis

• hypoxic-ischemic encephalopathy can also cause restricted diffusion in the hippocampus, cerebellar cortex, and deep grey nuclei, but cerebral cortex should also be involved

• chasing the dragon leukoencephalopathy

• posterior reversible encephalopathy syndrome