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

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

Terminology

This entityCHANTER likely fallsrepresents a severe form of acute opioid-induced neurotoxicity falling within a pathophysiologic spectrum with that includes paediatric opioid use‐associated neurotoxicity with cerebellar oedema (POUNCE) syndrome (which occurs in children), andopioid-associated amnestic syndrome (which involves the hippocampi alone) ². It is most commonly seen in the setting of fentanyl overdose ².

It is, however, 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

CT

Imaging showsCT primarily demonstrates cerebellar swelling and decreased attenuation due to oedema, with resultant obstructive hydrocephalus¹.

MRI

MRI is necessary to make the diagnosis as diffusion restriction is a key imaging feature.

In addition to cerebellar oedema, which may progress to causewith or without obstructive hydrocephalus²., 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. TheAlthough initially the cerebral cortex iswas reported as being spared ¹, subsequenly published cases do include occasional cortical involvement, particularly in the occipital poles ². Subcortical white matter involvement is uncommon ^1,2.

Treatment and prognosis

Importantly, unlike diffusion restriction seen in the setting of hypoxic ischaemic encephalopathy (HIE), which is generally considered irreversible and thus carried a poor prognosis, changes seen in CHANTER are largely reverible if mass effect and hydrocephalus can be successfully managed ^1,2.

Thus, treatment focuses of management of posterior fossa mass effect due to cerebeller oedema and resultant hydrocephalus. Management may include ^1,2:

• osmotic therapy: manitol and/or hypertonic saline

• extraventricular drain placement

• posterior fossa decompression

Additionally, due to decreased level of consciousness, these patients are often intubated and mechanically ventilated ¹.

Prognosis is dependent on the degree to which the above therapies are able to prevent brainstem compression and herniation. If successful some patients make a near-complete recovery whereas others remain debilitated by memory, motor and speech deficits ^1,2.

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-ischaemic 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

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

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