Hypoglycaemic encephalopathy is a brain injury that results from prolonged or severe hypoglycaemia.
On imaging, it can manifest on MRI as bilateral areas of increased signal on both T2 and FLAIR affecting the posterior limb of the internal capsule, cerebral cortex (in particular parieto-occipital and insula), hippocampus and basal ganglia. Restricted diffusion can be an earlier and sensitive tool, and is commonly reversible.
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Clinical presentation
Severe symptoms of hypoglycaemia are present, such as altered conscious state, loss of consciousness, seizures, etc.
Pathology
The pathophysiology is uncertain, but altered cellular physiology results in neuronal death 4-5,7. It is known that hypoglycaemia leads to cellular energy failure, as the brain is an obligate glucose metabolizer. The resulting energy shortage results in sodium/potassium pump failure and cellular swelling and tissue alkalosis 8. Some theories are based on cell damage due to increased extracellular aspartate and glutamate 7.
Aetiology
Any cause of profound hypoglycaemia 4:
overdose of hypoglycaemic medication (usually in diabetics)
pancreatic insulinoma
Radiographic features
As hypoglycaemia is usually recognised and managed promptly, MRI scans are not routinely performed unless there is a complicated recovery.
MRI
There are characteristic changes typically affecting the posterior limb of the internal capsule, cerebral cortex (in particular parieto-occipital and insula), hippocampus, and basal ganglia 1,3. These are typically bilateral. The cerebellum, brainstem and thalami are usually spared in adults but they are also involved in neonates 3,4,8. The splenium of the corpus callosum can also be affected, producing the so-called boomerang sign.
T1: low signal
T2: high signal
DWI/ADC: can be an earlier and sensitive tool showing reversible diffusion restriction 6
Treatment and prognosis
The clinical outcome has a direct relation with the severity and duration of the hypoglycaemic insult.
Differential diagnosis
hypoxic-ischaemic brain injury: may show symmetrical thalamic lesions 7
Creutzfeldt-Jakob disease (CJD): different clinical presentation
ischaemic infarct: usually focal and unilateral
seizure-related changes
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