A known patient of chronic kidney disease on maintenance haemodialysis was brought to the emergency room in unresponsive state. On examination GCS was 3/15, pupils were dilated and fixed. He was in cardiac asystole. 3 cycles of CPR were done and patient was intubated. Post resuscitation pupils became sluggishly reactive.
There was diffusion restriction in both cerebral, cerebellar hemispheres, basal ganglia and thalami. Gyri of both cerebral hemispheres are swollen, showing T2/FLAIR hyperintense signal with diffuse sulcal effacement and effacement of basal cisterns. Both cerebellar hemispheres, basal ganglia and thalami were swollen and showing T2/FLAIR hyperintense signal.
There was bilateral posterior scleral flattening with prominent perioptic CSF spaces and tortuous optic nerves - suggestive of increased intracranial pressure.
MRA was normal.
Patients with Hypoxic Ischaemic Encephalopathy (HIE) commonly present with altered consciousness, mostly in a comatose state, in addition to cardiopulmonary insufficiency and loss of protective airway reflexes .
Hypoxia leads to ATP depletion and lactate accumulation within cells leading to depolarization of presynaptic neuronal cells, release of glutamate and impaired glutamate reuptake . This results in glutamate receptors enhanced influx of ions (such as Ca+2, Na+ and Cl-) causing influx of water and activating calcium-dependent enzymes that damage cell membranes and mitochondria . Phylogenetically new structures neocortex, purkinje cells, caudate and putamen are more prone to hypoxic injury .
Diffuse cortical and deep grey matter involvement is the most common imaging pattern of HIE . HIE is invariably bilateral and symmetrical . Isolated basal ganglia involvement is very rare . Computed tomography (CT) show nonspecific signs such as cerebral oedema, sulcal effacement and decreased grey matter (GM)/white matter (WM) differentiation . HIE involved regions are swollen showing restricted diffusion on DWI with corresponding low ADC map values and T2/FLAIR hyperintensities . Some patients show laminar T1 hyper and T2 hypointensities representing cortical laminar necrosis . In few patients progressing to delayed leukoencephalopathy (usually apparent after 14 days), show white matter hyperintensities on T2, FLAIR and DWI with corresponding low ADC map values . White matter may show alternating T2 hyper (secondary to oedema or demyelination) and hypointensities (secondary to iron deposition) giving Double white matter pattern . In the chronic phase, CT/MR findings are mainly related to atrophic changes . Contrast enhancement may be seen in the cortex, basal ganglia and thalami, probably due to breakdown in the blood brain barrier . No contrast enhancement is seen after 2 months . MR spectroscopy shows decreased NAA, abnormal lactate and increased choline peak .
HIE patients are usually managed by Therapeutic hypothermia of 32-34°C for 12-24 hours . Independent of type of imaging pattern, overall prognosis of patients with HIE is very poor . Patients with isolated basal ganglia involvement or watershed pattern have a relatively better clinical outcome .
CO poisoning is frequently associated with globus pallidus involvement, post anoxic leukencephalopathy and haemorrhagic infarct . Combination of tonsillar herniation and absence of cerebral blood flow are highly sensitive and specific MR signs for brain death . Deep white matter, thalami, brain stem and cerebellum are typically spared in hypoglycaemic encephalopathy . Posterior Reversible Encephalopathy Syndrome (PRES) show no diffusion restriction on DWI .
Differential Diagnosis List
Hypoxic ischaemic encephalopathy
Carbon monoxide poisoning
PRES (Posterior reversible encephalopathy syndrome)
Hypoxic ischaemic encephalopathy