Kernicterus is bilirubin staining of the deep gray matter nuclei of the brain and brainstem. It is an anatomic diagnosis made at autopsy. Bilirubin is neurotoxic. Kernicterus was originally described in mature infants who died of severe Rh isoimmunization (such a case is rarely seen today). Extremely premature sick infants are at higher risk of kernicterus than mature infants.
Acute bilirubin toxicity appears in the first few days of life in term infants. Preterm infants are at risk for slightly longer.
Classic kernicterus (mature infants):
Prominent yellow staining of specific regions: Basal ganglia, lateral thalamic nucleus, hippocampus, geniculate bodies, nuclei of brainstem and floor of the fourth ventricle, dentate nucleus, inferior olive, anterior horn of spinal cord, cuneate and gracilis nuclei.
Vacuolization of cytoplasm, colouration (in frozen section) — early microscopic lesions. Loss of neurons and reactive astrocytosis.