Introduction
High bilirubin level at birth has been
considered as one of the most important
factors affecting the auditory system.
Although this disease does not have
thoughtful consequences in most infants, in
the absence of appropriate treatment, high
levels of blood serum bilirubin can result in
acute encephalopathy and brain damage
(1,2). When red blood cells are broken
down, unconjugated bilirubin enters into the
plasma. Normally, this type of bilirubin
molecules link together by liver enzymes
and make conjugated bilirubin that the body
is able to excrete. However, if the bilirubin
does not convert to a conjugated mode, it
accumulates in plasma and its concentration
increases. With increasing levels of serum
bilirubin, the substance passes through the
blood brain barrier and enters the central
nervous system. Kernicterus is a
neurological syndrome that is due to
unconjugated bilirubin deposits in brain cells
and nuclei (3). Due to the involvement of
vestibular nerve, oculomotor nerve,
cerebellum and cerebral basal ganglia,
patients with kernicterus develop symptoms
such as movement disorders, impaired eye
movements and hearing loss. The only
clinical sign of kernicterus may be
permanent sensorineural hearing loss (4,5).
Jaundice in the first day following the birth
is always pathologic. Likewise, if the
maximum level of bilirubin in term neonate
exceeds beyond 13 mg/dL, it is considered
pathologic (6). Severe hyperbilirubinemia is
defined as serum bilirubin levels above 17
mg/dL (7). It seems that auditory brainstem
nuclei including the cochlear nuclei, inferior
colliculus and superior olivary complex are
the most vulnerable parts of the auditory
system against high bilirubin concentrations.
Damage to these structures can lead to
Sensor-Neural Hearing Loss (SNHL) (3,8).
Studies that reviewed audiological findings
in children with a history of neonatal
hyperbilirubinemia have primarily used