Erythroblastosis Foetalis and the Hearing Organ: A Pathological Study

"Auditory neuropathy": physiologic and pathologic evidence calls for more diagnostic specificity

The term "auditory neuropathy" is being used in a rapidly increasing number of papers in the audiology/otolaryngology literature for a variety of individuals (mostly children) who fulfill the following criteria: (1) understanding of speech worse than predicted from the degree of hearing loss on their behavioral audiograms; (2) recordable otoacoustic emissions and/or cochlear microphonic; together with (3) absent or atypical auditory brain stem responses. Because of the general lack of anatomic foundation for the label "auditory neuropathy" as currently used, we review the anatomy of the auditory pathway, the definition of neuropathy and its demyelinating, axonal, and mixed variants. We submit that the diagnostic term "auditory neuropathy" is anatomically inappropriate unless patients have documented evidence for selective involvement of either the spiral ganglion cells or their axons, or of the 8th nerve as a whole. In view of biologic differences between peripheral nerves and white matter tracts in the brain, the term "auditory neuropathy" is inappropriate for pathologies affecting the central auditory pathway in the brainstem and brain selectively. Published reports of patients with "auditory neuropathy" indicate that they are extremely heterogeneous in underlying medical diagnosis, age, severity, test results, and that only a small number have undergone the detailed investigations that would enable a more precise diagnosis of the locus of their pathologies. The electrophysiology of peripheral neuropathies and the deficits expected with pathologies affecting the hair cells, spiral ganglion cells and their axons (auditory neuropathy sensu stricto), and brain stem relays are reviewed. In order to serve patients adequately, including potential candidates for cochlear implants, and to increase knowledge of auditory pathologies, we make a plea for more comprehensive evaluation of patients who fulfill the currently used audiologic criteria for "auditory neuropathy" in an effort to pinpoint the site of their pathologies. We suggest that the term auditory neuropathy be limited to cases in which the locus of pathology is limited to the spiral ganglion cells, their processes, or the 8th nerve, and that the term neural hearing loss be considered for pathologies that affect all higher levels of the auditory pathway, from the brainstem to the auditory cortex.

Incidence of cochlear involvement in hyperbilirubinemic deafness

Neonatal hyperbilirubinemia remains an important cause of childhood deafness, especially in developing countries. After neonatal hyperbilirubinemia, the auditory neural pathways, cochlea, or both may be affected. In this study, we aimed to determine the incidence of cochlear impairment and the appropriate means of hearing screening in hyperbilirubinemic neonates. A retrospective review of 1,032 pediatric patients with hearing loss revealed 67 cases (6.5%) of severe hyperbilirubinemia in the neonatal period. Thirty of these patients had neonatal hyperbilirubinemia as the single identifiable risk factor for hearing loss. In 26 of 30 cases (87%), otoacoustic emissions (OAEs) were absent, whereas in the remaining 4 cases (13%), robust emissions were detected despite an absent auditory brain stem response (ABR). Auditory screening of newborns with jaundice by OAEs possesses a significant risk of undiagnosed deafness. On the other hand, if the ABR is used as the single means of screening, auditory neuropathic conditions will probably be underlooked. Therefore, we recommend dual screening of hearing by ABR and OAEs in hyperbilirubinemic newborns.

Auditory brainstem responses in infants and children with anoxic brain damage due to near-suffocation or near-drowning

We studied auditory brainstem responses (ABRs) of sixteen infants and children with brain damage after anoxic accidents due to near-suffocation or near-drowning. The patients manifested cerebral palsy, mental retardation and/or epilepsy and showed poor responses in the behavioral audiometry. Auditory brainstem responses were abnormal in five of the patients in the near-drowning group (waves I, II and III only were present in three patients and the amplitudes of waves IV and V were low in two patients) but normal in most of the patients in the near-suffocation group. This difference in the ABRs between the two groups suggest that in infants and children anoxic brain damage due to near-drowning might involve not only the cerebral cortex and subcortical white matter but also the upper brainstem and midbrain.

A long-term study of hearing in children following neonatal hyperbilirubinemia

We conducted a long-term study of 85 children with known transient neonatal hyperbilirubinemia to determine if their hearing had been affected. None of the children had neural symptoms such as kernicterus. The children ranged in age from birth to 9 months and were studied by means of brainstem evoked response audiometry (BERA). Thirty-four of the children were studied sequentially between 15 and 80 months after the initial examination. Our results showed that there was no significant correlation between serum bilirubin concentrations and BERA thresholds or latencies. These findings indicate that, unlike manifest cases of kernicterus, neonatal hyperbilirubinemia does not affect neonatal hearing when treated promptly.

ABR in patients with congenital/early acquired sensorineural hearing loss, abnormal stapedius reflex thresholds and speech retardation

The auditory brain stem response (ABR) was recorded in 14 young subjects with mild to moderately severe congenital/early acquired sensorineural hearing loss and abnormal stapedius reflex thresholds. The speech problems of these patients as evaluated by experienced examiners were considered to be more pronounced than could be explained from the hearing loss as measured by the pure tone audiometry. Psychological testing yielded intelligence scores within normal limits or above average for age in 11. They all gave abnormal ABR, indicating dysfunction of the auditory brain stem pathways or, in a few cases, of the cochlear part of the auditory nerve. Presumably, the electrophysiologically demonstrable pathological changes were caused by perinatal complications or early life infectious disease. ABR may prove valuable in the evaluation of children with speech retardation.

Cochlear and brain stem responses in hearing loss following neonatal hyperbilirubinemia

The site of lesion in hearing loss following neonatal hyperbilirubinemia is unclear. Histopathological studies have implicated the brain stem auditory nuclei while other investigations have hinted at a lesion in the cochlea. In order to clarify this issue, attempts were made to record responses from the auditory pathway in 13 patients with hearing loss following neonatal hyperbilirubinemia. The neural response from the auditory nerve was absent in 11 of the 13 patients and present only in response to high intensity stimuli in 2 patients. However, the response of the cochlear hair cells (cochlear microphonic potential) was present in 9 of the 13 patients. In most other cases of sensorineural hearing loss, with no history of hyperbilirubinemia, the hair cell response was absent. This is functional evidence for auditory nerve damage in cases of hearing loss following neonatal hyperbilirubinemia while the hair cells are spared.

The combined correlated audiohistogram. Incorporation of the superior ventral cochlear nucleus

The state of the spheroid cells of the superior ventral cochlear nucleus (SVCN) must be accounted for along with that of stria vascularis, hair cells, and spiral ganglion neurons in the development of the combined correlated audiohistogram in cases of sensorineural hearing loss. For the stated evaluation, transverse sections through SVCN are marked off into ventrodorsally progressive zones corresponding to the frequency levels of the audiometric chart, and the loss of spheroid cells in each level is estimated on a percentage basis. The resultant "best fit" of pattern of cell injury with audiometric curve suggests that the anatomic frequency scale of SVCN parallels the logarithmic frequency scale of the standard audiometric chart.

Effect of hyperbilirubinemia on the inner ear in Gunn rats

The effect of hyperbilirubinemia on the inner ear was studied in fifteen jaundiced homozygous Gunn rats. Seven non-jaundiced heterozygous littermates served as controls. Histopathological examination of the temporal bone in these animals showed normal sensory and neuronal structures of the inner ear. This cannot be taken as conclusive evidence that a central, rather than a peripheral, lesion is the cause of hearing loss in hyperbilirubinemia.