Hearing Loss Factor – Changes In How Cochlea Works

The cochlea is the hearing portion of the inner ear that changes vibrational energy into nervous impulses that the brain interprets as sound. When there are changes in the manner in which the cochlea works, or when there are changes in how the nerve that leads from the ear to the brain transmits the neural energy, the result is sensorineural hearing impairment (SNHI). This condition affects approximately six of every 1,000 children; of that group, half have hearing loss at birth, and one in six is diagnosed with profound congenital SNHI.

Challenges exist in identifying affected children in a timely fashion, and in determining the cause of the SNHI. According to the National Institutes of Health, the average age of diagnosis in the early 1990s was estimated to be 2½ years for children with severe-profound SNHI. Awareness of this led to considerable interest in newborn hearing screening in the United States with subsequent legislation passing in the majority of states establishing universal testing programs. However, limitations of universal screening remain due to high false positive rates at the time of initial screening and the inability of screening programs to identify children with delayed onset SNHI. There is some concern that an initial pass of the newborn hearing screen may lower suspicion for hearing loss later, thus leading to delayed diagnosis of children with late onset SNHI; data on the extent of this problem are not available.

The cause of SNHI is unknown is most cases. A lack of consensus in the literature on the protocol for medical evaluation of children exits regarding this disorder. No large-scale effort similar to that directed toward early diagnosis has been undertaken to establish the etiology of SNHI. Consequently, researchers set out to characterize the etiology of SNHI in a group of children cared for at a tertiary care academic medical center between 1994 and 1998, and to describe the audiometric and radiologic findings in these children. Data was summarized from a review of the medical and audiometric records, and the results of CT scans of the temporal bone, in children with SNHI treated at a tertiary care university-affiliated children’s hospital.

The authors of the study, "Pediatric Sensorineural Hearing Impairment: Etiology, Severity, and Inner Ear Anomalies" are Ellis M. Arjmand MD PhD, Soham Roy MD, Avrum Pollock and Audra Webber, from the Children’s Hospital of Pittsburgh, Pittsburgh, PA, and Amy Brenski MD from the University of Texas Southwestern Medical Center, Dallas, TX. Their findings will be presented May 13, 2002, at the Annual Meeting of the American Society of Pediatric Otolaryngology being held at the Boca Raton Resort & Club, Boca Raton, FL.

Methodology: The records of 221 children with SNHI who were seen in the Pediatric Otolaryngology Department at Children’s Hospital of Pittsburgh between 1994 and 1998 were reviewed. All children in this series underwent CT imaging of the temporal bone; additionally, a review of the complete history and physical examination at the time of evaluation and a review of the past medical records were performed for every patient.

Medical evaluation varied, but typically, urinalysis, FTA-ABS and ESR blood screenings, thyroid function tests, serum chemistry, and complete blood count with platelets were obtained when the etiology could not be established clearly from the medical history. An ophthalmologic examination was also typically obtained. Genetics consults were obtained for children with facial dysmorphism or with a family history of SNHI. Neurology and/or developmental pediatric consultations were obtained for children with developmental delay or an abnormal neurological examination.

Results:Evaluation of the patients revealed the following:

Etiology: The cause of SNHI was categorized as acquired, hereditary/genetic, inner ear anomaly, or unknown. The findings were as follows: unknown 50.9 percent, hereditary / genetic 16.8 percent, and inner ear anomalies (IEA)16.8 percent, and acquired (perinatal or postnatal cause) 15.4 percent, Forty-one of 221 patients had perinatal or postnatal risk factors for SNHI. Of these 41 patients, seven were also found by CT scan to have an inner ear anomaly. For the remaining 34 of 221 children (15.4 percent), the cause of SNHI was characterized as acquired.

Radiographic Finding: Thirty-seven patients had abnormal temporal bone CT scans. Bilateral IEA were identified in 15 patients. Ten patients had right ear anomalies only, and 12 patients had left ear anomalies only. The IEA varied from isolated large vestibular aqueduct (LVA) to combined cochleovestibular anomalies in association with LVA.

Severity and Laterality: Complete audiometric data were available for 214 patients. One hundred and forty three had bilateral SNHI and 71 had unilateral SNHI. Of the 143 patients with bilateral SNHI, the hearing was symmetric in 102 (71 percent), and asymmetric in 41 (29 percent). Severity of hearing impairment varied widely for patients with both unilateral and bilateral SNHI. Only 30 percent of children in this group had mild SNHI.

Presentation: Data were available on how the patient presented for diagnosis for 219 children. Approximately half (108 of 219; 49 percent) failed a hearing screening evaluation. The age at the time of hearing screening varied. Parent concern regarding hearing impairment was reported for 91 of 219 children (41.5 percent); 66 of these 91 patients had not been diagnosed through a screening evaluation, thus the parent concern led directly to diagnosis for 30 percent of patients. An additional 18 patients (eight percent) were identified on the basis of speech and language delay, without a specific parental concern regarding hearing.

Conclusions: The etiology of sensorineural hearing impairment could be determined in only half of the patients, indicating that identifying the cause for the disorder remain challenging.

Temporal bone imaging led to the diagnosis of inner ear anomalies in approximately 17 percent of these children. Large vestibular aqueduct was the most frequently identified inner ear anomaly. A small number of patients with a known risk factor for SNHI were also found to have inner ear anomalies on CT scan.

The incidence of mild SNHI of unknown etiology in this group is low. If the findings are replicated in further studies, the researchers suggest a re-evaluation of hearing screening methods may be indicated.

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About The Author:

Jen Bead is a successful author and regular contributor to http://www.digital-hearing-aids-n-protection.com. Finding out more about hearing loss, so you can choose the digital hearing aids or therapy that is necessary.