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Ear development

The ear is a fascinating and complex appendage and organ. Formation is from structures called branchial arches. Branchial (from Greek branchia gills) arches are composed of endoderm on the internal aspect, by clefts composed of ectoderm on the external side with the central mesoderm containing the muscle, cartilage, vessels and nerves that will ultimately supply and establish the surrounding anatomic structures. Molecular signaling from the ectoderm leads the mesenchyme from the mesodermal (central) layer to eventually, if it works out as planned, to obliterate the clefts and and pouches. If clefts persist, they are given names, such as Type I branchial cleft cyst. When this signaling goes wrong, there are different degrees of anomalies, from absence of specific auricle components to microtia or even anotia if there is complete failure.

The ear begins to form the otic placode and vestibulocochlear ganglia at 3 weeks of gestation. The external canal then develops from the first branchial cleft at 4 weeks. By 28 weeks there is a fully open external canal. Failure to canalize can result in membranous or bony stenosis or atresia (from Latin a = no and Greek trēsisperforation, from tetrainein to pierce). Development of the auricle (external ear) begins at 5 weeks gestation with development of the auricular hillocks numbered from 1 through 6, derived from the first (mandibular) and second (hyoid) branchial arches. So the inner ear has already formed when the external ear begins.

The ear develops in a predictable manner, with various alterations in development resulting in predictable deformities when the process is interrupted. Knowledge of auricular development as well as normal external anatomy allows for precise evaluation of the ear and assists in selecting appropriate reconstructive techniques to optimize the complex 3-dimensional anatomical outcomes.

If you have a ear question, please do not hesitate to call me for an appointment. Office number is 989-839-6201, fax is 989-839-6202. Providers can page me through the Midland hospital operator. Patients can reach me by way of the patient portal.

Let me know how I can be of help to you.

Philip Harris, MD FARS
Ear Nose Throat and Cancer of the Head and Neck
Serving Gladwin, Clare, Midland and Alpena
Call for appointment and ask to see Dr. Harris

Did you know a simple audiogram may help predict your heart disease risk?

In a study titled Audiometric testing as a predictor for Cardiovascular disease published in
Laryngoscope 119 Mar 2009 researchers hypothesized that low-frequency hearing loss is associated with underlying cardiovascular disease. Their conclusion? Audiogram patterns correlate strongly with cerebrovascular and peripheral arterial disease and may represent a screening test for those at risk. Patients with low-frequency hearing loss should be regarded as at risk for cardiovascular events, and appropriate referrals should be considered.

What commonly causes hearing loss?
We know that environmental noise and exposures, systemic disease, and family inheritance can lead to hearing loss. Years ago Dr. Schuknecht correlated audiometric patterns to hearing loss. He described classic character of presbycusis (age related hearing loss) seen on audiometric tests to cochlear pathology. The Schuknecht classification, as a general template for age-related hearing loss, has been validated through investigation. The presbycusis patterns include strial, cochlear conductive, sensory, and neural hearing losses.

Presbycusis is typically the result of degeneration within the cochlea, most commonly to outer hair cells but also to inner hair cells, spiral ganglion neurons, or the stria vascularis.

What is the Stria Vascularis?
The stria vascularis, in the lateral wall of the cochlea, is critical for establishing the endocochlear potential necessary for the propagation of auditory signals to the central nervous system. The stria vascularis is a capillary-rich structure fed by radial branches of the spiral modiolar artery. Arteries feeding the stria vascularis are terminal vessels with no anastomoses to supplement
flow or accommodate for spasm or occlusion. Additionally, the strial capillary network is relatively sparse at the apex when compared with the dense organization at the base. These anatomical features leave the apical cochlea exquisitely sensitive to ischemia. A reduction in endocochlear potential and clinically significant hearing loss occurs almost immediately after vascular occlusion
or anoxia. The vascular anatomy of the stria at the cochlear apex (low frequencies) establishes this area as a sensitive marker for systemic cardiovascular disease.

What next?
So that lowly audiogram may be a real help to you after all. You should seek out a trained audiologist (CCC-A designation) to evaluate you, especially if you have low frequency hearing loss and risk factors such as hypertension, diabetes mellitus, hyperlipidemia/cholesterolemia, age >75 years, and a history of smoking or prior events like myocardial infarction, diagnosis of coronary artery disease, stroke, transient ischemic attack, and claudication.

Tag Archives: hearing

Ear Development

Can an Audiogram Predict Cardiovascular Risk?