False Air Bone Gap: What Is It & How To Fix It?

The audiogram, a crucial diagnostic tool, reveals potential hearing losses, sometimes complicated by the appearance of a false air bone gap. This discrepancy, often observed in otoscopy examinations revealing possible cerumen impaction, can mislead clinicians if not carefully interpreted. Such gaps may arise from a variety of factors, requiring a thorough understanding of bone conduction testing methodologies. Understanding the nuances of false air bone gaps helps audiologists at the American Academy of Audiology provide accurate diagnoses and recommend appropriate interventions.

In the realm of audiology, the air-bone gap (ABG) is a fundamental concept.

It signifies a difference between hearing thresholds obtained through air conduction and bone conduction testing.

Generally, an ABG indicates a potential conductive hearing loss, where sound is not efficiently transmitted through the outer or middle ear.

However, not all that glitters is gold, and not every ABG points to a genuine conductive issue.

This brings us to the core of our discussion: the false air bone gap.

A false air bone gap presents a deceptive discrepancy in audiometric results.

It can lead to misdiagnosis and inappropriate management strategies.

Understanding its nature, causes, and implications is crucial for accurate hearing assessment and optimal patient care.

The Significance of Identifying False ABGs

Why does discerning a true ABG from a false one matter so profoundly?

The answer lies in the potential consequences of misinterpretation.

A false ABG, if mistaken for true conductive hearing loss, can lead to unnecessary medical referrals, inappropriate treatment recommendations, and undue anxiety for the patient.

Consider the scenario where a child is incorrectly diagnosed with a conductive hearing loss due to a false ABG.

This could lead to unnecessary medical interventions.

Or, imagine an adult being fitted with hearing aids designed to compensate for a conductive component that doesn't exist.

Such errors not only waste resources but also delay appropriate intervention for any underlying sensorineural hearing loss.

Consequences of Misinterpreting a False ABG

The ramifications of misinterpreting a false ABG extend beyond individual patient care.

It also impacts the credibility of audiologic evaluations and the overall efficiency of the healthcare system.

False positives can skew prevalence data.

It may complicate research studies.

Furthermore, it erodes patient trust in audiological services.

Therefore, a comprehensive understanding of false ABGs is not merely an academic exercise but a critical component of responsible and ethical audiological practice.

In essence, a false air-bone gap distorts the picture of a patient's hearing ability, potentially leading to unnecessary interventions and delayed treatment. To understand how these deceptive gaps arise, we must first revisit the fundamental principles of air and bone conduction testing.

Air and Bone Conduction Testing: The Foundation

Audiometry hinges on two primary methods of assessing hearing: air conduction and bone conduction testing.

These tests provide distinct but complementary information about the auditory system's function.

By comparing the results of these tests, audiologists can pinpoint the location and nature of a hearing loss.

Understanding Air Conduction Testing

Air conduction testing assesses the entire auditory pathway, from the outer ear to the auditory cortex.

During this test, sounds are presented through headphones or insert earphones.

These sounds travel through the outer ear canal, vibrate the tympanic membrane (eardrum), and set the ossicles (middle ear bones) into motion.

This mechanical energy is then transmitted to the cochlea in the inner ear, where it is converted into electrical signals that are sent to the brain for interpretation.

Typical findings in air conduction testing are represented as thresholds at various frequencies.

These thresholds indicate the softest sound a person can hear at each frequency.

Demystifying Bone Conduction Testing

Bone conduction testing bypasses the outer and middle ear.

Instead, a bone vibrator is placed on the mastoid bone (behind the ear) or forehead.

The vibrator transmits sound directly to the inner ear via vibrations of the skull.

This stimulates the cochlea, allowing the auditory nerve to send signals to the brain.

Since bone conduction bypasses the outer and middle ear, it primarily reflects the function of the inner ear.

Therefore, bone conduction thresholds reveal the sensory capacity of the cochlea itself.

The Interplay: Air and Bone Conduction Results

In individuals with normal hearing, air and bone conduction thresholds are usually within 10 dB of each other.

This indicates that sound is efficiently traveling through the entire auditory pathway.

However, when a hearing loss is present, the relationship between air and bone conduction thresholds can reveal the type of hearing loss.

• Conductive Hearing Loss: Air conduction thresholds are poorer than bone conduction thresholds (an air-bone gap is present). This suggests a problem in the outer or middle ear, hindering sound transmission.
• Sensorineural Hearing Loss: Air and bone conduction thresholds are equally poor (no significant air-bone gap). This indicates a problem within the inner ear or auditory nerve.
• Mixed Hearing Loss: Both air and bone conduction thresholds are poorer than normal, but air conduction thresholds are significantly worse than bone conduction thresholds (an air-bone gap is present). This suggests a combination of conductive and sensorineural components.

The Audiogram: A Visual Representation of Hearing

The audiogram is a graph that visually summarizes the results of air and bone conduction testing.

It plots hearing thresholds at different frequencies (typically 250 Hz to 8000 Hz).

Air conduction thresholds are typically represented by circles (O) for the right ear and crosses (X) for the left ear.

Bone conduction thresholds are represented by brackets (< for the right ear and > for the left ear).

The audiogram provides a concise and readily interpretable picture of a person's hearing profile. It reveals the degree, type, and configuration of any hearing loss that may be present.

Defining the False Air Bone Gap: A Deceptive Discrepancy

Having explored the foundations of air and bone conduction testing, we can now turn our attention to the central topic: the false air bone gap. Understanding what it is, how it appears, and – crucially – what it doesn't mean is paramount to avoiding diagnostic errors.

What Exactly is a False Air Bone Gap?

A false air bone gap (ABG) occurs when air conduction thresholds are significantly poorer than bone conduction thresholds on an audiogram, but without an actual conductive component to the hearing loss. In simpler terms, it looks like a conductive hearing loss on the audiogram, but the problem isn't in the outer or middle ear.

The implication here is critical. A true air bone gap signals an obstruction or dysfunction somewhere in the outer or middle ear that prevents sound from efficiently reaching the inner ear. Think of earwax buildup, a perforated eardrum, or problems with the ossicles. The bone conduction result bypasses those components so if it is better than air conduction, then there is a good chance of conductive hearing loss.

A false ABG, however, is an artifact of the testing process itself. It’s a mirage, not a reflection of the patient’s true auditory status. The discrepancy doesn't reflect a real physical barrier to sound.

The Audiogram's Deceptive Appearance

On the audiogram, a false ABG manifests exactly as a true one does: air conduction thresholds plotted significantly lower (indicating poorer hearing) than bone conduction thresholds at the same frequencies. There's a clear "gap" between the two sets of results.

This is where the potential for misinterpretation arises.

The visual presentation alone is not sufficient to diagnose a conductive hearing loss. The audiologist must look beyond the audiogram to determine what is really going on.

It's crucial to remember that the audiogram is a tool, and like any tool, it's only as good as the skill and knowledge of the person using it.

A Crucial Distinction: Not a True Conductive Loss

The defining characteristic of a false ABG is that it does not represent a true conductive hearing loss. This point cannot be overstated. Misinterpreting a false ABG can lead to inappropriate medical referrals, unnecessary testing, and potentially even misguided interventions like surgery.

Therefore, recognizing and ruling out a false ABG is a fundamental responsibility of the audiologist. The remainder of this discussion will delve into the common causes of these deceptive discrepancies and, most importantly, how to avoid them.

Unveiling the Culprits: Common Causes of False ABGs

As we’ve established, a false air bone gap can lead to incorrect diagnoses and inappropriate management of hearing concerns. However, understanding what causes these "mirages" on the audiogram is the first step toward eliminating them. Let's delve into the common culprits behind these deceptive discrepancies, arming you with the knowledge to identify and avoid them.

Calibration Catastrophes: The Audiometer's Accuracy

The audiometer is the cornerstone of hearing testing. However, even the most sophisticated equipment is only as good as its calibration.

The Importance of Regular Calibration

Regular and accurate Calibration (Audiometric) is absolutely critical. It ensures that the sound intensities produced by the audiometer are precisely what they should be, across all frequencies.

Think of it like using a measuring tape that's been stretched out; all your measurements will be off. In audiology, even small errors in calibration can create artificial gaps between air and bone conduction thresholds.

The Impact of Improper Calibration

When an audiometer is out of calibration, it may present stimuli at inaccurate intensity levels. This can lead to inaccurate test results, including the appearance of a false ABG.

For instance, if the air conduction transducers are under calibrated (producing less sound than indicated), air conduction thresholds will appear poorer than they actually are, creating a false gap with bone conduction results.

Preventing False ABGs Through Calibration

Properly calibrated audiometric equipment is a fundamental defense against false ABGs. Adhering to recommended calibration schedules and protocols is essential.

This includes daily functional checks, regular biological calibration (listening checks), and annual electroacoustic calibration by a qualified technician. Maintaining meticulous records of calibration is also crucial for identifying potential issues.

The Occlusion Effect: A Low-Frequency Imposter

The occlusion effect is a natural phenomenon that can influence bone conduction thresholds, particularly at lower frequencies.

Defining the Occlusion Effect

When the ear canal is covered or occluded (for example, by headphones), the bone conduction signal at low frequencies is enhanced. This happens because the sound energy, which would normally escape the ear canal, is now trapped and reflected back towards the cochlea.

Bone Vibrator Placement and the False ABG

Improper placement of the bone vibrator (oscillator) can exacerbate the occlusion effect.

If the vibrator is not placed firmly and correctly on the mastoid process (or forehead), the resulting vibration can be dampened or distorted. This can lead to inaccurate bone conduction thresholds and, consequently, a false ABG.

Specifically, if the oscillator isn't flush, and you occlude the ear with a headphone, there can be an increase in the bone conduction score artificially.

Masking Missteps: Preventing Cross-Hearing

Masking is a critical technique used in audiometry to prevent the non-test ear from responding to the signal presented to the test ear, a phenomenon known as "cross-hearing."

The Purpose of Masking

The primary purpose of Masking (Audiology) is to isolate the ear being tested and ensure that the responses obtained are truly from that ear, and not the result of the signal crossing over to the other ear.

Masking and the False ABG

Insufficient or inappropriate masking can lead to a false air bone gap, particularly in cases of asymmetric hearing.

If the better ear hears the stimulus intended for the poorer ear, it can give artificially "better" bone conduction thresholds. This is when masking should be employed.

The amount of masking noise used must be sufficient to prevent cross-hearing, but not so excessive that it over-masks the test ear. Determining the appropriate masking level requires careful consideration of interaural attenuation (the amount of sound energy lost as it travels from one ear to the other) and the individual patient's hearing profile.

Otoscopic Oversights: The Impact of External Ear Issues

A thorough Otoscopy before audiometric testing is paramount. Overlooking even seemingly minor external ear issues can significantly impact the accuracy of air conduction results.

Collapsed Ear Canals and Artificial Air Conduction Results

Conditions like collapsed ear canals can artificially affect air conduction thresholds, especially when using supra-aural headphones. The pressure from the headphones can cause the ear canal to collapse, creating an obstruction and hindering the transmission of sound to the eardrum.

This can manifest as poorer air conduction thresholds and the illusion of an air-bone gap.

Differentiating False from True: When is it Really Conductive Hearing Loss?

While a false ABG can mimic conductive hearing loss, it's crucial to distinguish between the two.

Beyond the Audiogram: Evaluating Middle Ear Function

A true Conductive Hearing Loss involves a physical obstruction or dysfunction in the outer or middle ear. This could be caused by earwax, fluid in the middle ear, a perforated eardrum, or ossicular chain abnormalities.

Unlike a false ABG, true conductive hearing loss is generally supported by other audiological findings. Tympanometry, which measures middle ear function, and acoustic reflex testing, which assesses the stapedius muscle reflex, are valuable tools for evaluating the integrity of the middle ear system.

Abnormal tympanograms (e.g., a flat tracing indicating fluid in the middle ear) or absent acoustic reflexes can further support a diagnosis of conductive hearing loss, helping to differentiate it from a false ABG.

Detective Work: Diagnosing a False Air Bone Gap

Identifying a false air bone gap requires a systematic and thorough diagnostic process. It's a process akin to detective work, where audiologists meticulously gather evidence, analyze test results, and consider all potential contributing factors.

Case History: Uncovering Clues in the Patient's Narrative

A comprehensive review of the patient's medical history and reported symptoms forms the bedrock of this investigation.

It goes beyond merely noting down pre-existing conditions; it involves actively seeking clues that might suggest the absence of true conductive pathology.

For example, a history devoid of ear infections, trauma, or other conductive-related ailments should raise suspicion about the veracity of the ABG. Similarly, symptoms that don't align with conductive hearing loss (e.g., no complaints of muffled hearing or difficulty understanding speech in noise) warrant further scrutiny.

The Art of the Re-Test: Meticulous Air and Bone Conduction Testing

Repeating air and bone conduction testing is paramount, but it's not simply about running the same tests again. It's about meticulous technique.

This means ensuring proper earphone placement, verifying accurate transducer positioning on the mastoid process (for bone conduction), and carefully monitoring the patient's responses.

It is imperative that the audiologist pay very close attention to patient response behavior, method of responding (hand raise, button press), and overall attention/alertness.

Even slight variations in technique can significantly impact results, potentially eliminating or reducing the apparent air bone gap.

Calibration Verification: Ensuring Audiometric Accuracy

As previously discussed, the audiometer's calibration is the foundation upon which all audiometric results rest. Before accepting an unusual audiogram with an air bone gap, verification is key.

Therefore, verifying the calibration of the audiometer is an absolute necessity. This step confirms that the equipment is functioning within acceptable tolerances and that the presented stimuli are accurate.

If calibration issues are suspected, the audiometer should be recalibrated by a qualified technician before further testing.

Mastering Masking: Preventing Cross-Hearing Contamination

Masking is a critical procedure designed to prevent cross-hearing, where the non-test ear responds to the stimulus intended for the test ear.

Insufficient or inappropriate masking can artificially inflate air conduction thresholds in the test ear, creating a false air bone gap.

Therefore, careful attention must be paid to the proper implementation of masking procedures, ensuring that the masking noise is sufficient to isolate the test ear without over-masking.

The Occlusion Effect: Re-Evaluating Bone Conduction Thresholds

The occlusion effect, particularly prominent at low frequencies, can influence bone conduction thresholds when the ear is covered.

Failing to account for this effect can lead to an overestimation of bone conduction thresholds, further contributing to a false air bone gap.

When interpreting test results, audiologists should consider the potential influence of the occlusion effect and, if necessary, adjust their interpretation of the bone conduction thresholds accordingly.

Seeking Expert Insight: The Value of a Second Opinion

In ambiguous cases, or when the audiologist is unsure about the validity of the air bone gap, seeking a second opinion or consulting with experienced colleagues is highly recommended.

Experienced audiologists can offer valuable insights and alternative perspectives, helping to identify potential sources of error or misinterpretation.

This collaborative approach promotes accuracy and ensures that the patient receives the most appropriate diagnosis and management plan. In some cases, referral to an ENT (Ear Nose and Throat) physician may be warranted.

The Remedy: Correcting and Preventing False ABGs

Having navigated the complexities of diagnosing a false air bone gap, the focus now shifts to proactive measures. Addressing these gaps requires a multi-faceted approach encompassing technique refinement, rigorous equipment maintenance, and enhanced interpretive skills. The goal is not only to correct existing errors but to establish protocols that minimize their occurrence.

Refining Audiometric Technique Through Training

The cornerstone of preventing false ABGs lies in comprehensive and ongoing training for audiologists and audiology technicians. This should extend beyond initial certification. Regularly scheduled workshops and continuing education courses are crucial.

These sessions should emphasize:

• Proper earphone placement and bone oscillator positioning.
• Meticulous attention to patient response behaviors.
• Understanding the nuances of masking techniques.

Hands-on practice, coupled with expert observation, is invaluable in solidifying these skills. New hires must be carefully monitored to ensure they are not only performing the tests, but also understand the underlying principles.

Calibration: The Bedrock of Accurate Audiometry

As previously emphasized, the accuracy of audiometric equipment is non-negotiable. A strict calibration schedule must be implemented and meticulously followed.

This includes daily functional checks, regular biological calibration, and annual electroacoustic calibration by qualified technicians. Records of all calibrations must be diligently maintained. Any deviations from established standards should trigger immediate corrective action.

A proactive approach is essential. Minor discrepancies, even if seemingly insignificant, can compound over time and introduce systematic errors. Don't delay calibration—err on the side of caution.

Masking Protocols: Preventing Cross-Hearing

Inadequate or incorrect masking is a common culprit in the generation of false ABGs. Clear, standardized masking protocols are essential. These protocols should be readily accessible and consistently applied.

Audiologists must be thoroughly trained in the application of masking principles, including:

• Identifying situations where masking is necessary.
• Determining appropriate masking levels.
• Interpreting masked thresholds correctly.

Special attention should be given to cases of asymmetric hearing, where the risk of cross-hearing is heightened. Consider implementing routine checks of masking effectiveness, particularly for new or less experienced audiologists.

Optimizing Bone Oscillator Placement

Even seemingly minor variations in bone oscillator placement can significantly affect bone conduction thresholds. Audiologists must be trained to consistently position the oscillator correctly on the mastoid process.

This includes:

• Ensuring firm and stable contact with the skull.
• Avoiding placement on soft tissue or hair.
• Minimizing pressure artifacts.

Regularly review the recommended placement guidelines and provide ongoing feedback to staff. Visual aids and anatomical models can be helpful in reinforcing proper technique.

Accurate Audiogram Interpretation: Recognizing Patterns and Limitations

Accurate interpretation of the audiogram is crucial, including recognizing patterns suggestive of false ABGs. Audiologists must be aware of the limitations of the audiogram and the potential for artifacts.

They should also be skilled in:

• Correlating audiometric findings with the patient's case history and otoscopic examination.
• Recognizing discrepancies between audiometric results and expected patterns.
• Knowing when to seek additional testing or a second opinion.

Regularly review audiogram interpretation skills through case studies and group discussions. Encourage a culture of critical thinking and collaborative problem-solving.