Hearing after TBI

In case of traumatic brain injury, hearing loss is most commonly caused by the cracks in the pyramid of the temporal bone. The less common causes of hearing loss include traumatic damages to the central auditory pathways in the nuclear region (in this case, hearing loss develops on the affected side) or traumatic damages to the middle brain (hearing loss occurs from two sides and more greatly affects the spoken language).

To diagnose hearing disorders, specialists use whispering, tuning forks, speech and pure tone audiometry (superthreshold and threshold). They conduct experiments by Schwabach and Weber, perform infrared and ultrasonic audiometry, study dichotic and spatial hearing and conduct objective audiometry accompanied by the study of long-latency and short-medium evoked potentials.

Nevertheless, in the acute period of the traumatic brain injury, the patient cannot undergo hearing examination due to the impaired consciousness. Although in some cases it is possible to conduct examinations using whispering and a tuning fork. According to the indications, doctors can carry out a more extensive examination in the residual and subacute periods. When it comes to the central disorders, it may be difficult to determine the degree of damage to the auditory pathways in TBI. In this case, it is determined by comparing hearing disorders with taste, vestibular and other otoneurologic symptoms. Very many audiometric tests for the examination of patients with TBI cannot be applied because they tire the patient greatly.

The hearing disorders that can occur in traumatic brain injury can be divided into two broad categories:

  • Symptoms of irritation. Hyperacusis, subjective and objective noises, auditory hallucinations;
  • Symptoms of fallout. Hearing loss of varying degrees.

In many cases, these symptoms can be combined.

When both inner and middle ears are affected due to TBI, the damaged auditory receptor usually results in very pronounced subjective noises. When it comes to the central hearing loss, subjective noises are usually absent or weakly manifested, even if the injury was very severe and was accompanied by multiple hematomas, foci of bruises in the brain.

With the cracks in the middle cranial fossa, which occur with a ruptured internal carotid artery, a person develops carotid-cavernous fistula in the cavernous sinus. It is accompanied by objective and subjective noises, which are especially pronounced around the orbit of the eye on the affected side.

Hyperacusis (increased auditory sensitivity) often occurs in subacute and acute periods of minor and moderate traumatic brain injury. This disorder requires adherence to a special therapeutic and protective regimen for the patient. In rare cases, TBI that caused damage to the temporal lobe of the brain in the depth of the lateral sulcus can lead to auditory hallucinations.

In case of damaged middle ear or cochlea, Weber's experiment shows the sound of a clear lateralization (that is, the damaged cochlea localizes the sound in a better hearing ear, while in case of the damaged conductive media the sound is localized in the worse hearing ear). It is important to note that the lesion caused by traumatic damage to the auditory nuclei, VIII nerve root or the midbrain accompanied by deafness or unilateral hearing loss does not affect the sound lateralization in Weber's experiment. Also, in Weber’s experiment, the presence of a large bone defect localized in the temporal parietal region has no effect on sound lateralization.

Consequently, this change in sound occurs only in the peripheral lesion of the inner and middle ear. In Weber's experiment, retrocochlear unilateral hearing loss, deafness of any degree, a sharp change in the conductive environments of the cranial bones between the ear and the pedicle of the sounding tuning fork do not lead to sound lateralization.

In unilateral sensorineural hearing loss of any degree (truncal, nuclear, radicular, cochlear) ultrasound is always lateralized in the ear, which hears better. A severe TBI results in a pronounced deterioration in the perception of ultrasound through the bone in 25% of patients in the acute and residual periods. The worsened level of perception of ultrasound was often detected in patients with cracks in the pyramid of the temporal bone. A worsened perception of ultrasound indicates the presence of irreversible impairments of the sound perception in the root and nuclei of the VIII nerve, as well as in the inner ear.

The hearing disorders typical of nuclear, radicular and mesencephalic lesions can be very similar. Even with the use of the entire complex of modern audiological testing methods, it is difficult to detect the differences. Therefore, when analyzing audiological data, it is strongly recommended to compare it with taste, vestibular and other clinical and otoneurological data. The analysis of hearing disorders separated from the rest of the clinical picture is of little importance in the topical diagnosis of the severity of central hearing disorders that occur with the localisation of different lesions.

In the case of traumatic brain injuries that cause the development of cracks in the temporal bone pyramid, the pathogenesis of hearing disorders is characterized by high complexity and diversity. Damage can be caused to:

  • Sound-conducting systems of the inner and middle ear;
  • VIII nerve root;
  • Peripheral receptor;
  • Central auditory conducting and nuclear structures in the brainstem and above brain regions.

As a rule, transverse cracks on the side of the lesion lead to deafness, whereas in case of the cracks on the other side audiometry shows decreased hearing for the perception of high tones. With the sound intensity increased up to 110 dB, often a paradoxical drop in the intelligibility of speech is observed. In most cases, deafness on the side of the crack develops due to traumatic damage to the VIII nerve root or to the spiral organ receptor. It remains irreversible and resistant.

The longitudinal cracks of the pyramid of the temporal bone on the side of the lesion do not cause deafness, but a combined hearing loss according to the type of impairment of sound perception and sound transmission (in the middle and low frequency bands there is a clear bone-air "rupture" that disappears in the high frequency range).

Although the fracture line always passes through the middle ear in longitudinal cracks, all cases result in the damage to the structures of the inner ear. The audiometric method is the only way to detect it. Hearing is usually restored in the residual period of the injury, in case of longitudinal cracks in the range of low and medium frequencies, but in the high frequency zone it remains steadily reduced. In case of longitudinal fractures of the temporal bone, as well as in case of traverse cracks, the perception of high tones on the healthy side is reduced due to the contralateral shaking of the labyrinth.

Thus, hearing loss is one of the leading symptoms that develop due to the cracks in the pyramids of the temporal bones.

Here you can also read other articles on this topic:

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