Cochlear Implantation Benefits for Patients with Trauma-Induced Bilateral Hearing Loss: A Retrospective Analysis

Introduction

Head injuries, including traumatic brain injury (TBI) and craniofacial fractures, are significant challenges for modern medicine, particularly in the fields of neurology and otolaryngology. These injuries are problematic from both clinical and socio-economic perspectives [1–4]. TBI is one of the leading causes of death among individuals aged 15–44 years, resulting in the loss of productive members of society. In pediatric cases, these injuries typically are caused by falls, while traffic accidents are the predominant cause among young adults [5,6]. Other common causes of head injuries include domestic violence, falls from height, and incidents associated with alcohol abuse [7–9]. Identifying the exact cause of injury immediately can be difficult, especially when the patient is under the influence of intoxicants like alcohol or drugs, which complicates diagnosis and clinical assessment [9]. Cases arising from fights and major head traumas constitute a significant proportion of those handled by the courts. Such incidents frequently result in serious bodily injuries, including head trauma [10]. In Poland in 2023, according to police statistics, 2285 offenses involving brawls and major head traumas were recorded under Article 158 of the Penal Code, underscoring the magnitude of this issue [11,12]. Head injuries, including hearing impairment or even complete deafness, constitute permanent health impairment (Article 157 §1 of the Penal Code), for which Polish law provides strict penalties. The severity of the sanctions depends on the circumstances. In certain cases, such acts may be categorized as “grievous bodily harm” under Article 156 §1 of the Penal Code [12]. Such incidents require not only particular attention from the judiciary but also a multidisciplinary medical approach to ensure adequate treatment and rehabilitation for the victims.

The pathophysiology of head injuries involves both primary and secondary damage. Primary injuries can lead to superficial skin damage, skull fractures, and deep brain injuries, including damage to blood vessels and cranial nerves. Secondary injuries, caused by inflammatory processes and swelling, can further exacerbate the initial damage [9,13,14].

In cases of head injuries resulting from violence, studies show that blows, violent shaking, pushing, or strangulation often cause them. Up to 80–90% of domestic violence victims report injuries to the head, face, or neck. The prevalence of these injuries suggests they might can serve as markers for potential exposure to violence [15–17].

Head trauma frequently results in numerous neurological and otolaryngological complications, including various types of hearing loss, such as conductive, mixed, or sensorineural hearing loss. Deterioration or loss of hearing following head trauma can result from damage to both peripheral and central auditory structures. Injuries may include temporal bone fractures or labyrinth concussions, leading to varying degrees of hearing impairment [18,19]. Hearing loss due to head trauma is particularly common in cases involving temporal bone fractures, which can result in serious complications. Typical clinical symptoms in adult patients with temporal bone fractures include bleeding into the tympanic cavity (hemotympanum) and tympanic membrane perforation [20].

Sensorineural hearing loss (SNHL) results from dysfunction within the cochlea, which is situated in the temporal bone. The damage is usually to the sensory hair cells or spiral ganglion neurons of the auditory nerve [21,22]. The clinical examination for hearing loss includes an examination of the outer ear, followed by an otoscopy. Hearing thresholds are measured using pure-tone audiometry. This involves determining the softest sound the patient can hear at a particular frequency [21]. When patient cooperation is limited, hearing thresholds are assessed using auditory brainstem response (ABR) testing [23]. Treatment options for sensorineural hearing loss (SNHL) have advanced significantly. In cases of profound and permanent hearing loss, interventions such as cochlear implants or advanced hearing aids may be required [24–26]. In general, cochlear implantation is an effective treatment for sensorineural hearing loss. However, major head trauma can introduce additional circumstances that can make cochlear implantation impossible. Another solution that has been shown to be effective is the treatment of partial deafness in the case of residual hearing [27,28]. There is also need to analyze how vestibular system function is affected [29–31]. Considering the potential health consequences of cranial injuries, further research is essential to understand the mechanisms and effects of these injuries, including their impact on auditory functions. Monitoring the hearing of patients after head trauma is crucial to identify and treat potential consequences, which can arise both in the acute and chronic phases [32,33].

Therefore, this retrospective study evaluated outcomes from cochlear implantation in 9 patients with bilateral severe SNHL after major head trauma.

Material and Methods

INCLUSION CRITERIA:

The protocol of this retrospective study was approved by the Bioethics Committee (IFPS: KB/Application 4/2023) and conformed with the Declaration of Helsinki. All patients gave informed consent to be part of the study. Adult patients with hearing loss following major head trauma were selected for cochlear implant surgery based on the following criteria: (1) average hearing thresholds at 500, 1000, 2000, and 4000 Hz of 90 dB HL or worse and bone conduction thresholds at the limit of the audiometer’s capacity; (2) no benefit from hearing aids; (3) speech recognition test results in quiet environment below 50%, (4) hearing loss directly attributed to major head trauma.

PURE-TONE AUDIOMETRY:

All patients underwent preoperative pure-tone audiometry to determine air and bone conduction thresholds across frequencies ranging from 250 to 4000 Hz for BC and 125 to 8000 Hz for AC. The test was conducted using a Madsen Itera II audiometer (GN Otometrics, Denmark), calibrated headphones (H-39P Telephonics, NY, USA) in an IAC soundproof booth. This evaluation was repeated 12 months after surgery to assess residual hearing preservation. Residual hearing preservation (HP) was calculated using the Skarzynski et al (2013) method [34].

SPEECH PERCEPTION:

Preoperative speech audiometry was performed using Demenko and Pruszewicz monosyllabic Polish word test [35]. Tests were conducted in a quiet environment and in a noisy environment at a signal-to-noise ratio of +10 dB (SNR 10). Speech material was presented through a speaker positioned more than 1 meter from the patient in a quiet environment at 70 dB HL. The percentage of correctly repeated words (word recognition score, WRS) was recorded. Before the operation, patients were tested with hearing aids. A second test took place at the follow-up appointment 12 months after the operation. Subjects were tested with activated cochlear implants.

The tests were conducted using a Madsen Itera II audiometer (GN Otometrics, Denmark), calibrated headphones (H-39P Telephonics, NY, USA), and a speaker (Indiana Line Nano 2).

SURGICAL PROCEDURE:

The surgery was performed under general anesthesia [36]. During all surgeries, the BHS RoboticScope was used for safer, better, and more precise surgery [37]. The first stage involved an antromastoidectomy, which opens the mastoid cavity. A piece of the cortical layer was removed with a chisel and hammer before opening the mastoid process, to later use this fragment to isolate the mastoid cavity from the subcutaneous space where the internal part of the implant is placed. After head trauma, it is important to assess for fracture or other atypical findings in the mastoid, which can be associated with higher potential of contact with the dura. The second stage involved posterior tympanotomy to visualize the round window niche. In patients with limited access to the round window, there was need for drilling out part of the bony overhang with a 0.8–1.0 mm diamond burr. The third stage involves making an incision in the round window membrane to prepare for electrode insertion into the scala tympani. The electrode was then inserted through the round window into the scala tympani. The next step was to seal the area around the electrode entry and secure it in the posterior tympanotomy using tissue or a small piece of periosteum, sponge with antibiotic, and tissue glue. Finally, the receiver was secured to the bone in the periosteal pocket over bone that could be smoothened or when there was a bony bed and the skin behind the ear was sutured [38–40].

STATISTICAL ANALYSIS:

Basic descriptive statistics were determined for quantitative variables: minimum and maximum, mean and standard deviation, and numerical distributions were used for qualitative variables. The Wilcoxon test was used to look for a difference in speech scores. The level of statistical significance (P) was set at 0.05.

Results

STUDY GROUP CHARACTERISTICS:

The study group consisted of 9 patients (2 women and 7 men) who lost their hearing after major head trauma. At the time of surgery, patients were aged 24–64 years, with an average age of 44.6 years (SD=13.15). The duration of hearing loss ranged from 1 to 30 years, with an average of 10.2 years. The most common injuries sustained during the major head traumas were temporal bone fractures (44%, n=4), occipital bone fractures (44%, n=4), basal skull fractures (56%, n=5), sphenoid bone fractures (33%, n=3), intracerebral hemorrhage (22%, n=2), zygoma fractures (22%, n=2), concussions (78%, n=7), orbital fractures (22%, n=2), and frontal lobe brain injuries (44%, n=4). Most patients also experienced bilateral tinnitus. Detailed demographic data are provided in Table 1.

All patients underwent cochlear implantation under general anesthesia. MRI (magnetic resonance imaging) was conducted preoperatively to assess anatomical conditions. In each case, the surgeon achieved full electrode insertion. In 77.8% (n=7) of cases, the electrode was inserted via the round window, and cochleostomy was performed in 22.2% (n=2). No adverse events occurred during surgery. A Medel implant was used in 77.8% (n=7) of cases, an Advanced Bionics implant in 11.1% (n=1), and a cochlear implant in 11.1% (n=1). The most commonly used electrodes were Standard (33%, n=3) and Flex24 (22%, n=2). Other electrodes included Mid-Scala, Straight, Flex28, and Flex20. Table 2 summarizes the surgical data.

HEARING CONDITION:

All patients underwent pure-tone audiometry before and 12 months after cochlear implantation. The results showed bilateral hearing loss in all patients. Before surgery, the average hearing threshold in the operated ear was at least 98.75 dB. For no response or vibration sensation, the maximum audiometer capacity for each frequency was used. In the contralateral ear, 6 patients had profound hearing loss, while 3 had mild to moderate hearing loss, with average air conduction thresholds of 37.1 dB, moderate (M=55 dB), and severe (M=75 dB). The average hearing thresholds in both ears improved slightly 12 months after surgery. Figures 1 and 2 illustrate pre- and post-operative average hearing thresholds for the operated and contralateral ears.

SPEECH TESTING:

In 77.8% (n=7) of patients, the preoperative speech recognition test score with hearing aids was 0%. Only 2 patients had scores of 5% and 10%. Post-operative speech recognition results, both in quiet and noisy environments (SNR 10), are presented in Figure 3. Speech recognition scores in quiet environment ranged from 35% to 95%, with an average of 61.7% (SD=20.8%). Speech recognition with an active cochlear implant was significantly better than pre-surgery results (Z=−8.314; P<0.001). In a noisy environment, patients achieved results ranging from 5% to 65%, with an average of 32.8% (SD=17.5%). Figure 3 presents the detailed speech audiometry results for each patient.

Discussion

Our study showed significant improvement in speech understanding with the active cochlear implant. Before surgery, the average speech audiometry score with hearing aids was 1.6%, which increased to 61.7% in a quiet environment and 32% in a noisy environment after surgery.

The most common causes of traumatic brain injuries are traffic accidents and falls from height. However, head injuries resulting from violence are particularly challenging to treat, due to the additional psychological factors and stress that accompanies the judicial process [41,42attention has turned to the cognitive, affective, and behavioral sequelae of injuries across the severity spectrum, which are often more disabling than residual physical effects. Moderate and severe TBI can cause personality changes including impulsivity, severe irritability, affective instability, and apathy. Mild TBI, once considered a largely benign phenomenon, is now known to be associated with a range of affective symptoms, with suicidality, and with worsening or new onset of several psychiatric disorders including posttraumatic stress disorder and major depressive disorder. Repetitive head impacts, often in athletic contexts, are now believed to be associated with a number of emotional and behavioral sequelae. The nature and etiology of mental health manifestations of TBI (including a combination of brain dysfunction and psychological trauma and interrelationships between cognitive, affective, and physical symptoms]. Major head trauma can lead to severe health consequences, including hearing loss. Hearing loss resulting from such injuries is a significant clinical and social issue, as it greatly impacts patients’ quality of life [43yet limited studies have compared QoL inventories. In 2579 TBI patients, orthopedic trauma controls, and healthy friend control participants, we compared the Quality of Life After Brain Injury-Overall Scale (QOLIBRI-OS]. Polish law provides legal penalties for participating in a brawl or causing major head trauma that exposes another human to an immediate risk of death, or causing serious injury to health or significant impairment of organ function or health. The severity of the punishment is determined based on the specific circumstances of each case [12].

The patients in the present study experienced a range of consequences from violence: 44.4% (n=4) had temporal bone fracture, 44.4% (n=4) had occipital bone fracture, 55.6% (n=5) had skull base fracture, 33.3% (n=3) had sphenoid bone fracture, 22.2% (n=2) had intracerebral hemorrhage, 22.2% (n=2) had zygomatic bone fracture, 77.8% (n=7) had concussion, – 22.2% (n=2) had,orbital fracture, and 44.4% (n=4) had frontal lobe contusion. Greenberg et al [24] examined 25 patients with bilateral profound hearing loss caused by head trauma – the most common co-occurring effects of the injury were behavioral changes due to frontal lobe damage in 24% (n=6) and facial nerve paralysis in 12% (n=3). Khwaja et al [44] found the most frequent consequences of head trauma were temporal bone fractures (70% [n=16]), concussions (13% [n=3]), and intracerebral hemorrhage (13% [n=3]).

In the preoperative speech comprehension test (using hearing aids), the average speech understanding score was 1.6%. Postoperatively, the scores improved to 61.7% in quiet conditions and 32% in noisy conditions. In the study by Firszt et al [45] conducted under similar conditions to ours, the average speech comprehension score was 70% in a quiet environment and 30% in a noisy environment. Alves et al [46] studied auditory rehabilitation of patients who had cochlear implants following head trauma. During each follow-up visit, they conducted various tests to evaluate the benefits of implantation. Twelve months after device activation, they performed free-field speech audiometry with an active cochlear implant. The average speech comprehension score was 55% in quiet conditions and 35% in a noisy environment. Lubner et al [14] found significant improvement in speech – mean scores increased from 22% to 76% at the last follow-up, and 91% of participants reported improved quality of life.

Cochlear implantation can allow patients who have lost their hearing as a result major head trauma to return to the world of sounds. This translates into an improvement in their mental state and a return to social functioning [47].

Limitations of our study are the small group of participants, caused by the specific characteristics of the group. We also observed different types of traumas in our patients.

Conclusions

Hearing loss caused by major head trauma is a complex issue requiring a comprehensive approach to diagnosis and treatment. Understanding the mechanisms of injury, effective diagnosis, and appropriate treatment and rehabilitation are crucial for improving prognosis and quality of life. Cochlear implants give the ability to hear and understand speech to major head trauma patients, thus enabling them to interact with society through verbal communication. However, the challenges posed by this condition underscore the need for further research and the development of new diagnostic and therapeutic methods.