Diagnosis: Congenital Atresia with Anterior Facial Nerve Anatomy
The patient was born with a grade 3 microtia, which means that the affected ear has a developed lobule but no cartilaginous portion. He underwent multiple surgeries to reconstruct the auricle using rib cartilage. For grade 3 microtia cases, at least three operations are generally performed to reconstruct the auricle from rib cartilage. These procedures are usually spaced out by six to 12 months, and often require an inpatient hospital stay. The multiple procedures often leave the patient and the family exhausted, so when the time comes for a hearing reconstruction, they become scared of having to undergo yet another procedure. In some cases, the family's hesitation may also stem from the possibility of developing facial paralysis from the surgical reopening of the ear canal. While the likelihood of facial paralysis exists, its incidence in the hands of an experienced surgeon equipped with facial nerve monitoring course and high-resolution CT imaging is very low. Nonetheless, some families wait until the child turns 18, old enough to make the decision for his or her own hearing reconstruction. On occasion, this fear of facial paralysis is misguided as the cart is placed before the horse. Prior to making decisions on hearing reconstruction, a CT of the temporal bones needs to be obtained to evaluate the anatomy and see if the patient is a candidate for reopening of the ear canal (atresia repair).
Several criteria dictate the potential success rate of atresia repair. These include a well-developed mastoid, an aerated middle ear, the presence of ossicles that are connected to the stapes, the course of the facial nerve, open oval and round windows, among others. The course of the facial nerve in an atresia case is very different from that of a normal temporal bone. The middle ear space in an atresia patient is very small compared with a normal middle ear. The facial nerve courses through the temporal bone around the middle ear. The smaller the middle ear, the tighter the course of the nerve around that structure and a more acute the turn as it turns from the tympanic segment to the mastoid segment. Goycoolea, et al., described the middle ear in an atresia patient as a baseball, while that in a normal ear is a basketball (Goycoolea, et al. Saunders, 1989). As the facial nerve courses around a normal middle ear, it makes an approximately 120 degree angle around the basketball as it bends from the tympanic to the mastoid segment. However, in a small middle ear (akin to a baseball), that angle is 90 degrees or less. This causes the facial nerve to be more on the anterior and potentially interfere with atresia repair.
This patient underwent a CT scan of the temporal bone, which showed a poorly developed mastoid (Fig. 2). This indicates that the patient had a poor Eustachian tube function in that ear, which led to the mastoid's insufficient development. The mastoid was also filled with fluid—another indication of poor Eustachian tube function. The middle ear space between the cochlea and where the tympanic membrane should be is small. Evaluation of the coronal (Fig. 3, looking from the front toward the ear) and sagittal (Fig. 4, looking from the side toward the ear) images shows a very acute angle of the facial nerve leading to a very small space between the facial nerve and the temporomandibular joint. Therefore, this patient is not a candidate for atresia repair.
The situation of this patient is not new in the context of congenital atresia. Some families erroneously assume that a patient is automatically a candidate for atresia repair, but chose not to undergo any type of procedure because of facial paralysis fears. They wait for the child to grow up and make the decision. However, our general philosophy is to offer the family all options. If they wish to explore atresia repair, then we would obtain a CT of the temporal bones. It is not advisable to automatically get a CT of the temporal bones in children who are born with a microtia or atresia of the ear. The imaging process causes unnecessary radiation to the patient, especially since surgical procedures would not be undertaken until the child is 5 years old. At that point, the scan would have to be repeated, exposing the child for a second time to radiation rather than the first time. It is rare that the inner ear of a child with congenital atresia would be anomalous to the point of not having proper hearing function. This is because the inner ear develops very early during embryonic development and the ear canal develops much later. Therefore, inner ear anomalies causing sensorineural hearing loss are uncommon in patients with atresia.
The child with a maximum conductive hearing loss due to atresia is best treated with a soft-band bone-conduction device from a young age. Once the child turns 5 years old, surgical options can be discussed. These options include atresia repair and a percutaneous or transcutaneous bone-anchored hearing device. Percutaneous devices include the BAHA Connect and the Oticon Ponto. Transcutaneous devices include the Medtronic Sophono and the BAHA Attract. Percutaneous connections allow for better high-frequency amplification. However, percutaneous devices have the significant disadvantage of having an abutment coming through the skin. The incidence of abutment-related infections is very high, and there are rare risks of trauma to the abutment that protrudes through the skin exists (Arch Otolaryngol Head Neck Surg. 2010;136:1136). In our practice, percutaneous implants are reserved for older adults with high-frequency sensorineural hearing loss who get the device for single-sided deafness. In children, the use of FDA-approved transcutaneous devices is preferred. Since these devices involve the placement of a magnet next to the temporal bone, a preoperative MRI is obtained to evaluate the temporal lobe on the inside of the implant. This is done because the placement of the magnet will obscure the area under it on future MRI images, so any potential pathology needs to be identified prior to the surgical procedure.
An implantable hearing aid, such as the Vibrant Soundbridge device, holds great promise to improve the hearing of patients with this condition. Considering the current insurance climate in the United States, widespread clinical use of implantable hearing aid is unlikely in the near future. Another notable transcutaneous device is the Med-El Bonebridge, which is available in Europe but not in the United States.
BONUS VIDEOS: VISUAL DIAGNOSIS
Read this month's Clinical Consultation case, then watch the accompanying videos from Hamid R. Djalilian, MD, to review the patient's imaging for yourself.
- Video 1. Axial CT of the right temporal bone showing the contracted middle ear.
- Video 2. Coronal CT of the patient on the right showing the facial nerve anatomy.
- Video 3. Sagittal CT of the patient on the right showing the small space between the TMJ and the facial nerve.
- Video 4. Axial CT of the left ear showing the normal anatomy of the middle ear and mastoid.
- Video 5. Coronal CT of the left side demonstrating the normal facial nerve course.
- Video 6. Sagittal CT of the left temporal bone showing the large space between the facial nerve mastoid segment and the TMJ.
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