Active Middle Ear Implant in a Patient with Neurofibromatosis Type 1 and Multiple Calvarial Defects: A Case Report

Abstract

Bony abnormalities, including sphenoid dysplasia and calvarial defects, are well recognized in patients with neurofibromatosis type 1. However, having multiple calvarial defects is rare. We present a case of a 35-year-old Japanese male patient who was referred to our hospital because of hearing loss. He was diagnosed with neurofibromatosis type 1 during early childhood. Otoscopic examination revealed a protrusion from the anterior wall of the external auditory canal that obstructed the external auditory canal. Computed tomography findings revealed multiple defects and an uneven skull surface. Large bony defects of the anterior wall of the external auditory canal were also identified bilaterally. Conductive hearing loss was caused by temporomandibular joint herniation that was obstructing the external auditory canal in both ears. An active middle ear implant was implanted in the right ear. A floating mass transducer was placed into the round window niche using a round window coupler. The active middle ear implant improved postoperative audiometric thresholds to approximately 35 dB across all frequencies. No complications occurred for up to 30 months after the operation. An active middle ear implant is a feasible and valuable option for patients with neurofibromatosis type 1 and conductive hearing loss due to multiple skull defects that result in temporomandibular joint herniation.

Figure 1. a-d.

Preoperative otoscopic examination. Otoscopic examination in the (a) right and (b) left ear canals with the mouth closed. A diffuse protrusion of the anterior canal wall (black arrow) obstructs the canal completely. While the mouth is open, the anterior wall retracts anteriorly (black arrowhead) and the tympanic membrane (*) becomes visible in the (c) right and (d) left ears.

Figure 2. a-c.

Preoperative and postoperative pure-tone and speech audiograms. The preoperative pure-tone audiograms of the (a) right and (b) left ears. (a) The filled circles and triangles indicate hearing when opening the mouth and postoperative air conduction aided by the AMEI, respectively. (c) The unaided preoperative speech audiograms of both ears are also presented. (b) The black squares indicate the hearing level during mouth opening. (c) The black triangles indicate the postoperative speech audiogram aided with AMEI. Uncolored circles, right ear; X, left ear; AMEI, active middle ear implant.

Figure 3. a,b.

High-resolution computed tomography image of the skull. (a) Multiple calvarial defects with uneven skull surface can be identified in the axial computed tomography image of the skull. (b) Axial computed tomography findings of the right ear. White arrow indicates a doughnut-shaped radiation impermeable marker at the assumed implant sight of the bone-anchored hearing aid. White arrowhead indicates the bone defect of the skull. The assumed implant site of the bone-anchored hearing aid was near the bone defect of the skull with skull irregularities.

Figure 4. a-d.

Computed tomography images of the external auditory canal. (a and b) Axial and (c and d) coronal computed tomography images of the external auditory canal in the (a and c) right and (b and d) left ears. The computed tomography images show the entire bony defects of the anterior external auditory canal wall, leading to external auditory canal obstruction with the soft tissue (white arrow), which is caused by temporomandibular joint herniation in both ears.

Figure 5. a-c.

Intraoperative photographs of the AMEI. (a) The transmastoid procedure is restricted by the low-lying tegmen (black arrow) and the anteriorly situated sigmoid sinus (white arrow) in the right ear. (b) The posterior canal wall of the external auditory canal is partly removed to visualize the round window. The floating mass transducer with a round window coupler (white arrowhead) is placed into the round window niche. (c) The canal wall is reconstructed using a piece of conchal cartilage (blank arrow) to protect the cable from extrusion. AMEI, active middle ear implant.