Symptom: Asymmetric Mixed Hearing Loss

Abstract

A 69-year-old female presents as a consult regarding right-sided hearing loss and tinnitus. She has had the symptoms since the 1970s and was recommended surgery at that time, although it was not pursued. She is currently presenting because her symptoms have become worse over the past five years. The patient additionally endorses migraine headaches with vertigo. The patient denies any family history of hearing loss or ear surgery. Tympanic membranes are normal on microscopy. Weber test shows lateralization to the right ear and Rinne test shows bone conduction greater than air conduction on the right side. The patient had an audiogram completed (see Figure 1).Figure 1: The patient’s audiogram at presentation. Asymmetric mixed hearing loss, round window obliteration, Clinical Consultation.Figure 2: Axial (horizontal) CT of temporal bones showing the obliterated round window in the axial direction on the right. Asymmetric mixed hearing loss, round window obliteration, Clinical Consultation.Figure 3: Axial (horizontal) CT of temporal bones showing air (black) in a round window niche on the left. Asymmetric mixed hearing loss, round window obliteration, Clinical Consultation.Figure 4: Coronal (parallel to the face) CT of temporal bones showing the obliterated round window in the coronal direction. Asymmetric mixed hearing loss, round window obliteration, Clinical Consultation.Figure 5: Sagittal (vertical parallel to the ear) CT of temporal bones demonstrating the obliterated round window in the sagittal direction. Asymmetric mixed hearing loss, round window obliteration, Clinical Consultation.DIAGNOSIS: ROUND WINDOW OBLITERATION By Daim Tabba, BA, BS; Karen Tawk, MD; Mehdi Abouzari, MD, PhD; and Hamid R. Djalilian, MD Upon examination of the patient’s audiograms, it is evident that the patient primarily has an asymmetric (right-sided) mixed hearing loss. Typically, when a patient presents with a normal physical exam and conductive hearing loss, the most likely diagnosis is otosclerosis. Otosclerosis refers to abnormal bone remodeling in the inner ear such that the normally dense endochondral layer of the bony otic capsule is replaced by one or more foci of vascular bone leading to bony overgrowth. As this overgrowth develops, the stapes can no longer properly function and becomes fixated. As such, conduction gradually worsens.1 Cochlear involvement, as would be the case with round window involvement by the otosclerotic bone, can lead to sensorineural hearing loss and if the round window becomes obliterated, it can lead to conductive hearing loss. leading to a mixed hearing loss overall.2 Other potential pathologies linked to mixed hearing loss include the third-window effect, or an enlarged vestibular aqueduct (EVA). The third-window effect in EVA occurs from the loss of vibrations of the inner ear fluids through an enlarged vestibular aqueduct, which is effectively a third window into the inner ear. This diagnosis seems unlikely because it is rare that an individual reaches adulthood without symptoms. Mixed hearing loss due to this condition is usually seen in childhood. While superior canal dehiscence can cause mixed hearing loss, it would rarely be as severe as what was seen in this patient. Patients presenting with asymmetric hearing loss may require further work up such as magnetic resonance imaging (MRI). The current criteria hold asymmetry greater than 15 dB in three adjacent frequencies or a significant asymmetry at 3,000 Hz in the absence of significant asymmetric noise exposure as indicative of an MRI recommendation. At the same time, one can also consider other aspects of the audiological evaluation. In the case of this patient, there was a notable absence of acoustic reflexes, which supported the possibility of otosclerosis. However, there was also an absence of a Carhart notch. A Carhart notch is a drop in the bone conduction threshold at approximately 2,000 Hz such that it is worse than that at 1,000 and 4,000 Hz and typically seen in otosclerosis.1 In the case of this patient, the bone conduction threshold at 1,000 Hz was worse than that at 2,000 Hz, which would be less likely that the patient would have stapes fixation. This reinforces the need for further workup. The patient presented to the clinic with a completed computerized tomography (CT) scan. On CT, active otosclerotic plaques present as hypodense (grey) dots or rings around the cochlea due to impaired mineralization. Meanwhile, inactive otosclerosis is less visible on CT and can be hyperintense (bright white). For this patient, it appears that the patient has an intact ossicular chair with no active otosclerotic foci or hypodensity around the cochlea. This suggests that the patient’s symptoms, if due to otosclerosis, are due to inactive otosclerosis. Obliteration of the round window (RW) with bone (complete coverage of the RW with bone) can be congenital or acquired. The acquired form is most commonly caused by otosclerosis. Rarely, the condition can be congenital in nature. Congenital atresia of the round window (non development) is seen as part of other anomalies including incomplete partition anomalies (Mondini, etc.), mandibulofacial dysostosis, and Coloboma of the eye, Heart defects, Atresia of the choanae, Retardation of growth and/or development, Genital and/or urinary abnormalities, and Ear abnormalities and deafness (CHARGE) association, in addition to cases of congenital atresia of the ear canal. The round window is approximately 1.5–2.1 mm horizontally, 1.9 mm vertically, and 0.65 mm in thickness. The round window niche is the area of the cochlea where there is an overhanging bone over the round window, termed tectulum. This bone covers the round window membrane often and due to overlying adhesions, etc. sometimes the surgeon cannot fully visualize the round window membrane. This anatomy combined with the rarity of round window atresia can cause this to be missed. In addition, this abnormality can be missed on imaging and a significant number of patients with round window atresia are not diagnosed until middle ear surgery in an attempt to improve their conductive hearing loss. The round window needs to be evaluated in more detail especially in patients with mixed hearing loss where no other middle ear abnormalities are found. Patients with round window atresia generally have audiograms showing a mixed but mostly conductive hearing loss, with an air-bone gap of 30–40 dB.3 Surgeons have attempted to open the round window surgically to restore the second window into the cochlea, which allows for better transmission of sound vibration into the cochlea. The surgical treatment of round window atresia has a high sensorineural hearing loss chance, likely due to excessive sound transmission from drilling on the basal turn of the cochlea. In addition, keeping the round window intact while drilling off the overlying surface bone creates the risk of perilymph fistula, which can cause sensorineural hearing loss and vertigo postoperatively. It has been theorized that the lack of success in the round window opening procedures may be due to other unrecognized anomalies of the middle ear or possible third window abnormalities, which were unknown at the time of these older reports. It is also worth noting that the round window appears obliterated on the CT. This is suggestive of otosclerotic bony growth that likely happened when the patient was in her 20s and had active otosclerosis at that time that obliterated the round window. Since then, the otosclerosis focus has become inactive and appears similar to a normal cochlear bone on CT. If the patient’s round window abnormality were to have been due to a congenital problem, it would have been present since birth, but in this patient it began later in life. This is more likely to have been due to otosclerosis. BONUS ONLINE VIDEOS: VISUAL DIAGNOSIS Video 1. Axial (horizontal) CT of temporal bones showing the obliterated round window in the axial direction. Video 2. Coronal (parallel to the face) CT of temporal bones showing the obliterated round window in the coronal direction. Video 3. Sagittal (vertical parallel to the ear) CT of temporal bones demonstrating the obliterated round window in the sagittal direction (video starts on the right ear and then goes to the left ear). Video 4. Axial (horizontal) CISS sequence MRI demonstrating the inner ear anatomy with fluid in the cochlea and vestibule. Video 5. Coronal CISS sequence MRI showing the inner ear anatomy with fluid in the cochlea and vestibule in the coronal direction. Video 6. Sagittal CISS sequence MRI demonstrating the inner ear anatomy with fluid in the cochlea and vestibule in the sagittal direction.