Otosclerosis is a common condition that affects the middle ear, specifically the tiny bones (ossicles) responsible for transmitting sound vibrations. It is characterized by abnormal bone growth, leading to the fixation of the stapes bone within the oval window, resulting in hearing impairment. This article aims to provide an overview of otosclerosis, including its anatomy, causes, types, clinical features, audiometry, differential diagnosis, treatment options, complications, and follow-up.
Anatomy
The labyrinth is divided into three sections: the bone labyrinth, the perilymphatic labyrinth, and the membranous labyrinth.
There are three levels in the bone labyrinth: endosteal, bony (enchondral), and periosteal.
- The otic labyrinth, also known as the endolymphatic labyrinth, is a membrane-filled structure that includes the utricle, saccule, cochlear duct (scala medium), semicircular ducts, endolymphatic duct, and sac.
- It is endolymph-filled.
- Space or labyrinth within the perilymph (periotic labyrinth): The otic labyrinth is surrounded by the perilymph-filled periotic labyrinth. Scala tympani, scala vestibuli, and perilymphatic spaces of semicircular and endolym[1]phatic ducts make up this structure.
- Otic capsule (bony labyrinth): Three layers make up this structure: endosteal, enchondral, and periosteal.
Otosclerosis types
- Stapedial Otosclerosis: Stapedial otosclerosis is The most typical. It results in conductive deafness and stapes fixation.
- Cochlear Otosclerosis: This condition affects the petrous portion of the temporal bone, a section of the round window, and several locations inside the bony labyrinth.
It exhibits irreversible SNHL, which is most likely brought on by toxic substances released into the inner ear's fluid.
- Histologic Otosclerosis: A histological study can only identify histologic otosclerosis. The patient is still symptomless.
Alternative Diagnosis
These include the subsequent CHL-related causes. With the use of ear microscopy, siegalization, impedance audiometry, and exploratory tympanostomy, they can be distinguished:
- Serous otitis media
- Medial otitis adhesiva
- Tympanosclerosis
- Mounting the malleus head on the attic
- An osseous discontinuity
- Congenital stapes fixation
Audiometry
1) Lower frequencies are more affected by conductive hearing loss.
2) Carhart's Notch: The bone conduction curve has a dip (from 500 to 4,000 Hz), with the highest at 2,000 Hz (15 dB) and 5 dB at 4,000 Hz (5 dB at 500 Hz, 10 dB at 1,000 Hz, and 15 dB at 2,000 Hz). The stapedectomy procedure is successful when the Carhart's notch is removed.
3) Air-bone gap: The magnitude of the air-bone gap serves as a proxy for the degree of footplate fixation.
4) The pattern and degree of participation of the oval window cannot be predicted by audiometry. During the stapedectomy procedure, it is decided upon during an exploratory tympanostomy.
5) Cochlear otosclerosis is indicated by mixed hearing loss with an aspect of SNHL.
Ending Thought:
Otosclerosis is a common cause of progressive hearing loss, primarily affecting the middle ear. Understanding the causes, types, and methods of diagnosis is crucial for early detection and appropriate treatment. If you suspect you may have otosclerosis or are experiencing hearing loss, consult an ENT specialist for a comprehensive evaluation and personalized treatment options. With the right management, individuals with otosclerosis can experience improved hearing and a better quality of life.
