**Core Concept**
Sensorineural deafness, also known as sensorineural hearing loss, is a type of hearing loss that affects the inner ear or the nerve pathways from the inner ear to the brain. This condition can be caused by various factors, including genetic mutations, infections, or trauma. In cases where hearing aids are ineffective, surgical or technological interventions may be required.

**Why the Correct Answer is Right**
Cochlear implants are a type of auditory implant that bypass damaged or non-functioning parts of the ear and directly stimulate the auditory nerve, allowing individuals to perceive sound. They consist of an external microphone and processor, a transmitter, and an internal receiver and electrode array. In children with severe sensorineural deafness who do not benefit from hearing aids, cochlear implants can significantly improve speech recognition and communication skills. The implantation procedure involves surgically inserting the electrode array into the cochlea, followed by activation and programming of the device.

**Why Each Wrong Option is Incorrect**
**Option A:** Fenestration surgery, a procedure that involves creating a new opening in the oval window to improve sound conduction, is typically performed in cases of otosclerosis, a type of conductive hearing loss. It is not suitable for sensorineural deafness.

**Option B:** Stapes mobilisation, also known as stapedotomy or stapedectomy, is a surgical procedure that involves removing or modifying the stapes bone to improve sound conduction in cases of otosclerosis. It is not applicable to sensorineural deafness.

**Option D:** Conservative management, including the use of hearing aids, is the initial approach for managing sensorineural deafness. However, in cases where hearing aids are ineffective, more invasive interventions like cochlear implants may be necessary.

**Clinical Pearl / High-Yield Fact**
Cochlear implants are most effective when implanted before the age of 5, as early auditory experience is crucial for language development and speech recognition.

**Correct Answer:**
✓ Correct Answer: C. Cochlear implant.