HEARING IMPAIRMENT

The ear consists of three parts: external , middle and inner ear with each part performing a certain function in sound transmission and transduction. Pic. Credit : Wikipedia

Anatomy of the Ear

The cochlea has a fascinating architecture being spiral having 2 and half turns and furtherly divided into sacla tympani, scala vestibuli and scala media in between having the organ of corti. Pic. credit Gray’s anatomy

Internal architecture of the cochlea

It’s the part of the cochlea responsible for transforming the sound from its mechanical state into neural impulses. The basilar membrane oscillate causing the hair cells to brush against the tectorial membrane and creating an action potential transmitted into the cochlear nerve bundles. Pic. Credit Wikipedia.

The Organ Of Corti

Sagittal T2 WIs MR through mid-lAC shows all four normal nerves:

Arrow ; Facial nerve. Open arrow; Cochlear nerve. Curved arrow; Inferior vestibular nerve. Superior vestibular nerve not labeled. Pic. Credit Diagnostic imaging series, head and neck

Contents of internal auditory canal

Diagram and MRI image through inferior lAC shows normal inferior cerebellar peduncle-cochlear nuclei (arrow), cochlear nerve(open arrow) & inferior vestibular nerve (curved arrow). Pic. Credit Diagnostic imaging series, head and neck

Vestibulo-cochlear nerve

The sound neural impulses is transmitted through the cochlear nerve and relay into different brain stem centers before reaching the auditory center. Pic Credit Wikipedia.

The hearing Pathway

The final stage of impulse travel is within the auditory cortex A1 lying at the superior temporal lobe and is tonotopic same as the cochlea then A1 is associated with surrounding 2ry auditory cortex for further sound processing. Pic. Credit Wikipedia

the Central Auditory cortex A1

As a general rule CT and otoscope are used to evaluate the external and middle ear while MRI is used to evaluate inner ear contents

Following are examples of causes of hearing impairment through imaging

Often referred to as swimmer’s or surfer’s ear due to cold water irritation and causing conductive hearing impairment. CT Pic. Credit Radiology assistant

Bilateral bony Exostosis of the external ear

Congenital disorder where the external canal is not formed and closed by bony coverage causing conductive hearing impairment, CT is important to assess for the middle and inner ear structure to guide the surgical intervention need. CT Pic. Credit Radiology assistant

Congenital external canal Artesia

The ear drum perforation can occur either traumatically, inflammatory or with middle ear pathology. Normal ear drum appearance by otoscope is seen above and perforated ear drum is seen below. Pic Credit entbristol.co.uk

Ear drum perforation

Complete opacification of the tympanic cavity and mastoid air cells with soft tissue in chronic otitis media in coronal CT image causing conductive hearing impairment. CT Pic. Credit Radiology assistant

Otitis media

Congenital or Acquired tumor formed of epithelial cells causing erosion of the bony ossicles and tympanic cavity leading to conductive hearing impairment. The lesion is noted on the right side with normal left side. CT Pic. Credit Radiology assistant

Cholesteatoma

Upperpicture shows transverse fracture through the petrous (arrows) causing cochlear and facial nerve injury and resulting in SNHL. Pic Credit Joel D. Swartz, Radiographics

Lower picture shows longtudinal fracture through the petrous (yellow arrow) causing incodo-malleous dislocation (blue arrow) resulting in Conductive HL. CT Pic. Credit Radiology assistant

Petrous bone fractures

Widening of the vestibular aqueduct is the most common cause of congenital SNHL. Pic Credit Joel D. Swartz, Radiographics

Vestibular aqueduct syndrome

Acoustic schwannoma or neuroma (arrow) is a tumor arising from the covering sheath of the vestibulo-cochlear nerve causing SNHL, it may be bilateral in cases of neurofibromatosis type II. CT Pic. Credit Radiology assistant

Acoustic Shwannoma

A case of bilateral otoscelrosis which is a metabolic disease causing calcification of either the oval window causing conductive HL or the cochlea itself causing SNHL. CT Pic. Credit Radiology assistant

Otosclerosis

A case of MS with plaques noted at the cochlear nuclei bilaterally (arrows) causing SNHL. Pic Credit Joel D. Swartz, Radiographics

Central hearing affection

Right temporal brain tumor in MRI image affecting the A1 cortex and causing unilateral SNH impairment. Pic. Credit vabrainandspine.com

Central hearing affection

Cochlear implant is a device used to fix SNH impairment in the lower picture is an implant electrode passing through the facial recess to the scala tympani intra-opratively. Upper Pic. Credit Wikipedia

Cochlear implant