RD7.2 | Imaging in ENT — Glossary

'As Low As Reasonably Achievable' — the radiation-protection principle (per AERB) underpinning the restraint in imaging uncomplicated otitis media and the use of dose-optimised temporal-bone CT protocols.

Acute pyogenic infection of the middle ear; a clinical diagnosis in which imaging is reserved for suspected complications such as acute mastoiditis, abscess, facial palsy, labyrinthitis or intracranial spread.

An implant that stimulates the cochlear nucleus in the brainstem, bypassing the cochlear nerve; considered when cochlear nerve aplasia makes a conventional cochlear implant impossible.

The space between the cerebellum, pons and petrous temporal bone through which CN VII and VIII pass; the site of vestibular schwannoma, meningioma and epidermoid.

Abnormal accumulation of keratinising stratified squamous epithelium in the middle-ear cleft; erodes bone; on HRCT appears as non-dependent soft tissue with bony erosion and restricts diffusion (bright on non-EPI DWI, low ADC) on MRI.

High-resolution heavily T2-weighted MRI sequences in which CSF is bright, outlining the IAM nerves, cochlea and labyrinth; used to screen the IAM for small schwannomas and to assess cochlear nerve aplasia/hypoplasia.

Complication of ASOM in which infection erodes the bony septa between mastoid air cells, making them confluent and fluid-filled on HRCT; an indication for cortical mastoidectomy.

An electronic device that electrically stimulates the cochlear nerve to restore useful hearing; requires a patent cochlea AND an intact cochlear nerve, both confirmed on pre-operative imaging.

A spectrum of congenital inner-ear anomalies (e.g. common cavity, incomplete partition) seen on HRCT that cause SNHL and influence cochlear-implant feasibility and surgical approach.

Absence or under-development of the cochlear nerve, assessed on CISS/FIESTA oblique-sagittal images through the IAM; aplasia contraindicates a conventional cochlear implant.

Chronic middle-ear infection with persistent perforation and discharge; divided into mucosal/tubotympanic ('safe') and squamous/atticoantral ('unsafe', cholesteatomatous) types.

Congenital widening of the vestibular aqueduct (wider than the adjacent posterior semicircular canal, or midpoint diameter >~1.5 mm) on HRCT; the commonest imaging-detectable congenital cause of paediatric SNHL, causing fluctuating/progressive loss.

The bony canal carrying the facial nerve through the temporal bone; erosion/dehiscence (commonly the tympanic segment) on HRCT warns of an exposed nerve at risk of palsy and intra-operative injury.

Contrast MRI (T1) that highlights enhancing lesions; the reference standard for detecting a vestibular schwannoma and characterising other CPA/IAM masses in SNHL.

High-resolution sub-millimetre CT of the temporal bone reconstructed with a bone algorithm; the workhorse modality for CSOM and complications, mapping bony erosion, ossicular status and the surgical roadmap.

The bony canal transmitting the facial (CN VII) and vestibulocochlear (CN VIII) nerves from the cerebellopontine angle to the inner ear; the key target of MRI in retrocochlear SNHL.

Pathological new bone formation within the membranous labyrinth (loss of cochlear fluid signal on T2, bony in-filling on CT) that can obliterate the cochlea; important to detect early because it narrows the window for cochlear implantation.

Erosion of the lateral semicircular canal by cholesteatoma, creating a labyrinthine fistula; on HRCT it warns of vertigo, sensorineural hearing loss and the risk of a 'dead ear' if breached during surgery.

Surgical removal of mastoid air-cell disease; canal-wall-up or canal-wall-down (modified radical) approaches are chosen partly on the basis of HRCT findings of disease extent and erosions.

CSOM with a central perforation and no cholesteatoma or bone erosion; on HRCT, middle-ear/mastoid opacification without erosion of the scutum, ossicles or critical canals.

Diffusion-weighted MRI sequence with reduced susceptibility artefact at the skull base; the sequence of choice for detecting cholesteatoma (restricts diffusion) and for post-operative recurrence surveillance, often replacing second-look surgery.

Abnormal otospongiotic bone around the cochlea seen as pericochlear lucency on HRCT; usually causes conductive loss via stapes fixation but can produce a sensorineural or mixed component (cochlear otosclerosis).

The attic recess between the scutum laterally and the neck of the malleus medially; the typical site of a non-dependent cholesteatoma mass on HRCT.

A lesion of the cochlear nerve or central auditory pathway (beyond the cochlea), such as a vestibular schwannoma; suggested by asymmetric SNHL with poor speech discrimination and best evaluated by MRI of the IAM/CPA.

The sharp bony spur at the lateral wall of the attic (epitympanum); blunting/erosion of the scutum on HRCT is an early characteristic sign of attic cholesteatoma.

Hearing loss arising from the cochlea (sensory) or the cochlear nerve/central pathway (neural/retrocochlear), as distinct from conductive loss of the external/middle ear.

Intracranial complication of otitis media seen as a non-enhancing filling defect in the sigmoid/transverse sinus on post-contrast MRI or MR venography; a neurosurgical/ENT emergency.

CSOM with an attic or marginal perforation and cholesteatoma causing bone erosion; the type that threatens the facial nerve, labyrinth and intracranial structures.

The thin bony roof separating the middle ear and mastoid from the middle cranial fossa; dehiscence on HRCT warns of intracranial extension, CSF leak and dural exposure during surgery.

A benign Schwann-cell tumour of the vestibular division of CN VIII at the IAM/CPA; the prototypical retrocochlear cause of asymmetric SNHL; an avidly enhancing 'ice-cream-cone' mass on gadolinium-enhanced MRI.