Asymmetric sensorineural hearing loss — suspected vestibular schwannoma

ACR AC Hearing Loss and/or Vertigo; ACR AC Tinnitus

A targeted internal auditory meatus study, not a brain scan and not a temporal bone CT. The lesion being sought is often only a few millimetres and sits inside a canal that routine brain sequences do not resolve.

Audiometrically confirmed asymmetric sensorineural hearing loss, unilateral tinnitus without a conductive or pulsatile explanation, or unexplained unilateral vestibular failure.

Referenced decision support — confirm against your local protocol.

Decision support, not a directive. Protocols and timings shown are typical published ones — your local protocol takes precedence, and the vetting radiologist decides.

The request in front of you

Everything is optional. Leave a field alone and the answer assumes nothing — the verdict updates as you go.

Study requested

What the referrer actually asked for. It is evidence of intent, not a constraint on the right answer.

Contrast as written

What the request form says, not what it should say.

Age

Pick a band, or type an exact age if it matters.

years

Pregnancy status

Renal risk factors

The question a vetter can actually answer from the request. An explicit “none known” is a real answer, and it removes checks rather than deferring them.

Previous contrast reaction

The pathway — tap anything already done

Marking a study complete moves the answer on. A patient arrives partway through a pathway far more often than at the start of one.

Accept as requested

MRI IAM — with gadolinium

MRI Internal Auditory Meati / Cerebellopontine Angles

What we'd amend, and why

A small intracanalicular schwannoma is a millimetric filling defect within the cerebrospinal fluid of the internal auditory canal, and resolving it requires submillimetre sections targeted at the canal rather than whole-brain coverage. Contrast adds the intralabyrinthine and neuritic causes that a fluid-sensitive screen alone cannot show, and it separates a small tumour from a vascular loop or a normal nerve bundle. Contrast-enhanced CT is markedly less sensitive for this region and does not substitute.

Nothing needs resolving before this goes ahead. Routine checks below are owned downstream.

How was this decided?

pathwayadult — Adults
rulerule-mr-device-screening — MR safety screening for implants and foreign bodies; checked by Radiographer at the scanner
rulerule-contrast-reaction-premed — Prior contrast reaction and elective premedication; checked by Nurse before the scan
rulerule-gadolinium-renal — Kidney function and gadolinium-based contrast; checked by Radiographer at the scanner
rulerule-pregnancy-gadolinium — Gadolinium in known or possible pregnancy; checked by Radiographer at the scanner
rulerule-iv-access — Intravenous access adequate for the planned injection; checked by Radiographer at the scanner

Decision support only. Local protocol takes precedence.

Handled at the scanner(2)nothing for you to do

Settled and owned downstream. Each returns to a radiologist only on the stated trigger.

MR safety screening for implants and foreign bodies
Complete the MR safety questionnaire, verify implant labelling and its stated conditions of use against this scanner and this protocol, and ensure no ferromagnetic object enters Zone IV.
Radiographer at the scannerBefore the scan
Flags back if: An implant or retained foreign body that is MR Unsafe, unlabelled, or cannot be identified; or an MR Conditional device whose stated conditions this scanner or the requested protocol cannot satisfy; or a credible unexcluded intraocular metallic foreign body history.
Intravenous access adequate for the planned injection
Site and test a cannula that supports the protocol flow rate, preferring an antecubital or large forearm vein, and observe the injection for extravasation. A 20-gauge or larger cannula is preferred for flow rates of 3 mL/s or more.
Radiographer at the scannerAt the scanner
Flags back if: No cannula can be sited that supports the protocol flow rate — for example only a 22-gauge hand or foot cannula for a CT angiogram needing 4–5 mL/s; or the only available access is a central line or port that is not labelled power-injectable; or an extravasation occurs.

Pathways

Big forks are separate pathways; the first whose conditions match is the one used.

Adults

Matches your inputsDefault

Role	Study & protocol	Why this answers the question
First line	MRI Internal Auditory Meati / Cerebellopontine Angles MRI IAM — with gadolinium usually appropriate	A small intracanalicular schwannoma is a millimetric filling defect within the cerebrospinal fluid of the internal auditory canal, and resolving it requires submillimetre sections targeted at the canal rather than whole-brain coverage. Contrast adds the intralabyrinthine and neuritic causes that a fluid-sensitive screen alone cannot show, and it separates a small tumour from a vascular loop or a normal nerve bundle. Contrast-enhanced CT is markedly less sensitive for this region and does not substitute.
Reasonable alternative	MRI Internal Auditory Meati / Cerebellopontine Angles MRI IAM — unenhanced high-resolution screen	A high-resolution heavily T2-weighted screen without gadolinium is widely used as the first study for this question and has high sensitivity for a schwannoma large enough to matter, at no contrast exposure and in a shorter slot. Its weakness is the non-mass causes — labyrinthitis, neuritis, intralabyrinthine tumour — which is exactly why an abnormal or unexplained screen is completed with contrast rather than reported as negative.
Problem solving	CT Temporal Bones CT Temporal Bones — High Resolution	Belongs to the conductive and mixed loss question rather than this one: ossicular pathology, otosclerosis, cholesteatoma, congenital anomaly and post-traumatic loss. It is also the planning study before cochlear implantation. It cannot assess the eighth nerve and does not answer asymmetric sensorineural loss.

Pitfalls

Booking a routine brain MRI, whose slice thickness cannot exclude a small intracanalicular lesion.
Reporting a negative unenhanced screen as excluding all causes when labyrinthitis and intralabyrinthine schwannoma need contrast to be seen.
Requesting temporal bone CT for a sensorineural loss, which answers a different anatomical question entirely.
Missing bilateral lesions and the wider implication of neurofibromatosis type 2 in a younger patient.
Overlooking sudden sensorineural hearing loss as a presentation of anterior inferior cerebellar artery territory infarction, where the brain sequences matter as much as the canal.
Letting the scan set the pace in sudden sensorineural hearing loss. Corticosteroid treatment is time-dependent and started on the audiogram; the imaging runs alongside it, and a waiting-list slot for the internal auditory meati is not a reason for anyone to wait.

Priors — what to pull first

For a known schwannoma on surveillance, measure on the same plane and in the same axis as the previous study; growth is a millimetre-scale judgement.
After radiosurgery, transient central loss of enhancement and modest swelling are expected and are not progression.

What makes a good request

Include the audiogram result and which ear. Asymmetry is defined audiometrically, and a request without it cannot be triaged.
There is a real difference in practice between guideline bodies here. The ACR rates MRI of the internal auditory canals without and with contrast as the most appropriate initial study, while many centres screen with high-resolution heavily T2-weighted sequences alone and reserve gadolinium for an abnormal or equivocal screen. Both are defensible; local policy should decide, and the card records the divergence rather than hiding it.
Pulsatile tinnitus is a different question with a vascular differential and does not belong on this pathway.
Sudden sensorineural hearing loss is an otological emergency and a different clock from the elective asymmetry question. Corticosteroid treatment is started within days on audiometric confirmation and must not wait for a scan, and the imaging is arranged alongside it rather than in front of it. Where the sudden loss comes with vertigo, ataxia or any other neurological sign, the differential includes labyrinthine or anterior inferior cerebellar artery infarction — that patient needs brain sequences with diffusion in the same study, and a prodromal sudden deafness preceding a full cerebellar infarct is a recognised and repeatedly missed pattern.

Scoring this once it is done

The classification and risk tools this question ends in.

Koos Classification (Vestibular Schwannoma)

How these studies are acquired

Contrast, phases and timing for every study on the pathways above.

MRI IAM — with gadolinium MRI IAM — unenhanced high-resolution screen CT Temporal Bones — High Resolution

Confirm locally

MRI IAM — with gadolinium: timings are typical — confirm against local protocol.
Timings, contrast volumes and rates above are typical published values. Your department's protocol, scanner and patient population decide the actual numbers.
Safety thresholds and premedication policy follow local policy where it differs from the cited guidance.

References

Implemented from the cited published sources. Educational and workflow support only; confirm against current guidelines and local policy before clinical use.