12MRI in Tinnitus (IAC/brain, vestibular schwannoma)

FWhat MRI is asked to exclude

When tinnitus is unilateral or accompanied by asymmetric sensorineural hearing loss, the single most important diagnosis to exclude is a vestibular schwannoma — a benign tumour of the eighth nerve that classically presents with unilateral tinnitus, asymmetric SNHL and sometimes imbalance. MRI of the internal auditory canal (IAC), cerebellopontine angle (CPA) and brain is the reference standard because of its soft-tissue resolution [2025].

The same study also excludes other retrocochlear and central causes — meningioma, epidermoid, demyelination, a neurovascular loop — so a single well-chosen MRI answers the broad “is there a structural lesion behind this asymmetry?” question that the audiogram raised.

TThe sequences that matter

Two complementary sequence types do the work. A high-resolution heavily T2-weighted sequence (CISS/FIESTA, sub-millimetre, of the IAC/CPA) produces a bright-fluid “cisternographic” view in which the dark eighth-nerve complex and any filling defect or mass stand out; this is highly sensitive for intracanalicular schwannomas. Post-contrast T1 with gadolinium then confirms an enhancing lesion and characterises it — a vestibular schwannoma enhances avidly and homogeneously within the IAC/CPA [2025].

Many centres screen with high-resolution T2 alone and add gadolinium only when the T2 is abnormal or equivocal, balancing sensitivity against cost and contrast exposure. When the indication is pulsatile rather than asymmetric tinnitus, the protocol shifts: MR angiography and MR venography are added to interrogate arterial and venous sources [2024].

CYield, triage and the role of ABR

Because the prevalence of vestibular schwannoma in asymmetric SNHL is only a few percent, the field has long debated how to triage who gets the scan. Auditory brainstem response was historically used as a gatekeeper, but its sensitivity for small intracanalicular tumours is limited, and MRI outperforms it — which is why MRI has become the standard when an asymmetric pattern crosses an audiometric threshold [2004]. Various asymmetry criteria (for example a defined inter-aural gap at adjacent frequencies) are used to decide whom to image, keeping yield acceptable [2014].

The practical message: ABR may still inform selection in resource-limited settings, but it does not replace MRI for definitively excluding a small schwannoma.

CPitfalls and interpreting a normal scan

Several pitfalls deserve respect. Neurovascular loops of the AICA contacting the eighth nerve are commonly seen on high-resolution T2 but are frequently incidental; attributing tinnitus to a loop should be cautious. Incidental findings — small white-matter hyperintensities, arachnoid cysts — are common and rarely explain tinnitus. Gadolinium carries small risks (allergy, and accumulation considerations), so it is added by indication, not reflexively. Finally, MRI is contraindicated or complicated by certain implants and severe claustrophobia, where CT or surveillance strategies may be needed.

A normal MRI in a patient with unilateral tinnitus is genuinely reassuring — it excludes the lesion that mattered — but it does not abolish the tinnitus, and the consultation should pivot to counselling and audiological management rather than further scanning [2013].