4Functional vs Structural Tinnitus

FTwo questions, not one

The oldest way to sort tinnitus asks who can hear it — only the patient (subjective) or also the examiner (objective). A complementary, more recent framework asks a different question: is there something to find? Here tinnitus is split into structural disease, where an identifiable anatomical lesion generates or transmits the sound, and functional tinnitus, where the ear and brain look structurally intact but the auditory system is mis-firing [2013].

These two axes are not the same. Most objective tinnitus is structural, but the reverse is not guaranteed: a tumour can produce a purely subjective ringing, and a turbulent vessel that no examiner can auscultate is still structural. Holding both questions in mind — who hears it, and will imaging show a cause — is what makes the classification clinically useful [2013].

TStructural tinnitus: a lesion to find

Structural tinnitus is the symptom of a discrete pathology. The classic culprits are space-occupying or remodelling lesions — a vestibular schwannoma in the cerebellopontine angle, a dural arteriovenous fistula or glomus tumour, otosclerotic bone remodelling of the otic capsule — together with vascular anomalies such as a sigmoid-sinus diverticulum or high-riding jugular bulb [2013]. The unifying feature is that the cause is visible: on MRI, CT, angiography, otoscopy or audiometric pattern, the abnormality declares itself.

This matters because structural tinnitus is the slice of the differential where the stakes are highest and where a cure may exist. Resecting a schwannoma, embolising a fistula or correcting a venous sinus problem can address the sound at its source, which is rarely possible in functional disease [2008].

TFunctional tinnitus: a system, not a lesion

In functional tinnitus the imaging is clean, yet the patient hears a phantom sound. The mechanism is altered function — maladaptive plasticity following cochlear deafferentation, increased central gain, tonotopic-map reorganisation and aberrant thalamocortical activity — rather than any single removable lesion [2013]. This is the largest group by far: the chronic, bothersome, idiopathic tinnitus that fills tinnitus clinics is overwhelmingly functional.

Reframing the common case as a disorder of neural function reshapes management. Because there is no lesion to excise, treatment shifts toward modulating the maladaptive network — sound therapy, cognitive behavioural approaches, amplification of deafferented input and neuromodulation — rather than surgery [2014].

CWhy the dichotomy steers imaging

The practical payoff of the functional/structural split is that it predicts diagnostic yield. The clinician’s job at first contact is to estimate the pre-test probability that a lesion is present, because that probability decides whether contrast MRI of the internal auditory canals, CT/MR angiography or simple reassurance is the right next step [2014].

Red flags raise the structural probability and lower the threshold to image: unilateral or markedly asymmetric tinnitus, pulsatility, sudden or rapidly progressive hearing loss, and focal neurological signs [2013]. Their absence — bilateral, non-pulsatile, gradual tinnitus with a symmetrical high-frequency audiogram — makes a functional picture overwhelmingly likely, and indiscriminate imaging is then low-value [2014]. The dichotomy thus operationalises a single question patients ask: “will the scan show why?”