ECochG Atlas · Module 09

9Perilymph fistula

Fifty years of controversy, in Hornibrook's phrase. ECochG with intra-test postural manoeuvres (Gibson 1992) is one of the few functional tests for PLF — and remains useful in the rare clinical situation where the question is ‘is perilymph leaking right now?’

Role of ECochG · Historic with niche use

Adjunctive functional test. Useful when clinical suspicion is high and other tests are equivocal. Cochlin-tomoprotein (CTP) testing has emerged as a more specific biochemical alternative where available.[2009][2012]

FClinical presentation

A perilymph fistula (PLF) is an abnormal communication between the perilymphatic space and the middle ear, allowing perilymph to escape. The classic settings:[2012]

Iatrogenic — after stapedectomy or other otologic surgery (the original setting where PLF was described).
Barotrauma — flying, diving, severe straining, or rapid altitude change.
Head trauma — temporal bone fracture or significant head injury.
Spontaneous — the most controversial category; symptom-based diagnosis without obvious precipitant.

Symptoms overlap considerably with Ménière's disease and SCD: fluctuating SNHL, episodic vertigo, tinnitus, aural fullness. Two features are more suggestive of PLF specifically: (1) symptoms triggered by Valsalva, exertion, or postural change, and (2) a positive temporal relationship to barotrauma or surgery.

The diagnosis remains controversial because the symptoms are non-specific, the imaging is rarely positive, and the gold standard is tympanotomy with direct visualisation of perilymph at the oval or round window — an invasive endpoint that not every suspected case warrants.[2012]

Wackym and colleagues have also drawn attention to overlapping third-window entities (e.g. cochlea-facial nerve dehiscence) that can mimic PLF clinically and on ECochG, further muddying the differential where imaging is non-diagnostic.[2019]

TThe Gibson postural-change protocol

Gibson, in a landmark 1992 paper, observed during stapedectomy and cochleostomy that the ECochG was unchanged on simply opening the round or oval window — but changed dramatically when perilymph was suctioned out. Increasing intrathoracic pressure (Valsalva) returned the trace to baseline as perilymph refilled.[1992] He then developed an office-based test based on this observation:

Place a transtympanic needle electrode in the round window niche under local anaesthesia.
Record a baseline click ECochG.
Ask the patient to perform a closed-glottis Valsalva manoeuvre.
Record during and after the Valsalva.
A strongly positive test: AP amplitude increases by > 15% during Valsalva (with or without an SP decrease).[1992]

Campbell and Abbas reported a related protocol in the same era, using head-down and other postural manoeuvres rather than Valsalva; the underlying principle — looking for a change in SP or AP during a manoeuvre that alters intrathoracic or intracranial pressure — is the same.[1992]

Condition	SP/AP ratio	AP amplitude	Interpretation
Baseline (sitting)	0.55 (elevated)	0.9 µV (reduced)	Reduced perilymph volume — small AP, relatively prominent SP.
During Valsalva	0.32 (normal)	1.2 µV (recovered)	Intrathoracic pressure transiently restores perilymph; AP grows back, SP shrinks.

Fig 9.1Schematic of the Gibson 1992 postural-change protocol. With an active perilymph fistula, the baseline trace shows a reduced AP and elevated SP/AP ratio reflecting reduced perilymph volume. Valsalva temporarily restores perilymph pressure, the AP grows back and the SP shrinks, and the ratio returns toward normal. A > 15% AP amplitude gain or a clear SP reduction is considered a positive test.[1992]

TCurrent alternatives and a candid limitation

Two developments since Gibson's protocol have changed how clinicians approach suspected PLF:

Test	Characteristics	Practical role
ECochG with Valsalva	Functional, real-time, but requires TT needle electrode and skilled interpretation. Sensitivity 60–75% in best series; specificity uncertain.[1992][2012]	Most useful when other tests are equivocal.
Cochlin-tomoprotein (CTP) — preferred where available	Biochemical marker found in perilymph but not normally in middle ear fluid. CTP detected in a middle ear lavage sample identifies perilymph with high specificity.[2009]	Increasingly first-line where assay is accessible.
Tympanotomy (gold standard)	Direct visualisation of perilymph at the oval or round window.[2012]	Unambiguous endpoint — but invasive and carries operative confounders (local anaesthetic mistaken for perilymph).
Campbell & Abbas postural ECochG	Head-down / postural manoeuvre variant of Gibson's functional test.[1992]	Historic; less widely used than Valsalva protocol.

The honest limitation

Hornibrook's "fifty years of controversy" review captures the underlying problem: PLF lacks reliable symptoms (Ménière's, SCD, and PLF overlap), lacks a non-invasive gold standard (tympanotomy is the only definitive test), and lacks an unambiguous functional test (the ECochG postural-change protocol is helpful but not definitive). Where a CTP assay is available it is increasingly the first-line investigation because of its specificity; where it is not, ECochG with Valsalva remains a reasonable option in selected cases. In either pathway, surgical exploration is reserved for cases where the clinical and test evidence consistently points to PLF.[2012][2009]

TCase 9.1 — diver with posture-triggered symptoms

Case 9.1 · Trainee level

A 28-year-old recreational scuba diver presents with right-sided hearing loss, tinnitus, and vertigo that began during a rapid ascent two weeks ago. Audiogram shows a 35 dB SNHL across mid-frequencies on the right. CT temporal bones is normal. MRI is unremarkable. He has been treated empirically with corticosteroids without improvement. Symptoms worsen with Valsalva and with bending over. The team is considering ECochG with postural manoeuvres.

Which is the most reasonable role for ECochG in this case?

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