vHIT Atlas

Reporting a vHIT

A complete vHIT report describes three things, in this order: technical adequacy, the numerical findings, and the clinical interpretation. Reports that lead with interpretation and bury the technical caveats produce false-positive diagnoses. Reports that give numbers without saying what they mean produce uncertainty for the referring clinician. A well-written report does both.

1. Technical adequacy

Always state, up front, whether the recording is technically adequate. Comment on:

Number of acceptable impulses obtained per direction (the standard threshold is at least 10).
Peak head velocities achieved (target 150–250°/s).
Any goggle slippage detected, and what was done about it (re-fitted? excluded affected impulses?).
Any canal where data quality precluded interpretation (often the vertical canals in patients with neck stiffness).

A report that contains the phrase "adequate impulses obtained in all canals with peak velocities 170–220°/s; no goggle slippage detected" is more clinically useful than the same report without it. The referring clinician needs to know whether to trust the numbers.

2. Numerical findings

Report gain values for each canal, with the reference range used. The five-tier classification (normal ≥ 0.80, mild 0.70–0.79, moderate 0.40–0.69, severe 0.20–0.39, profound < 0.20) is widely accepted for the lateral canals. Where relevant, also report saccade characteristics: presence and dominance (overt vs covert), peak velocity, latency.

Asymmetry is worth calculating explicitly. Side-to-side asymmetry > 8% in lateral canals is suspicious even when each side is individually within range. The asymmetry calculation: |right − left| / (right + left) × 100%.

3. Clinical interpretation

The interpretation is where the report becomes a diagnostic tool. Useful phrasing patterns:

"The pattern of reduced gain in the right lateral and right anterior canals with preserved right posterior canal is consistent with right superior vestibular neuritis or any pathology affecting the superior division of the vestibular nerve."
"Bilateral symmetric reduction of all six canals with overt saccades, in the clinical context of aminoglycoside exposure, is consistent with vestibulotoxic bilateral vestibulopathy. Bárány criteria for bilateral vestibulopathy are met."
"Normal vHIT across all six canals. This finding does not exclude episodic vestibular conditions such as BPPV or vestibular migraine, which characteristically have normal interictal high-frequency VOR."

The phrase "consistent with" is doing important work in these examples. vHIT identifies patterns consistent with various pathologies; it does not diagnose pathologies in isolation. Confident diagnostic phrasing should be reserved for situations where the test result combined with strong clinical context leaves no realistic alternative.

Pitfalls to call out in the report

When a report contains findings that could be artefact, say so explicitly. Examples:

Asymmetric gains with one side showing values > 1.1 are likely goggle slippage; recommend repeat.
Bilaterally low gains without saccades, particularly with low peak head velocities, may reflect poor technique rather than bilateral pathology.
Unilateral abnormal vertical canal gain in isolation, without a clear superior- or inferior-nerve pattern, may reflect plane-misalignment artefact rather than disease.

Integrating vHIT with other tests

Few clinical questions are answered by vHIT alone. The integration patterns to know:

vHIT + calorics: dissociation (vHIT preserved, calorics reduced) is highly specific for Meniere disease.
vHIT + VEMPs: superior vestibular neuritis affects vHIT in the lateral/anterior canals and ocular VEMP (utricular function); inferior neuritis affects posterior canal vHIT and cervical VEMP (saccular function).
vHIT + audiometry: unilateral hearing loss with abnormal vHIT shifts the diagnosis from neuritis toward labyrinthitis, schwannoma, or AICA stroke depending on tempo and context.
vHIT + rotational chair: the chair test probes mid-frequency function (typically 0.01–1 Hz) and is useful when vHIT and calorics disagree.

A vestibular workup is usually most informative when at least two of these are obtained. vHIT alone is a perfectly reasonable single test for clearly peripheral acute presentations (vestibular neuritis); for chronic or complex cases, combine.

When the picture doesn't fit any archetype

Real patients sometimes produce vHIT findings that don't match any disease pattern. The decision tree:

If technical adequacy is borderline, repeat the test. Most apparent "unusual" patterns turn out to be artefact.
If the test is technically clean, ask whether the patient might have two superimposed pathologies. Vestibular neuritis plus subsequent BPPV is common; a known schwannoma patient who develops a new BPPV will look strange.
Consider central pathology. Wrong-way saccades, dysmetric saccades, and inappropriate saccade timing all point toward central involvement^{[Chen L 2014]}.
Consider rare conditions: superior canal dehiscence, perilymph fistula, vestibular paroxysmia. These are uncommon enough that pattern recognition alone won't catch them; the history matters.

The art of saying "the test is normal but"

A normal vHIT in a symptomatic patient is not the end of the workup — it is information. Useful report phrasing:

"Normal vHIT. In the context of episodic positional vertigo, this finding supports BPPV; suggest positional manoeuvres to confirm."
"Normal vHIT. In the clinical context provided, vestibular migraine and Meniere disease remain in the differential. Consider audiometry and calorics."
"Normal vHIT despite ongoing symptoms. The high-frequency VOR is intact; consider low-frequency canal function (calorics) and otolith function (VEMPs) before excluding peripheral disease."

Key teaching points

Structure every report as: technical adequacy → numerical findings → clinical interpretation.
Use "consistent with" rather than diagnostic certainty unless the picture is unambiguous.
Always state asymmetry; side-to-side > 8% in lateral canals is suspicious.
A normal vHIT does not exclude episodic vestibular disease; explain this when reporting normals in symptomatic patients.
Integrate with calorics, VEMPs, and audiometry — vHIT alone rarely settles complex cases.

Interpretation and reporting