TABLE 2.

Differentiating middle ear from third-window lesions

Lesion	Middle ear	Third-window lesion
Air-bone gap	0–60 dB, may involve all frequencies	0–60 dB, greatest at frequencies <2,000 Hz
Bone conduction thresholds	Rarely < 0 dB	May be negative (−5 to −20 dB or better) for frequencies <2,000 Hz
Acoustic reflex	Absent	Present
VEMP response	Absent	Present, thresholds lower than normal
OAEs	Absent	May be present
Umbo velocity on laser Doppler vibrometry	Variable: low normal-stapes fixation; abnormally low-malleus fixation; abnormally high-ossicular discontinuity	High normal
Sound- and/or pressure-induced vertigo	Absent	May be present
CT/MRI scan	May show middle ear abnormality	Inner ear lesion
Exploratory tympanotomy	Ossicular lesion, fixation or discontinuity	Normal ossicular mobility

CT indicates computed tomography; MRI, magnetic resonance imaging; OAE, otoacoustic emission; VEMP, vestibular evoked myogenic potential.