Condition · Retrocochlear

Vestibular Schwannoma

Eighth-nerve tumour — elevated or absent reflexes with abnormal decay

A lesion on the afferent limb

The schwannoma compresses the eighth nerve — the afferent limb of the reflex arc. Reflexes elicited by stimulating the affected ear are elevated or absent, and the response that is present may show abnormally rapid decay during a sustained tone.

Reflex decay as the key sign

Reflex decay is tested at 500 and 1000 Hz only, because even normal ears show decay at higher frequencies. A drop to 50% or less of the initial amplitude within 10 seconds is a positive (abnormal) result.

The reflex signature

Stim. Right
Stim. Left
Probe Right
Elevated
110 dB HL
Present
90 dB HL
Probe Left
Absent
Present
95 dB HL
The characteristic four-cell grid for this condition.

Stimulating the affected (right) ear gives elevated or absent reflexes in both probe positions; stimulating the healthy ear gives normal reflexes — a horizontal 'stimulus-ear' pattern.

Reflex decay

0s2s4s6s8s10s0%50%100%50% criterion
Positive (abnormal) decay — amplitude reaches 50% at about 7.1 s. Pathological reflex decay — amplitude falls to 50% or less of its initial value within 10 s at 500 or 1000 Hz — is a classic retrocochlear sign.

Pure-tone audiogram

0204060801002505001k2k4k8kFrequency (Hz)Hearing level (dB HL)
○ Right ear✕ Left ear
Right ear: asymmetric high-frequency sensorineural loss. Asymmetry is the cardinal audiometric clue.

Frequencies plotted: 250, 500, 1k, 2k, 4k, 8k Hz.

References for this page

  1. Anderson H, Barr B, Wedenberg E (1970). Early diagnosis of eighth-nerve tumours by acoustic reflex tests. Acta Oto-Laryngologica, Suppl. 263, 232–237.
  2. Jerger S, Jerger J (1977). Diagnostic value of crossed versus uncrossed acoustic reflexes: Eighth nerve and brainstem disorders. Archives of Otolaryngology, 103(8), 445–453.
  3. Katz J (Ed.) (2015). Handbook of Clinical Audiology (7th ed.). Wolters Kluwer, Philadelphia.
  4. Hall JW (2014). Introduction to Audiology Today. Pearson, Boston.
Want to contrast this with another condition? The comparison tool places any two reflex signatures side by side.