Bilaterally Abnormal Head Impulse Tests Indicate a Large Cerebellopontine Angle Tumor

Abstract

Background and PurposeTumors involving the cerebellopontine angle (CPA) pose a diagnostic challenge due to their diverse manifestations. Head impulse tests (HITs) have been used to evaluate vestibular function, but few studies have explored the head impulse gain of the vestibulo-ocular reflex (VOR) in patients with a vestibular schwannoma. This study tested whether the head impulse gain of the VOR is an indicator of the size of a unilateral CPA tumor.MethodsTwenty-eight patients (21 women; age=64±12 years, mean±SD) with a unilateral CPA tumor underwent a recording of the HITs using a magnetic search coil technique. Patients were classified into non-compressing (T1-T3) and compressing (T4) groups according to the Hannover classification.ResultsMost (23/28, 82%) of the patients showed abnormal HITs for the semicircular canals on the lesion side. The bilateral abnormality in HITs was more common in the compressing group than the non-compressing group (80% vs. 8%, Pearson's chi-square test: p<0.001). The tumor size was inversely correlated with the head impulse gain of the VOR in either direction.ConclusionsBilaterally abnormal HITs indicate that a patient has a large unilateral CPA tumor. The abnormal HITs in the contralesional direction may be explained either by adaptation or by compression and resultant dysfunction of the cerebellar and brainstem structures. The serial evaluation of HITs may provide information on tumor growth, and thereby reduce the number of costly brain scans required when following up patients with CPA tumors.

Dissociated Results between Caloric and Video Head Impulse Tests in Dizziness: Prevalence, Pattern, Lesion Location, and Etiology

“…14 We defined the cutoff value for a caloric abnormality as more than 25% of caloric paresis according to Jongkee's formula, or less than 20°/s of the sum of four absolute slow-eye velocities obtained from both ears with bithermal irrigation. 14,15 An abnormal horizontal vHIT was defined as a gain less than 0.8 or more than 1.2 with corrective catch-up or back-up saccades. The vHIT gain was calculated as the ratio of the eye velocity relative to the head velocity during a 40-ms window centered at the peak head acceleration.…”

“…The vHIT gain was calculated as the ratio of the eye velocity relative to the head velocity during a 40-ms window centered at the peak head acceleration. 14 In addition to the absolute vHIT gain, we also calculated the asymmetry index (AI) for the vHIT gain following a previously described method. 8 Other evaluations for audiovestibular functions included pure-tone audiometry, cervical and ocular vestibular-evoked myogenic potentials, subjective visual vertical, and the rotational chair test were performed on a selective basis.…”

Comparison of caloric and head‐impulse tests during the attacks of Meniere's disease

“…15 Abnormal VOR gain was defined when the values were outside the mean 6 2 SDs obtained from the age-, sex-matched normal controls (< 0.70 or > 0.99 for the horizontal canals [HCs], < 0.70 or > 1.03 for the anterior canals [ACs], and < 0.74 or > 1.00 for the posterior canals [PCs]). 15…”

Bilateral Vestibular Dysfunction

“…4). 66 In this instance, the ipsilesional caloric paresis and positive HITs to the lesion side are explained by the involvement of the vestibular nerve, whereas positive HITs to the contralesional side along with GEN is ascribed to floccular compression. 40 Metastasis to bilateral vestibular nerves is a rare cause of rapidly progressive BVD.…”