title: Bilaterally Abnormal Head Impulse Tests Indicate a Large Cerebellopontine Angle Tumor.
abstract: OBJECTIVE
  Tumors 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.
  
  
  METHODS
  Twenty-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.
  
  
  RESULTS
  Most (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.
  
  
  CONCLUSIONS
  Bilaterally 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.
authors.affiliation: Department of Biomedical Laboratory Science, Kyungdong University, Goseong, Korea.
authors.forename: Hyo Jung
authors.initials: HJ
authors.lastname: Kim
authors.affiliation: Department of Neurology, Seoul National University College of Medicine, Seoul National University Bundang Hospital, Seongnam, Korea.
authors.forename: Seong Ho
authors.initials: SH
authors.lastname: Park
authors.affiliation: Department of Neurology, Seoul National University College of Medicine, Seoul National University Bundang Hospital, Seongnam, Korea. jisookim@snu.ac.kr.
authors.forename: Ji Soo
authors.initials: JS
authors.lastname: Kim
authors.affiliation: Department of Otolaryngology, Seoul National University College of Medicine, Seoul National University Bundang Hospital, Seongnam, Korea.
authors.forename: Ja Won
authors.initials: JW
authors.lastname: Koo
authors.affiliation: Department of Neurosurgery, Seoul National University College of Medicine, Seoul National University Bundang Hospital, Seongnam, Korea.
authors.forename: Chae Yong
authors.initials: CY
authors.lastname: Kim
authors.affiliation: Department of Neurosurgery, Seoul National University College of Medicine, Seoul National University Bundang Hospital, Seongnam, Korea.
authors.forename: Young Hoon
authors.initials: YH
authors.lastname: Kim
authors.affiliation: Department of Neurosurgery, Seoul National University College of Medicine, Seoul National University Bundang Hospital, Seongnam, Korea.
authors.forename: Jung Ho
authors.initials: JH
authors.lastname: Han
keywords: cerebellopontine-angle tumor; flocculus; head impulse test; vertigo; vestibulo-ocular reflex