Bilaterally Abnormal Head Impulse Tests Indicate a Large Cerebellopontine Angle Tumor

BACKGROUND AND PURPOSE: 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.

Abnormal Head Impulse Test in a Unilateral Cerebellar Lesion

BACKGROUND: The findings of head impulse tests (HIT) are usually normal in cerebellar lesions. CASE REPORT: A 46-year-old male presented with progressive dizziness and imbalance of 3 weeks duration. The patient exhibited catch-up saccades during bedside horizontal HIT to either side, which was more evident during the rightward HIT. However, results of bithermal caloric tests and rotatory chair test were normal. MRI revealed a lesion in the inferior cerebellum near the flocculus. CONCLUSIONS: This case provides additional evidence that damage to the flocculus or its connections may impair the vestibulo-ocular reflex only during high-speed stimuli, especially when the stimuli are applied to the contralesional side. By observing accompanying cerebellar signs, the abnormal HIT findings caused by a cerebellar disorder can be distinguished from those produced by peripheral vestibular disorders.

Isolated Flocculus Infarction Mimicking Acute Labyrinthitis

Acute vestibular syndrome characterized by vertigo, spontaneous nystagmus, and postural instability is caused by a unilateral injury to either peripheral or central vestibular structures. However, central vestibular syndromes, such as labyrinthine ischemia due to occlusion of anterior inferior cerebellar artery (AICA), may cause abrupt unilateral labyrinthine dysfunction that mimics peripheral vestibulopathy. Here we report an AICA infarction with isolated flocculus lesion on magnetic resonance imaging mimicking acute labyrinthitis with vertigo, unidirectional horizontal-torsional nystagmus, ipsilesional sensorineural hearing impairment, and positive head-thrust test without any typical findings of floccular lesion.

Unilateral vertebral artery hypoplasia masquerading as benign paroxysmal positional vertigo: A case report.

Unilateral vertebral artery hypoplasia has been reported as possibly contributing to acute ischemia stroke or migraine with aura and could be related to episodic positional vertigo. An 88-year-old man presented with episodic vertigo whenever he rotated his head 90° to the right. He had experienced this for the last two years. Benign paroxysmal positional vertigo was initially suspected, but Epley’s canalith repositioning procedures failed to cure the symptom. The symptom was finally confirmed as related to right vertebral artery hypoplasia (VAH) after he had received a battery of studies, including an electronystagmogram, a color-coded duplex sonogram, and a magnetic resonance imaging/ angiogram. Thus, conservative treatment and life-style change were recommended and led to a decrease in recurrence. Herein we report this case and the oto-neurological significance of vertebral artery hypoplasia. In conclusion, one-sided head rotation related to episodic vertigo might be attributable to VAH.

The Change in the Expression of Gamma-Amino Butyric Acid A Receptor Subunits in Rat's Flocculus / 听力学及言语疾病杂志

Objective To observe the expression of gamma-amino butyric acid A receptor(GABAA receptor)?3、?1、? subunits in rat flocculus following unilateral labyrinthectomy(UL).Methods 24 wistar rats were randomly divided into two groups.18 animals received unilateral labyrinthectomy while the others maintained labyrinthine well.After removing left labyrinthine,the change of GABAA receptor ?3、?1、? subunits was detected by immunohistochemistry.Results GABAA receptor ?1、? subunits in flocculus was induced on the operated side after unilateral labyrinthectomy.The most expression was on the 1st day flocculus of following UL.The expression is descending from the 3rd day to 7th day flocculus of following UL.The GABAA receptor ?3 subunit immunostaining in flocculus was weak and did not change in the process of vestibular compensation.Conclusion GABAA receptor ?1、? subunits were induced increase in the flocculus after unilateral labyrinthectomy.The alteration in the resting discharge of the central vestibular neurons may be caused by the increase of GABAA receptor ?1、? subunits in the flocculus.But the significance of the change of GABAA receptor ?1、? subunits in the vestibular compensation is still unknown.Our study suggests that GABAA receptor ?3 subunits may not participate in constructing GABAA receptor in the flocculus.