Cerebellopontine Angle Tumors: Bilateral Flocculus Compression as Cause of Associated Oculomotor Abnormalities

Abstract

Oculomotor abnormalities of pursuit, OKN, gaze as well as saccade are frequently found in patients with large cerebellopontine angle tumors. Evidence is presented in support of the proposition that bilateral flocculus compression is likely responsible for the majority of oculomotor abnormalities noted in these patients. An hypothesis for the genesis of Bruns' as well as bilateral gaze paretic nystagmus is put forward. Successful tumor removal implies that pursuit and optokinetic nystagmus are more sensitive than the other oculomotor functions to the compressive effects of a cerebellopontine angle mass.

Bruns' Nystagmus in Patients With Vestibular Schwannoma

“…The authors were not blinded to tumor size when making their assessment of nystagmus. A number of articles have concurred with the findings of this study that the percentage of patients with nystagmus increases with increasing tumor size (3,4,7,8,10,11).…”

“…Based on the existing literature, the prevalence of nystagmus in patients with VS varies from 41 to 50% (3,4,7,8,11), which is similar to this series. These figures may be an overestimate because smaller tumors, which are less likely to be associated with nystagmus, may not have come to surgery, especially with the recent increase in popularity of watch wait and rescan management.…”

“…Most commonly, there is a fine horizontal peripheral vestibular nystagmus on contralateral gaze. However, in some patients, particularly those with large tumors, there may be, in addition, a coarse, jerking gaze, paretic nystagmus on ipsilateral gaze (1,2,4,6,8). This is called Bruns' nystagmus.…”

Small vestibular schwannomas can cause gait instability

“…Since VS mostly originates from the vestibular nerve (inferior or superior vestibular nerve), it may cause deficits of vestibular function [4,9]. Previous reports have already demonstrated post labyrinth disorders caused by VS on audiological examination, such as abnormalities in auditory brainstem responses.…”

“…Vestibulospinal abnormalities such as gait instability may be observed in VS, but mostly in cases with large tumors [2,3]. Since VS usually grows slowly, compensation by central vestibular mechanisms will occur at the same time [4]. When the VS becomes large, combined with compression and compensation, it is difficult to determine how much of a vestibulospinal abnormality is caused by the VS itself.…”