The relationship between caloric response, oculomotor dysfunction and size of cerebello-pontine angle tumours

Seventy-nine consecutive patients, 70 patients with acoustic neurinomas (ACN) and 9 patients with cerebello-pontine angle tumours of other etiology (o-CPA) were analysed with respect to tumour size and the result of the caloric and oculomotor tests. The size of the tumour was judged by the largest diameter calculated from the computerized tomography. A highly significant linear relationship between tumour size and caloric side difference was found for the group of ACN patients who had normal oculomotor function. A unilateral loss of caloric response on the tumour side was found in 75% of the ACN patients with tumours larger than 20 mm, but not in any of the ACN patients with tumours smaller than 10 mm. Oculomotor dysfunction (OMD), defined as disturbed pursuit eye movements and/or gaze nystagmus was frequently found in the patients with ACN larger than 20 mm (77%), and was present in all but one of the o-CPA patients. However, the caloric response on the tumour side was significantly more impaired in the group of ACN patients with OMD than in the o-CPA group. A combined view of the oculomotor and caloric test results offers a possibility to obtain a rough estimate of tumour size as well as to distinguish ACNs from other types of tumours in the cerebello-pontine angle.