Acoustic tumour volume and the prediction of facial nerve functional outcome from intraoperative monitoring

Abstract

The long-term facial function in 26 patients undergoing surgery to remove an acoustic neuroma has been related to the tumour volume (ml) estimated by computerized tomogram (CT) reconstruction techniques. Analysis of data allowed accurate categorization into ‘small’ (= < 5 ml) and ‘large’ (< 5 ml) tumours, which gave the maximum prognostic distinction between two groups for facial recovery. Thus, of the 14 patients with small volume tumours, 11 achieved a good (House grade I or II) facial outcome compared with 1 out of 12 patients with large tumours. Combined with the information derived from the assessment of intraoperative facial nerve electrical integrity using a combined nerve stimulator and EMG monitor, long-term facial function was predictable for all small tumours denned by volume. This represented a 15% improvement in prediction of facial recovery when denning tumour size by maximum linear dimension (small = < 2.5 cm, large < 2.5 cm). The calculations of volume obtained using a simplified ellipsoidal model compared well with CT reconstructed values (r² = 0.85), and gave identical prediction and outcome comparisons.

Key Words:

• Acoustic neuroma
• facial nerve monitoring
• tumour volume
• facial recovery