Vestibular Schwannoma Measurements-Is Volumetric Analysis Clinically Necessary?

Objective: 1) To compare vestibular schwannoma maximum linear dimensions and calculated volume with measured volume in accurately determining tumor volume and growth. 2) To determine natural growth history of vestibular schwannomas utilizing volumetric measurements in an observed patient population.

Study Design: Retrospective chart review.

Setting: Tertiary academic referral.

Patients: One hundred fifty two adults with a vestibular schwannoma who underwent observational management with sequential magnetic resonance imaging (MRI) scans (496 scans).

Intervention: MRI scans.

Main Outcome Measures: Tumor volume calculated from linear dimensions compared with measured volume. The percentage change in tumor size (linear or volume) between consecutive MRI scans.

Results: The percentage change in tumor size between consecutive MRIs is significantly different between maximum linear dimension (MLD) and measured tumor volume (p = 0.03), but no difference exists in the percentage change between measured and calculated tumor volume (p = 0.882 for three linear measurements, p = 0.637 for two linear measurements). The overall number of growing tumors is 57.2% (n = 87) with an average growth rate of 62.6%. If a criterion for growth of 20% change is used, 32.2% of tumors monitored by linear volume would have demonstrated growth while 57.2% of tumors with measured volume demonstrated growth.

Conclusion: Maximum linear dimensions are a significantly less sensitive measure of tumor growth compared with measured volumes. Calculated tumor volume utilizing three linear measurements is an accurate predictor of both measured tumor volume and tumor growth.