Three-dimensional segmented volumetric analysis of sporadic vestibular schwannomas: comparison of segmented and linear measurements.

OBJECTIVE: To compare 3-D segmented volumetric analysis of vestibular schwannomas (VS) with traditional linear tumor measurement on serial magnetic resonance imaging (MRI) studies to assess volume and growth rates. STUDY
DESIGN: Case series with retrospective chart review.
SETTING: Tertiary care medical center.
METHODS: This analysis identified 24 VS patients clinically followed with serial gadolinium enhanced images. Maximum linear dimensions (MLD) were obtained from gadolinium-contrasted T1 sequences from 3 serial MRI scans per RECIST guidelines. MLD was cubed (MLD(3)) and orthogonal analysis (OA) was carried out to provide volumetric estimates for comparison with segmented data. Segmented volumetric analysis (SVA) was performed with semi-automated 3-D conformal procedure. Tumor volume, percentage change in volume, and interval percentage change were compared using paired 2-tailed t tests.
RESULTS: The average interval between MRIs was 2.6 years. Volume estimates differed significantly between SVA and OA and MLD(3) at all intervals. Linear growth measurements averaged 0.5 mm/y (5.4%). Volumetric growth was 50 mm(3)/y (22.8%) with SVA, 110 mm(3)/y (19.6%) with OA, and 210 mm(3)/y (14.4%) with MLD(3) estimates. Differences between MLD and both MLD(3) and SVA were significant, but significance between MLD(3) and SVA was only identified in interval analysis. Progression was identified in 75% more patients with SVA than OA, MLD(3), or MLD.
CONCLUSIONS: VS assume complex configurations. Linear measurements inaccurately estimate tumor volume and growth compared with segmented analysis. SVA is a useful clinical tool that accurately assesses tumor volume. Use of outcomes such as tumor volume and percentage of volume change may be more sensitive in assessing tumor progression compared with linear measurements.