Three-dimensional volumetrics for tracking vestibular schwannoma growth in neurofibromatosis type II.

OBJECTIVE: Vestibular schwannomas (VS) are common, benign, VIIIth cranial nerve tumors. Treatment in patients with the genetic disorder neurofibromatosis type II (NF2) is complicated by their development of bilateral VS and risk of complete deafness. Intervention decisions consider several clinical factors including tumor size and growth rate evaluated using magnetic resonance imaging. The current study evaluated the relative sensitivity of volumetric versus linear diameter measurement for assessing VS growth rate and progression.

METHODS: Retrospective analysis was performed on 43 magnetic resonance imaging scans acquired longitudinally (range, 2-7 yr) from 10 patients with NF2. Fifteen VS were measured (five patients had unilateral lesions meeting inclusion criteria) using both maximum linear diameter and semiautomated volumetric analysis. Progression was defined according to Response Evaluation Criteria in Solid Tumors and its volumetric (cubed linear) equivalent. Measurement techniques were compared by assessing sensitivity to lesion growth.

RESULTS: Volumetric measures were significantly more sensitive to VS growth, both for total change and change per year percentages; cubed linear growth measures (proportional to volume growth) underestimated volume growth by 50%. Seven lesions showed progression on volumetric analysis, but two of these did not show progression based on linear measures. Thus, for 29% of lesions showing progression based on volume, linear measures did not detect progression.

CONCLUSION: Linear measurements underestimate VS growth rate compared with volumetric measures in NF2 patients. These results provide clear, quantitative proof that diameter measures are not as sensitive to change as volumetric measurements and that volumetric measurements should be strongly considered when making VS treatment decisions.