Comparing Linear and Volumetric Tumor Measurements During Observation of Growing Sporadic Vestibular Schwannomas.

Objective: To assess the correlation between linear and volumetric changes in vestibular schwannomas (VS).

Study Design: Retrospective imaging review was performed on patients diagnosed with sporadic VS from 2000 to 2019 who demonstrated linear growth on observation with serial magnetic resonance imaging (MRI).

Setting: Two large tertiary care centers.

Methods: Changes in diameter on serial MRI scans, measured by 1995 American Academy of Otolaryngology-Head and Neck Surgery guidelines, were compared to changes in volume, calculated by segmentation.

Results: Ninety-two patients had VS confined to the internal auditory canal (IAC) with 236 MRIs analyzed, and 108 patients had VS involving the cerebellopontine angle (CPA) with 193 MRIs analyzed. The Spearman rank correlation coefficients between changes in diameter and volume for IAC and CPA tumors were 0.43 (p < .001) and 0.65 (p < .001), respectively. Linear diameter increases of 1 to <2 mm corresponded to a median volume change of 32% (interquartile range [IQR]: 6%-86%) for IAC tumors, compared to 23% (IQR: 13%-40%) for CPA tumors. Linear diameter increases of 2 to <3 mm (ie, the minimum linear diameter change classically considered "true growth") corresponded to a median volume change of 42% (IQR: 23%-100%) and 47% (IQR: 26%-69%) for IAC and CPA tumors, respectively.

Conclusion: Changes in linear diameter significantly correlated with changes in volume for IAC and CPA tumors, although diameter changes that did not meet the definition of linear growth (<2 mm) had corresponding median volume changes in excess of 20% for both IAC and CPA tumors.