Imaging Characteristics of Paragangliomas and Schwannomas

Continuous variables are expressed as the means ± SD and were analysed by independent t-tests for normally distributed data or Mann-Whitney tests for non-normally distributed data. For the qualitative variables, the Chi square test was used to compare the sample proportions of the two groups. Generalized estimating equations based on a binary logistic regression model were used to determine whether lesion type (retroperitoneal extra-adrenal paragangliomas or schwannomas) was associated with any of the individual binary factors. In this context, stepwise variable selection was performed to determine whether the combination of two or more of the aforementioned imaging features represented a significant independent predictor of schwannoma or paraganglioma. These tests were performed separately for each reader. Kappa coefficients were not used for this determination because the very high prevalence rates of certain imaging features for many of the binary factors was expected to produce misleadingly low values [8 (link), 10 ]. All reported p values are two-sided and considered statistically significant when less than 0.05. SPSS version 19.0 software (IBM Corporation, Armonk, NY, USA) was used for all computations.