A longitudinal study to assess the volumetric growth rate of spinal intradural extramedullary tumour diagnosed with schwannoma by magnetic resonance imaging.

PURPOSE: Spinal intradural extramedullary (IDEM) schwannoma diagnosed by magnetic resonance (MR) imaging is sometimes detected incidentally. Because the natural history of spinal IDEM schwannoma has not been established well, questions remain regarding whether small and asymptomatic tumour has to be removed. We aimed to assess the natural history of spinal schwannoma diagnosed by MR imaging using an accurate and reliable method.
METHODS: All patients who were diagnosed with spinal IDEM schwannoma by MR imaging and did not undergo surgical resection immediately were recruited. A number of 56 tumours were enrolled finally. Tumour volume was measured using the volume quantification method from the baseline through the final follow-up. Receiver operating characteristics plots were used to define cut-off value of discrimination.
RESULTS: The probable schwannoma grew 5.45% [median value of volumetric growth rate (VGR); interquartile range 0.14-14.19] annually with a mean surveillance interval of 43.6 months. Of the 56 tumours, some tumours kept growing rapidly and the others did not. The median annual VGR of the growing and stable probable schwannomas was 13.02 and -0.09%, respectively (P<0.001). They can be roughly divided by 2.5% of the annual VGR and usually maintained each growth pattern and the cross-over rate to growth pattern was 15.6%.
CONCLUSIONS: Spinal probable IDEM schwannoma grew 5.45% of the tumour volume annually and can be divided into growing and stable tumours. The tumour that grows≥2.5% of volume per year needs a careful inspection because it may be not benign schwannoma and keep growing continuously.