Natural Progression and Factors Predicting Growth of Retroperitoneal Schwannoma

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Background: Although knowledge of the natural history of retroperitoneal schwannoma, including growth rate, would be useful when determining the indications and timing of surgical treatment for such nonpalpable tumors, the existing evidence is unclear. We examined the natural history of retroperitoneal schwannoma and assessed whether magnetic resonance imaging (MRI) and clinical findings predict future growth. Methods: Among patients with retroperitoneal schwannoma treated in our department during the period from January 1, 2015 through December 31, 2015, eight who underwent follow-up assessment by MRI and did not undergo tumor resection for longer than 1 year were enrolled. Changes in lesion size were examined in relation to selected clinical and MRI findings. In cases of pressure erosion in the vertebral body, change in the size of the intraosseous region was compared to change in the size of the whole lesion. Results: Median absolute growth rate (AGR) was 1.9 cm³ per year, median relative growth rate (RGR) was 5.6% per year, and median tumor volume doubling time (VDT) was 3.1 years. AGR, RGR, and VDT were not associated with any clinical variable. RGR and VDT values in the intraosseous region were about twice those of the whole lesions. Conclusions: The growth rates of retroperitoneal schwannomas varied. Additionally, no MRI or clinical findings predicted growth of retroperitoneal schwannoma. Therefore, careful follow-up is necessary for this tumor type, especially for lesions with bone erosion.