Natural history of peripheral nerve schwannomas.

Background: Little information about the natural history of peripheral nerve schwannomas exists in the literature. The aim of this study was to determine the natural history of those tumors both in sporadic and schwannomatosis cases to determine their growth rates and patterns.

Methods: In 44 patients from 3 surgical centers, hospital charts, follow-up records, and imaging studies were reviewed. Of these patients, 7 had sporadic schwannomatosis. Histological diagnosis was obtained in 37 patients (84%). Tumor growth rates were determined by calculating the absolute and relative growth rates.

Results: On the 47 tumors analyzed, the median tumor size at diagnosis was 1.8 cm, and the majority of tumors were located in the lower limb (62%). The absolute growth rate ranged from - 1.13 to 23.17 cm/year (mean, 1.69 cm/year). Relative annual growth rates ranged from - 9 to 166%/year (mean, 33.9%/year). There was no clear correlation between initial tumor size, age at diagnosis, and tumor growth rate. Six patients (13%) harbored "fast-growing" tumors (absolute growth rate > 2 cm/year and relative growth rate > 35%/year) while 19% of tumors demonstrate no growth or negative growth. In schwannomatosis patients, each tumor displayed a distinct growth pattern.

Conclusion: This study confirms the slow-growing nature of most, but not all, peripheral nerve schwannomas. Additional studies are mandatory to explore the environmental factors influencing growth in sporadic cases and the precise growth patterns in schwannomatosis cases to detect the rare cases of malignant transformation and pave the way to the evaluation of future clinical trials.