Schwannoma with uncharacteristic rapid growth and high Ki-67 index: illustrative case.

backgroundSchwannomas typically show slow growth and a low risk of recurrence. The authors report a rare case of a 56-year-old woman with a spinal schwannoma that exhibited rapid recurrence and an atypically high Ki-67 index (8.9%), suggesting a more aggressive behavior than usually observed in benign schwannomas. OBSERVATIONS: The patient initially presented with worsening low back and right sciatic nerve pain, resulting in difficulty walking independently. MRI revealed a dumbbell-shaped tumor compressing the cauda equina. A partial resection was performed to preserve nerve function, and pathology showed typical schwannoma features but with a Ki-67 index of 8.9%. The tumor rapidly regrew within 2 months, necessitating a second surgery and additional radiotherapy. Although MRI at 11 months after radiotherapy showed a tendency for tumor growth, subsequent MRI scans at 20 months after radiotherapy demonstrated a reduction in tumor size, indicating effective tumor control by the radiotherapy. LESSONS: Among pathologically classified conventional schwannomas, those with a high Ki-67 index can have an atypical course that would not be considered benign. Adjuvant radiotherapy can be effective in controlling tumor growth in such atypical cases. Further research is recommended for managing such atypical cases. https://thejns.org/doi/10.3171/CASE24529.