Radiation-induced osteosarcoma of the frontoparietal calvaria 6 years after oligodendroglioma treatment: illustrative case.

backgroundRadiation-induced sarcoma (RIS) is an exceptionally rare occurrence following radiation therapy, and manifestation usually occurs after a several-year latency period. Herein, the authors report the development of a radiation-induced osteosarcoma of the frontoparietal calvaria following treatment for an oligodendroglioma in an 84-year-old woman. OBSERVATIONS: The patient had been diagnosed with a grade III anaplastic oligodendroglioma when she was 78 years old. She had undergone resection and subsequent chemoradiation therapy for treatment of the tumor. In the following years, she experienced progressive neurological decline, which was complicated by multiple ischemic strokes and seizure episodes. When she was approximately 84 years of age, a small mass was noted overlying the previous craniotomy site during examination. Several months later, approximately 5 years after chemoradiation therapy, she presented to the emergency department with a suspected stroke. Examination revealed that the mass had rapidly grown and was pressing into the intracranial space. She underwent craniotomy, and specimens were taken. Pathological analysis demonstrated a high-grade osteosarcoma. LESSONS: Despite the lesion's rarity, suspicion for RIS should be raised with the rapid growth of a mass at the site of previous radiotherapy. Furthermore, it is especially important to carefully monitor vulnerable patients who may not be able to recognize or report the development of a growing mass. https://thejns.org/doi/10.3171/CASE24535.