Skull base osteosarcoma presenting with cerebrospinal fluid leakage after CyberKnife® treatment: a case report

INTRODUCTION CyberKnife® radiation is an effective treatment for unresectable skull base tumors because it can deliver a highly conformational dose distribution to the complex shapes of tumor extensions. There have been few reports of severe complications with this treatment. This is the first published case report to our knowledge of cerebrospinal fluid leakage induced by CyberKnife® radiotherapy. CASE PRESENTATION A skull base tumor was identified on magnetic resonance imaging in a 78-year-old Asian woman with a headache in her forehead. An endoscopic transnasal tumor resection was performed; however, the tumor, invading into the cavernous sinuses and optic canal, was not completely removed. During the subtotal resection of the tumor, no cerebrospinal fluid leakage was observed. Osteosarcoma was histologically diagnosed, and CyberKnife® radiation was performed to the residual tumor considering the aggressive feature of the tumor with a molecular immunology Borstel-1 index of 15%. Five months after the treatment, magnetic resonance imaging showed definite tumor shrinkage, and the patient had been living her daily life without any troubles. After another month, the patient was transferred to our clinic because of coma with high fever, and computed tomography demonstrated severe pneumocephalus. Rhinorrhea was definitely identified on admission; therefore, emergency repair of the cerebrospinal fluid leakage was performed using an endoscope. Dural defects at the bottom of the sella turcica were identified under careful endoscopic observation and fat tissue was patched to the dural defects. Follow-up computed tomography proved complete disappearance of air from the cisterns 2 weeks after the surgery, and the patient was discharged from our hospital without any neurological deficits. CONCLUSION CyberKnife® radiation is one of the effective treatments for skull base tumors; however, the risk of cerebrospinal fluid leakage should be considered when tumor invasion to the dura mater is suspected. Emergency surgical treatment is required when cerebrospinal fluid leakage is induced by the radiotherapy because the leakage is not expected to be healed by palliative treatments.