Delayed Imaging Response After Chemoradiotherapy in a Patient with Unresectable Brainstem Pilocytic Astrocytoma

Adult brainstem gliomas (BSGs) are rare malignant tumors of the central nervous system (CNS) that are difficult to resect completely via surgery, so chemoradiotherapy (CRT) is the primary treatment modality. However, there is substantial interpatient variability in therapeutic response to CRT among patients with BSGs. Here we present a case of a 41-year-old man who had experienced right limb weakness for 3 months. Brain MRI showed a solid-cystic mass in the brainstem, involving the medulla oblongata and the cervical spinal cord. The pathological diagnosis was pilocytic astrocytoma, CNS WHO Grade 1. Since the solid-cystic mass in the brainstem was unresectable, the patient received concurrent CRT followed by temozolomide (TMZ) maintenance chemotherapy. No significant change in tumor size was observed after concurrent CRT. Notably, 15 months after radiotherapy (19 months since the initial diagnosis), the tumor size decreased significantly. Up to the latest follow-up, the patient has maintained sustained partial remission.