A Rare Case of External Brain Tamponade after Craniectomy: Clinical Challenges and Management

External brain tamponade is an uncommon but serious postoperative complication of decompressive craniectomy, characterized by the accumulation of subgaleal cerebrospinal fluid causing mass effect on the brain. We report the case of a 45-year-old woman with previously resected right frontotemporal glioblastoma who underwent repeat craniectomy for tumor recurrence. Twenty-five days later, she developed sudden swelling at the operative site along with acute neurological deterioration. Computed tomography revealed a large subgaleal fluid collection compressing the underlying brain parenchyma, consistent with external brain tamponade. The patient underwent urgent drainage of the collection along with ventriculoperitoneal shunt placement, resulting in rapid clinical and radiological improvement. This case underscores the importance of recognizing delayed postoperative complications after craniectomy and highlights the need for prompt imaging and intervention to prevent irreversible neurological damage.