Subdural hygroma due to traumatic rupture of a middle cranial fossa arachnoid cyst that has transformed into a chronic subdural hematoma after burr hole operation: A case report.

Background: Middle cranial fossa arachnoid cysts (MFACs) cause subdural hygromas due to head trauma or spontaneous rupture. We report the case of a patient who has performed burr hole surgery for subdural hygroma and chronic subdural hematoma (CSDH) caused by the rupture of an arachnoid cyst. Case Description: A 30-year-old man fell off a motorbike and hit his head. Head computed tomography (CT) revealed left MFAC and left subdural hygroma. The subdural hygroma increased over time, and the symptoms of intracranial hypertension developed. Therefore, burr hole operation was performed without the use of a subdural drain. Approximately half a month after surgery, head CT revealed that the density of the arachnoid cyst and subdural hygroma increased and that the subdural hygroma transformed into CSDH. Therefore, a burr hole operation was performed again, and a hematoma cavity drain was left. After surgery, the symptoms of intracranial hypertension improved, and subdural collection did not recur. Conclusion: The increase in CSDH may have disrupted the flap-valve mechanism of the arachnoid cyst and subdural collection. When performing a burr hole operation for a subdural hygroma caused by the rupture of an arachnoid cyst, placement of a subdural drain may be desirable, and consideration of the possibility of CSDH is necessary.