A unique case of Sylvian arachnoid cyst complicated by chronic subdural hematoma.

Background: Arachnoid cysts (ACs) complicated by chronic subdural hematoma (CSDH) are a rare but distinct entity. Case Description: A 27-year-old man previously diagnosed with Sylvian AC presented to the hospital with a persistent headache. He was not aware of any preceding head trauma. However, he frequently performed bench presses at the gymnasium, especially 4 weeks prior. The patient did not exhibit any neurological deficits at presentation. Computed tomography revealed slightly low-density areas in the right cerebral convexity. Magnetic resonance imaging revealed compressive masses in the right middle fossa and cerebral convexity. The patient underwent a craniotomy. Reflection of the dura mater exposed thickened arachnoid membrane. Making an incision resulted in the egress of fluid hematoma. The membrane separating the subdural hematoma and inner AC possessed fine vasculature and adjacent holes. Furthermore, there were fragile clots adhered to the inner wall of the cyst. Microscopic findings of the separating membrane were consistent with inflammatory granulation tissue, similar to those of the outer membrane of CSDH. Conclusion: Exertional hypertension associated with the bench press may result in the rupture of fine arteries distributed over the AC wall. Under certain circumstances, the AC wall may transform into the outer membrane of CSDH.