LAUSR

Arachnoid cysts are a common incidental finding on magnetic resonance imaging (MRI) performed for other clinical reasons. They can be found in the brain or spine and are mostly of congenital origin due to splitting of the arachnoid membrane. The vast majority are asymptomatic, with signs and symptoms varying according to size and location. Intracystic hemorrhage is a rare complication. In symptomatic cases, treatment predominantly consists of endoscopic fenestration [4, 5, 7]. In recent years, the features of diffuse large cell B-cell lymphoma (DLBCL), referred to as fibrin-associated DLBCL, have been reported in cases of chronic blood effusions [1]. Fibrin-associated DLBL, which has a favorable clinical outcome, should be distinguished from chronic inflammation-associated DLBCL, which is an aggressive tumor. Fibrin-associated DLBCL has been described in cases throughout the body; however, only isolated intracranial cases have been described, which were found in the subdural space. Here we present the case of an elderly man with an unsuspected fibrin-associated DLBCL in an arachnoid cyst. We would like to draw attention to this entity, which has likely been underestimated in the routine evaluation of subdural hematoma (SDH) or subarachnoid cysts. An 81-year-old man presented with intermittent tremor and gait ataxia. The patient was diagnosed with classical parkinsonism and L-Dopa treatment was started. Later, the patient developed short-term memory disturbances and the gait ataxia progressed. Based on the MRI findings, a right frontotemporal arachnoid cyst with focal bleeding was suspected. Intraoperatively, the