Abstract
It is well known that chronic subdural hematoma (CSDH) occasionally arises in patients harboring an arachnoid cyst (AC) located in the middle fossa. Although the pathogenesis of CSDH associated with ACs remains unknown, several possible mechanisms have been proposed. In many reported cases, the patients with ACs in the middle fossa would be symptomatic according to development of CSDH. A 9-year-old girl presenting with a headache, nausea, and diplopia was referred to our department. Magnetic resonance imaging showed an AC in the left-side middle fossa and ipsilateral CSDH with a remarkable mass effect. Irrigation of the CSDH, partial removal of the outer membrane of the AC and CSDH, and endoscopic cystocisternostomy were performed to relieve her symptoms. Postoperative clinical course was excellent. Histopathological examination of the outer membrane of the CSDH demonstrated an arachnoid cell layer and hemorrhage from the granulation inside the membrane, and collagen fibers outside the membrane. These findings strongly suggested that the membrane and the content of the CSDH were derived from the outer membrane of the AC, and the CSF including the hemorrhage within the membrane, respectively. Laceration and hemorrhage from granulation tissue within the outer membrane of the AC are considered as one of the developmental mechanisms of the CSDH associated with AC in the middle fossa.
Highlights
Arachnoid cysts (ACs) located in the middle fossa infrequently present with chronic subdural hematoma (CSDH) [1]-[7]
Since Davidhoff and Dyke first reported the co-existence of arachnoid cysts and chronic subdural hematomas [15], it has been well known that the ACs located in the middle fossa occasionally associated with the development of CSDH [1]-[8]
Injury of the bridging veins or vessels running in the AC wall due to the easy transfer of pressure through the cyst facilitates the influx of the blood into the subdural space [3] [7] [12]
Summary
Arachnoid cysts (ACs) located in the middle fossa infrequently present with chronic subdural hematoma (CSDH) [1]-[7]. Most of the patients with ACs located in the middle fossa are asymptomatic, CSDH can render these patients to become symptomatic [9] [10]. Laceration of the cyst wall leads to the formation of granulation and the subsequent hemorrhage of the cyst wall [13] [14]. These possible theories of CSDH associated with AC pathogenesis have undergone long speculation, but none have been demonstrated on pathological examination. The mechanism of CSDH development in our case is discussed
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