Traumatic subdural hygroma: pathology and meningeal enhancement on magnetic resonance imaging.

Five patients with traumatic subdural hygroma are reported with reference to its pathology and meningeal enhancement on magnetic resonance imaging. Hygromas showed initially iso- and, later, high intensity on both T1- and T2-weighted images compared with the intensity of the cerebrospinal fluid. In all cases of the thick hygromas, magnetic resonance imaging with gadolinium diethylene-triamine-pentaacetic acid showed meningeal enhancement. Intravenously injected radioisotope immediately flowed into the hygromas, but computed tomographic cisternography and gross inspection during the surgery showed no evidence of an influx of cerebrospinal fluid into the hygromas. Microscopic examination of the enhanced meninges revealed vascularized neomembrane with numerous fenestrations and pinocytosis underneath the dura mater. It is suggested from these data that the subdural neomembrane is associated with the development of the traumatic subdural hygromas. Meningeal enhancement would be useful to clarify the growing mechanism of traumatic subdural hygromas.