Encysted Subdural Hematoma
Although hematomas of the “dura mater” were described by Virchow in 1857, the relative frequency of this lesion has been fully realized only during the past ten years. The lesion consists of an encysted collection of old blood attached to the inner surface of the dura over the convexity of one or both cerebral hemispheres. In this communication, I shall consider only the encysted form of hematoma and shall not include traumatic subdural effusion (fluid hematoma of Munro1) or the acute subdural hematoma which produces immediate symptoms and is generally accompanied by a laceration of the brain. The latter two lesions are so different in their morphological and clinical aspects as to deserve separate consideration.
The accident responsible for the encysted subdural hematoma is a minor one, as a rule, and the force of the blow usually is exerted in an anteroposterior direction. The resulting dislocation of the brain within the cranial cavity stretches and tears one or more of the short cerebral veins communicating with the immobile sagittal sinus. There occurs at once a large extravasation of blood over the convexity of the hemisphere in the subdural space. The bleeding ceases when the intracranial pressure reaches a level at which no more blood can leave the torn vein. This degree of intracranial pressure is not incompatible with life and the immediate symptoms may be mild and transient.
The subsequent behavior of the subdural clot is unique. The usual regressive changes and absorption do not occur with a clot in. . .