[Acute subdural hematoma of arteriolar origin. Traumatic or spontaneous?].
Acute subdural hematomas are usually related to the rupture of a bridging vein with or without tearing of brain matter. In some instances the origin of the hemorrhage is due to the shearing of a cortical arteriole bleeding directly into the subdural space, generally after a minor head trauma. Ten cases were reviewed at Geneva's Neurosurgical clinic over a period of thirteen years (1973-1986). They represent less than 5% of all acute and subacute subdural hematomas treated during that period. Subdural hematomas of venous origin are usually encountered on previously normal brain whereas those of arteriolar origin are thought to result from the disruption of a small arteriolar knuckle adhering to the arachnoid and dura. While the majority of arteriolar hematomas reported here and in the literature are of traumatic origin, some are undoubtedly spontaneous. The clinical features of these hematomas are characterized by a high incidence of falsely localising motor signs, presumably due to the so called Kernohan's phenomenon. Their treatment requires a wide exposure, allowing identification and coagulation of the bleeding source located in most instances around the Sylvian fissure. Although a rare entity, the existence of arteriolar subdural hematomas must be emphasized, since any delay in their treatment may result in a dramatic outcome.