Spontaneous arterial subdural hematoma.

the occurrence of spontaneous arterial subdural hematomas is very rare. We report five patients who presented with sudden severe headache and who developed progressive neurological deficits, two becoming comatose. None had a history of trauma. A diagnosis of subarachnoid hemorrhage was suspected in all patients, but all proved to have subdural hematomas caused by "spontaneous" rupture of a cortical artery. Nineteen similar cases have been reported in the English literature. The source of bleeding was identified as a cortical artery located near the sylvian region in four of our five patients and in most of the reported cases. There are several possible anatomical situations that may predispose a cortical artery to "spontaneous" rupture: (a) spontaneous rupture of a cortical artery at the point of origin of a fragile arterial twig, especially a right-angled branch, a point of potential weakness; (b) rupture of a small artery traversing the subdural space and connecting a cortical artery to the dura mater (a "bridging" artery); (c) adhesions between a cortical artery and arachnoid or dura mater; (d) a knuckle of cortical artery protruding through the arachnoid and adherent to the dura mater. In each situation, the artery is probably torn by a sudden movement of the brain during a vigorous head movement, not severe enough to be considered trauma.