[Origin of spinal subdural hematomas: a postmortem anatomical study].

OBJECTIVE: Although the mechanism by which cranial subdural hematomas form is known, the formation of spinal subdural hematomas is less clearly defined. The aim of this study was to identify vessels that can be found in the dural sac and whose rupture might lead to the formation of spinal subdural hematomas. MATERIAL AND METHOD: The dura mater, subdural space, and the arachnoid mater were studied in samples of dural sac taken from the eleventh thoracic vertebra to the fifth lumbar vertebra. The samples were taken from 3 fresh cadavers. Some were fixed in glutaraldehyde, dehydrated, and metallized with gold for scanning electron microscopy. Others were fixed in glutaraldehyde, treated with osmium tetroxide, and embedded in an epoxy resin for observation under a transmission electron microscope. RESULTS: Small hematomas--some on the internal surface of the dura mater and others surrounding nerve roots--were found within a thin, translucent arachnoid mater. Vessels measuring up to 100 microm were found within the dura mater, between its inner and outer laminae. Venules and capillaries were observed in the subdural space and in the arachnoid mater. CONCLUSIONS: Vessels are present between the laminae of the dura mater, in the subdural space, the arachnoid mater, and in spinal nerve roots. The rupture of these vessels could account for the formation of spinal subdural hematomas.