"Spinal subdural haematomas (SSDH) are much less common than epidural haematomas; however, progression of symptoms due to compression tends to be faster 1."
"Subdural haematomas occur within the dural sac; therefore, in contradistinction to epidural haematomas, the epidural fat is preserved and the dura is not displaced inward. The haematoma is bounded by the paired lateral denticulate ligaments and the dorsal septum, forming the inverted Mercedes-Benz sign on axial images 1. As such, it compresses the nerve roots but does not extend into the neural foramina or make direct contact with bone. Naturally, smaller collections will not expand the potential subdural space and will, therefore, not create the inverted Mercedes-Benz sign."