Is this subdural or extradural blood? It isn’t quite crescent shaped and it isn’t quite lens shaped. So how can you tell?
Well shape isn’t everything. This is subdural blood because it is crossing the lambdoid suture. Extradural hemorrhage is contained by the periosteum of the inner table of the skull and therefore does not cross cranial sutures. Handy little fact to remember.You can see the suture for yourself on the bone window CT image here: http://radiopaedia.org/cases/subdural-haemorrhage-3