Acute subdural hematomas (SDHs) are generally not difficult to detect on CT scans due to their typical crescentric shape and hyperdensity (65–90 HU) relative to the cerebral cortex (Fig. 45.1). However, recognition of subdural hematoma that has similar attenuation value to the gray matter may be challenging at times. The diagnosis is based on the “thickened cortex sign,” where subdural hematoma overlies the cortex, as well as effacement of cortical sulci (Fig. 45.2). When the hematoma is relatively larger, secondary signs of mass effect may also be present such as inward buckling of the white matter, shift of midline structures, and compression of the lateral ventricles.
Isodense subdural hematomas are likely to be missed unless the index of suspicion is high. This is especially true if the collections are bilateral and symmetrical, or unilateral but very small and with no associated mass effect. A missed diagnosis may result in improper management and possible discharge from the hospital. In some cases, an initially missed subdural hematoma may come to attention later with its expansion, increased mass effect, and possibly secondary brain injury.