Subdural haematomas are far more common than epidural haematomas and acute subdural haematomas are one of the leading causes of death and disability in patients with severe traumatic brain injury.
Subdural haematomas are due to an accumulation of blood between the dura and arachnoid. This is most often due to head injury resulting in a tear of the bridging cortical veins as they cross the subdural space to enter a dural venous sinus (usually the superior saggital sinus). Blood from the ruptured vessels could then spread quickly through the subdural space resulting in a classical crescent-shaped appearance. Subdural haematomas are usually more extensive than epidural haematomas, and easily spread along the falx, tentorium and around the anterior and middle fossa floors. In contrast to epidural haematomas, subdural haematomas may cross suture lines. Bilateral subdural haematomas may occur in 15% of cases.
Acute subdural haematoma
The non-contrast cranial CT shown here (Figure 1) is from an elderly patient with a recent fall and head injury resulting in an acute left-sided subdural haematoma . The haematoma is causing significant mass effect and the contents of the left cerebral hemisphere could be seen to be compressed resulting in a mid-line shift to the right cerebral hemisphere. An acute subdural haematoma is considered to be a neurosurgical emergency and requires urgent evacuation.
Bilateral subacute subdural haematoma
This non-contrast cranial CT scan (Figure 2) is from a patient with bilateral subacute subdural haematoma. The haematoma on the right side is isodense . On the left side, however, there is a mixture of densities – the upper part being relative isodense, whilst the lower part hypodense . Such a mixed pattern is not uncommon and is usually due to recurrent haemorrhage into a pre-existing subdural haematoma, hence resulting in a mixture of densities.