What is the diagnosis?
This is a typical appearance of a subdural haemorrhage.
What types of patient present with subdural haemorrhages?
The typical patient group are the elderly, often with vague confusion or neurological signs. The cause for these bleeds is usually damage to the bridging veins between the brain and the dura and as the brain atrophies with age, these can get stretched. Minor head trauma can lead to impressive imaging changes. Other groups are those with abnormal coagulation and also those with significant alcohol disease for a number of reasons (accelerated atrophy, higher risk of head injury, altered coagulation pathways).
Can you tell from this CT if this is acute or chronic?
Yes - this is likely a chronic subdural. If this was an acute bleed, the collection is typically hyperdense or brighter than the adjacent brain tissue. In those with altered coagulation or active bleeding, you can sometimes see mixed densities as the blood is mixing. In cases like this, as the clot and proteins have broken down and resolved, what is left is closer in appearance to fluid and is hypodense on CT.
There is a cresentic, concave collection surrounding the left cerebral lobes. It is uniformly hypodense.
There is also evidence of mass effect with compression of the left lateral ventricle and a few millimeters of midline shift to the opposite side.
From other imaging, no evidence of bony injury.