What is meant by subdural collection left temporoparietal region with mass effect. acute on chronic sdh?

Shifting: Subdural hematomas (sdh) are typically slow bleeds between the layers which cover the brain and spinal cord ("meninges"). As the blood collects, it pushes on the other structures (brain tissue, ventricles, etc.) causing the so-called "mass effect." a bleed which has been ongoing is termed chronic, but a recent event (injury, fall, etc.) can exacerbate the ongoing bleed ("acute-on-chronic").

Blood on the brain: This describes a collection of blood between the dura, the outer membrane covering the brain and the brain itself. There is enough blood to push on the brain itself (mass effect).Acute is fresh blood. Chronic is older blood that has different consistency and looks different on mri. Usual cause is head injury.

Hemorrage : The subdural collection has mixed densities, thus suggesting that it may be older with blood clot that is liquifying mixed with newer blood . These are usually the result of a traumatic brain injury. The acute on chronic refers to the differences in age of clot. The fact that there is mass effect suggests that this has reached sufficient size to "compress" the brain. Surgery is the treatment.

SDH: It means blood over the brain some of which is old and some is new, causing pressure over the brain leading to brain injury.