A subdural hygroma (SDG) is a collection of cerebrospinal fluid (CSF), without blood, located under the dural membrane of the brain. Most subdural hygromas are believed to be derived from chronic subdural hematomas. They are commonly seen in elderly people after minor trauma but can also be seen in children following infection or trauma. One of the common causes of subdural hygroma is a sudden decrease in pressure as a result of placing a ventricular shunt. This can lead to leakage of CSF into the subdural space especially in cases with moderate to severe brain atrophy. In these cases the symptoms such as mild fever, headache, drowsiness and confusion can be seen, which are relieved by draining this subdural fluid. Etiology and Pathophysiology
Subdural hygromas require two conditions in order to occur. First, there must be a separation in the layers of dura mater of the brain. Second, the resulting subdural space that occurs from the separation of layers must remain uncompressed in order for CSF to accumulate in the subdural space resulting in the hygroma. The arachnoid mater is torn and cerebrospinal fluid (CSF) from the subarachnoid space accumulates in the subdural space. Hygromas also push the subarachnoid vessels away from the inner table of the skull. Subdural hygroma can appear in the first day, but the mean time of appearance is 9 days on CT scan.
Immersion may refer to:

The arts
"Immersion", a 2012 story by Aliette de Bodard
Immersion, a French comic book series by Léo Quievreux
Immersion (album), the third album by Australian group Pendulum
Immersion (film), a 2021 Chilean thriller film
Immersion (series), a webseries which test the concepts of video games in real life, created by Rooster Teeth Productions
Immersion journalism, a style of journalism

Science and technology
Immersion lithography or immersion microscopy, optical techniques in which liquid is between the objective and image plane in order to raise numerical aperture
Immersion (mathematics), a smooth map whose differential is everywhere injective, related to the mathematical concept of an embedding
Immersion (virtual reality), the perception of being physically present in a non-physical world, created by using VR

Other uses
Immersion baptism, a type of baptism whereby the subject is immersed in water
Immersion Corporation, a haptic technology developer
Immersion heater, a kind of water heater
Immersion therapy, overcoming fears through confrontation
Language immersion, a method of teaching a second language in which the target language is used for instruction