Intracranial bleeding
Types of intracranial hemorrhage are roughly grouped into intra-axial and extra-axial. The hemorrhage is considered a focal brain injury; that is, it occurs in a localized spot rather than causing diffuse damage over a wider area. Intra-axial bleeding
Intra-axial hemorrhage is bleeding within the brain itself, or cerebral hemorrhage. This category includes intraparenchymal hemorrhage, or bleeding within the brain tissue, and intraventricular hemorrhage, bleeding within the brains ventricles (particularly of premature infants). Intra-axial hemorrhages are more dangerous and harder to treat than extra-axial bleeds. Extra-axial bleeding
Extra-axial hemorrhage, bleeding that occurs within the skull but outside of the brain tissue, falls into three subtypes:

Epidural hemorrhage (extradural hemorrhage)  which occur between the dura mater (the outermost meninx) and the skull, is caused by trauma. It may result from laceration of an artery, most commonly the middle meningeal artery. This is a very dangerous type of injury because the bleed is from a high-pressure system and deadly increases in intracranial pressure can result rapidly. However, it is the least common type of meningeal bleeding and is seen in 1% to 3% cases of head injury. Patients have a loss of consciousness (LOC), then a lucid interval, then sudden deterioration (vomiting, restlessness, LOC)
Head CT shows lenticular (convex) deformity. Subdural hemorrhage results from tearing of the bridging veins in the subdural space between the dura and arachnoid mater. Head CT shows crescent-shaped deformity
Subarachnoid hemorrhage, which occur between the arachnoid and pia meningeal layers, like intraparenchymal hemorrhage, can result either from trauma or from ruptures of aneurysms or arteriovenous malformations.
Blood is seen layering into the brain along sulci and fissures, or filling cisterns (most often the suprasellar cistern because of the presence of the vessels of the circle of Willis and their branch points within that space). The classic presentation of subarachnoid hemorrhage is the sudden onset of a severe headache (a thunderclap headache). This can be a very dangerous entity and requires emergent neurosurgical evaluation and sometimes urgent intervention. Cerebral contusion
Cerebral contusion is bruising of the brain tissue. The piamater is not breached in contusion in contrary to lacerations. The majority of contusions occur in the frontal and temporal lobes. Complications may include cerebral edema and transtentorial herniation. The goal of treatment should be to treat the increased intracranial pressure. The prognosis is guarded. Diffuse axonal injury
Diffuse axonal injury, or DAI, usually occurs as the result of an acceleration or deceleration motion, not necessarily an impact. Axons are stretched and damaged when parts of the brain of differing density slide over one another. Prognoses vary widely depending on the extent of the damage. Compound head injury
Overlying scalp laceration and soft tissue disruption in continuity with a skull fracture constitutes "compound head injury", and has higher rates of infection, unfavorable neurologic outcome, delayed seizures, mortality, and duration of hospital stay. Signs and symptoms
Three categories used for classifying the severity of brain injuries are mild, moderate or severe. Mild brain injuries
Symptoms of a mild brain injury include headaches, confusion, ringing ears, fatigue, changes in sleep patterns, mood or behavior.