Skull fracture
A skull fracture is a break in one or more of the bones in the skull caused by a head injury. Isolated skull fractures are not very serious injuries, but the presence of a skull fracture may indicate that significant enough impact occurred to cause brain trauma, which is quite serious.  Broken fragments of skull can lacerate or bruise the brain or damage blood vessels. If the fracture occurs over a major blood vessel, significant bleeding can occur within the skull, so head injury patients with skull fracture have many more intracranial hematomas (especially epidural hematomas) than those without fractures. Another complication of skull fractures is dissection of cerebral arteries, which can limit blood flow to the brain. However, the bone fracture helps dissipate energy from a blow, so less force is transmitted to the brain, so having a skull fracture is not a good predicter of intracranial injury.
A fracture in which the skin is also broken is called an open fracture or compound fracture. Penetrating head injuries are those that cause a fracture in the skull and breach the dura mater, the outermost membrane of the brain's meninges.
Fractures of the skull can be comminuted, depressed, linear or diastatic.

# Linear fracture
Linear skull fractures, the most common type of skull fracture, occur in 69% of patients with severe head injury. Usually caused by widely distributed forces, linear fractures often occur when the impact causes the area of the skull that was struck to bend inward, making the area around it buckle outward.
In rare cases, a linear fracture can develop and lengthen as the brain swells, in what is called a growing fracture. This can cause growth of cysts in the meninges. Diastatic fractures are linear fractures that cause the bones of the skull to separate at the skull sutures in young children whose skull bones have not yet fused. They are usually caused by impact with a wide area such as a wall.

# Comminuted fracture
Comminuted skull fractures, those in which a bone is shattered into many pieces, can result in bits of bone being driven into the brain, lacerating it. Depressed skull fractures, a very serious type of trauma occurring in 11% of severe head injuries, are comminuted fractures in which broken bones are displaced inward. This type of fracture carries a high risk of increasing pressure on the brain, crushing the delicate tissue. Complex depressed fractures are those in which the dura mater is torn. Depressed skull fractures may require surgery to lift the bones off of the brain if they are causing pressure on it.
One example of this type of fracture occurred on October 14, 2006 to goal keeper Petr Cech during an English football match. He was immediately escorted off the field and required emergency surgery.

# Basilar skull fracture
Basilar skull fractures, breaks in bones at the base of the skull, require more force to cause than cranial vault fractures. Thus they are rare, occurring as the only fracture in only 4% of severe head injury patients. Basilar fractures have characteristic signs: blood in the sinuses; a clear fluid called cerebrospinal fluid (CSF) leaking from the nose or ears; raccoon eyes (bruising of the orbits of the eyes that result from blood collecting there as it leaks from the fracture site); and Battle's sign (caused when blood collects behind the ears and causes bruising).