Types
Linear fracture
Linear skull fractures are breaks in the bone that transverse the full thickness of the skull from the outer to inner table. They are usually fairly straight with no bone displacement. The common cause of injury is blunt force trauma where the impact energy transferred over a wide area of the skull.Linear skull fractures are usually of little clinical significance unless they parallel in close proximity or transverse a suture, or they involve a venous sinus groove or vascular channel. The resulting complications may include suture diastasis, venous sinus thrombosis, and epidural hematoma. In young children, although rare, the possibility exists of developing a growing skull fracture especially if the fracture occurs in the parietal bone. Depressed fracture
A depressed skull fracture is a type of fracture usually resulting from blunt force trauma, such as getting struck with a hammer, rock or getting kicked in the head. These types of fractures—which occur in 11% of severe head injuries—are comminuted fractures in which broken bones displace inward. Depressed skull fractures present a high risk of increased pressure on the brain, or a hemorrhage to the brain that crushes the delicate tissue.Compound depressed skull fractures occur when there is a laceration over the fracture, putting the internal cranial cavity in contact with the outside environment, increasing the risk of contamination and infection. In complex depressed fractures, the dura mater is torn.
Anatomy
The human skull is anatomically divided into two parts: the neurocranium, formed by eight cranial bones that houses and protect the brain—and the facial skeleton (viscerocranium) composed of fourteen bones, not including the three ossicles of the inner ear. The term skull fracture typically means fractures to the neurocranium, while fractures of the facial portion of the skull are facial fractures, or if the jaw is fractured, a mandibular fracture.The eight cranial bones  are separated by sutures : one frontal bone, two parietal bones, two temporal bones, one occipital bone, one sphenoid bone, and one ethmoid bone.The bones of the skull are in three layers: the hard compact layer of the external table (lamina externa), the diploë (a spongy layer of red bone marrow in the middle, and the compact layer of the inner table (Lamina interna).Skull thickness is variable, depending on location. Thus the traumatic impact required to cause a fracture depends on the impact site. The skull is thick at the glabella, the external occipital protuberance, the mastoid processes, and the external angular process of the frontal bone.