|Classification and external resources|
A piece of a skull with a depressed skull fracture
A skull fracture is a break in one or more of the eight bones that form the cranial portion of the skull, usually occurring as a result of blunt force trauma. If the force of the impact is excessive, the bone may fracture at or near the site of the impact and cause damage to the underlying physical structures contained within the skull such as the membranes, blood vessels, and brain, even in the absence of a fracture.
While an uncomplicated skull fracture can occur without associated physical or neurological damage and is in itself usually not clinically significant, a fracture in healthy bone indicates that a substantial amount of force has been applied and increases the possibility of associated injury. Any significant blow to the head results in a concussion, with or without loss of consciousness.
A fracture which occurs in conjunction with an overlying laceration which tears the epidermis and the meninges or runs through the paranasal sinuses and the middle ear structures, resulting in the outside environment being in contact with the cranial cavity is termed a compound fracture. Compound fractures may either be clean or contaminated.
There are four major types of skull fractures; linear fractures which are the most common and usually require no intervention for the fracture itself, depressed fractures which are usually comminuted with broken portions of bone displaced inward may require surgical intervention if there is underlying tissue damage, diastatic fractures in which the sutures of the skull widen usually affects children under three, and basilar fractures which occur in the bones at the base of the skull.
The human skull is anatomically divided into two parts: the neurocranium formed by eight cranial bones which houses and protects the brain, and the facial skeleton (viscerocranium) composed of fourteen bones not including the three ossicles of the inner ear. The term "skull fracture" is typically used to describe fractures to the neurocranium while fractures of the facial portion of the skull are classified as "facial fractures, or if the jaw is fractured, a "mandibular fracture".
There are three layers in the bones of the skull: the hard compact layer of the external table (lamina externa), the diploë which is a spongy layer in the middle containing red bone marrow and the compact layer of the inner table (Lamina interna).
Skull thickness is variable depending upon location thus the traumatic impact required to cause a fracture depends on the site of the impact. The skull is thick at the glabella, the external occipital protuberance, the mastoid processes, and the external angular process. Where the skull is covered with muscle, there is no underlying diploë formation between the internal and external lamina which results in a thin area of bone more susceptible to fractures.
Skull fractures occur more easily at the thin squamous temporal and parietal bones, the sphenoid sinus, the foramen magnum (the opening at the base of the skull through which the spinal cord passes), the petrous temporal ridge, and the inner portions of the sphenoid wings at the base of the skull. The middle cranial fossa, a depression at the base of the cranial cavity forms the thinnest part of the skull and is thus the weakest part. This area of the cranial floor is weakened further by the presence of multiple foramina as a result this section is at higher risk for basilar skull fractures to occur. Other areas more susceptible to fractures are the cribriform plate, the roof of orbits in the anterior cranial fossa, and the areas between the mastoid and dural sinuses in the posterior cranial fossa.
Linear skull fractures are breaks in the bone that transverse the full thickness of the skull from the outer to inner table, are usually fairly straight and involve no displacement of the bone. The common method of injury is blunt force trauma in which the energy from the blow is transferred over a wide surface area of the skull.
Linear fractures of the skull 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 skull 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 are displaced inward. Depressed skull fractures carry a high risk of increased pressure on the brain, or a hemorrhage to the brain, crushing the delicate tissue.
Compound depressed skull fractures occur when there is a laceration over the fracture, resulting in the internal cranial cavity being in contact with the outside environment increasing the risk of contamination and infection. Complex depressed fractures are those in which the dura mater is torn. Depressed skull fractures may require surgery to lift the bones off the brain if they are placing pressure on it.
Diastatic skull fracture
Diastatic fractures occur when the fracture line transverses one or more sutures of the skull causing a widening of the suture. While this type of fracture is usually seen in infants and young children as the sutures are not yet fused it can also occur in adults. When a diastatic fracture occurs in adults it usually affects the lambdoidal suture as this suture does not fully fuse in adults until about the age of 60.
Diastatic fractures can occur with different types of fractures and it is also possible for diastasis of the cranial sutures to occur without a concomitant fracture. Sutural diastasis may also occur in various congenital disorders such as cleidocranial dysplasia and osteogenesis imperfecta.
Basilar skull fracture
Basilar skull fractures are linear fractures that occur in the floor of the cranial vault (skull base), which require more force to cause than other areas of the neurocranium. 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 (rhinorrhea) or ears (otorrhea); periorbital ecchymosis often called 'raccoon eyes' (bruising of the orbits of the eyes that result from blood collecting there as it leaks from the fracture site); and retroauricular ecchymosis known as "Battle's sign" (bruising over the mastoid process).
Growing skull fracture
A growing skull fracture (GSF) also known as a craniocerebral erosion or leptomeningeal cyst due to the usual development of a cystic mass filled with cerebrospinal fluid is a rare complication of head injury usually associated with linear skull fractures of the parietal bone in children under 3. It has been reported in older children in atypical regions of the skull such as the basiooccipital and the base of the skull base and in association with other types of skull fractures. It is characterized by a diastatic enlargement of the fracture.
There are various factors associated with the development of a GSF with the primary causitive factor being a tear in the dura mater. The skull fracture enlarges due in part to the rapid physiologic growth of the brain which occurs in young children and brain cerebrospinal fluid (CSF) pulsations in the underlying leptomenigeal cystic mass.
Cranial burst skull fracture
A cranial burst skull fracture usually occurring with severe injuries in infants less than 1 year of age is a closed, diastatic skull fracture with cerebral extrusion beyond the outer table of the skull under the intact scalp.
Acute scalp swelling is associated with this type of fracture. In equivacal cases without immediate scalp swelling the diagnosis may be made via the use of Magnetic resonance imaging thus insuring more prompt treatment and avoiding the development of a "growing skull fracture".
Compound skull fracture
A fracture which occurs in conjunction with an overlying laceration which tears the epidermis and the meninges or runs through the paranasal sinuses and the middle ear structures, resulting in the outside environment being in contact with the cranial cavity is termed a compound fracture.
The most serious complication of compound skull fractures is infection. Increased risk factors for infection include visible contamination, meningeal tear, loose bone fragments and presenting for treatment more than eight hours after initial injury.
Compound elevated skull fracture
A compound elevated skull fracture is a rare type of skull fracture where the fractured bone is elevated above the intact outer table of the skull. This type of skull fracture is always compound in nature. It may be caused during an assault with a weapon in which the initial blow penetrates the skull and the underlying meninges and upon retrieval of the weapon lifts the fractured portion of the skull outward. It may also be caused by a rotation of the skull while being struck in a case of blunt force trauma, a rotation of the skull while striking an inanimate object as in a fall or it may occur during transfer of a patient after the initial compound head injury.
Neurological deficits in skull fractures
The presence of a concussion or skull fracture in trauma patients without intracranial hemorrhage or focal neurologic deficits was indicated in long term cognitive impairments and emotional lability at nearly double the rate as those patients without either complication.
In a study of emergency room patients suspected of having suffered closed head injuries, neuropsychological testing and computerized tomography (CT) scans came back with normal results. The patients did not differ in Closed head injury (CHI) scores as measured by the Glasgow Coma Scale (GCS).
Those with a skull fracture were shown to have "neuropsychological dysfunction, even in the absence of intracranial pathology or more severe disturbance of consciousness on the GCS".
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