The Anatomy of the Parietal Bone

A Bone on Each Side of the Skull

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Parietal bone of the skull

Sebastian Kaulitzki / Science Photo Library / Getty Images

 

The parietal bone is an irregularly shaped bone which extends to cover the top of the skull along with some of each side of the skull. Due to its location on the skull, the parietal bone also touches other parts of the skull, including the frontal bone, temporal bone, and occipital bone. The parietal bone not only protects the brain and other internal structures, but also helps maintain the overall shape of the head.

The parietal bone and other bones in the skull are not fused together until the age of 2, as cartilage continues to join these bones through infancy. Even after this point, the bones of the skull are not fully fused until the age of 20, when cartilage is no longer present in the outer skull.

Anatomy

The parietal bone assumes a vaguely rectangular shape, with four main angles. The frontal angle is the highest and located closest to the front of the head. The sphenoidal angle is the smallest angle which is also located near the front of the head. The sphenoidal angle sits lower than the frontal angle. The occipital angle is toward the back of the parietal bone and is located near the top of the occipital bone. The occipital bone lies at the base of the skull. The last angle is the mastoid angle which also joins with the occipital bone, but is lower than the occipital angle.

Other areas called margins are identified on the parietal bone. Similar to the angles of the parietal bone, margins point toward which bones the parietal bone touches. The frontal margin can be found at the front of the parietal bone. The occipital margin can be found at the base of the parietal bone at the back of the skull. Both the squamous and sagittal margins are found where the parietal bone sits at the top of the skull.

There are also structures on the outer surface of the parietal bone. Among these structures includes the parietal tuber, which is located in the middle of the parietal bone. Also present is a curved line called the superior temporal line which allows fascia to attach to the skull. This fascia, similar to fascia anywhere in the body, allows for the joining of muscle and bone.

An adjacent line called the inferior temporal line allows the temporalis muscle to attach to the skull. The temporalis muscle allows for movement of the jaw, assisting in actions such as chewing and talking.

The parietal foramen, or opening, at the back of the parietal bone gives way for the parietal emissary vein to pass through. This vein allows for drainage of the sinuses located within the facial bones.

Anatomical Variations

Anatomical variations of the parietal bone most frequently include the lack of bone formation in place of cartilage. This lack of fusion causes instability within the skull and places a child or adult at an increased risk for brain injury upon even minor trauma to the skull.

Medical professionals may also confuse skull fractures with sutures, or joining marks, between each bone of the skull. This can lead to misdiagnosis and unnecessary treatments in certain children or adults. One of the variations which is often confused for a fracture is the wormian bone. This variation can also be associated with conditions such as dysplasia and a bone disorder called osteogenesis imperfecta.

Function

The parietal bone works with the other bones of the skull to form a protective casing around the brain and other internal structures. There is no movement or sensation associated with this bone, as its primary function is a mechanical landmark to prevent injury and protect important structures which are vital to life. The placement of the parietal bone amidst other bones of the skull also provides support and protection to the structure of the face.

Other functions within the protective nature of the parietal bone include acting as a go-between for veins, arteries, and other blood vessels within the brain. There are openings and passages which allow for these blood vessels to perform their functions of transporting blood and other bodily fluids to and from the brain.

Associated Conditions

Gorham-Stout disease is a bone disorder which can affect the bones of the skull, as well as the jaw, pelvis, ribs, spine, and collarbone. This disorder has no known cause and often leads to physical deformity along with major decline in function. Gorham-Stout disease causes continual and damaging bone loss followed by an excess of lymphatic vessels within the area of bone loss. This disorder can affect several bones across the body and can lead to multiple fractures and loss of bone density.

Another condition specifically impacting the bones of the skull is craniosynostosis. This condition causes deformity of an infant’s skull due to the rapid closure of cartilage between the bones of the skull. This causes physical deformity to the outside of the skull which may also lead to deformed physical features and symptoms such as vision changes, developmental delays, headaches, and more.

Incomplete bone formation, called enlarged parietal foramina, can cause large openings within the parietal bone. This will cause a soft area in the skull which remains throughout most of an individual’s life. Soft spots in the skull can cause increased pressure which may lead to seizures, changes in the scalp, migraines, permanent brain damage, and skull fractures.

Skull fractures can also result from trauma to the head. The severity of skull fractures varies based on how many bones were affected along with whether or not the fracture opened the skin, ruptured blood vessels, and caused brain damage.

Rehabilitation

An open fracture of the skull which caused brain damage, open skin, and disjointed bones, will be treated differently than a closed fracture of the skull. Closed fractures of the skull are often treated by ensuring there is no internal bleeding or major changes in function. Minor brain damage may result from closed fractures of the skull, which would warrant follow-up by a neurologist, speech therapist, physical therapist, and/or occupational therapist.

An open fracture of the skull can cause more severe brain damage and infection if not treated properly. This type of fracture must be surgically fused to allow for proper healing. Neurological and surgical follow-up is then indicated, along with a combination of therapies depending on the individual’s deficits. Certain treatments may be specific to the type of brain injury which results from a severe skull fracture. Not all skull fractures will result in damage to the brain, as some are classified as head injuries rather than brain injuries due to their primarily physical involvement.

Rehabilitation provided by physical, occupational, and speech therapists focuses on improving function and quality-of-life. Treatments include re-educating the brain to perform certain tasks, strengthening the upper and lower body, improving an individual’s ability to swallow, speak, and chew, and modifying diets to allow for changes in the oral-motor systems. Other therapies may include improving an individual’s ability to walk, toilet, feed, dress, and bathe themselves.

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