What are cranial bones?
Your skull provides structure to your head and face while also protecting your brain. The bones in your skull can be divided into the cranial bones, which form your cranium, and facial bones, which make up your face.
There are several types of bones within your body, including:
- long bones
- short bones
- flat bones
- irregular bones
- sesamoid bones
There are two types in your cranium:
- Flat bones. As their name suggests, these bones are thin and flat, though some of them have a slight curve.
- Irregular bones. These are bones with complex shapes that don’t fit into any of the other categories.
There are eight cranial bones, each with a unique shape:
- Frontal bone. This is the flat bone that makes up your forehead. It also forms the upper portion of your eye sockets.
- Parietal bones. This a pair of flat bones located on either side of your head, behind the frontal bone.
- Temporal bones. This is a pair of irregular bones located under each of the parietal bones.
- Occipital bone. This is a flat bone located in the very back of your skull. It has an opening that allows your spinal cord to connect to your brain.
- Sphenoid bone. This is an irregular bone that sits below the frontal bone. It spans the width of your skull and forms a large part of the base of your skull.
- Ethmoid bone. This is an irregular bone located in front of the sphenoid bone. It makes up part of your nasal cavity.
Your cranial bones are held together by unique joints called sutures, which are made of thick connective tissue. They’re irregularly shaped, allowing them to tightly join all the uniquely shaped cranial bones. The sutures don’t fuse until adulthood, which allows your brain to continue growing during childhood and adolescence.
Explore the interactive 3-D diagram below to learn more about the cranial bones.
Several injuries and health conditions can impact your cranial bones, including fractures and congenital conditions.
A fracture refers to any type of break in a bone. There are several types of skull fracture that can affect cranial bones, such as:
- Depressed. This refers to a fracture that makes part of your skull appear sunken.
- Linear. A linear fracture in a cranial bone means there’s a break in the bone, but the bone itself hasn’t moved.
- Basilar. This type involves a break in one of the bones near the base of your skull, such as the sphenoid bone. This is a serious condition requiring immediate treatment.
- Diastatic. A diastatic fracture occurs along one of the sutures of your skull, making it wider than usual. It’s usually seen in infants.
In many cases, skull fractures aren’t as painful as they sound, and they often heal on their own without surgery. However, more severe fractures may require surgery.
Some infants are born with a condition called craniosynostosis, which involves the premature closing of skull sutures. This leads to an unusually shaped skull and can sometimes affect facial features.
There are several types of craniosynostosis, depending on the sutures they affect:
- Bicoronal synostosis. Infants with this type may have a flattened and elevated forehead.
- Coronal synostosis. This type can cause flattening on one side of the forehead and impact the shape of the eye socket and nose.
- Lambdoid synostosis. This can lead to flattening on one side of the back of the skull. It can also affect the positioning of the ear or cause the skull to tilt sideways.
- Metopic synostosis. This can cause a triangle-shaped skull or pointed forehead. It can also make the eyes appear closer together.
- Sagittal synostosis. This type may cause the forehead to bulge out. The area around the temples might also appear very narrow, making the head look elongated.
Craniosynostosis requires surgical treatment to avoid later complications.
Some other conditions that can affect the cranial bones include:
- Cleidocranial dysplasia. Mutations to a specific gene cause unusual development of the teeth and bones, including the cranial bones. Common symptoms include a sloped forehead, extra bone within skull sutures, and an enlarged skull.
- Craniometaphyseal dysplasia. This is an inherited condition that causes thickening of the cranial bones, which can lead to a protruding forehead and wide-set eyes.
- Paget’s disease of bone. New bone tissue is rapidly made due to unusual behavior of osteoclasts, which are a type of bone cell. People with this condition are more prone to fractures because the affected bone is usually weaker.
- Fibrous dysplasia. This causes the development of scarlike tissue instead of bone tissue due to a mutation in bone-producing cells. It tends to only affect a single bone at a time, though more may be involved in some cases.
- Osteomas. An osteoma is a benign overgrowth of bone on the skull. People with osteomas typically have no symptoms. However, if the growth puts pressure on a nerve, it can cause hearing and vision problems. These usually resolve once the growth is removed.
Symptoms of a cranial bone condition
With all the structures in your head and neck, it’s sometimes hard to pinpoint when symptoms are coming from an issue with the cranial bones.
Symptoms that suggest some type of cranial bone fracture include:
- bruising around the eyes or behind your ears
- clear fluid or blood draining from your ears or nose
- a feeling of weakness in your face
Symptoms of a structural issue with the cranial bones include:
- a dull, aching pain
- numbness or tingling in your face
- hearing or vision problems
- unusually shaped head or facial features
Your cranial bones are the main defense system for your brain, so it’s important to maintain their health by:
- Wearing a helmet. Always wear a helmet when riding anything on wheels, including bikes, skateboards, and scooters. Replace damaged or dented helmets and make sure they fit properly.
- Fastening your seatbelt. Always wear a seatbelt when traveling in a car.
- Reducing your risk of falling. Secure anything, such as loose electrical cords, that could cause someone to trip. If you have mobility issues, consider installing handrails and grab bars in areas, such as the shower or stairs.
If you have an infant, be sure to monitor their head for anything unusual. You can also make sure you child doesn’t stay in one position for too long. Some ways to do this include:
- alternating the direction your baby’s head faces when putting them to bed
- holding your baby when they’re awake instead of placing them in a crib, swing, or carrier, when possible
- changing the arm you hold your baby with when feeding
- allowing your child to play on their stomach under close supervision