The Anatomy of the Frontal Bone

The frontal bone, most commonly referred to as the forehead, supports the front and back of the skull. In infancy, the frontal bone is connected by frontal suture, a joint that divides the two halves of the frontal bone. As an infant starts to grow, this frontal suture fuses the frontal bone together into one solid piece.

Anatomy

The structure of the frontal bone consists of three parts: squamous, orbital, and nasal.

The squamous part of the frontal bone is the largest section. The outside of the squamous part is flat, but the inside is concave, consisting of frontal sinuses, a supraorbital notch, which allows for the supraorbital nerve to provide sensory function to the nose and a large part of the upper eyelids, and the superciliary arch (what is your brow ridge).

The orbital part of the frontal bone forms the top of orbit bone and ethmoid sinuses, which are located between your eyes and nose. Two openings at the front and back of the orbital part of the frontal bone allow for nerves to run through to the sinuses.

Last, the nasal part of the frontal bone helps form the structure of the nose itself.

Location

The frontal bone is located in front of the skull, above the nasal bones and in front of the parietal bones, which form the sides of the skull.

The frontal bone is also surrounded by seven articulating bones to create joints.

Anatomical Variations

Infants have a space between the frontal and parietal bones called a fontanelle.

All babies will have fontanelles to start, there is one at the back of the head and an anterior fontanel, which is on the top of the head. The fontanelle at the back of the head typically closes by the time the baby is two months old and the top fontanelle between seven months and 18 months of age.

Delayed cases of a fontanel closure may be a sign of:

• Achondroplasia (a type of dwarfism)
• Hypothyroidism
• Down syndrome
• Increased intracranial pressure
• Rickets (a condition that results in soft bones due to lack of vitamin D, calcium, or phosphate)

Alternatively, intracranial pressure could be a result of a fontanelle closing too soon.

Some depression or swelling of a fontanelle in an infant is completely normal and can flag possible health risks, as the fontanelle will appear sunken if an infant is dehydrated.

Other anatomical variations of the frontal bone include a fracture anywhere within the bone itself, which is usually diagnosed by one of the following signs:

• Pain
• Swelling
• Facial asymmetry
• Facial tingling or numbness
• Facial hematoma
• A grating sound in or around the frontal bone, which may be joints or bones rubbing against each other.
• Double vision as a result of a fracture or injury in the frontal bone near the orbit area.

Function

The frontal bone is one of the eight bones that together form the cranium, otherwise known as the protective case of the brain.

In between the brain and frontal bone is cerebrospinal fluid. This fluid is in between the meninges, which surround the brain. These padded layers and cerebrospinal fluid keep the brain safe, and prevent it from hitting against the skull.

While many nerves pass through the frontal bone to provide motor and sensory function to the different regions of the head, the frontal bone itself doesn’t provide and motor or sensory function. However, the center of the frontal bone has a sponge-like consistency and is filled with stem cells that go on to form red blood cells, white blood cells, and platelets that are distributed into the bloodstream.

Associated Conditions

Conditions associated with the frontal bone include hyperostosis frontalis interna and craniosynostosis.

With hyperostosis frontalis interna a portion of the the frontal bone is thicker than normal. A variety of conditions have been associated with it — including seizures, headaches, obesity, diabetes insipidus, excessive hair growth, and sex gland disturbances — but no cause-and-effect relationship has been established. It is quite common; as many as 12% of women may have some degree of thickening of the frontal bone. (Insert ref here) Most experts believe this finding is usually a variant of normal anatomy.

Craniosynostosis happens in infants when any sutures close early. This results in an abnormally-shaped skull because the bones are restricted and can’t expand with the brain's growth. If left untreated, craniosynostosis can lead to permanent head deformities, seizures, developmental delays, and increased brain pressure.

Rehabilitation

Hyperostosis frontalis interna has no known treatment. Instead, healthcare providers have to treat the symptoms, such as headaches and seizures, which can be done with medication.

Craniosynostosis treatment typically requires surgery, where a surgical team will release the fused frontal bone and reshape the areas that have been deformed from the closure. This is done as early as possible for the infant (typically around eight months of age) because an infant's bones are extremely malleable and bone growth happens more quickly to accommodate brain growth.

A Word From Verywell

It's important to keep in mind that the frontal bone and skull are separate from the brain, particularly if you're trying to determine whether you're dealing with a head injury or a brain injury. While most head injuries can be repaired with minimal long-lasting effects, a traumatic brain injury may lead to a permanent motor or sensory loss.

If you think you have a frontal bone injury, your safest bet is to get it checked by your healthcare provider. who can diagnose you correctly, ruling out a more serious brain injury in addition to providing you with the best treatment plan possible.