How does cranial vault size change with age?

By early adulthood, the cranial vault, or the bony structure protecting the brain, is generally believed to have reached its maximum size. However, recent studies reveal a more complex picture, showing subtle but significant changes in skull dimension and shape continue throughout the aging process.

Quick Summary

The cranial vault undergoes continuous bone remodeling throughout adulthood, leading to subtle changes in its internal and external shape, such as thickening of the frontal bone and inward compression, which can reduce intracranial volume over time.

Key Points

• Subtle Changes: While major growth ceases by early adulthood, subtle changes in cranial vault shape and volume continue throughout life due to ongoing bone remodeling.

• Inner Table Thickening: A key age-related change is the thickening of the inner layer of the frontal bone, which can slightly decrease the space available for the brain over time.

• Gender Differences: Studies have shown that inner skull thickening is generally more pronounced in women, potentially influenced by hormonal changes post-menopause.

• External Expansion: The outer layers of the skull can also experience bone deposition, with some research noting an expansion of the forehead, especially near the supraorbital rim.

• Impact on Research: The dynamic nature of the cranial vault is an important factor for neuroimaging studies, as ignoring these changes can lead to underestimations of brain atrophy in older subjects.

• Facial Proportions: Bone remodeling of the skull and facial skeleton can alter facial proportions, affecting features like eye sockets and the jawline.

The Adult Cranial Vault: A Dynamic, Not Static, Structure

Conventional wisdom suggests that once puberty ends, the skull, like most of our skeleton, ceases to grow. While the large growth spurts of childhood and adolescence are over, research in craniofacial aging paints a more nuanced picture. The bones of the cranial vault are not static but are in a constant state of turnover, with old bone tissue being resorbed and new tissue being formed. This dynamic process, known as bone remodeling, leads to measurable changes in the vault's dimensions and shape over time, impacting both its internal volume and external appearance.

The Process of Bone Remodeling and Its Impact on the Cranial Vault

Bone remodeling is a lifelong process carried out by specialized cells: osteoblasts, which form new bone, and osteoclasts, which resorb old bone. In younger, healthy adults, these processes are balanced. However, with aging, this equilibrium shifts, leading to more resorption than formation in some areas and the reverse in others.

• Inner Table Thickening: A notable change in older adults is the thickening of the inner table of the frontal bone, a phenomenon also known as hyperostosis frontalis interna (HFI). This thickening is more pronounced in women, particularly after menopause, and directly reduces the intracranial volume (ICV)—the space available for the brain.

• Outer Table Expansion: While the inner table may thicken, some studies show a continuous expansion of the outer table of the frontal bone, especially around the supraorbital rim. This bone deposition contributes to a more prominent forehead appearance in some older individuals.

• Regional Shape Changes: The skull's changes are not uniform. Some research using 3D imaging has demonstrated significant adult skull shape changes with increasing age. For males, this includes a relative expansion of the temporal regions, while the frontal and posterior parietal regions experience relative compression. Females also show internal expansion but with more compression in the frontal region along the midline.

Comparing Cranial Changes Over the Lifespan

To understand the full scope of how the cranial vault changes, it is helpful to compare the dramatic growth of youth with the subtle remodeling of older age.

Feature	Childhood & Adolescence	Adulthood & Senior Years
Primary Driver	Rapid brain growth; fusion of sutures.	Continuous bone remodeling; shifting balance between resorption and formation.
Suture Closure	Fontanelles close early; sutures ossify over time, allowing for expansion.	Most sutures are fully fused by the mid-twenties, creating a rigid structure.
Overall Size Change	Significant and rapid increase in overall head circumference and intracranial volume.	Minimal change in overall outer circumference, but internal volume can decrease due to bone thickening.
Key Mechanisms	Bone deposition along suture lines and at the ends of growing bones.	Resorption and deposition on inner and outer surfaces in response to physiological pressures and hormonal changes.
Resulting Appearance	Proportion of head to body changes; features become more emphasized.	Subtle alterations in facial proportions, changes to features like eye sockets and jaw angle.

The Impact of Cranial Changes on Brain and Health

The reduction in intracranial volume due to age-related skull thickening can have significant implications for brain health studies. When measuring brain atrophy (shrinkage) in older adults using imaging, researchers must account for the decreasing space within the skull to avoid underestimating the actual tissue loss. This is an important consideration in understanding the effects of normal aging versus neurological diseases.

In addition, age-related changes can affect facial features. Resorption of bone around the orbits can make the eyes appear deeper-set, and changes in the maxilla and mandible can affect the angle of the jaw and increase the appearance of nasolabial folds.

Factors Influencing Age-Related Cranial Changes

Several factors contribute to the ongoing transformation of the cranial vault:

• Hormonal Changes: Hormones like estrogen play a significant role in bone remodeling. The decrease in estrogen levels in postmenopausal women is linked to increased bone resorption and is thought to contribute to the more pronounced inner skull thickening seen in females.
• Mechanical Stress: The functional theory of bone remodeling suggests that bone adapts in response to mechanical demand. In the facial skeleton, the loss of teeth can lead to increased bone resorption in the jaw.
• Underlying Conditions: While mostly a benign part of aging, certain conditions can affect skull morphology. For instance, severe brain atrophy or other pressure changes can trigger a response in the skull.
• Genetics: An individual's genetics can influence bone density and remodeling rates, affecting how their cranial features change over time.

Conclusion

The human cranial vault is not the static, unchangeable structure it appears to be after adolescence. Through continuous, though slowing, bone remodeling, its inner and outer surfaces are subject to subtle shifts throughout life. The thickening of the inner table, particularly in women, reduces intracranial volume, a crucial consideration for neuroimaging and brain research. This process contributes to overall changes in facial appearance and provides a window into the complex biological processes that accompany aging. For a deeper dive into the broader aspects of bone health, consider exploring authoritative resources like those provided by the National Institute of Arthritis and Musculoskeletal and Skin Diseases (NIAMS).

Frequently Asked Questions

At what age does the cranial vault stop growing?

Significant outward expansion of the cranial vault stops by the end of puberty, typically in the late teens or early twenties. However, subtle internal and external remodeling of the bone continues throughout life, meaning it is never truly static.

Can my head size change as I get older?

Yes, your head size and shape can change subtly with age. While the overall circumference remains relatively stable after early adulthood, internal bone thickening and external bone deposition cause measurable shifts in cranial dimensions and facial features over time.

What is bone remodeling, and how does it affect the skull with age?

Bone remodeling is the continuous process where old bone tissue is resorbed by osteoclasts and new bone is formed by osteoblasts. In older age, this balance can shift, leading to changes like thickening of the inner cranial table and reshaping of facial bones.

Does the brain shrink with age, and does this affect the cranial vault?

Yes, the brain does shrink with age, a process called atrophy, which can lead to a decrease in brain volume. Some studies suggest that the thickening of the inner cranial table may be a response to the loss of brain volume.

Is cranial vault size change a normal part of aging?

Yes, the subtle bone remodeling and dimensional changes in the cranial vault are a normal physiological part of the aging process. While generally benign, they are a fascinating aspect of how the skeleton continues to adapt throughout life.

Are there any health concerns related to cranial vault changes in older adults?

For most individuals, age-related changes to the skull are not a health concern. However, in certain clinical contexts, such as neuroimaging, the reduction in intracranial volume needs to be considered to accurately assess brain atrophy. Rapid, unusual changes may warrant medical evaluation.

Do male and female cranial vaults change differently with age?

Research indicates that some age-related changes can differ between sexes. For instance, the thickening of the inner frontal bone (hyperostosis frontalis interna) has been observed to be more pronounced in women, especially post-menopause.