It can be alarming to suddenly discover that you have a dip or dent in the crown of your head. In most cases, though, this is benign and does not require medical attention. The human skull is not perfectly smooth, and even if it was, there are many reasons for lumps, bumps, ridges, and valleys in the layer of tissue and skin covering the skull.
The skull itself has several ridges and valleys because the plates of the skull only fuse (or suture) in infancy. Sutures are a type of fibrous joint or synarthrosis only seen in the skull. The Sharpey’s fibres that bind the skull bones together allow for a little elasticity to persist in the skull even into adulthood.
Normal Lines on the Human Skull
Identifying the suture lines on a human skull can give you a good indication of where you are likely to feel dips in the middle of your head.
The metopic suture joins the two lateral halves (frontal bones) of the front of the skull, while the sagittal suture joins the two halves (parietal bones) at the back of the skull. The coronal suture joins the front and back of the skull, and the lambdoid suture joins the skull itself to the occipital bone at the base of the skull. There is also a squamosal suture that joins the parietal bone to the temporal bone (above the temple).
The anterior (front) fontanelle is the area where the four main bones of the skull meet in the crown of the head. This is one of many areas of the skull where you are likely to feel a difference in the otherwise ‘smooth’ bone. The posterior fontanelle is the area where the parietal bones and the occipital bone meet. There is also a sphenoid fontanelle on either side of the skull where the parietal, temporal, and frontal bones meet. And, there is a mastoid fontanelle on both sides of the skull where the occipital, temporal, and parietal bones meet.
These fontanelles allow for the plates of a baby’s skull to move as the baby passes through the birth canal. It is common, therefore, for a baby’s head to look somewhat ‘squashed’ immediately after birth. This is called birth moulding and usually resolves within a few days of birth.
For most infants, the posterior fontanelle closes two to three months after birth. The sphenoidal fontanelle closes next, at around six months of age, and the mastoid fontanelle closes at 6-18 months. The anterior fontanelle is normally the last to close at 18–24 months. In some infants, the cranial sutures may close prematurely, affecting the growth and resulting shape of the skull. This is called craniosynostosis.
Craniosynotosis and Positional Plagiocephaly – Abnormalities in Skull Formation
Craniosynotosis tends to affect male infants more than female infants in a 3:1 ratio. This condition has a genetic cause in some cases and can also result from various nutrient deficiencies or excesses, as well as from hormonal (endocrine) disturbances, blood disorders, and other issues.
Abnormalities in the shape of an infant’s head can also occur from seemingly innocuous things, such as sleeping on one side more than the other or spending a lot of time flat on their back. This can result in something called positional plagiocephaly, where the back of the baby’s head is flatter than usual. Regular position changes help to resolve the issue by allowing the skull to grow properly.
More Common Causes of Dents in the Skull
In most cases, the lumps and bumps we feel in the skull are simply the result of rather unnoteworthy items that put pressure on the head without us really realizing. Dents and dips in the skull may be related, for example, to the use of hair clips, hats, glasses, headphones, or braiding and hair wraps. These create pressure in specific areas of the scalp and, over time, can lead to abnormalities in the shape of the skull.
Such dents can range from relatively minor and largely unnoticeable to defects that cause a misshapen appearance. If you have a couple of dips in the middle of your skull, one on either side of the midline, consider whether you have a habit of pushing your glasses or sunglasses up there to rest when you’re not using them.
Aside from mechanical pressure, several other issues can cause dents and dips in the scalp. These include:
- Cutis verticis gyrata – causing deep, linear skin folds on the scalp, usually from the front to the back of the skull
- Psoriasis and eczema – especially if a person has scratched at irritated skin, leading to scarring
- Nevus sebaceus – a benign hamartoma, usually smooth and flat at birth but becoming raised at puberty
- Pilar or trichilemmal cyst – benign cysts that are usually soft and mobile, formed through keratinization
- Lipoma – a fatty tumor that is usually asymptomatic, but that can be tender, especially after trauma.
Primary nonessential cutis verticis gyrata (CVG) has been associated with neurologic problems including seizures, as well as schizophrenia and mental retardation. Secondary CVG is caused by an underlying issue, such as inflammation related to psoriasis and eczema. As such, the dents and dips in the scalp may feel more pronounced when the general (systemic) level of inflammation is high in the body, such as after trauma or injury, or when a person is ill or stressed. The condition may also arise after the use of anabolic steroids and has been linked to some rare conditions. Many people do not notice these ridges until they have their head shaved (for cosmetic or surgical reasons).
Treating Dents in the Middle of Skull
Most indentations in the scalp do not require treatment and have a benign cause. However, some people choose to have surgery to remove lipomas or cysts, and surgery may also be desired for more extreme cases of CVG. Surgery is often carried out in infancy for craniosynostosis, in order to allow a baby’s brain room to grow properly. For some scalps bumps and ridges, treating the underlying inflammation or infection can help abnormalities to settle down. Where indentations are a result of persistent pressure on the scalp, from braids and hair fasteners, for instance, the dents may resolve after undoing braids and massaging the affected areas of the scalp before letting it rest.
In very rare instances (only 300 or so cases have been documented), dips and dents in the skull may be a result of a condition called Gorham’s Stout disease, also known as vanishing bone disease and phantom bone disease. If you are concerned about dents or ridges in the middle of your skull, or elsewhere, talk to your healthcare worker, especially if you have any unexplained symptoms such as fatigue, nausea, headaches, weight loss or weight gain, dizziness, confusion, or have recently experienced a bump to the head.