The human head, a complex structure, naturally exhibits a wide range of shapes and sizes. Most differences are benign, representing normal variation or stemming from common factors during infancy. The skull’s ability to mold in early life means external pressures or internal growth dynamics can lead to noticeable changes. Understanding the cause is the first step, as some variations signal underlying medical conditions requiring specialized attention. Causes are broadly categorized as those originating from developmental positioning, genetic factors, or those acquired later due to pathology or trauma.
Head Shape Changes Stemming from Infancy
The shape of an infant’s head is highly susceptible to external forces because the skull bones are not yet fully fused, separated by flexible sutures and soft spots called fontanelles. The “Back to Sleep” campaign, which recommends infants sleep on their backs, significantly reduced Sudden Infant Death Syndrome (SIDS). This positioning, however, led to an increase in deformational head shape variations, such as positional plagiocephaly or brachycephaly.
Positional plagiocephaly involves a flattened area on one side of the back of the head, often resulting in a slight parallelogram shape. This flattening may correlate with an anterior displacement of the ear and forehead on the same side. Brachycephaly is a symmetrical flattening across the entire back of the head, making the head wider than it is long. These positional conditions are cosmetic and do not affect brain development.
A contributing factor to positional flattening is torticollis, where neck muscles cause the baby’s head to tilt or turn predominantly to one side. This preference concentrates pressure on a specific area of the soft skull. Simple repositioning efforts, including supervised “tummy time,” are recommended to alleviate pressure and allow the head to round out.
A less common cause is craniosynostosis, which occurs in about 1 in 2,000 births. This condition involves the premature fusion of one or more cranial sutures, which should remain open for rapid brain growth. When a suture closes too early, the skull cannot expand perpendicularly, causing abnormal head growth. Craniosynostosis can restrict brain growth and increase pressure if untreated, making early diagnosis important.
Genetic Conditions and Syndromic Variations
Head shape and size can be determined by intrinsic genetic factors, independent of external pressure. Conditions affecting overall head size, such as microcephaly and macrocephaly, often have a genetic basis. Microcephaly is defined as a head circumference significantly smaller than average, often due to issues that disrupted normal brain development.
Macrocephaly is characterized by an abnormally large head circumference. This can be a benign, inherited trait known as familial macrocephaly, where large head size runs in the family without neurological problems. However, it can also be syndromic, associated with conditions like Sotos syndrome or Neurofibromatosis type 1. In these cases, macrocephaly results from genetic mutations causing true brain enlargement (megalencephaly).
Specific gene mutations can cause craniofacial syndromes that directly impact skull and face development. Syndromes like Apert and Crouzon are examples of syndromic craniosynostosis, often linked to FGFR2 gene mutations. These defects cause premature fusion of multiple cranial and facial sutures, resulting in a characteristic head shape, shallow eye sockets, and midface underdevelopment. Other physical findings, such as fused fingers and toes in Apert syndrome, help distinguish these conditions.
Acquired Factors and Pathological Causes
Head shape changes can occur later in childhood or adulthood due to factors altering the formed skull structure. Trauma, such as a severe head injury, can result in permanent deformation if it fractures or depresses the skull bones. These changes are localized and related to the mechanical force of the impact.
Internal diseases that increase pressure within the skull can distort the bony structure. Acquired hydrocephalus, an abnormal buildup of cerebrospinal fluid, increases intracranial pressure. This pressure can cause skull plates to expand or separate, leading to an abnormally large head size, especially before sutures close. Tumors or large cysts can similarly exert localized pressure, causing skull bulging.
In adults, Paget’s disease of bone can change the skull’s shape and size. This metabolic disorder disrupts normal bone recycling, causing new bone to grow quickly, resulting in disorganized, enlarged, and weak tissue. If the skull is affected, this overgrowth can cause increased head size, headaches, and sometimes hearing loss.
Medical Assessment and Next Steps
When a head shape variation is noticed, a medical professional begins with a thorough physical examination and history, which is often sufficient to determine the cause. The doctor carefully feels the head for ridging along the suture lines, which indicates premature fusion (craniosynostosis). The head shape is assessed from various angles, looking for the characteristic parallelogram shape of positional plagiocephaly or deformities associated with fused sutures.
Head circumference measurements are taken and plotted on growth charts to check for microcephaly or macrocephaly. This also determines if the head size is growing disproportionately to the child’s body. If the initial assessment suggests craniosynostosis or internal pathology, imaging tests are the next step.
Plain X-rays provide an initial view of the sutures, but a computed tomography (CT) scan with three-dimensional (3D) reconstruction is the most accurate tool to confirm if a suture is prematurely closed.
If craniosynostosis or a complex craniofacial syndrome is diagnosed, a referral to a specialist team is warranted. This team typically includes a pediatric neurosurgeon and a craniofacial plastic surgeon. A geneticist may also be consulted for conditions affecting the entire body. The specialist confirms the diagnosis, assesses potential for restricted brain growth, and determines the optimal intervention, which is usually surgery for craniosynostosis.