This article has been professionally reviewed by Dr. Duong Van Sy, a resident in Pediatrics and Neonatology at Vinmec International General Hospital, Hai Phong.
In most cases, a sunken or slightly pulsating fontanel in a newborn is considered normal. This is due to the blood flow through the area. However, a sunken fontanel can also be a warning sign of serious conditions such as dehydration and malnutrition…
1. Fontanels in Newborns
In newborns, there are two soft spots on the head called fontanels. Fontanels can vary slightly in size. The posterior fontanel is usually smaller, about 0.6 cm, and triangular in shape. The anterior fontanel is larger, about 2.5 cm, located at the top of the head, and diamond or kite-shaped. If the fontanel is significantly smaller or larger than the average size, the baby should be evaluated as soon as possible.
Fontanels play a role in making it easier for the baby to be born. Specifically, when a baby is born, the bones of the baby's head are soft and connected by tissues. As the baby passes through the birth canal, the fontanels allow the baby's skull to be flexible, fitting together to help the baby pass through more easily. Additionally, fontanels provide space for the baby's brain to grow, similar to adults.
Fontanels are soft but are protected by a very thick membrane until the bones join together. Therefore, mild impacts such as wearing a hat or shampooing will not affect the fontanel.
The fontanels will stretch out within the first 2-3 months and then begin to close. Since the posterior fontanel is smaller, it will close before the anterior fontanel. The posterior fontanel usually closes when the baby is 2-4 months old, while the anterior fontanel closes when the baby is about 18-24 months old, but in some cases, it can close earlier, around 9-12 months. Until it closes, the baby's fontanel is always flat, neither sunken nor bulging.
2. What Causes a Sunken Fontanel in Newborns?
Generally, a sunken or slightly pulsating fontanel in a newborn is considered normal. This is due to the blood flow through this area. However, a sunken fontanel can also indicate several conditions that parents should be aware of. A sunken fontanel may be a sign of:
- Dehydration: This is the primary cause of a sunken fontanel in newborns. Dehydration occurs when the body lacks sufficient fluids to maintain normal functions. This is a serious condition, and parents should be aware of the signs to seek medical attention promptly and prevent complications.
- Malnutrition: Malnutrition can also cause a sunken fontanel. This symptom often accompanies dehydration and can make the condition more severe. Malnourished newborns may exhibit additional symptoms such as low weight, dry and easily falling hair, fatigue, lethargy, and poor skin turgor.
- Acute toxic colitis: In rare cases, acute toxic colitis can cause a sunken fontanel. While rare, this condition is life-threatening.
- Kwashiorkor: This is a form of severe malnutrition in young children, caused by depletion of protein intake. Even with treatment, children with this syndrome may not fully recover. However, delayed treatment can lead to permanent physical and mental disabilities. Untreated, it can lead to coma, shock, and even death.
- Diabetes insipidus: This is not a form of diabetes but a rare condition where the kidneys cannot conserve water, leading to a sunken fontanel in newborns. Treatment will vary depending on the severity.
3. Diagnosis and Treatment of a Sunken Fontanel in Newborns
Typically, doctors will use the following methods to diagnose a sunken fontanel in a newborn:
- Physical examination: This includes observing and touching the sunken fontanel area. The doctor will assess the skin's turgor, as poor turgor can indicate dehydration.
- Inquiring about symptoms: The doctor may ask about when the sunken fontanel appeared to assess the severity of the condition.
- Tests: Blood and urine tests are often ordered for newborns with a sunken fontanel. Blood tests such as Complete blood count which evaluate the quantity and quality of red and white blood cells, can help detect infections, anemia caused by dehydration. Urine tests can help identify underlying conditions. Additional tests, such as comprehensive metabolic panels, may be ordered to assess the levels of various chemicals and fueling metabolism in the body.
Once the cause of the sunken fontanel has been determined, the doctor will prescribe appropriate treatment. Treatment will vary depending on the underlying cause. Specific treatments include:
- Increasing fluid intake: This is the primary treatment for dehydration. Parents can increase their baby's fluid intake by feeding them more frequently.
- Electrolyte supplementation: Doctors may prescribe electrolyte solutions specifically formulated for infants to improve malnutrition. However, if the baby is dehydrated due to the high sugar and salt content in electrolyte solutions, this method should be avoided as it can worsen dehydration.
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