Fontanelles are gaps between the skull bones of a newborn. These are formed when two or more cranial bones are placed side by side. There are six fontanelles found on a newborn’s skull. They are located on the top, back, sides of the head, and behind the eye.
Fontanelles or soft spots provide flexibility to the baby’s skull to pass through the birth canal. They also allow the brain to grow along with the skull bones. The molding process of the skull continues for months after birth and results in the closure of these soft spots.
The average time for the closure is 18 months, and sometimes, 12 months (1). The fontanelle at the back of the head closes when the baby is one to two months old, whereas the soft spot at the top of the head is the last to close at seven to 19 months (2).
A normal fontanelle should feel firm and curve slightly inwards. If you notice significant sinking of a soft spot, it is a cause for concern. Read this post to know the causes, signs, and treatment options for sunken fontanelle.
Signs Of Sunken Fontanelle
As your child grows, the soft spots begin to harden, and the gaps tend to close. But if you find your baby’s soft spot sunken inwards and if it looks like a dent on the head, it could be a sunken fontanelle.
A sunken fontanelle could also be a sign of dehydration or malnutrition; so, you may also find signs including lethargy, dry mucous membranes, and low urine output (2).
What Causes Sunken Fontanelle?
Abnormalities of the fontanelle such as bulging, sinking, large size, small size, and early or delayed closures need attention. Below are some possible reasons for sunken fontanelle in babies.
The fontanelle of a well-hydrated baby appears flat and firm. One of the primary reasons for sunken fontanelle is dehydration. Poor feeding or loss of excess water from the body could result in dehydration. Other symptoms of dehydration include
- Yellow urine
- Dry or sticky mouth
- Less or no wet diapers
- Sunken eyes,
- Dry lips
- Dry mucous membranes (3)
Malnutrition can also cause a sunken fontanelle. If your baby shows poor weight gain and asymmetric growth, it could cause sunken fontanelle. Other signs of malnutrition include
- Dry and inelastic skin
- Failure to thrive (3)
3. Diabetes insipidus
Sometimes, the dehydration can be due to an underlying medical condition, such as diabetes insipidus, which could lead to sunken fontanelle. The symptoms of diabetes insipidus are similar to diabetes mellitus, except that the urine may not contain high sugar levels. Other symptoms include
- Extreme thirst
- Excessive urination,
- Dry skin
- Weight loss
- Muscle pain
- Rapid heart rate
- Fatigue (4)
4. Kwashiorkor and Marasmus
The deficiency of protein and energy may also cause sunken fontanelle in babies. Kwashiorkor and marasmus are two of the main conditions associated with the insufficient intake of proteins and calories. These are characterized by irritability, lack of interest, and sunken fontanelle in babies. Additional symptoms include sunken groins, buttocks, face, and thighs (5).
A baby’s sunken fontanelle can be felt with the hand. It will appear soft and like a dent on the head. Along with this, if you find additional symptoms of dehydration or malnutrition, talk to your pediatrician as it could be a medical emergency.
Diagnosis Of Sunken Fontanelle
The doctor might do a physical examination and examine and feel the area to determine any abnormalities in the structure of the fontanelle. The doctor may also examine the baby’s heart rate, breathing, and skin condition for signs of dehydration or malnutrition.
Next, the doctor would ask questions to determine if they are suffering from dehydration or malnutrition. The questions could revolve around the baby’s feeding habits and whether they are urinating normally.
After knowing the case history, the doctor may prescribe tests to determine the underlying medical condition causing sunken fontanelle. These tests may include
- Blood tests
- Urine analysis
- Complete blood count
- Tests to check the vitamin and iron content
Treatment For Sunken Fontanelle
If the reason for the sunken fontanelle is dehydration, it needs immediate medical attention. The doctor might administer infant fluids orally. If the baby is suffering from diarrhea or vomitings, then the fluids might be administered intravenously.
In case your baby is malnourished, the essential nutrient should be delivered slowly, keeping the calorie intake at 60–80% of the total requirement for the age (5).
Prevention Of Sunken Fontanelle
Unless there is an underlying medical condition involved, sunken fontanelle can be prevented. Ensure your baby is well-hydrated, and stick to the feeding schedule. If your baby has started consuming solids, then include nutritious foods in their diet.
When To Call The Doctor?
If your baby has feeding difficulties or shows signs of excess thirst, produces low urine, or is lethargic and shows abnormal vital signs, contact your pediatrician.
Dehydration and malnutrition in babies should be addressed as soon as possible because if neglected, it could lead to long-term complications. And even if your baby does not show a sunken fontanelle but fails to thrive or gain weight, it is best to consult your pediatrician.
2. Fontanelles – sunken; University Of Florida Health
3. Joseph Kiesler and Rick Ricer; The Abnormal Fontanel; American Family Physician (2003).
4. Diabetes Insipidus; Histiocytosis Association
5. Owuraku A. Titi-Lartey and Vikas Gupta; Marasmus; StatPearls (2020).