Observing a dip in your baby’s soft spot, known as the fontanelle, can be alarming. This natural feature on an infant’s head can offer a valuable clue about a baby’s well-being. Understanding the context behind a sunken fontanelle is important for taking appropriate action. This article explains the fontanelle, the common reasons for a sunken appearance, and when to seek medical help.
Understanding the Fontanelle and Its Normal Appearance
The fontanelle, or soft spot, is a space between the bony plates of the skull that have not yet fused together. The skull consists of several bone sections joined by fibrous joints called sutures, which provide necessary flexibility. This flexibility allows the baby’s head to compress during delivery and accommodates the brain’s rapid growth during the first year of life.
Babies are typically born with several fontanelles, but the two most prominent are the anterior and posterior spots. The larger, diamond-shaped anterior fontanelle is on the top of the head and is the one most often noticed by parents. The smaller, triangular posterior fontanelle is toward the back and usually closes within the first two months. A normal fontanelle should feel soft and flat, possibly with a slight inward curve when the baby is calm and upright. A gentle pulsation in this area is also normal, reflecting blood flow from underlying vessels.
Dehydration: The Primary Cause of a Sunken Soft Spot
A noticeably sunken fontanelle is often one of the first physical indicators that an infant’s body fluid volume is low. Dehydration occurs when the body loses more fluid than it takes in, typically due to illness involving vomiting, diarrhea, or fever. A reduction in total body fluid volume leads to a decrease in the cerebrospinal fluid surrounding the brain. This fluid reduction causes the tissues underneath the fontanelle to retract, making the soft spot appear concave.
Assessing dehydration severity requires observing the soft spot alongside other signs. Mild dehydration may be indicated by a decrease in wet diapers, which should typically be six to eight in a 24-hour period. Signs of moderate dehydration include a dry mouth and tongue, a lack of tears when crying, and dry, less elastic skin. More concerning symptoms include sunken eyes, unusual sleepiness, or lethargy. If a sunken fontanelle is observed with any of these symptoms, immediate attention is needed to replenish lost fluids.
Other Factors Causing a Sunken Appearance
While dehydration is the most common cause, a slightly sunken appearance is not always an emergency. A mildly curved fontanelle may be a normal variation for some healthy infants. The appearance of the soft spot can also be affected by gravity and the baby’s position.
When a baby is held upright, the fontanelle may naturally appear more indented than when the baby is lying down. If the indentation returns to its normal flat appearance when the baby lies down, and the baby is alert and well-hydrated, the slight dip is likely benign. Rapid weight loss, such as from a change in feeding or a brief illness, may also contribute to a temporarily sunken look. In rare cases, chronic malnutrition or failure to thrive can cause the fontanelle to appear sunken over a longer period.
When Immediate Medical Attention is Necessary
A sunken fontanelle requires immediate medical attention if it is significantly depressed and accompanied by other warning signs. Severe dehydration symptoms include extreme irritability, excessive vomiting, or persistent diarrhea that prevents fluid intake. A high fever, which contributes to rapid fluid loss, combined with a sunken spot also warrants an urgent visit to a healthcare provider.
It is important to know the difference between a sunken and a bulging fontanelle. A soft spot that is tense or bulging when the baby is calm signals a different, serious issue, such as increased pressure inside the skull. This can indicate conditions like meningitis, a brain infection, or hydrocephalus (a buildup of fluid in the brain). If you notice a sunken fontanelle with severe dehydration indicators, or if the soft spot is bulging and hard, seek emergency medical care promptly.