The harm of posterior fontanelle depression

We all know that the body structure of children is somewhat different from that of adults soon after birth. For example, if you put a lighted candle in front of a child, they will try to grab it, but you will find that they cannot grab it accurately because their retina is different from what we see. Also, babies have a fontanelle, which is divided into anterior and posterior parts. What harm will it cause if the posterior fontanelle is sunken?

The fontanelle refers to the gap in the skull formed by the loose connection of the skull bones of infants and young children. There are anterior fontanelle and posterior fontanelle. The posterior fontanelle is close to the occipital part of the head. It is a triangular gap formed by the sutures between the parietal bones and the occipital bones on both sides. The anterior fontanelle is at the top of the head. It is a diamond-shaped gap formed by the sutures between the frontal bones and the parietal bones on both sides.

Under normal circumstances, the posterior fontanelle is very small or closed when the baby is born, only large enough to accommodate a fingertip, and closes at the latest 6 to 8 weeks after birth. The oblique diameter of the anterior fontanelle is approximately 1.5 to 2.5 cm at birth. After birth, as the head develops, the head circumference gradually increases and the anterior fontanelle also increases. Six months after birth, the skull gradually becomes smaller as it ossifies and usually closes between one and a half years old.

In a very small number of babies, due to maternal infection during embryogenesis or other diseases, the brain is poorly developed and the head is small. The head circumference is small at birth, and the anterior fontanelle closes prematurely 5 to 6 months after birth, causing microcephaly. For a few babies, when they are 5 to 6 months old, the fontanelle is only the size of a fingertip and seems to be about to close, but in fact it has not ossified. This is not premature closure. As long as the head circumference is normal, not less than 46 cm at one year old and not less than 47 to 48 cm at two years old, it is normal and there is no need to worry.

The posterior fontanelle usually closes 3 months after birth, while the anterior fontanelle does not close until 1 and a half years old. The "skylight" or "fontanelle" that people often refer to mainly refers to the anterior fontanelle.

The surface of the fontanelle is the scalp, underneath it is the meninges, and then the brain and cerebrospinal fluid. Place your finger gently on the fontanelle and you can feel the beating. That is because the cerebrospinal pressure changes with the heart beat and blood pressure, which is consistent with the pulse. When a normal baby is sitting, the fontanelle is slightly sunken.

The cerebrospinal fluid in the skull is constantly exchanged with the body's blood and tissue fluid to maintain balance. When the body loses more water, the cerebrospinal fluid in the ventricles will also decrease, the pressure will decrease, and the fontanelle will become noticeably sunken. If an infant develops this symptom after vomiting or diarrhea, it means that the body is already moderately dehydrated and must be replenished with water in time. Otherwise, due to the infant's poor natural adjustment ability and insufficient tolerance, circulatory failure may occur, which is life-threatening. Extremely thin infants with severe malnutrition due to improper feeding may also have a sunken fontanelle, and at this time, they need to strengthen nutrition and feed properly.

A very small number of babies have small heads due to poor brain development due to maternal infection during embryogenesis or other diseases. The head circumference is small at birth, and the fontanelle closes prematurely 5-6 months after birth, resulting in microcephaly; the head is small and pointed, the forehead is narrow, the nose bridge is sunken, the lower jaw is small and retracted, and there is also intellectual disability. Children with cretinism caused by hypothyroidism will have a fontanelle that takes a long time to close; they will also have fewer and lighter eyebrows, a sunken nose, a wide distance between their eyes, and mental retardation.