Fontanelle

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Fontanelle

A fontanelle (or fontanel) is an anatomical

Human anatomy

Human anatomy, which, with physiology and biochemistry, is a complementary basic medical science is primarily the scientific study of the morphology of the adult human body....
feature on an infant's skull

Skull

The skull is a bone structure found in the head of many animals. The skull supports the structures of the face and protects the head against injury....
.

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Posterior Fontanelle Question

Encyclopedia

A fontanelle (or fontanel) is an anatomical

Human anatomy

Skull

The skull is a bone structure found in the head of many animals. The skull supports the structures of the face and protects the head against injury....
. Fontanelles are soft spots on a baby's head which, during birth, enable the bony plates of the skull to flex, allowing the child's head to pass through the birth canal. The ossification

Ossification

Ossification is the process of bone formation, in which connective tissues, such as cartilage are turned to bone or bone-like tissue. The ossified tissue is invaginated with blood vessels....
of the bones of the skull cause the fontanelles to close over by a child's second birthday. The closures eventually form the sutures of the neurocranium. Although there are the two anterior and posterior fontanelles, there are two more fontanelles of interest, the mastoid fontanelle, and the sphenoidal fontanelle.

The skull of a newborn consists of five main bones: two frontal bone

Frontal bone

The frontal bone is a bone in the human skull that resembles a Cockle in form, and consists of two portions:* a vertical portion, the squama frontalis, corresponding with the region of the forehead....
s, two parietal bone

Parietal bone

The parietal bones are bones in the human skull and form, by their union, the sides and roof of the cranium. Each bone is irregularly quadrilateral in form, and has two surfaces, four borders, and four angles....
s, and one occipital bone

Occipital bone

The occipital bone, a saucer-shaped membrane bone situated at the back and lower part of the skull, is trapezoid in shape and curved on itself. It is pierced by a large oval aperture, the foramen magnum, through which the cranial cavity communicates with the vertebral canal....
. These are joined by fibrous sutures, which allow movement that facilitates childbirth

Childbirth

Childbirth is the culmination of a human pregnancy or gestation period with the delivery of one or more newborn infants from a woman's uterus. The process of normal human childbirth is categorized in three stages of labour: the shortening and dilation of the cervix, descent and delivery of the infant, and delivery of the placenta.....
and brain

Brain

The brain is the center of the nervous system in all vertebrate, and most invertebrate, animals. Some primitive animals such as cnidarian and echinoderm have a decentralized nervous system without a brain, while sponges lack any nervous system at all....
growth

Cell growth

The term cell growth is used in the contexts of Cell development and cell division . When used in the context of cell division, it refers to growth of cell populations, where one cell grows and divides to produce two "daughter cells"....
. At birth, the skull features a small posterior fontanelle
Posterior fontanelle

The posterior fontanelle is triangular in form and is situated at the junction of the sagittal suture and lambdoidal suture. It generally closes at about 6 months from birth....
, an open area covered by a tough membrane

Biological membrane

A biological membrane or biomembrane is an enclosing or separating amphipathic layer that acts as a barrier within or around a cell . It is, almost invariably, a lipid bilayer, composed of a double layer of lipid-class molecules, specifically phospholipids and cholesterol, with occasional integral membrane protein intertwined, some o...
, where the two parietal bones adjoin the occipital bone (at the lambda

Lambda (anatomy)

The occipital angle is rounded and corresponds with the point of meeting of the Sagittal suture and lambdoidal sutures?a point which is termed the lambda ; in the fetus this part of the skull is membranous, and is called the posterior fontanelle....
). This fontanelle usually closes during the first several months of an infant's life.

The much larger, diamond-shaped anterior fontanelle
Anterior fontanelle

The anterior fontanelle is the largest, and is placed at the junction of the sagittal suture, coronal suture, and frontal suture; it is lozenge-shaped, and measures about 4 cm in its antero-posterior and 2.5 cm in its transverse diameter....
where the two frontal and two parietal bones join generally remains open until the child is about two years of age, however, in cleidocranial dysostosis

Cleidocranial dysostosis

Cleidocranial dysostosis, also called Cleidocranial dysplasia, is a hereditary congenital disorder due to haploinsufficiency caused by mutations in the CBFA1 gene, located on the short arm of chromosome 6....
it is often late in closing or may never close. The anterior fontanelle's is useful clinically. Examination of an infant includes palpating the anterior fontanelle. A sunken fontanelle indicates dehydration

Dehydration

Dehydration is the removal of water from an object. In Physiology terms, it entails a relative deficiency of water molecules in relation to other dissolved solutes....
, whereas a very tense or bulging anterior fontanelle indicates raised intracranial pressure

Intracranial pressure

Intracranial pressure, , is the pressure in the cranium and thus in the brain tissue and cerebrospinal fluid ; this pressure is exerted on the brain's intracranial blood circulation vessels....
.

Parents may worry that their infant may be more prone to injury at the fontanelles. In fact, although they may colloquially be called "soft-spots", the membrane covering the fontanelles is extremely tough and difficult to penetrate. However, the fontanelles allow the infant brain to be imaged using ultrasonography

Medical ultrasonography

Diagnostic sonography is an ultrasound-based diagnostic medical imaging technique used to visualize subcutaneous body structures including tendons, muscles, joints, vessels and internal organs for possible pathology or lesions....
. Once they are closed, most of the brain is inaccessible to ultrasound imaging, as the bony skull presents an acoustic barrier.

In the congenital abnormality called cleidocranial dysostosis

Cleidocranial dysostosis