Fontanelle
Overview
A fontanelle is an anatomical
Human anatomy
Human anatomy is primarily the scientific study of the morphology of the human body. Anatomy is subdivided into gross anatomy and microscopic anatomy. Gross anatomy is the study of anatomical structures that can be seen by the naked eye...

 feature on an infant's skull
Human skull
The human skull is a bony structure, skeleton, that is in the human head and which supports the structures of the face and forms a cavity for the brain.In humans, the adult skull is normally made up of 22 bones...

.
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 laying down new bone material by cells called osteoblasts. It is synonymous with bone tissue formation...

 of the bones of the skull causes the fontanelles to close over by 18 months up to a child's second birthday. The closures eventually form the sutures of the neurocranium.
Encyclopedia
A fontanelle is an anatomical
Human anatomy
Human anatomy is primarily the scientific study of the morphology of the human body. Anatomy is subdivided into gross anatomy and microscopic anatomy. Gross anatomy is the study of anatomical structures that can be seen by the naked eye...

 feature on an infant's skull
Human skull
The human skull is a bony structure, skeleton, that is in the human head and which supports the structures of the face and forms a cavity for the brain.In humans, the adult skull is normally made up of 22 bones...

.

Anatomy

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 laying down new bone material by cells called osteoblasts. It is synonymous with bone tissue formation...

 of the bones of the skull causes the fontanelles to close over by 18 months up to a child's second birthday. The closures eventually form the sutures of the neurocranium. Other than the anterior and posterior fontanelles, the mastoid fontanelle and the sphenoidal fontanelle are also significant.

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 cockleshell 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 which, when joined together, form the sides and roof of the cranium. Each bone is roughly quadrilateral in form, and has two surfaces, four borders, and four angles. It is named from the Latin pariet-, wall....

s, and one occipital bone
Occipital bone
The occipital bone, a saucer-shaped membrane bone situated at the back and lower part of the cranium, is trapezoidal in shape and curved on itself...

. 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 birth of one or more newborn infants from a woman's uterus...

 and brain
Brain
The brain is the center of the nervous system in all vertebrate and most invertebrate animals—only a few primitive invertebrates such as sponges, jellyfish, sea squirts and starfishes do not have one. It is located in the head, usually close to primary sensory apparatus such as vision, hearing,...

 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 a gap between bones in the human skull, triangular in form and situated at the junction of the sagittal suture and lambdoidal suture. It generally closes in 6-8 weeks from birth. A delay in closure is associated with congential hypothyroidism....

    , an open area covered by a tough membrane
    Biological membrane
    A biological membrane or biomembrane is an enclosing or separatingmembrane that acts as a selective barrier, within or around a cell. It consists of a lipid bilayer with embedded proteins that may constitute close to 50% of membrane content...

    , 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 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 two to three months of an infant's life. This is called intramembranous ossification. The mesenchymal connective tissue turns into bone tissue.

  • The much larger, diamond-shaped anterior fontanelle
    Anterior fontanelle
    The anterior fontanelle is the largest fontanelle, 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 also called Runx2, located on the short arm of chromosome 6....

     it is often late in closing or may never close. The anterior fontanelle is useful clinically. Examination of an infant includes palpating the anterior fontanelle.

  • Two smaller fontanelles are located on each side of the head, more anteriorly the sphenoidal (between the sphenoid, parietal, temporal, and frontal bones) and more posteriorly the mastoid (between the temporal, occipital, and parietal bones).

Clinical significance

A sunken fontanelle indicates dehydration
Dehydration
In physiology and medicine, dehydration is defined as the excessive loss of body fluid. It is literally the removal of water from an object; however, in physiological terms, it entails a deficiency of fluid within an organism...

, whereas a very tense or bulging anterior fontanelle indicates raised intracranial pressure
Intracranial pressure
Intracranial pressure is the pressure inside the skull and thus in the brain tissue and cerebrospinal fluid . The body has various mechanisms by which it keeps the ICP stable, with CSF pressures varying by about 1 mmHg in normal adults through shifts in production and absorption of CSF...

.

The fontanelle may pulsate, and although the precise cause of this is not known, it is perfectly normal and seems to echo the heartbeat, perhaps via the arterial pulse within the brain vasculature, or in the meninges
Meninges
The meninges is the system of membranes which envelopes the central nervous system. The meninges consist of three layers: the dura mater, the arachnoid mater, and the pia mater. The primary function of the meninges and of the cerebrospinal fluid is to protect the central nervous system.-Dura...

. This pulsating action is how the soft spot got its name - fontanelle means "little fountain."

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 imaging technique used for visualizing 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, because the bony skull presents an acoustic barrier.

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 also called Runx2, located on the short arm of chromosome 6....

 the skull fontanelle may be enlarged, and may be slow to close or may never close.

In dogs

Not all open fontanelles are connected with hydrocephalus. In many young dogs the skull bones are not fused at birth, but instead will close slowly over a three- to six-month period. Occasionally these bones fail to close, but the dog is still healthy. In these cases, however, the dog's owners need to be very careful, since any injury or bumps to the animal's head could cause significant brain damage, as well as conditions like epilepsy.
The source of this article is wikipedia, the free encyclopedia.  The text of this article is licensed under the GFDL.
 
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