###### Created: 2023-05-17 18:15 ###### Areas & Topics: #medicine #anatomy #obstetrics ###### Note Type: #permanent ###### Connected to: [[Newborn Head Shape Abnormalities]] - When a baby is born, its skull is not fully developed in the same way that an adults is. - When you look at a baby's skull, you might see what some parents know as 'soft spots'. - These soft spots are known medically as fontanelles. - A fontanelle is a membranous areas that connects the sutures between the skull bones. - The presence of fontanelles allows the skull bones to overlap when exiting the vaginal canal during birth (since the membranous tissue can move as opposed to being solid bone), protecting the baby's brain. - It also allows the skull to rapidly grow and change shape as the brain develops and grows over time. - There are 6 fontanelles, which are the anterior fontanelle, posterior fontanelle, a pair of mastoid fontanelles and a pair of sphenoid fontanelles. - The fontanelles will eventually each close and all will have disappeared by around 18 months after birth, but the skull bones themselves will not fully ossify until around age 30. ### Etymology - The word fontanelle comes from the old french word 'fontenele', a version of the word 'fontaine' meaning spring (as in a natural spring). - This is because the fontanelles are likened to a dent in the ground where a spring rises from, since the fontanelle is a depression in the infant skull and also because the fontanelles (especially the anterior one) can sometimes be seen pulsating. ### Descriptions Anterior Fontanelle - The anterior fontanelle is found at the front of the infant skull, between the frontal and parietal bones and is diamond-shaped. - It is the largest fontanelle and the most useful clinically due to its size and location. - It is typically the last fontanelle to close, around 1 to 2 years after birth. Posterior Fontanelle - The posterior fontanelle is triangular and found at the back of the skull between the parietal and occipital lobes. - It normally is the first fontanelle to close, around 2 months after birth. Sphenoidal Fontanelles - The sphenoidal fontanelles are a pair, found on either side of the skull at the junction of frontal bone, parietal bone, temporal bone and sphenoid bone. - The union of these 4 bones when the fontanelles ossify is known as the pterion. - They are sometimes known as the anterolateral fontanelles and normally close around 6 months after birth. Mastoid Fontanelles - The mastoid fontanelles are a pair, found on either side of the skull at the intersection of the temporal, parietal, and occipital bones. - They are sometimes known as the posterolateral fontanelles and generally close at anytime from around 6 to 18 months after birth. ### General Information - Infants of African descent tend to have larger fontanelles on average (especially when referencing the anterior fontanelle). - Fontanelles in boys tend to close sooner than girls, on average. - Before closing, the fontanelle areas can be used as a way to ultrasound a baby's brain (ultrasound of the brain normally isn't possible as the skull is too thick for the sound waves to penetrate). - The fontanelles eventually close via intramembranous ossification. Pulsation - The anterior fontanelle can sometimes be seen pulsating, which is a normal finding. - It isn't known exactly why this happens, but the pulsation tends to be in time with the infant heartbeat, suggesting it might be associated with the blood vessels in the meninges passing under the fontanelle. Toughness - Parents might worry that the fontanelles are particularly weak or sensitive areas of the baby's skull that are prone to injury. - In fact, the membranous tissue forming the fontanelles is very tough and extremely difficult to penetrate (I wouldn't recommend testing this in anyway, but its good to know so parents don't worry too much about it.) ### Clinical Fontanelle Signs & Changes - The fontanelles (especially the anterior and posterior one) can be used to indicate changes inside the baby's skull, which might indicate other important conditions. - The best way to assess them is through direct observation and palpation. - It is best to try and do this when the baby is happy and agreeable, as crying or being angry (the baby, not you) may cause the fontanelle to bulge or feel full. Normal Findings - The anterior fontanelle might be softly pulsating in normal conditions. - Fontanelles are typically flat and firm. Sunken - A sunken, or depressed fontanelle most often indicates dehydration. - Dehydration can be caused by a variety of reasons, including infection, malnutrition etc. and should be investigated appropriately. Bulging - A bulging or raised fontanelle indicates raised intercranial pressure (ICP). - They are a wide range of reasons why this might occur, some of which can be life-threatening, and therefore this needs to be assessed thoroughly. - You can confirm if there is raised ICP by percussing the fontanelle. - If there is raised ICP, percussion should produce a dull note that lacks resonance or that sounds like a cracked pot (this is known as the [[Macewen's Sign]] or the 'cracked pot' sign). N.B. always remember that a baby crying or being angry can cause the fontanelle to bulge as well, so you should use your clinical judgement to decide if there are other underlying causes for the bulging fontanelle. Enlarged - A fontanelle which is larger than you would normally see, or which takes longer than normal to close might indicate an underlying pathology. - Enlarged fontanelles tend to be caused by genetic disorders, but can be caused by other conditions as well. - The most common causes include Achondroplasia, [[Down's Syndrome]], Congenital Hypothyroidism, raised ICP and Rickets. Third Fontanelle - In a small amount of cases (around 6%) there might be a third fontanelle present between the anterior and posterior fontanelles. - The presence of a third fontanelle is most often associated with [[Down's Syndrome]] or congenital infections (e.g. rubella). - If seen, it should be screened to rule out any serious underlying causes. Bruits - The fontanelles can also be auscultated as part of their assessment. - In some cases, bruits can be heard which can indicate serious pathologies including heart failure, multiple haemangiomas or arteriovenous malformation. ### Infant Skull Fun Facts - The parietal eminences are the widest part of the infant skull. - The mastoid process is not present on the infant skull, but develops when it is pulled by the sternocleidomastoid muscle whilst moving the neck over time. ### StatPearl Questions A first-time mother is nursing her newborn baby after delivery and notices a small indentation on the back of his head while nursing him. The nursing staff reassures the mother that this is a normal finding in newborns. The fontanelle located at the junction of the sagittal and lambdoidal sutures usually closes by what age? A. The first day of life B. The second week of life C. The first month of life D. The second month of life Answer: D A 3-week-old boy presents with parental concerns about several soft spots on his head. His father is very worried that something is wrong with his son. The healthcare provider calmly reassures the father that these are fontanelles and that they are normal anatomical structures during infancy. He provides the appropriate education and reassures the father that they will close at different times during development. The fontanelle located at the junction of the sagittal, coronal, and frontal suture lines usually closes by what age? A. The first month of life B. The sixth month of life C. The first of life D. The second year of life Answer: D ![[maxresdefault 1.jpg]] ![[p2547-f1.gif]] ![[1280px-Human_anterior_fontanelle_1_month_dscn1449.jpg]] ### Sutures of the Skull ![[Pasted image 20230517182025.png]] ### Sources Anatomy, Head and Neck: Fontanelles - StatPearls https://www.ncbi.nlm.nih.gov/books/NBK542197/ Fontanelles - Wikipedia https://en.wikipedia.org/wiki/Fontanelle