Fontanelle - wikipedia Fontanelle This article is about the human anatomical feature. For other uses, see Fontanelle ( disambiguation ). `` Soft spot '' redirects here. For the Clem Snide album, see Soft Spot. Fontanelle The skull at birth, showing the anterior and posterior fontanelles. The skull at birth, showing the lateral fontanelles. Details Identifiers Latin fonticuli cranii TA A02. 1.00. 027 FMA 75437 Anatomical terminology ( edit on Wikidata ) A fontanelle ( or fontanel ) ( colloquially, soft spot ) is an anatomical feature of the infant human skull comprising any of the soft membranous gaps ( sutures ) between the cranial bones that make up the calvaria of a fetus or an infant. Fontanelles allow for rapid stretching and deformation of the neurocranium as the brain expands faster than the surrounding bone can grow. Premature complete ossification of the sutures is called craniosynostosis. After infancy, the anterior fontanelle is known as the bregma. Contents 1 Structure 1.1 Closure 2 Clinical significance 2.1 Disease 2.1. 1 Fontanelles -- bulging 2.1. 2 Fontanelles -- sunken 2.1. 3 Fontanelles -- enlarged 3 In other animals 3.1 In dogs 4 Additional images 5 References Structure The skull of a baby consists of five main bones : two frontal bones, two parietal bones, and one occipital bone. These are joined by fibrous sutures, which allow movement that facilitates childbirth and brain growth. Posterior fontanelle is triangle - shaped. It lies at the junction between the sagittal suture and lambdoid suture. At birth, the skull features a small posterior fontanelle with an open area covered by a tough membrane, where the two parietal bones adjoin the occipital bone ( at the lambda ). The posterior fontanelles ossify within 2 or 3 months after birth. This is called intramembranous ossification. The mesenchymal connective tissue turns into bone tissue. Anterior fontanelle is a diamond - shaped membrane - filled space located between the two frontal and two parietal bones of the developing fetal skull. It persists until approximately 18 months after birth. It is at the junction of the coronal suture and sagittal suture. The fetal anterior fontanelle may be palpated until 18 months. In cleidocranial dysostosis, however, it is often late in closing or may never close. Examination of an infant includes palpating the anterior fontanelle. Two smaller fontanelles are located on each side of the head, more anteriorly the sphenoidal or anterolateral fontanelle ( between the sphenoid, parietal, temporal, and frontal bones ) and more posteriorly the mastoid or posterolateral fontanelle ( between the temporal, occipital, and parietal bones ). During birth, fontanelles enable the bony plates of the skull to flex, allowing the child 's head to pass through the birth canal. The ossification of the bones of the skull causes the anterior fontanelle to close over by 9 to 18 months. The sphenoidal and posterior fontanelles close during the first few months of life. 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. Closure In humans, the sequence of fontanelle closure is as follows : The posterior fontanelle generally closes 2 to 3 months after birth ; The sphenoidal fontanelle is the next to close around 6 months after birth ; The mastoid fontanelle closes next from 6 to 18 months after birth ; and The anterior fontanelle is generally the last to close between 18 -- 24 months. Clinical significance 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. This pulsating action is how the soft spot got its name -- fontanelle is borrowed from the old French word fontenele, which is a diminutive of fontaine, meaning `` spring ''. It is assumed that the term spring is used because of the analogy of the dent in a rock or earth where a spring arises. 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. Fontanelles allow the infant brain to be imaged using ultrasonography. Once they are closed, most of the brain is inaccessible to ultrasound imaging, because the bony skull presents an acoustic barrier. Disease Fontanelles -- bulging A very tense or bulging anterior fontanelle indicates raised intracranial pressure. Increased cranial pressure in infants may cause the fontanelles to bulge or the head to begin to enlarge abnormally. It can occur due to : Encephalitis -- swelling ( inflammation ) of the brain, most often due to infections Hydrocephalus -- a buildup of fluid inside the skull Meningitis -- infection of the membranes covering the brain Abusive Head Trauma ( AHT ) previously called Shaken Baby Syndrome Fontanelles -- sunken A sunken ( also called `` depressed '' ) fontanelle indicates dehydration or malnutrition. Baby anterior fontanelle 1 month Fontanelles -- enlarged The fontanelles may be enlarged, may be slow to close or may never close most commonly due to causes like : Down syndrome Hydrocephalus Intrauterine growth restriction ( IUGR ) Premature birth Rarer causes include : Achondroplasia Apert syndrome Cleidocranial dysostosis Congenital rubella Neonatal hypothyroidism Osteogenesis imperfecta Rickets In other animals In apes the fontanelles fuse soon after birth. In chimpanzees the anterior fontanelle is fully closed by 3 months of age. In dogs One of the more serious problems that can affect canines is known as an `` open fontanelle, '' which occurs when the skull bones at the top of the head fail to close. The problem is often found in conjunction with hydrocephalus, which is a condition in which too much fluid is found within and around the brain, placing pressure on the brain and surrounding tissues. Often the head will appear dome - shaped, and the open fontanelle is noticeable as a `` soft spot '' on the top of the dog 's head. The fluid - filled spaces within the brain, known as ventricles, also become swollen. The increased pressure damages or prevents the development of brain tissue. 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. Additional images Fontanelle. Anterior fontanelle. Cranial sutures shown from top of head. References Wikimedia Commons has media related to Fontanelle ( anatomy ). Jump up ^ `` fontanelle ''. TheFreeDictionary. Retrieved 24 April 2013. ^ Jump up to : Beasley, Melanie. `` Age of Closure of Fontanelles / Sutures ''. The Center for Academic Research and Training in Anthropogeny ( CARTA ). Retrieved 24 April 2013. Jump up ^ `` USMLE Step 2 : Secrets ''. editor1 = Theodore X. O'Connell. editor2 = Adam Brochert. book = USMLE Step 2 : Secrets. ed = 3rd. page = 271 ^ Jump up to : MedlinePlus Encyclopedia Fontanelles - bulging Jump up ^ `` Online Etymology Dictionary ''. www.etymonline.com. Retrieved 2016 - 04 - 02. ^ Jump up to : `` Fontanels ''. Boundless. Retrieved 3 October 2016. Jump up ^ Waxman, Stephen G. Clinical Neuroanatomy. 25th ed. New York : Lange Medical / McGraw - Hill, Medical Pub. Division, 2003. Jump up ^ MedlinePlus Encyclopedia Fontanelles - sunken ^ Jump up to : MedlinePlus Encyclopedia Fontanelles - enlarged Jump up ^ `` Open Skull Bones May, May Not Be Sign of Deadly Disorder ''. Terrificpets.com. Retrieved 2012 - 10 - 24. Compound structures of skull Neurocranium Calvaria Diploë Asterion Pterion Stephanion Inion Bregma Lambda Fossae anterior middle posterior cranial cavity Base of skull Fontanelle anterior posterior sphenoidal mastoid Facial skeleton Nasion Gonion Both dacryon zygomatic arch temporal fossa infratemporal fossa pterygomaxillary fissure pterygopalatine fossa Retrieved from `` https://en.wikipedia.org/w/index.php?title=Fontanelle&oldid=835125571 '' Categories : Human anatomy Skull Neonatology Hidden categories : Pages with unresolved properties Use dmy dates from April 2017 Talk Contents About Wikipedia Български Čeština ChiShona Deutsch Español Esperanto فارسی Français Ido Bahasa Indonesia Italiano עברית ქართული Kaszëbsczi Lietuvių Magyar Nederlands Norsk nynorsk Polski Português Română Runa Simi Русский Suomi Svenska ไทย Türkçe Українська 粵語 Žemaitėška 22 more Edit links This page was last edited on 6 April 2018, at 18 : 28. 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Question: when does a baby's posterior fontanelle close
Answer: 2 or 3 months after birth