by IBYC KRAMES · Cited by 146 — The diagnosis of an abnormal fontanel requires an understanding of the wide variation of normal. At birth, an infant has six fontanels.
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Examination ofa newbornÕs fon- tanels offers the physician a win- dow into the infantÕs developing brain and general state ofhealth. The word ÒfontanelÓis derived from the Latin fonticulus and the Old French fontaine,meaning a little fountain or spring. 1-3The normal fontanel varies widely in shape and time ofclosure.The incidence ofabnor- mal fontanel differs,depending on the abnor- mality and cause. JUNE15,2003 / V OLUME 67,N UMBER12www.aafp.org/afp AMERICANFAMILY PHYSICIAN 2547Anatomy of the FontanelsFontanels are the fibrous,membrane-cov- ered gaps created when more than two cranial bones are juxtaposed,as opposed to sutures, which are narrow seams offibrous connective tissue that separate the flat bones ofthe skull. A newborn has six fontanels (Figure 1) :theanterior and posterior,two mastoid,and two sphenoid.4The rhomboid-shaped anterior fontanel,located at the juncture ofthe two The diagnosis of an abnormal fontanel requires an understanding of the wide variation of normal. At birth, an infant has six fontanels. The anterior fontanel is the largest and most important for clinical evaluation. The average size of the anterior fontanel is 2.1 cm, and the median time of clo- sure is 13.8 months. The most common causes of a large anterior fontanel or delayed fontanel clo- sure are achondroplasia, hypothyroidism, Down syndrome, increased intracranial pressure, and rickets. A bulging anterior fontanel can be a result of increased intracranial pressure or intracranial and extracranial tumors, and a sunken fontanel usually is a sign of dehydration. A physical exam- ination helps the physician determine which imaging modality, such as plain films, ultrasonogra- phy, computed tomographic scan, or magnetic resonance imaging, to use for diagnosis. (Am Fam Physician 2003;67:2547-52. Copyright© 2003 American Academy of Family Physicians)The Abnormal Fontanel JOSEPH KIESLER,M.D.,and RICK RICER,M.D.,University ofCincinnati College ofMedicine,Cincinnati,Ohio PROBLEM-ORIENTED DIAGNOSISMembers of various family practice depart- ments develop articles for ÒProblem-Oriented Diagnosis.Ó This article is one in a series from the Department of Family Practice at the University of Cincinnati College of Medicine. Guest coordinator of the series is Susan Montauk, M.D. ILLUSTRATIONS BY CHRISTY KRAMESMetopic suture AnteriorfontanelParietal bone Squamous suture PosteriorfontanelOccipitalboneLambdoidstructure Mastoid fontanel TemporalboneSphenoidfontanelSphenoid boneZygomaticboneFrontal bone Coronal suture Frontal bone ParietalboneAnterior fontanelCoronal suture Sagittalsuture PosteriorfontanelLambdoid suture Occipital bone FIGURE 1. (Left) Lateral view of the newborn skull. (Right) Superior view of the newborn skull. Redrawn with permission after Netter FH. Atlas of human anatomy. Summit, N.J.: Ciba-Geigy, 1994. .
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parietal and two frontal bones,is the most prominent.The superior sagittal dural venous sinus is partially situated beneath the anterior fontanel.The triangular posterior fontanel is located at the junction ofthe occipital and two parietal bones. 1,5Growth and Development of the Skull The flat bones ofthe skull develop as part of the membranous neurocranium.Needle-like spicules radiate from a primary ossification center toward the periphery.These irregular bone islands are remodeled into flattened sheets ofbone by osteoblast and osteoclast activity.During fetal and postnatal life,the membranous bones enlarge by resorption centrally and by apposition ofnew layers at the edges ofthe sutures. 5Growth ofthe cranium is triggered by brain growth,two thirds ofwhich occurs by two years ofage.Except for the metopic suture between the frontal bones,which closes at two years ofage,the sutures remain open until brain growth ceases in the second decade of life.6Once a suture is fused,growth perpen- dicular to that suture is restricted.Therefore, fontanel size is influenced by brain growth, dural attachments,suture development,and osteogenesis. 7Examination of the FontanelsPHYSICALEXAMINATION The newbornÕs skull is molded during birth. The frontal bone flattens,the occipital bone is pulled outward,and the parietal bones over- ride.These changes aid delivery through the birth canal and usually resolve after three to five days. 8The newbornÕs skull should be evaluated for shape,circumference,suture ridges,and size ofanterior and posterior fontanels.Size is cal- culated by the average ofthe anteroposterior and transverse dimensions 9(Figure 2) .The fontanels should be examined while the infant is calm and held in both supine and upright positions.In select cases,such as new- borns with multiple hemangiomas or heart failure,the anterior fontanel is auscultated to detect a bruit,which can indicate an arteri- ovenous malformation. 10Palpation ofthe fontanel in the upright position may reveal a normal,slight pulsation.Ifthe fontanels are closed and intracranial pressure has increased,percussion produces a Òcracked- potÓsound (dull,lacking resonance),known as MacewenÕs sign. Any associated dysmorphic facial features should be noted.Asymmetry ofthe head is detected by looking at the infantÕs head from above.Head circumference is an important indicator ofbrain development and should be monitored over time,especially ifa fontanel closes early. 6,11IMAGINGPlain radiographs ofthe skull are the least expe nsive way to evaluate the sutures and cranial bones,but they are limited by the lack ofmineralization ofthe neonatal cranium. Bridging ofbone over a suture,an indistinct suture,or sclerosis along the suture margins indicates fusion.Cortical thinning,widened sutures,and a beaten-metal appearance known as ÒthumbprintingÓare associated with increased intracranial pressure. 12Ifthe anterior fontanel is open,ultrasonog- raphy is useful to evaluate ventricular dilata- tion. 13A computed tomographic (CT) scan can detect a fused suture,dilated ventricles,en- larged subarachnoid space,brain size,or an intracranial or extracranial mass. 14Magnetic resonance imaging (MRI) can detect cortical and white-matter abnormalities,such as de- generative diseases,and document the extent ofcalvarial masses.Disadvantages ofCT scans 2548AMERICANFAMILY PHYSICIAN www.aafp.org/afp VOLUME 67,N UMBER12 / J UNE15,2003 FIGURE 2. Measurement of the anteriorfontanel.abAnteroposterior (a) and transverse (b) diametersa + b = anterior fontanel size2
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and MRI include cost,the need for sedation, and,in the case ofCT,irradiation. 13,15Normal Fontanel POSTERIORFONTANEL At birth,the average size ofthe posterior fontanel is 0.5 cm in white infants and 0.7 cm in black infants. 16The fontanel usually is com- pletely closed by two months ofage. 10ANTERIORFONTANEL The key feature ofa normal anterior fontanel is variation.On the first day ofan infantÕs life, the normal fontanel ranges from 0.6 cm to 3.6 cm,w ith a mean of2.1 cm. 17Black infantshave larger fontanels (1.4 cm to 4.7 cm). 16Thefontanels offull-term and preterm infants are similar in size once preterm infants reach term. The fontanel can enlarge in the first few months oflife, 18and the median age ofclosure is 13.8 months.By three months ofage,the anterior fontanel is closed in 1 percent ofinfants;by 12 months,it is closed in 38 percent;and by 24 months,it is closed in 96 percent.Anterior fontanels tend to close earlier in boys than in girls;the initial size ofthe fontanel is not a pre- dictor ofwhen it will close. 19Abnormal Anterior Fontanel LARGEFONTANELANDDELAYED FONTANELCLOSURE A list ofthe medical conditions associated with a large fontanel or delayed fontanel closure can be found in Table 1 .20,21Achon- droplasia,congenital hypothyroidism,Down syndrome,rickets,and increased intracranial pressure are among the most common condi- tions.Achondroplasia is an autosomal-dominant disorder ofthe epiphyseal plate cartilage that results in dwarfism. 22At birth,the infant has an enlarged head,low nasal bridge,prominent forehead,and shortened extremities,in addi- tion to a large fontanel. 9An elevated thyroid-stimulating hormone level on a newborn screening usually detects congenital hypothyroidism,but an abnor- JUNE15,2003 / V OLUME 67,N UMBER12www.aafp.org/afp AMERICANFAMILY PHYSICIAN 2549TABLE 1Conditions Associated with an Enlarged Anterior Fontanel and Delayed Closure Enlarged Delayed Conditionsfontanelclosure Most common Achondroplasia Congenital hypothyroidism Down syndrome Increased intracranial pressure Normal variationFamilial macrocephaly RicketsLess commonSkeletal disorders Acrocallosal syndrome (seizures, polydactyly, mental retardation) ApertÕs syndrome (craniosynostosis, proptosis, hypertension) Campomelic dysplasia (prenatal growth deficiency, large cranium, bowed legs)Hypophosphatasia (polyhydramnios, short, deformed limbs, soft skull)Kenny-Caffey syndrome (hypoparathyroidism, dwarfism, macrocephaly) Osteogenesis imperfecta (shortened limbs, wormian calvarial bones)Chromosomal abnormalities Trisomy 13 (polydactyly, microcephaly, cleft lip and palate) Trisomy 18 (growth retardation, small cranium, open metopic suture) Congenital infectionsRubella (low birth weight, cataracts, Òblueberry muffinÓ skin lesions)Syphilis (saddle nose deformity, joint swelling, maculopapular rash)Drugs and toxinsAminopterin-induced malformation (craniosynostosis, absences of frontal bones, hypertelorism) Fetal hydantoin syndrome (microcephaly, broad nasal bridge, hypoplasia of nails)Dysmorphogenetic syndromes Beckwith-Wiedemann syndrome (macrosomia, abdominal wall defect, macroglossia) Zellweger syndrome (high forehead, flat occiput, abnormal ears, hypotonia)Cutis laxa (pendulous skin folds, hoarse cry)VATER association (vertebral defects, anal atresia, tracheoesophageal fistula, renal dysplasia) Otopalatodigital syndrome (frontal bossing, broad terminal phalanges, syndactyly)MiscellaneousMalnutrition (poor weight gain, asymmetric growth) Hydranencephaly (macrocephaly, thinned skull vault, primitive reflexes preserved) Intrauterine growth retardation (birth weight less than 2 standard deviations below mean) Information from references 20 and 21.
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mally large anterior fontanel in conjunction with an open posterior fontanel can be an early sign ofthe disorder.Myxedema and growth deficiency are later signs. A third fontanel between the anterior and posterior fontanels is associated with hypo- thyroidism and Down syndrome. 23Inf antswith Down syndrome often have a single pal- mar crease,flat occiput and facies,rounded ears,and slanted palpebral fissures. Rickets resulting from vitamin D deficiency rarely occurs in the United States but is one of the five most common childhood diseases in developing nations.Risk factors include breastfeeding without vitamin D supplemen- tation,dark skin,and low sunlight exposure. One ofthe signs ofrickets is craniotabes,a softened outer table ofthe occipital bone that buckles under pressure,producing a reaction similar to a ping-pong ball indenting and pop- ping back out.Craniotabes is not present at birth but develops over the first few months of life.Craniotabes can occur normally in pre- mature infants and in children younger than six months.18,24,25Disorders associated with increased intra- cranial pressure that results in an abnormally large fontanel or delayed fontanel closure are discussed later in this article. SMALLFONTANELOREARLYFONTANELCLOSURE Fontanel closure that occurs as early as three months ofage can be within normal limits,but careful monitoring ofhead circumference in such cases is essential to exclude a pathologic condition.The fontanel sometimes can be open but difficult to detect during a physical examination.Craniosynostosis and abnormal brain development are associated with a small fontanel or early fontanel closure. 20Craniosynostosis is the premature closing ofone or more cranial sutures,resulting in an abnormal head shape.The condition can be idiopathic or caused by hyperthyroidism, hypop hosphatasia,rickets,or hyperparathy- roidism.20It is also associated with more than 50 syndromes,such as ApertÕs,CrouzonÕs and PfeifferÕs.The risk ofprimary isolated cranio- synostosis is 0.4 per 1,000 live births,and the sagittal suture is most commonly involved. Examination at birth ofan infant with cra- niosynostosis might reveal a ridge over a suture or lack ofmovement along a suture when al- ternating sides are gently pressed.Overriding of sutures from the normal molding process should resolve within the first few days oflife. 9Later physical findings in infants with primary craniosynostosis include stunted cranial growth,increased intracranial pressure,pro- ptosis,strabismus,and hearing impairment. 26Plain radiographs ofthe skull are used for initial evaluation.Ifcraniosynostosis is pre- sent,a three-dimensional CT scan is obtained to detect any underlying brain abnormalities and to assist planning for surgery. 27Abnormal brain development that results in microcephaly also can cause a small ante- rior fontanel or early fontanel closure.Prena- 2550AMERICANFAMILY PHYSICIAN www.aafp.org/afp VOLUME 67,N UMBER12 / J UNE15,2003 The AuthorsJOSEPH KIESLER, M.D., is an assistant professor and director of the underserved resi- dency track in the Department of Family Medicine at the University of Cincinnati Col- lege of Medicine. He graduated from and completed a family medicine residency at the University of Cincinnati College of Medicine. RICK RICER, M.D.,is professor and vice-chair for educational affairs in the Department of Family Medicine at the University of Cincinnati College of Medicine. He received his medical degree from Ohio State University College of Medicine, Columbus, and com- pleted a family medicine residency at DeWitt Army Hospital in Ft. Belvoir, Va. Address correspondence to Joseph Kiesler, M.D., University of Cincinnati, Department of Family Medicine, 2446 Kipling Ave., Cincinnati, OH 45239 (e-mail: kieslehj@ fammed.uc.edu). Reprints are not available from the authors. TABLE 2Differential Diagnosis of Microcephaly Most commonChromosomal defects Congenital infections Fetal alcohol syndrome Hypoxic-ischemic encephalopathy Normal genetic variation Others Autosomal dominant or recessive types Dysmorphic syndromes Malnutrition Maternal phenylketonuria Normal variation Structural brain defects Universal craniosynostosis Information from references 20 and 28.
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tal trauma to the brain,such as maternal alco- hol abuse,and postnatal trauma,such as hy- poxia,are potential causes ofmicrocephaly. 20Table 2 20,28lists the different ial diagnosis for microcephaly. BULGINGORSUNKENFONTANELS Disorders associated with increased intra- cranial pressure can cause a bulging anterior fontanel.The most common disorders are meningitis,encephalitis,hydrocephalus, hypoxic-ischemic injury,trauma,and intra- cranial hemorrhage. 20Table 3 20lists the differ-ential diagnoses for a bulging fontanel.Palpa- tion may reveal a tense fontanel that feels similar to bone. 23Meningitis and encephalitis also cause tem- perature instability,poor feeding,and irri- tability.Ifmeningitis is suspected,a lumbar puncture should be performed to evaluate the cerebrospinal fluid for Gram stain,protein, glucose,cell count,and culture.A CT scan of a child with meningitis shows the subarach- noid space expanding into the anterior fontanel.21Hydrocephalus can result from an imbal- ance between the production and the absorp- tion ofcerebral spinal fluid.This condition affects 3 per 1,000 live births.Most cases occur before two years ofage,while the anterior fontanel is still open.Physical signs include an abnormal rate ofhead growth,frontal bossing ofthe forehead,widened sutures,and dilated scalp veins.Imaging with ultrasonography, CT,or MRI shows enlarged ventricles in the absence ofbrain atrophy.Because ultrasonic waves will not penetrate bone,the anterior fontanel must be open ifultrasonography is used for diagnosis. 13,15Hypoxic-ischemic injury results in cyto- toxic edema and diffuse brain swelling.Asso- ciated findings include poor feeding, decreased muscle tone,respiratory difficulties, and alterations in consciousness.Intracranial hemorrhage can be intraventricular,paren- chymal,subarachnoid,or subdural.Associ- ated findings include decreased muscle tone, seizures,decreased hematocrit,vomiting,and alterations in consciousness. 20Tumors also should be considered in the dif- ferential diagnosis ofa bulging fontanel.Der- moid tumors ofthe scalp are the most frequent lesions presenting over the anterior fontanel and also may be found over the posterior fontanel.29,30They usually are slow-growing and nontender,and they are twice as common among girls.A CT scan is necessary to exclude intracranial involvement. 30Brain tumors, which can present with signs ofincreased intracranial pressure and focal neurologic findings,are best diagnosed with MRI. 31The primary cause ofa sunken fontanel is dehydrat ion.Other signs include reduced Abnormal FontanelJUNE15,2003 / V OLUME 67,N UMBER12www.aafp.org/afp AMERICANFAMILY PHYSICIAN 2551TABLE 3Differential Diagnosis of a Bulging Fontanel Hydrocephalus Space-occupying lesionsBrain tumor Intracranial hemorrhage Brain abscessInfectionsMeningitis Encephalitis Roseola Shigella Mononucleosis Lyme disease Mastoiditis Cerebral malaria Cysticercosis PoliomyelitisEndocrine disorders Hyperthyroidism Hypoparathyroidism Pseudohypoparathyroidism AddisonÕs disease Hypothyroidism Cardiovascular disorders Congestive heart failure Dural sinus thrombosis Information from reference 20.Hematologic disorders Polycythemia Anemia LeukemiaMetabolic disorders Diabetic ketoacidosis Electrolyte disturbance Hepatic encephalopathy Uremia Galactosemia Hypophosphatasia Osteoporosis Maple syrup urine diseaseMiscellaneousHypervitaminosis A Lead encephalopathy Aluminum toxicity Brain contusions Hypoxic-ischemic injury Coronal synostosis TraumaDermoid cyst
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Abnormal Fontanelperipheral perfusion,poor skin turgor,and sunken eyes. 32Final Comment An abnormal fontanel in an infant can indi- cate a serious medical condition.Therefore,it is important to understand the wide variation of normal,how to examine the fontanels,and which diagnoses to consider when an abnor- mality is found.Consultation with a pediatric neurosurgeon should be considered ifthe diag- nosis or presence ofan abnormality is unclear. The authors thank Bruce Giffin, Ph.D., Department of Cell Biology, Neurobiology, and Anatomy at the Uni- versity of Cincinnati, for review of the manuscript. The authors indicate that they do not have any con-flicts of interest. Sources of funding: none reported.REFERENCES1.Soames R. Skeletal system. In: Gray H, Williams PL, Bannister LH, eds. GrayÕs Anatomy: the anatomical basis of medicine and surgery. 38th ed. New York: Churchill Livingstone, 1995:425-736. 2.WebsterÕs II New Riverside university dictionary. Boston: Riverside Publishing Co., 1984.3.Simpson DP. CassellÕs Latin dictionary: Latin-Eng- lish, English-Latin. New York: Macmillan, 1968. 4.Adeyemo AA, Omotade OO. Variation in fon- tanelle size with gestational age. Early Hum Dev 1999;54:207-14.5.Sadler TW, Langman J. LangmanÕs Medical embry- ology. 8th ed. Philadelphia: Lippincott Williams & Wilkins, 2000.6.Dale J, Maurer PK. Abnormal head. In: Ziai M, ed. Bedside pediatrics: diagnostic evaluation of the child. Boston: Little, Brown, 1983. 7.Liptak GS, Serletti JM. Pediatric approach to cranio- synostosis. Pediatr Rev 1998;19:352.8.The skeletal system. In: Moore KL, Persaud TV, eds. The developing human: clinically oriented embryol- ogy. 6th ed. Philadelphia: Saunders, 1998:414-21. 9.Fletcher MA. Physical diagnosis in neonatology. Philadelphia: Lippincott-Raven, 1998.10.Haslam R. Neurologic evaluation. In: Behrman RE, Kliegman RM, Arvin AM, Nelson WE, eds. Nelson Textbook of pediatrics. 15th ed. Philadelphia:Saunders, 1996:1667-77.11.Green M. Pediatric diagnosis: interpretation of symptoms and signs in children and adolescents. 6th ed. Philadelphia: Saunders, 1998.12.Sundine MJ. Clinical findings and treatment of chil- dren with abnormal head shapes. J Ky Med Assoc 1999;97:248-54.13.Machado HR, Martelli N, Assirati JA Jr., Colli BO. Infantile hydrocephalus: brain sonography as an effective tool for diagnosis and follow-up. Childs Nerv Syst 1991;7:205-10.14.Nard J. Abnormal head size and shape. In: Gart- ner JC, Zitelli BJ, eds. Common and chronic symp- toms in pediatrics: a companion to the atlas of pediatric physical diagnosis. St. Louis: Mosby, 1997: 95-109.15.Barkovich AJ. Pediatric neuroimaging. 3d ed. Philadelphia: Lippincott Williams & Wilkins, 2000. 16.Faix RG. Fontanelle size in black and white term newborn infants. J Pediatr 1982;100:304-6. 17.Popich GA, Smith DW. Fontanels: range of normal size. J Pediatr 1972;80:749-52.18.Kliegman RM. The newborn infant. In: Behrman RE, Kliegman RM, Arvin AM, Nelson WE, eds. Nel- son Textbook of pediatrics. 15th ed. Philadelphia: Saunders, 1996:433-40.19.Duc G, Largo RH. Anterior fontanel: size and clo- sure in term and preterm infants. Pediatrics 1986; 78:904-8.20.Tunnessen WW, Roberts KB. Signs and symptoms in pediatrics. 3d ed. Philadelphia: Lippincott Williams & Wilkins, 1999. 21.Rothman SM, Lee BC. What bulges under a bulging fontanel? Arch Pediatr Adolesc Med 1998;152:100-1.22.Cotran RS, Kumar V, Robbins SL. RobbinsÕ Patho- logic basis of disease. 4th ed. Philadelphia: Saun- ders, 1989.23.Taeusch HW, Sniderman S. Initial evaluation: his- tory and physical examination of the newborn. In: Taeusch HW, Ballard RA, eds. AveryÕs Diseases of the newborn. 7th ed. Philadelphia: Saunders, 1998:334-53.24.Barness LA. Manual of pediatric physical diagnosis. 6th ed. St. Louis: Mosby, 1991. 25.Tomashek KM, Nesby S, Scanlon KS, Cogswell ME, Powell KE, Parashar UD, et al. Nutritional rickets in Georgia. Pediatrics 2001;107:E45.26.Sundine MJ. Abnormal head shapes in children: classifications and syndromes. J Ky Med Assoc 1999;97:202-7.27.Park TS, Robinson S. Nonsyndromic craniosynosto- sis. In: McLone DG, ed. Pediatric neurosurgery: surgery of the developing nervous system. 4th ed. Philadelphia: Saunders, 2001:345-62.28.Bellet P. The diagnostic approach to common symptoms and signs in infants, children, and ado- lescents. Philadelphia: Lea & Febiger, 1989. 29.Martinez-Lage JF, Torroba A, Lopez F, Monzonis MC, Poza M. Cranial fasciitis of the anterior fontanel. Childs Nerv Syst 1997;13:626-8.30.Ruge JR, Tomita T, Naidich TP, Hahn YS, McLone DG. Scalp and calvarial masses of infants and chil- dren. Neurosurgery 1988;22:1037-42. 31.Hart BL, Benzel EC, Ford CC. Fundamentals of neu- roimaging. Philadelphia: Saunders, 1997.32.Mackenzie A, Shann F, Barnes G. Clinical signs of dehydration in children. Lancet 1989;2:1529-30. 2552AMERICANFAMILY PHYSICIAN www.aafp.org/afp VOLUME 67,N UMBER12 / J UNE15,2003
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