Anterior Fontanelle usually closes between 10-24months
Posterior fontanelle usually closes by 2 months


-early closure can be assoc w/ microcephaly, craniosynostosis, hyperthyroidism, or hypoparathyroidism. 
-Persistent enlargement of the anterior fontanelle in children with microcephaly may be due to a syndrome (eg, Down syndrome, trisomy 13 or 18, 5p- [cri-du-chat], Rubinstein-Taybi) or toxins



Early closure — Early closure of the anterior or posterior fontanelle is not uncommon in an otherwise normal child. However, it should alert the examiner to the possibility of developing microcephaly. (See "Etiology and evaluation of microcephaly in infants and children".)
____________
Other causes of early closure of the anterior fontanelle include [6,7]:


¦Craniosynostosis (see "Overview of craniosynostosis" and "Craniosynostosis syndromes") 
¦Hyperthyroidism (see "Clinical manifestations and diagnosis of hyperthyroidism in children and adolescents", section on 'Clinical manifestations')
¦Hypophosphatasia (see "Systemic conditions associated with periodontal disease in children", section on 'Hypophosphatasia')
¦Hyperparathyroidism (see "Clinical manifestations of primary hyperparathyroidism")

The approach to the child with early closure of the anterior fontanelle depends upon associated clinical findings, including ridging at the suture lines (suggestive of craniosynostosis), decreasing head circumference (suggestive of microcephaly), etc.

Delayed closure — The most common causes of delayed closure of the anterior fontanelle include [7,8]:
_______________

¦Normal variation
¦Congenital hypothyroidism (see "Clinical features and detection of congenital hypothyroidism")
¦Primary megalencephaly (see "Etiology and evaluation of macrocephaly in infants and children", section on 'Increased brain')
¦Increased intracranial pressure (see "Idiopathic intracranial hypertension (pseudotumor cerebri): Clinical features and diagnosis" and "Elevated intracranial pressure (ICP) in children")
¦Down syndrome (see "Clinical features and diagnosis of Down syndrome")
¦Rickets (see "Overview of rickets in children")

Other causes of delayed closure of the anterior fontanelle are listed in the Table (table 1). Many of these disorders are associated with an enlarged anterior fontanelle and have dysmorphic features that help to make the diagnosis.

Auscultation — Occasionally, auscultation of the skull for a bruit is helpful in detecting an arteriovenous malformation. A transmitted cardiac murmur may give rise to an audible cranial bruit, eliminated readily by gentle pressure over the ipsilateral carotid artery. An audible bruit in a child during the first several years of life may not be abnormal. Systolic bruits assume more significance as the child gets older.

Transillumination — Intracranial defects, such as hydranencephaly and hydrocephalus, can be 

Common causes  
Normal variation 
Congenital hypothyroidism 
Primary megalencephaly 
Increased intracranial pressure (of any etiology) 
Down syndrome 
Rickets 
Skeletal disorders  
Achondroplasia* 
Osteogenesis imperfecta* 
Cleidocranial dysostosis* 
Apert syndrome* 
Campomelic dysplasia 
Otopalatodigital syndrome, Type II 
Achondrogenesis-hypochondrogenesis, Type II 
Acrocallosal syndrome 
Antley-Bixler syndrome 
Hypophosphatasia* 
Pycnodysostosis* 
Schinzel-Giedion syndrome 
Kenny syndrome* 
Lenz-Majewski hyperostosis* 
Stanesco dysostosis 
Chromosomal abnormalities  
Down syndrome* 
Trisomy 13* 
Trisomy 18* 
 Endocrine disorders  
Hypothyroidism* 
Rickets* 
Drugs/toxins  
Fetal hydantoin syndrome 
Aminopterin-induced malformation 
Aluminum toxicity 
Dysmorphogenetic syndromes  
Russell-Silver syndrome* 
Rubinstein-Taybi syndrome* 
Hallermann-Streiff syndrome* (Oculomandibulofacial syndrome) 
Zellweger syndrome* (cerebrohepatorenal syndrome) 
Robinow syndrome* 
Cutis laxa* 
Progeria 
VATER association* 
Aase syndrome 
Melnick-Needles syndrome 
Conradi-Hunermann syndrome 
Otopalatodigital syndrome 
Saethre-Chotzen syndrome 
Miscellaneous  
Primary megalencephaly 
Malnutrition* 
Congenital syphilis*