Fontanelles are soft, membranous, fibrous-tissue-covered gaps located at the junctions of two or more cranial sutures in the neonatal and infant skull, forming where cranial bones have not yet fully ossified. A newborn has six fontanelles: the anterior, posterior, two anterolateral (sphenoidal), and two posterolateral (mastoid); the anterior fontanelle — diamond-shaped, at the junction of the coronal and sagittal sutures — is the largest and most clinically significant, persisting until approximately 18 months of age, while the posterior fontanelle closes by 1-2 months. Unlike craniosynostosis, which involves premature fusion of sutures, fontanelles are a normal, physiologically necessary feature that must remain open to allow the brain to expand faster than surrounding bone can grow. Clinically, Fontanelle morphology reflects intracranial and systemic status: a sunken fontanelle suggests dehydration, while a bulging fontanelle signals elevated intracranial pressure from conditions such as meningitis, hydrocephalus, or intracranial hemorrhage. Pathological fontanelle findings are coded by the underlying etiology when identified; a bulging anterior fontanelle without confirmed diagnosis maps to R68.1 (nonspecific symptoms peculiar to infancy). Fontanelles are commonly confused with cranial sutures — sutures are the linear fibrous joints between adjacent bones, while fontanelles are the wider membranous junctions where multiple sutures and bones converge.
French fontaine, from Late Latin fontana (fon-TAH-nah), from Latin fons / fontis (FONZ / FON-tis)
“spring,” “fountain,” “source of flowing water” — descriptive root referring to the visible pulsation of the fontanelle, likened to a bubbling spring
-elle
French -elle (EL)
Diminutive noun-forming suffix — “little,” “small” — indicating a small or minor version of the root noun
The word entered English in the 1540s as fontanelle (noun), borrowed from French fontanelle (diminutive of fontaine, “fountain”), from Late Latin fontana, from Latin fons (“spring, source”) — literally “little fountain.” The name reflects the visible, rhythmic pulsation of the anterior fontanelle in infants, which early anatomists likened to a small bubbling spring. The root fons (“spring, source”) connects fontanelles to terms like fontanelle (little spring → soft spot), the anatomical landmark bregma (the central cranial meeting point), and the veterinary equivalent molera (persistent fontanelle in Chihuahuas). The diminutive suffix -elle is productive in anatomical French-derived terminology, appearing also in organelle, lamelle/, and prunelle.
🔀 ALIASES / ALTERNATE TERMS
Fontanel(American English spelling variant; used interchangeably with fontanelle in all clinical and coding contexts)
Soft spot(lay term; universally understood by parents and caregivers; used during well-child visits and parent education)
Anterior fontanelle(the diamond-shaped, clinically dominant soft spot at the bregma; persists 7-19 months; assessed for hydration status and ICP)
Posterior fontanelle(triangular; located at the lambda; closes 1-2 months; often already closed at birth)
Sphenoidal fontanelle(anterolateral fontanelle; one of four smaller fontanelles; located at the pterion)
Mastoid fontanelle(posterolateral fontanelle; one of four smaller fontanelles; located at the asterion)
Bregmatic fontanelle(alternate anatomical name for the anterior fontanelle; named for the bregma landmark)
Bulging fontanelle(clinical descriptor for elevated or tense fontanelle; sign of raised ICP; coded to underlying cause or R68.1 if no confirmed etiology)
Sunken fontanelle(clinical descriptor for depressed fontanelle; primary sign of dehydration in infants; coded to underlying cause)
Delayed fontanelle closure(associated with conditions including cleidocranial dysostosis, hypothyroidism, Down syndrome, and rickets; coded to primary diagnosis)
🔗 RELATED TERMS
Craniosynostosis — the opposite pathological state; premature fusion/ossification of one or more cranial sutures before brain growth is complete; classified under Q75.0 and site-specific codes; may cause skull deformity and elevated ICP
Cranial sutures — fibrous joints (synarthroses) between adjacent cranial bones; fontanelles form where multiple sutures converge; sutures remain open until adulthood while fontanelles close in infancy
Bregma — the anatomical landmark at the junction of the coronal and sagittal sutures; the location of the anterior fontanelle; used as a cranial reference point in neurosurgery and anthropology
Lambda — the junction of the sagittal and lambdoid sutures; location of the posterior fontanelle; another key cranial landmark
Pterion — the H-shaped junction of four bones (frontal, parietal, temporal, sphenoid) at the site of the sphenoidal fontanelle; clinically important due to underlying middle meningeal artery
Asterion — meeting point of parietal, occipital, and mastoid portions of temporal bone; site of the mastoid (posterolateral) fontanelle; surgical landmark for posterior cranial fossa access
Hydrocephalus — excess CSF accumulation causing elevated ICP, which manifests as a bulging, tense fontanelle; a key reason fontanelle assessment is performed at every well-child visit
Meningitis — infectious/inflammatory condition causing elevated ICP and bulging fontanelle in infants; critical differential when fontanelle is tense and accompanied by fever
Cleidocranial dysostosis — congenital disorder causing delayed or absent fontanelle closure (sometimes persisting into adulthood); associated with absent or hypoplastic clavicles; Q74.0
Rickets — metabolic bone disease (vitamin D deficiency) associated with widened sutures and delayed fontanelle closure; E55.0
Craniosynostosis (premature) — pathological counterpart to open fontanelles; may require surgical correction (cranial vault remodeling); coded Q75.0
Intracranial pressure — the pressure exerted within the skull; directly reflected by fontanelle tension; the anterior fontanelle serves as a non-invasive ICP monitor in infants
Cranial ultrasound(imaging through the open fontanelle) — primary diagnostic tool for evaluating intracranial structures in neonates; performed via the anterior fontanelle window; CPT 76506
Rickets, active (delayed fontanelle closure, widened sutures)
Q90.9
Down syndrome, unspecified (delayed fontanelle closure association)
🔧 COMMON CPT CODES (Fontanelle-Related Diagnosis & Treatment)
CPT Code
Description
76506
Ultrasound, brain (including brainstem); real time with image documentation (performed through open anterior fontanelle window in neonates/infants)
61000
Subdural tap through fontanelle or suture, infant; initial
61001
Subdural tap through fontanelle or suture, infant; subsequent taps (performed to relieve built-up blood or CSF and reduce intracranial pressure)
62270
Spinal puncture, lumbar, diagnostic (often performed alongside fontanelle evaluation to rule out meningitis)
21175
Reconstruction, bifrontal, for craniosynostosis (e.g., plagiocephaly, trigonocephaly); with orbital involvement, requiring bone grafts (craniosynostosis — premature fontanelle fusion)
21180
Reconstruction, extracranial, osseous and/or cartilaginous structure(s) of forehead (cranial vault remodeling for craniosynostosis)
61316
Incision and subcutaneous placement of cranial bone graft (autograft), with or without fixation
99461
Initial history and examination, normal newborn (includes fontanelle assessment at birth)
99391
Preventive medicine, individual counseling, infant (age < 1 year) — includes routine fontanelle palpation at well-child visits
⚠️ Coding Note: Fontanelle abnormalities are symptom-driven findings — always code the confirmed underlying etiology first (e.g., G91.1 for obstructive hydrocephalus, G03.9 for meningitis) with the fontanelle finding as a secondary/supporting code only when separately documented and clinically significant; if no confirmed diagnosis is established, use R68.1 for a bulging fontanelle in infancy. On inpatient profee claims, do not default to R68.1 if the admitting or attending provider has documented a confirmed diagnosis — sequence the confirmed condition as principal. A common undercoding pitfall is failing to capture P96.3 (wide cranial sutures of newborn) in the neonatal period when documented in the H&P or newborn exam — documentation triggers include phrases such as “anterior fontanelle widely open,” “sutures widely split,” or “large soft spot noted on exam.” For craniosynostosis cases requiring surgical intervention, ensure the operative report specifies which suture(s) are involved for site-specificity; Q75.0 is the billable code, but clinical documentation should support the type (e.g., sagittal, coronal, metopic, lambdoid) for medical necessity. Cranial ultrasound CPT 76506 is the primary imaging code when performed through the fontanelle window — verify the imaging report documents the fontanelle was used as the acoustic window, as this supports medical necessity for the neonatal/infant patient population.
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