Fontanelle

Aka: Fontanelle, Fontanel, Anterior Fontanelle, Posterior Fontanelle

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II. Definitions

  1. Fontanelle size measurement
    1. Obtain anteroposterior diameter (AP)
    2. Obtain transverse diameter (T)
    3. Size = (AP + T) / 2
  2. Anterior Fontanelle
    1. Junction of coronal Suture and sagittal Suture
    2. Mean newborn size: 2.1 cm (larger in black infants) and may range up to 3-6 cm diameter
    3. Often enlarges in first few months of life
    4. Closes between 4 to 26 months (median 13.8 months)
    5. Closes by 3 months in 1% of infants
    6. Closes by 24 months in 96% of infants
  3. Posterior Fontanelle
    1. Junction of lambdoidal Suture and sagittal Suture
    2. Mean newborn size: 0.5 to 0.7 cm and may range up to 1 to 1.5 cm
    3. Closes by 2 months

III. Exam: Anterior Fontanelle

  1. Palpate Fontanelle with infant sitting upright quietly
    1. Fontanelle should feel soft
    2. Fontanelle should not be sunken or bulging
  2. Other examination features
    1. Auscultate for bruit (suggests AV Malformation)
    2. Macewen's Sign (percussion of Fontanelle)
      1. Dull cracked-pot sound suggests increased ICP

IV. Causes: Abnormal Anterior Fontanelle

  1. Bulging Fontanelle causes
    1. Crying, coughing or Vomiting
    2. Increased Intracranial Pressure
      1. Hydrocephalus
      2. Meningitis or Encephalitis
      3. Hypoxic-ischemic injury
      4. Trauma
      5. Intracranial Hemorrhage
      6. Dermoid tumors of the scalp
  2. Sunken Fontanelle causes
    1. Decreased Intracranial Pressure (Dehydration)
  3. Large Fontanelle or delayed closure
    1. Congenital Hypothyroidism
    2. Trisomy 21 (Down Syndrome)
    3. Rickets (with Hypophosphatemia)
    4. Achondroplasia
    5. Increased Intracranial Pressure
  4. Small Fontanelle or early closure
    1. Early closure may be normal
    2. Always evaluate for Microcephaly
    3. Craniosynostosis

V. References

  1. Bates (1991) Physical Exam, Lippincott, p. 586
  2. Fuloria (2002) Am Fam Physician 65(1):61-8 [PubMed]
  3. Kiesler (2003) Am Fam Physician 67(12):2547-52 [PubMed]

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