Posterior Fontanelle Size

Definition Length of the posterior fontanelle (Fig. 7.29).

Landmarks The posterior fontanelle is a triangular structure. Measure from the anterior corner (A) to the midpoint (B) on a line connecting the two posterolateral margins created by the occipital bone (Fig. 7.29).

Instruments Spreading calipers or a tape-measure can be used.

Position The head should be held erect with the eyes facing forward.

Alternative The neonate may lie prone.

Remarks The posterior fontanelle is usually closed in neonates and only 3 percent of normal newborn infants have a posterior fontanelle that measures more than 2 cm. A third (or parietal) fontanelle may be found in about 5 percent of normal infants about 2 cm anterior to the posterior fontanelle. It occurs with greater frequency in Down syndrome and in congenital rubella syndrome. Fig. 7.30 shows normal values for posterior fontanelle size in African American and Caucasian American children at birth.

Pitfalls If the sagittal suture is widely patent, the anterior border of the posterior fontanelle may be difficult to distinguish.

Posterior Fontanelle
Figure 7.30 Comparison of posterior fontanelle size in African American and Caucasian American populations, both sexes, at birth. From Faix (1982), by permission.

African American

Mean 0.70 cm

1.60 cm

Caucasian +2SD

1.60 cm

Caucasian +2SD

Fontanelle Size

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  • luisa
    Is flat 1cm anterior fontanel normal?
    6 years ago
  • benjamin
    How to measure posterior fontanelle?
    4 years ago
    What is the measurement of the posterior fontanelle?
    4 years ago
  • yvonne
    Which instruments are used in fontanelle circumference?
    4 years ago
  • emily
    Where to find posterior fontanelle?
    3 years ago
    What is the measurements of the posterior fontanelle?
    2 years ago
  • Adaldrida Baggins
    How to find the posterior fontenelle on a newborn?
    2 years ago
  • Brigitte
    What is the size of posterior fontanel?
    3 months ago

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