CorpusHuman Anatomy
SkeletalRegion

Fontanelles

Fonticuli cranii

Also known as: fontanels, soft spots, anterior fontanelle, posterior fontanelle

Membrane-covered gaps between the incompletely ossified cranial bones of the fetus and infant, found where several sutures meet. They permit moulding during birth and rapid brain growth, and are a clinical window on intracranial pressure and hydration.

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Overview

Anterior fontanelle size≈2 cm (range 0.6–3.6 cm)
Anterior closure≈13–24 months
Posterior closure≈6–8 weeks

There are six fontanelles. The anterior (bregmatic) fontanelle — diamond-shaped, the largest (≈2 cm mean diameter, range 0.6–3.6 cm) — lies at the junction of the frontal and two parietal bones (coronal, sagittal and metopic sutures) and closes between ≈13 and 24 months. The posterior (lambdoid) fontanelle, triangular, lies between the parietals and occipital and closes by ≈6–8 weeks after birth. The paired sphenoidal (anterolateral) fontanelles at the pterion close at ≈6 months and the paired mastoid (posterolateral) fontanelles at the asterion between ≈6 and 18 months.

The anterior fontanelle is palpated in every infant examination with the baby calm and upright: it should be soft, flat and slightly pulsatile. During delivery, the overlapping of the vault bones at the sutures and fontanelles (moulding) reduces the diameter of the fetal head; the fontanelles and sutures felt on vaginal examination indicate the position of the presenting head (e.g. occipito-anterior).

Location

At suture junctions of the infant skull: bregma, lambda, pterion and asterion.

Parts & subdivisions

  1. Anterior (bregmatic) fontanelle
    Diamond-shaped; ≈2 cm; closes ≈13–24 months.
  2. Posterior (lambdoid) fontanelle
    Triangular; closes ≈6–8 weeks.
  3. Sphenoidal (anterolateral) fontanelles
    At the pterion; close ≈6 months.
  4. Mastoid (posterolateral) fontanelles
    At the asterion; close ≈6–18 months.

Function

  • Allow moulding of the head during vaginal birth
  • Accommodate rapid brain growth during infancy
  • Provide a clinical window to assess intracranial pressure and hydration

Clinical significance

Bulging vs sunken fontanelle

A tense, bulging fontanelle in a calm, upright infant indicates raised intracranial pressure (meningitis, hydrocephalus, haemorrhage); a sunken fontanelle suggests dehydration.

Abnormal closure

Delayed closure or a large fontanelle: congenital hypothyroidism, rickets, achondroplasia, Down syndrome, osteogenesis imperfecta, cleidocranial dysplasia, raised ICP. Premature closure: craniosynostosis, microcephaly, hyperthyroidism.

Compiled from standard anatomy and physiology references — see the Skeletal System sources. For education only; not medical advice.