posteriorfontanelle

The posterior fontanelle, also called the occipital fontanelle, is the smaller soft spot at the back of a newborn's skull. It marks the gap between developing skull bones where the cranial sutures have not yet fused.

Location and appearance: It lies on the midline at the junction of the sagittal and lambdoid sutures near the occipital bone. It is diamond- or triangular-shaped and much smaller than the anterior fontanelle.

Development: The posterior fontanelle is usually present at birth and closes relatively early, typically within the first two to three months of life, though there is normal variation among individuals.

Clinical significance: During newborn examination the posterior fontanelle is palpated to assess skull shape and cranial growth. A tense or bulging fontanelle may indicate increased intracranial pressure or fever, while a depressed fontanelle can suggest dehydration or poor hydration. Because it closes early, changes after the first months are less informative than those of the anterior fontanelle; the anterior fontanelle is more commonly used to gauge intracranial status.

Variations and disorders: Premature infants often have larger fontanelles and slower closure; in some cranial abnormalities or syndromes, the posterior fontanelle may be absent or close prematurely.

See also: Fontanelle; Anterior fontanelle; Cranial sutures.