Anterior fontanelle (AF) is a diamond shaped defect in the frontal and parietal bones.
It is between two frontal bones anteriorly and two parietal bones laterally. It is formed by joining of metopic suture (anteriorly), saggital suture (posteriorly) and coronal sutures (laterally).
Usually 3 cm x 3 cm in AP and transverse diameters
The anterior fontanelle becomes smaller gradually and normally closes between 9 to 18 months. It is smaller at birth (because of moulding) and apparently increases in size in 3-6 months.
If the anterior fontanelle persists beyond 18 months - Try to look for a cause. If the anterior fontanelle persists beyond 24 months - it is pathological.
METHOD OF EXAMINATION -
Child in upright position and not crying or straining.
Normal AF is slightly depressed and pulsatile.
SIGNIFICANCE OF ANTERIOR FONTANELLE -
Palpation of floor of the anterior fontanelle reflects the intracranial status -
Depressed in dehydration
Elevated in raised intracranial tension
It facilitates moulding of the head.
As it remains membranous long after birth, it helps in accommodating the marked brain growth, the brain becoming almost double its size during first year of life.
Diagnostic & therapeutic taps -
Subdural tap - From lateral endpoint towards tragus and go 0.5 to 1 cm deep.
Ventricular tap - Point towards nasion - go 2.5-3 cm deep.
Monitoring of intracranial tension can be done using a `Fontanometer'.
Its palpation through per vaginal examination denotes degree of flexion of the head during labour.
PATHOLOGIES OF ANTERIOR FONTANELLE -
Delayed closure of AF -
iv)Raised intracranial tension
Tense Bulging AF -
i)Crying childNalsalva manoeuvre
Depressed AF -
Pulsatile AF -
1) Normal in certain infants
ii)Venous sinus thrombosis (obstruction to venous return)
iii)Raised pulse pressure e.g. Patent ductus arteriosus, aortic regurgitation.