Neonatal Skull

How does the neonatal skull differ from the adult skull?

It has a disproportionately large cranium compared with the face.

What is the neonatal face-to-cranium ratio?

Approximately 1:8.

What is the adult face-to-cranium ratio?

Approximately 1:1.

What causes facial growth during childhood?

Growth of:

• Oral apparatus (jaws, teeth, muscles of mastication, tongue)

• Respiratory system (nasal cavities and paranasal sinuses)

What is the structure of neonatal skull bones

Smooth and bilaminar with no diploë.

Are skull bones fully ossified at birth?

No, ossification is incomplete and bones are mobile.

How are neonatal skull bones connected?

By fibrous tissue or cartilage.

What are fontanelles?

Unossified membranous intervals (“soft spots”) between skull bones.

Which fontanelles are clinically most important?

Anterior and posterior fontanelles.

Describe the anterior (bregmatic) fontanelle.

• Diamond-shaped

• Between frontal bones (anterior) and parietal bones (posterior)

• Closes by 18 months

Describe the posterior (lambdoid) fontanelle.

• Triangular

• Between parietal bones and occipital bone

• Closes by end of the 1st year

Where is the anterolateral (sphenoidal) fontanelle?

Junction of frontal, parietal, squamous temporal, and greater wing of sphenoid bones.

Where is the posterolateral (mastoidal) fontanelle

Junction of temporal, parietal, and occipital bones.

How does the tympanic part of the temporal bone differ at birth?

It is a C-shaped ring, not a curved plate.

What is the condition of the external auditory meatus in newborns?

Almost entirely cartilaginous.

How is the tympanic membrane positioned at birth?

• Nearer the surface

• Faces more inferiorly

How does the ear change during childhood?

• Tympanic plate grows laterally

• Bony meatus forms

• Tympanic membrane faces more laterally

Is the mastoid process present at birth?

No

Why does the mastoid process develop later?

Due to pull of the sternocleidomastoid muscle when the child moves the head.

Where is the mastoid antrum located at birth?

About 3 mm deep to the floor of the suprameatal triangle.

Where is the mastoid antrum at puberty?

Up to 15 mm from the surface due to skull growth.

How is the mandible structured at birth?

Two separate right and left dentary bones joined by a midline symphyseal joint.

When do the dentary bones fuse?

By the end of the first year at the symphysis menti.

Describe the angle of the mandible at birth..

Obtuse

How do the head and coronoid process relate at birth?

• Head is level with upper margin of body

• Coronoid process lies higher than the head

When does the mandible assume adult shape?

After eruption of permanent teeth.

How does aging affect the mandible?
A:

• Loss of teeth reduces mandible size

• Alveolar part becomes smaller

• Ramus becomes oblique

• Head bends posteriorly

• Loss of teeth reduces mandible size

• Alveolar part becomes smaller

• Ramus becomes oblique

• Head bends posteriorly