Fetal Skull ANATOMY

Fetal Skull Introduction

• The fetal skull is the most challenging part of a baby to pass through the mother's pelvis.
• Understanding skull anatomy helps determine labor progress and delivery method.
• Skull bones protect the delicate brain.
• The smallest fetal skull diameter must fit within the largest maternal pelvic diameter for normal vaginal delivery.
• Malpresentations (wrong presentation) require careful attention.

Fetal Skull Components

• Vault: Composed of:

  • Two frontal bones joined by the frontal suture
  • Two parietal bones joined by the sagittal suture
  • One occipital bone joined to the parietal bones by the lambdoid suture
  • Frontal and parietal bones are joined by the coronal suture
  • Temporal bones join the parietal bones on each side.

• Face: The area from the chin-neck junction to the nose and supra-orbital ridges (brow). Consists of 16 bones.

• Base: The area includes the lower part of the skull

Vault Bones

• Frontal Bone: Forms the forehead; fuses into a single bone after 8 years.
• Parietal Bones: Located on either side of the skull; important in skull formation.
• Occipital Bone: Found at the back and base of the skull; connects to the cervical vertebrae.

Sutures

• Sutures are the fibrous joints between skull bones.
• They are flexible in fetuses allowing for skull changes during birth.
• Lambdoid suture, sagittal suture, and coronal suture join parietal and occipital bones.
• Sutures are important for fetal skull shape and deformation.

Fontanelles

• Fontanelles are the spaces between the bones of the fetal skull.
• They are membranous areas covered with membranes keeping the brain protected.
• Crucial landmarks for identifying birth position.
• Anterior fontanel (bregma): A large diamond-shaped space near the baby's forehead. Usually closes by 18 months.
• Posterior fontanel (lambda): A smaller triangular space near the baby's back of the head.

Landmarks and Diameters

• Vertex: Area between the anterior fontanel, two parietal bones, and the posterior fontanel. Ideal presentation for vaginal delivery.
• Bregma: The anterior fontanel.
• Brow: Area from the anterior fontanel to the eyesockets.
• Face: Area from the eyes to the chin.
• Occiput: Area between the posterior fontanel and skull base.
• Glabella: The bridge of the nose,
• Mentum: The chin
• Longitudinal Diameters: Measurements relating different spots on the skull, important in determining positioning. Examples are Suboccipito-bregmatic, suboccipito-frontal etc,
• Transverse Diameters: Measurements across the skull. Examples are Biparietal, Subparietal-supraparietal, Bitemporal, Bimastoid.