Fetal Skull, Schemes and Mind Maps of Anatomy

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Fetal Skull

Matthew Idowu OLATUBI

Introduction

• The skull contain the brain (delicate)
• Maybe subjected to pressure as the head passes through the birth canal
• Large in relation to the fetal body and mother’s pelvis
• The head is the most difficult to be born whether it comes first or last.
• Understanding of the landmarks and the measurements of the fetal skull is important to recognize presentations and positions - Helps in making appropriate decision

• The fetal head consist of :
  • The scalp,
  • The skull, and
  • Its contents

The Scalp

• The scalp is the outer soft part of the head
• It consist of:
  • The skin on which the hair grows
  • Connective tissue on which the skin rests
  • Aponeurosis with some muscle fibres which are situated mainly to the sides of the head
  • Loose connective tissue
  • Periosteum which covers the bones of the skull

Bones of the Vault

• There are five main bones in the vault
• The occipital bone
• Two parietal bones
• Two frontal bone

The Occipital Bone

• Lies at the back of the head and forms the region of the occiput
• Part of it contributes to the base of the skull as it contains the foramen magnum - Protect the spinal cord as it leaves the skull
• At the centre is occipital protuberence

Two Frontal Bones

• Form the forehead or sinciput
• At the centre of each is a frontal boss or frontal eminence
• The frontal bones fuse into a single by 8 years of age
• In addition to these five bones, the upper part of the temporal bone is also flat and forms a small part of the vault

The sutures

• They are cranial joints and are formed where two bones adjoin.
• The are of great obstetrical importance, they allow overlapping of the bones of the vault during labour
• The overlapping is called moulding
• The sutures closes immediately after birth

Fontanelles

• Fontanelles are membranous spaces at the point of junction of the sutures.
• Anterior fontanelle or bregma:
• Posterior fontanelle or lambda

Anterior fontanelle

• Found at the junction of the sagittal, coronal and frontal sutures
• It is broad, kite shaped and recognisable vaginally because a suture leaves from each of the four corners
• Measures 3 – 4 cm long and 1. 5 – 2 cm wide
• Closes at 18 months
• Pulsations or cerebral vessels can be felt through it

Regions of the skull

• Occiput: region between the foramen magnum and the posterior fontanelle - The part below the occipital protuberance is called suboccipital region - The protuberance can be seen and felt as a prominent point on the posterior aspect of the skull
• Vertex: bounded by the posterior fontanelle, the two parietal eminences and the anterior fontanelle

Regions of the skull

• Sinciput or brow: extend from the ant fontanelle and the coronal suture to the orbital ridges
• The face: small in newborn baby
  • Extend from the orbital ridges and the root of the nose to the junction of the chin and the neck
  • The point between the eyebrows is known as the glabella
  • The chin is termed the mentum and it an important landmark

Diameters of the fetal skull

• Occipitofrontal: 11. 5 cm from the occipital protuberance to the glabella
• Mentovertical: 13. 5 cm point of the chin to the highest point of the vertex, slightely rearer the posterior than to the anterior
• Submentovertical: 11. 5 cm point where the chin joins the neck to the highest point on the vertex
• Submentobregmatic: 9. 5 cm from the point where the chin joins the neck to the center of the bregma

Attitude of the Fetal head

• Describe the degree of flexion or extension of the head on the neck
• Determines which diameter will present in labour and influence the outcome