Fetal Skull Badeea Seliem Soliman Assistant Prof. of gynecology and obstetrics Zagazig university

Fetal Skull Vault – Face – Base The vault is composed of soft bones separated by sutures and fontanelles.

Vault is subdivided into Forehead Vertex Occiput

1) Forehead From Bregma to root of the nose.

Bounded: (2) Vertex It is an area of the vault of skull Anteriorly anterior fontanelle Posteriorly posterior fontanelle Laterally line passing through parietal eminence

3) Occiput From posterior fontanelle to the external occipital Protuberance.

Bones of the vault IS (7 bones) 2 frontal bones 2 parietal bones 2 temporal bones 1 occipital bone The bones of the vault are not joined thus changes in the shape of the fetal head during labor can occur due to moulding

Sutures (number = 6) Spaces between skull bones. Made of un-ossified membranes which allows movements of cranial bones to decrease the skull diameters.

Sutures = 6 in number - Sagittal suture - Frontal suture - Coronal suture Lambdoidal sutures 2 Temporal sutures

Fontanels : Areas where sutures meet 6 in numbers

2 anterior temporal fontanelles at the junction of temporal and coronal sutures 2 Posterior temporal fontanelles at the junction of temporal &lambdoidal sutures no obstetric importance.

Anterior fontanelle Posterior fontanelle obstetric importance.

Posterior fontanelle (Lambda) Anterior fontanelle (Bregma) Small - Lozenge shaped - Large Obliterated at FT Obliterated at 1.5y after birth Formed by meeting of 3 bones Connected to 3 sutures - Formed by meeting of 4 bone - Connected to 4 sutures Bony floor Soft membranous floor With moulding of the head, over-riding of surrounding bones one parietal bond-­overrides the other and both override the occipital bone With moulding —> no over-riding of bones as they are widely separated from the start

Obstetric importance of ant. & post. Fontanelle 1- Diagnosis of vertex presentation 2- Detection of the position of the occiput (anterior or posterior or lateral) 3- Detection of the degree of flexion or deflexion of the head.

FETAL SKULL DEFINITIONS Bregma  Ant fontanelle Brow  lies between Bregma &root of the nose Face  lies between root of the nose & subra orbital ridges and chin Occiput boney prominence behind post fontanelle Vertex Diamond shaped area between ant & post fontanelles & parietal eminences

FETAL SKULL SUTURES Frontal suture  between 2 frontal bones Sagittal suture  between 2 parietal bones Coronal suture  between parietal & frontal Lambdoid suture  between parietal & occipital Temporal suture  between inferior margin of the parietal & temporal bones

FETAL SKULL FONTANELLES Anterior fontanelle  Diamond shaped space between coronal & sagittal suture - ossifies at 18 m Posterior fontanelle (lambda)  Triangle shaped space between sagital suture & Lambdoidal suture

Diameters of Fetal Skull

Diameters of fetal skull Longitudinal (6) Transverse (4)

Longitudinal Diameters (6)

1- Suboccipito bregmatic (9.5 cm) From sub occipital point to center of anterior fontanelle The diameter of engagement in occipito anterior position when head is completely flexed

2- Suboccipito - frontal (10 cm) From sub occipital point to anterior end of Bregma. 1- Diameter of engagement in vertex presentation with mild deflexion of the head. 2- Diameter that distends the vulva in occipito anterior if the head is allowed to extend after crowning.

Importance: 3- Occipito -frontal (11.5 cm): From the occipital protuberance to the root of the nose. Importance: -Diameter of engagement in O.P. 2- The diameter that distends the vulva in face to pubis delivery with O.P. 3-The diameter that distends the vulva if the head extends before crowning in O A.

4- Sub mento- bregmatic (9.5 cm) From the junction of the neck and chin to the centre of the bregma. Importance: It is the engaging diameter in face presentation with completely extended head.

5- Sub mento -vertical (11.5 cm) From the junction of the neck and chin to the vertical point (a point on the sagittal suture midway between the anterior and posterior fontanelles) 1- Diameter of engagement in face presentation with the head incompletely extended. 2- Diameter that distends the vulva in face delivery (m.a.).

6- Mento- vertical (13.5-14 cm): From the tip of the chin to the vertical point. Importance: It is the diameter facing the pelvic brim in brow presentation. It is more than the largest diameter of the pelvic brim

Longitudinal Diameters (6) Suboccipito bregmatic (9.5 cm) Suboccipito -frontal (10 cm) Occipito -frontal (11.5 cm) Sub mento- bregmatic (9.5 cm Sub mento -vertical (11.5 cm) Mento-vertical (13.5-14 cm)

Q: What is the name of diameter number 3 – 4 – 5?

Transverse diameters (4)

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