FETAL SKULL

                                    FETAL SKULL

Introduction:

Fetal skull is the bony part which protects the fetal brain & has to pass through the maternal pelvis to be born.

Parts of fetal skull:

• Vault
• Face 
• Base

Bones of vault:

• Frontal bones-2
• Parietal bones-2
• Occipital bone-1
• Temporal bones-2

Sutures of vault:

• Frontal suture: Between 2 frontal bones
• Coronal suture: Between frontal & parietal bone
• Saggital suture: Between 2 parietal bones
• Lamdoidal suture: Between parietal & occipital bone
• Squamous suture: Between Temporal & parietal bone on either side.

Regions of fetal skull:

• Vertex: A quadrangular area bounded anteriorly by bregma & coronal suture Posteriorly by lamda & lamdoidal sutures & laterally by parietal eminence.
• Brow: An area bounded by bregma & coronal sutures on one side & root of nose & supra orbital ridges on either side.
• Face: Area bounded by root of nose & supra orbital ridges on one side & by the junction of floor of mouth with neck on the other side.
• Sinciput: An area lying in front of anterior fontanel & corresponds to area of brow.
• Occiput: Area limited to occipital bone.

Landmarks of fetal skull:

• Vertex
• Face
• Brow
• Glabella
• Occiput
• Sinciput
• Mentum
• Parietal eminence

Fontanelles of fetal skull:

Wide gap in the suture line is called fontanel.

ANTERIOR FONTANEL:

• Also called as bregma
• Shape: diamond
• Bounded by:
• Anteriorly- Frontal bone
• Posteriorly- Saggital suture
• Laterally- Coronal suture
• Floor is made by membrane
• Measures- 3-4 * 1.5-2.5 cm.
• Ossification  at 18 months

Importance of anterior fontanel:

• Denotes degree of flexion by palpation during vaginal examination.
• Facilitates moulding
• Helps in accommodating fetal brain growth as the brain becomes almost double in size at the first year of life.
• Palpation of it reflects intracranial status: 
• Depressed- Dehydration 
• Elevated: Raised intracranial tension
• Blood collection or exchange transfussion in case of scalp infusion.
• Withdrawal of CSF .

POSTERIOR FONTANEL:

• Formed by junction of 3 sutures
• bounded by:
• Anteriorly- saggital suture
• Laterally- lamdoidal suture
• Shape- Triangular
• Measures about- 1.2 * 1.2 cm
• Ossification- 3 months.

Saggital fontanelle & Posteriolateral fontanelle both on either side have no clinical implications.

Moulding:

• Sliding of bones under each other thereby reducing diameters of fetal skull is called as moulding.
• During normal delivery an moulding of 4 mm diameter is common.
• Grade 1- Bones are not touching each other & no overlapping.
• Grade 2- Overlapping but easily separated.
• Grade 3-  Fixed overlapping

Diameters of fetal skull:

1] Anterioposterior diameters

2] Transverse diameters

1] Anterio-posterior diameters:

• Suboccipito bregmatic diameter: Below the occipital protuberance to the center of bregma- 9.5 cm
• Subocciputo frontal diameter: Below the occipital protuberance to the center of frontal suture- 10 cm
• Occipito frontal diameter: From occipital protuberance to glabella- 11.5 cm
• Mento vertical diameter: Loingest diameter. From the midpoint of chin to highest point of vertex- 14cm
• Submento vertical diameter: From the point where chin joints the neck to highest point of vertex- 11.5cm.
• Submento bregmatic diameter: From the point where chin joints the neck to the center of bregma-     9.5cm.

2] Transverse diameters:

• Biparietal diameter: Longest transverse diameter. distance between to parietal eminences- 9.5 cm.
• Bitemporal diameter: Distance between 2 farthest point of coronal suture- 8 cm.
• Supra-sub parietal diameter: From the point below 1 parietal eminence to the point placed above the other parietal eminence on opposite side - 8.5 cm.
• Bimastoid diameter: Distance between 2 mastoid process- 7.5 cm.

Clinical Implications:

• The sutures & fontanels are used for identification of presentation & position of fetus.
• The engaging diameter is an important factor that determines the progress of labor.