Fetal Skull Flashcards
What does the vault consist of?
Two frontal bones
Two parietal bones
Two temporal bones
One occipital bone
What are the three sections of the fetal skull?
Vault
Base
Face
What are the central points of ossification?
Can be identified on the vault
Frontal bosses, parietal eminences, occipital protuberance
What is the sinciput?
The forehead
What is the bregma?
The anterior fontanelle
What is the mentum?
The chin
What is the lambda?
Posterior fontanelle
What is the vertex?
Highest point of fetal skull, midway between the parietal eminences
What is the occiput?
Area over the occipital bone
What is the glabella?
Bridge of the nose
How are the bones of the fetal skull connected?
Sutures composed of soft fibrous tissue
What is the purpose of sutures?
Allow the bones of the fetal skull to move and overlap
What are the four sutures and what do they join?
Frontal suture- joins the frontal bones
Sagittal suture- Unites the two parietal bones
Coronal suture- joins the frontal bones to the parietal bones
Lambdoidal suture- Unites the posterior margins and the parietal bones to the occipital bone
Describe the bregma
Anterior fontanelle
Located where to two frontal and parietal bones meet
Kite shaped
2cm wide 3 cm long
When does the bregma ossify?
Around 18 months of age
Describe the lambda
Posterior fontanelle
Where the parietal bones meet the occipital bone
Closes soon after birth
What are the two types of measurements of the fetal skull?
Longitudinal
Transverse
Describe the two transverse diameters
Biparietal diameter - average 9.5cm
Between the parietal eminences
Widest transverse diameter
Crowning of the head occurs once this this diameter has passed through the introitus
Bitemporal diameter- between the two extreme points of the coronal suture
8cm usually little significance
Describe the 6 key longitudinal diameters
Subocciptal bregmatic (SOB) - 9.5cm, vertex presentation, well flexed attitude
Subocciptal frontal (SOF) - 10cm, occipitoposterior presentation, partially flexed attitude
Occipital frontal (OF) - 11.5cm, cephalic presentation, erect attitude
Mentovertical (MV) - 13.5cm, brow presentation, partially extended attitude
Submentovertical (SMV) - 11cm, face presentation, partially extended
Submentobregmatic (SMB) - 9cm, face presentation, extended attitude
What is moulding?
The overlapping of fetal skull bones at the suture lines
When does moulding occur?
As the skull passes through the pelvis during delivery
It is a normal adaptation as the skull passes through the small diameters of the maternal pelvis
How can moulding assist delivery?
Can reduce diameters of the fetal skull by 1.5cm
How will moulding differ in pre and post term infants?
Pre term- skull is less ossified so moulding can be excessive. This puts strain on structures beneath skull such as folds of the dura mater covering the cerebral hemispheres
Post term- increased ossification so less opportunity for them to move. Not usually a problem.
What is the dura mater?
Tough, outermost membrane enveloping the brain and spinal cord (outermost layer of the meninges)
Folds of the dura mater dip in between the hemispheres of the cerebrum, this is called the falx cerebri
