Foetal Skull Flashcards
Describe the skull
- Consists of 29 bones
- Ovoid shaped
- Consists of vault, base and face
What are the skull bones divided into?
- Vault
- 2 frontal
- 2 parietal
- 2 temporal
- 1 occipital
What is the vault?
Dome-shaped part between the orbital ridges and the nape of the neck
Describe the occipital bone
- Lies at the back of the head
- Ossification centre = occipital protuberance
Describe the parietal bones
- Lie on either side of the skull
- Ossification centres = parietal eminences
Describe the frontal bones
- Form the forehead and sinciput
- Ossification centres = frontal eminences
What is the base?
Firmly united bone protecting the vital centres of the medulla oblongata
Describe the face
- 14 small bones
- Firmly united and non-compressible
- Extends from orbital ridges to neck
- The point between the eyebrows in known as the glabella
What are the 4 regions of the foetal skull?
- Forehead/ Sinciput region (brow)
- Vertex
- Occiput
- Face
Describe the forehead/ sinciput region
Extends from the anterior fontanelle and the coronal suture to the orbital ridges
Describe the vertex
Bounded by the posterior fontanelle, the 2 parietal eminences and the anterior fontanelle
- Vertex positing = head first
Describe the occiput
- Lies between the foramen magnum and posterior fontanelle
- The part below the occipital protuberance is known as the sub-occipital region
Name 3 landmarks
- Occipital protuberance
- Mentum (chin)
- Glabella
What is a suture?
- The cranial joints formed when 2 bones meet
- Soft, fibrous tissue where ossification is not complete
- Allows moulding during labour and birth and expansion of brain development
What is ossification?
The hardening of the bones of the vault from the ossification centre outwards
What are the 4 sutures called?
- Frontal - between 2 halves of the frontal bone
- Sagittal - between 2 parietal bones
- Lamboidal - separates occipital bone and 2 parietal bones
- Coronal - separates front bones from parietal bones
What is a fontanelle?
A membranous non-ossified area where 2 or more sutures meet
Describe the anterior fontanelle
- Diamond/kite shaped
- Formed by junction of sagittal, coronal and frontal sutures
- Larger than the posterior fontanelle
- Closes at 18 months of age
What should the anterior fontanelle feel like during a VE?
- 4 sutures felt emanating from the fontanelle
- Demonstrates de-flexed head
- Alerts practitioners to larger diameter coming through pelvis
- Indicates direct occipital position
What is another name for the anterior fontanelle?
Bregma
Describe the posterior fontanelle
- Triangular
- Smaller than the anterior fontanelle
- Formed by junction of lamboidal and sagittal sutures
- Closes at 6 weeks
What should the posterior fontanelle feel like during a VE?
- 3 sutures felt emanating from fontanelle
- Well-flexed head position
- Smaller diameter presenting
- Indicated occipitoanterior position
What is another name for the posterior fontanelle?
Lambda
What are the 9 diameters of the foetal skull?
- Suboccipitobregmatic
- Suboccipitofrontal
- Occipitofrontal
- Mentovertical
- Submentovertical
- Submentobregmatic
- Biparietal
- Bisacromial
- Bitrochanteric
Describe the suboccipitobregmatic diameter
- Below the occipital bone to the centre of the anterior fontanelle
- 9.5cm
Describe the suboccipitfrontal diameter
- Below the occipital bone to the centre of the frontal bone/ suture
- 10cm
Describe the occipitofrontal diameter
- The occipital protuberance to the glabella (frontal bone)
- 11.5cm
Describe the mentovertical diameter
- From the point of the chin straight upwards to the highest point on the vertex
- 13.5cm
Describe the submentovertical diameter
- From the point where the chin meets the neck, straight upwards to the highest point on the vertex
- 11.5cm
Describe the submentobregmatic diameter
- From the point where the chin meets the neck to the centre of the bregma
- 9.5cm
Describe the biparietal diameter
- Stretched between the parietal eminences and is the engaging/crowning diameter
- 9.5cm
Describe the bisacromial diameter
- Stretched between the acromion processes on the 2 shoulder blades
- Articulation of the clavicles on the sternum may reduce this diameter slightly
- 12cm
Describe the bitrochanteric diameter
- Stretches between the greater trochanters of the femurs
- This is the presenting diameter in breech presentation
- 10cm
What are the 3 main types of presentation?
- Vertex
- Face
- Brow
Describe vertex presentation
- When head is well-flexed, sub-occipitobregmatic and biparietal diameters present
- Sub-occipitofrontal diameter distends vaginal orifice
- When head is deflexed, presenting diameters are occipitofrontal and biparietal
- This arises when occiput is in posterior position
- If this remains, occipitofrontal diameter distends vaginal orifice
Describe face presentation
- When head is completely extended, presenting diameters are submentobregmatic and bitemporal
- Submentovertical diameter distends the vaginal orifice
Describe brow presentation
- Occurs when head is partially extended and mentovertical and bitemporal diameters present
- Vaginal birth unlikely
What are the 5 main possible presenting parts?
- Cephalic
- Breech
- Face
- Brow
- Shoulder
Define moulding
The change in shape of the foetal head that takes place during its passage through the birth canal
Why does moulding occur?
- Bones of vault allow a slight degree of bending as they are soft and able to override sutures
- Results from pelvic girdle pressure
- Enables skull to alter shape and negotiate pelvis
- Diameters can be increased/decreased up to 1.5cm
- Frontal bones pushed to anterior edge of 2 parietal bones and occipital bone pushed under parietal bones
What relevance do sutures and fontanelles have to practice?
- To diagnose position of foetal head in labour
- Check foetal head for moulding
- Placing SE clip away from fontanelle
- Position is important for fixing ventouse cup
What is the favourable position for labour?
Lie - longitudinal Presentation - cephalic Position - left/right occipitoanterior Attitude - flexion Denominator - occiput Presenting part - posterior part of anterior parietal bone
Why is it important for the midwife to understand normal labour?
- To detect normal progresses of labour
- Awareness of abnormal mechanisms
- Aids delivery technique
- Assists in recognising shoulder dystocia
What does it mean if the fontanelle is sunk/ raised?
Sunk = dehydrated Raised = infection
What may cause bleeding in the great cerebral vein?
A tear in the tentorium cerebella
What is a caput succedaneum?
- Swelling caused by fluid under the skin
- Caused by pressure on the cervix at delivery
- Resolves within 24 hours
What is a cephalic haematoma?
- Swelling seen over 1 of 2 parietal bones
- Results in blood escaping from ruptured blood vessels between skull and periosteum
- Caused by trauma during delivery (e.g. forceps, ventouse)
- Occurs a few hours after birth up to 18 months
