FETAL Skull for undergraduate

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Fetal Skull
Badeea Seliem Soliman Assistant Prof. of
gynecology and obstetricsZagazig university
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Fetal SkullVault Face Base

• The vault is composed of soft bones separated by
  sutures and fontanelles.

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Vault is subdivided into

• Forehead
• Vertex
• Occiput

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1) Forehead
From Bregma to root of the nose.
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(2) Vertex It is an area of the
vault of skull

• Bounded
• Anteriorly
• anterior fontanelle
• Posteriorly
• posterior fontanelle
• Laterally
• line passing through
• parietal eminence

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3) Occiput
From posterior fontanelle to the external
occipital Protuberance.
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Bones of the vault IS (7 bones) 2 frontal
bones2 parietal bones 2 temporal bones1
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

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

• - Sagittal suture
• - Frontal suture
• - Coronal suture
• Lambdoidal sutures
• 2 Temporal sutures

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Fontanels Areas where sutures meet
6 in numbers
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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.
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Anterior fontanelle

• Posterior fontanelle

obstetric importance.
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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 gt no over-riding of bones as they are widely separated from the start
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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.

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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

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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

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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

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Diameters of Fetal Skull
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Longitudinal Diameters (6)
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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

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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.
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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.
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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.
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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.).

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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

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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)

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

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Transverse diameters (4)
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(1) Biparietal diameter (9.5 cm)Between The 2
parietal eminencesIt is the engaging diameter
with synclitism.
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2- Supraparietal -subparietal diameter (9
cm)From above the parietal eminence to below the
opposite eminence.Importance It engages in A.
P. diameter of the inlet in case of asynclitism.
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3- Bitemporal ( 8 cm) Between the
anterior ends of the temporal sutures.
Importance It engages in the oblique diameter
in O.P. Position
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4- Bimastoid ( 7.5 cm) Between The tips of the
2 mastoid processes.
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Transverse diameters of Fetal Skull
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Biparietal
Bitemporal
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Important Definitions
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Fetal Attitude

• It is the relations of the fetal parts to each
  other, it is in a general flexion attitude i.e.
  all joints are flexed

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• Complete Flexion
• Most common ( in Vertex
  presentation)
• Deflexion In O.P position.
• Military attitude Midway between flexion
• extension (brow).
• Complete extension In face presentation.

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Lie The relation between the longitudinal axis
of the fetus to that of the mother.
Types 1) Longitudinal (99.5 ).
2-Oblique or transverse (0.5 ).
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Presentation It is the lowermost part the fetus
the part related to the pelvic brim and first
felt by vaginal examination.
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N.BIn term pregnancy cephalic presentation is
more common than breech

• Because of
• The head is heavier so it occupies the LUS
• The buttocks are larger so it occupies the fundus

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Position The relation of the back of the fetus
to the right or to the left sides of the mother
and whether it is directed anteriorly or
posteriorly.

• 1 st position The back is left and anterior.
• 2 nd position The back is right and anterior.
• 3 rd position The back is right and posterior.
• 4 th position The back is left and posterior

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The denominator A landmark on the presenting
part denoting the position

• Occiput ------------------- in vertex.
• Frontal bone------------- in brow .
• Chin ----------------------- in Face.
• Scapula ------------------- in shoulder
• Sacrum -------------------- in Breech

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Vertex ---------------- occiput
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In vertex presentation (the commonest), There
are 8 positions
- Right and left occipito-anterior - Right and
left occipito- posterior - Right and left
occipito-transverse - Direct occipito anterior
and posterior
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8 positions
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Fetal Position
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The fetal compass rose
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O.A is more common than O.P because

• The concavity of the front of the fetus
• (due to its flexion) fits
• into the convexity of
• lumbar lordosis of
• maternal spine.

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LOA is more common than ROA and ROP is more
common than LOP because

• In LOA and ROP the head enters the pelvis in the
  right oblique diameter which is more favorable
  than the left oblique
• (2) Dextro-rotation of the head favours LOA if
  the back is directed to left side and ROP if the
  back is directed to right side.

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Passage of the widest transverse diameter of
the presenting part through the plane of the
pelvic inlet.Example B.P.D. in cephalic
presentation
Engagement
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Timing of engagementIn
PG (last 3 4 weeks)In MP it usually occurs
in the 1st stage or with onset of 2nd
stage

• Detection of engagement
• Abdominally by 1st pelvic grip (Rule of fifths).
• Vaginally (Rule of station).

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Station The level of the
head in the pelvis.
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Abdominally (Rule of fifths).
Detection of engagement
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Rule of fifths

• 0 station 2/5 of the head are felt abdominally
• above symphysis pubis
• 1 station 1/5 of the head is felt
• 2 station none of the fetal head is felt
  
• -1 station 3/5 head is felt
• -2 stations 4/5 head is felt
• -3 station the whole head (5/5) is felt

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Vaginally(Station of the head) The level of the
vertex is assessed in relation to the level of
ischeal spines At this level it is called
station (0) above this level is by minus every 1
cm and below by pulse every 1 cm
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Station of the head

• 0 The lowest part of the head is felt vaginally
  at
• the level of the ischial spine.
• 1 If 1 cm. below the level of ischial spines.
• 2 If 2 cm below the level of ischial spines.
• 3 If 3 cm. below the level of ischial spines
• -1 If 1 cm above the level of ischial spines.
• -2 If 2 cm above the level of ischial spines.
• -3 If 3 cm above the level of ischial spines.

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Causes of Non-engagement of fetal head
In 20 of cases no cause is found.
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Synclitism Asynclitism
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Synclitism When the 2 parietal bones are at the
same level
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Synclitism
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Asynclitism

• One parietal bone is presented below the other
  due to lateral inclination of the head, the
  sagittal suture lies nearer to the promontory or
  symphysis.

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• Value
• Asynclitism brings the shorter sub parietal -
  Supraparietal (9 cm) to enter the pelvis instead
  of B.P.D. (9.5cm).
• - Slight degree of asynclitism may occur in
  normal labour

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Posterior asynclitism (anterior parietal bone presentation Anterior asynclitism (posterior parietal bone presentation,
The anterior parietal bone is lower and the sagittal suture is nearer to the promontory. - It occurs more in MP due to laxity of the anterior abdominal wall. The posterior parietal bone is lower and the sagittal suture is nearer to the symphysis pubis. It occurs more in PG due to tense abdominal wall.
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Anterior parietal bone presentation is more
favorable than posterior parietal bone
presentation because
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Because

• (1) During correction of asynclitism, the head
  meets only the resistance of the sacral
  promontory while in posterior parietal bone
  presentation the head meets the resistance of the
  whole length of symphysis.
• (2) The head lies more in the pelvic axis with
  anterior parietal bone presentation.
• (3) With posterior parietal bone presentation
  ------ LUS more liable to stretch and rupture.

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• MCQ

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(1) The greatest diameters of the normal fetal
head is which of the following?

1. Occipito frontal
2. Suboccpito bregmatic
3. Bitemporal
4. Biparital
5. Mento vertical

(E)
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(2) The relation of the fetal parts to each other
determines which of the following?

1. Presentation of the fetus
2. Lie of the fetus
3. Attitude of the fetus
4. Position of the fetus
5. Intention of the fetus

(c)
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(3) In vertex presentation, what fetal part
determined the fetal position?

1. Mentum
2. Sacrum
3. Acromion
4. Occiput
5. Sinciput

(D)
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(4) The relationship of the long axis of the
fetus to that of the mother called IS

1. Lie
2. Presentation
3. Attitude
4. Posture
5. Position

(A)
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(5) Regarding the fetal skull fontanelles, one
of the following is true

• There are 3 fontanelles
• The posterior fontanelle is closed at 28 weeks of
  gestation
• The anterior fontanelle is closed at birth
• The anterior fontanelle is irregular in shape
• The posterior fontanelle is triangular in shape

(E)
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(6) The incorrect statement regarding fetal
presentation

1. It is the part of the fetus that enters the
   maternal pelvis first.
2. It is always cephalic
3. In cephalic presentation, it is more common to be
   vertex
4. In face presentation the head is completely
   extended
5. The denominator is always the lowest part of the
   presenting area

( E )
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(7) The correct statement for anterior fontanelle
(Bregma) is

• Triangular in shape
• Smaller than the posterior fontanelle
• Has bony floor
• Becomes obliterated 18 months after birth

( D )
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(8) The correct statement for biparietal diameter
of fetal head

1. Extend from a point below one parietal bone to a
   point above the opposite eminence
2. It is the engaging diameter in brow presentation
   
3. It is 9.5 cm in length
4. All of the above

( c )
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(9) Concerning the occipto frontal diameter, all
of the following are true EXCEPT

1. It extends from occipital protuberance to root of
   the nose
2. It is 9.5 cm I length
3. It is the diameter of engagement in after coming
   head of breech.
4. It is the diameter distending the vulva in face
   to pubis delivery

()
( B )
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(10) As regards the mento vertical diameter, all
of the following are true EXCEPT

1. It is 13.75 cm in length
2. It is the diameter of engagement in face
   presentation
3. It extends from tip of chin to the verticle point
4. It is larger than the largest diameter of pelvic
   inlet

( B )
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(11) The shortest diameter of the pelvic cavity
is

1. The external conjugate
2. Diagonal conjugate
3. The bispinous
4. The true conjugate
5. The transverse

( C )
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Short questions
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What are the various types of fetal
presentations?

• What are the different cephalic presentations?

How is position determined?
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What is the definition of mal presentation?

• What is the Rule of fifths?

Causes of non engagement ?
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Definition of

1. Lie
2. Vertex
3. Attitude
4. Engagement
5. Pelvic brim
6. Synclitism
7. Asynclitism
8. Station of the head

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Thank you