FETAL SKULL INCLUDING BONES AND DIAMETERS

FETAL SKULL
• The fetal skull contains the delicate brain, which
may be subjected to great pressure as the head
passes through the birth canal.
• It is large in relation to the fetal body and in
comparison with the mother’s pelvis, there for
some adaptation between the skull and pelvis
must take place during labour.
• The head is the most difficult part to be born
whether comes first or last.

Ossification
The bones of the fetal head originate in two different
ways.
1. The face is laid down in cartilage and is almost
completely ossified at birth, the bones being fused
together and firm.
2. The bones of the vault are laid down in membrane.
They ossify from the centre outwards and this
process is incomplete at birth leaving gaps, which
form the sutures and fontanelles.
• The ossification centre on each bone appears as a
boss or protuberance.

FETAL SKULL
• Skull is divided in to :
Facial
skeleton
Cranium
Vault (roof) Base

Adult Skull
Facial skeleton
14 small bones
• Zygomatic -2
• Maxillae-2
• Nasal -2
• Lacrimal -2
• Palatine -2
• Inferior conchae -2
• Vomer -1
• Mandible -1
Cranium
• Occipital bone(1)
• Parietal Bone (2)
• Frontal Bone (1)
• Temporal(2)
• Sphenoid (1)
• Ethmoid (1)

The skull is divided in to :-
• Base
• Vault
• Face

• Base
Composed of bones that are firmly united to
protect the vital centres in the medulla.

Vault
• Large, dome- shaped part above an imaginary
line drawn between the orbital ridges and the
nape of the neck.
• Vault the bones are thin and pliable at birth
which allows the skull to alter slightly in shape
during birth.

• Face
Composed of 14 small bones which are firmly
united and non-compressible.

Facial skeleton
14 small bones
• Zygomatic -2
• Maxillae-2
• Nasal -2
• Lacrimal -2
• Palatine -2
• Inferior conchae -2
• Vomer -1
• Mandible -1

BONES OF THE VAULT
• There are five main bones in the vault of the fetal
skull.
• Occipital bone(1)
• Parietal Bone(2)
• Frontal Bone(2)
• In addition to these five the upper part of
temporal bone is also flat and forms a small part
of the vault.

BONES OF THE VAULT
Occipital bone(1)
• Lies at the back of the head and
forms the region of the occiput.
• Part of it contributes to the base
of the skull as it contains the
foramen magnum, which
protects the spinal cord as it
leaves the skull.
• Its centre is occipital
protuberance.

BONES OF THE VAULT
Parietal Bone (2)
• Lie on either side of the skull.
• The ossification centre is parietal eminence.

BONES OF THE VAULT
Frontal Bone:(2)
• Form the forehead or sinciput.
• The ossification centre is frontal boss or
frontal eminence.
• The frontal bones fuse in to a single bone by 8
years of age.

BONES OF THE VAULT
• In addition to these five the upper part of
temporal bone is also flat and forms a small
part of the vault.

SUTURES
SUTURES :- cranial joints and are formed where
two bones adjoin.
1. Lambdoidal suture
2. Sagital or longitudinal suture
3. Coronal suture
4. Frontal suture

SUTURES
Lambdoidal suture: It separates the occipital
bone from the two parietal bones.

SUTURES
Sagital or longitudinal suture: lie between two
parietal bone

SUTURES
Coronal suture: separates the parietal bones
from the frontal bones. Passing from one
temple to the other.

SUTURES
Frontal suture: Between two frontal bones.
Also known as the metopic suture

SUTURES
Lambdoidal suture: It separates the occipital
bone from the two parietal bones.
Sagital or longitudinal suture: lie between two
parietal bone
Coronal suture: separates the parietal bones
from the frontal bones. Passing from one
temple to the other.
Frontal suture: Between two frontal bones.

Importance
1. It permits gliding movement of one bone
over the other during moulding of the head
2. Digital palpation of sagittal suture during
internal examination in labour gives an idea
of the manner of engagement of the head ,
degree of internal rotation of the head and
degree of moulding of the head.

FONTONALLES
Where two or more sutures meet, a fontanelle is
formed. Of the many fontanelles ( 6 in numbers ),
two are of obstetric significance.
• Anterior fontonalle or bregma
• Posterior fontonalle or lambda
• Sphenoidal or anterolateral fontanelle
• Mastoid or posterolateral fontanelle

Anterior fontonalle or bregma
• Formed by joining of the four
sutures in the midplane. Anteriorly -
frontal suture , posteriorly- sagital,
coronal on either side
• Diamond shaped or broad kite
shaped
• It closes by 18 months.
• It becomes pathological, if it fails to
ossify even after 24 months.
• AP & Transverse diameters are
approximately same it is 3 cm each

Importance:
1. Its palpation through internal
examination denotes the degree of
flexing of the head.
2. It facilitates moulding of the head.
3. It helps in accommodating the brain
growth . The brain doubles its size during
the first year of life.
4. Palpation of the floor reflects intracranial
status-depressed in dehydration, elevated
in raised intracranial tention

5. Collection of blood & exchange transfusion can
be performed through it.
6. CSF can be drawn through the lateral angle of
the anterior fontanalle from the lateral
ventricle.

Posterior fontanalle or lambda
• It is formed by junction of three suture lines –
sagital suture anteriorly & lambdoid suture on
either side .
• Shaped like Greek letter lambda. It is
triangular in shape & measures about
1.2cm×1.2cm
• Close by 6 weeks of age

FONTANELLES
• Two smaller fontanelles are located on each
side of the head

FONTANELLES
• More anteriorly the sphenoidal or
anterolateral fontanelle (between the
sphenoid, parietal, temporal, and frontal
bones).

FONTANELLES
• More posteriorly the mastoid or
posterolateral fontanelle (between the
temporal, occipital, and parietal bones).

Areas of fetal skull or Regions of the
fetal skull:
1. Occiput
2. Vertex
3. Brow or sinciput
4. Face

Areas of fetal skull or Regions of the fetal
skull
Occiput
The region lies between foramen magnum &
posterior fontanelle.
The part below the occipital protuberance is
suboccipital region

skull:
Vertex
 It is an area bounded by the posterior fontenelle, the
two parietal eminences & the anterior fontanelle.
Of the 96 %of the babies born head first, 95 %
present by the vertex

skull
Brow or sinciput
Extends from anterior fontanelle and the coronal
sutures to the orbital ridges

skull
Face:
Bounded by root of the nose & supra orbital ridges to
junction of the floor of the chin and the neck. The
point between the eyebrows is glabella. The chin is
termed the mentum.

skull:
Occiput: The region lies between foramen magnum &
posterior fontanelle.
Vertex: It is an area bounded by the posterior
fontenalle, the two parietal eminences & the
anterior fontanelle.
Brow or sinciput: Bounded by anterior fontanelle
coronal sutures root of the nose & supra orbital
ridges.
Face: Bounded by root of the nose & supra orbital
ridges to the junction of the chin and the neck.

DIAMETERS OF FETAL SKULL
Transverse diameters
1. Biparietal
2. Bitemporal
3. Super –subparietal
4. Bi –mastoid diameter

Transverse diameter
Biparietal diameter 9.5 cm Distance between two
parietal eminences

Transverse diameter
Super –
subparietal
8.5
cm
From a point placed
below one parietal
eminences to a point
placed above the other
parietal eminences of
the opposite side

Transverse diameter
Bi- temporal
diameter
8 cm Distance between the antero
–inferior ends (furthest
point ) of the coronal suture.

Transverse diameter
Bi –mastoid
diameter
7.5cm Distance between the
tips of the mastoid
processes

Transverse diameter
Biparietal diameter 9.5 cm Distance between two parietal
eminences
Super –subparietal 8.5 cm From a point placed below one
parietal eminences to a point
placed above the other parietal
eminences of the opposite side
Bi- temporal
diameter
8 cm Distance between the antero –
inferior ends (furthest point ) of
the coronal suture.
Bi –mastoid
diameter
7.5cm Distance between the tips of the
mastoid processes

Anterio-posterior or longitudinal

Suboccipito
bregmatic
(SOB)
9.5cm From the nape of the neck (below
the occipital protuberance) to the
centre of the bregma

Suboccipito
frontal(SOF)
10cm From the nape of the neck (below
the occipital protuberance) to the
centre of the frontal suture.(2)

Occipito-
frontal
(OF)
11.5cm From the occipital eminence to
the root of the nose (glabella).

Mentovertical (MV) 14 cm Mid point of the chin to the
highest point of the sagital
suture.(4)

Sub mentovertical
(SMV)
11.5cm Junction of the floor of
the mouth and neck to
the highest point on the
sagital suture.(6)

Submento-
bregmatic(SMB)
9.5 cm Junction of the floor of the
mouth and neck to the
centre of bregma.

Suboccipito
bregmatic
(SOB)
9.5cm From the nape of the neck
(below the occipital
protuberance) to the centre of
the bregma
Suboccipito
frontal (SOF)
10cm From the nape of the neck
(below the occipital
protuberance) to the centre of
the frontal suture.
Occipito-
frontal (OF)
11.5cm From the occipital eminence to
the root of the nose (glabella).

Mentovertical
(MV)
14 cm Mid point of the chin to the
highest point of the sagital
suture
Sub mentovertical
(SMV)
11.5cm Junction of the floor of the
highest point on the sagital
suture
Submento-
bregmatic (SMB)
9.5 cm Junction of the floor of the
centre of bregma.

Attitude of fetal head
• Degree of flexion or extension of the head on
the neck.
• The Attitude of fetal head determines which
diameters will present in labour and therefore
influences the outcome

Presenting diameters
Two –antero-posterior or longitudinal and a
transverse diameter. The diameters presenting in
the individual cephalic or head presentations are:
Vertex presentation
• Head is well flexed-suboccipitobregmatic
diameter and biparietal diameter present (both
9.5cm)
• Head is not flexed but erect –occipitofrontal
(11.5cm) and the biparietal diameter (9.5cm)

Presenting diameters
Brow presentation
Head is partially extended- the mentovertical
diameter (13.5cm) and the bitemporal
diameter (8.2cm) present
Face presentation
Head is completely extended –
submentobregmatic (9.5cm) and bitemporal
diameter (8.2cm) present

MOULDING
• Alteration of the shape of the fore coming
head while passing through the resistant birth
passage during labour.
• During normal delivery an alteration of 4mm
in skull diameter commonly occurs.
• It disappears with in few hours after birth.

Importance of moulding
• Slight moulding enables the head to pass more easily
through the birth canal.
• Extreme moulding as met in disproportion may
produce severe intracranial disturbance in the form
of tearing of tentorium cerebelli or subdural
hemorrhage.
• Shape of moulding can be an useful information
about the position of the head occupied in the pelvis.

Caput succedaneum
• It is the formation of swelling due to stagnation
of fluid in the layers of the scalp beneath the
griddle of contact over the periosteum.
• Swelling is diffuse , boggy and is not limited by
the suture line.
• Occurs after rupture of membrane.
• Disappears spontaneously with in 24 hrs after
birth.

Importance
• Indicates the static position of head for a long
time.
• Location of caput gives idea about position of
head occupied in the pelvis and the degree of
flexion (In left position the caput will be over
the right parietal bone. In right position caput
it will be in the left parietal bone.

Mechanism of formation:
Dilation of cervix

Lack support over the presenting part

The tissues with support will get compressed

Obstruction of venous return and lymphatic
dranage

Stagnation of fluid & appearance of a swelling

CEPHAL HEMATOMA
• Collection of blood in between the pericranium
and the flat bone of the skull.
• Due to rupture of a small emissary vein from the
skull and may be associated with fracture of the
skull bone.
• Usually unilateral & over a parietal bone. Swelling
is limited by the suture lines of the skull as the
pericranium is fixed to the margins of the bone.
• It develops after birth. Gradually develops after
12-24 hrs.
• It will take months or weeks to disappear.

CAPUT SUCCEDANEUM
1. Formation of swelling due to
stagnation of fluid in the
layers of the scalp beneath
the griddle of contact over
the periosteum.
2. Swelling is diffuse , boggy
and is not limited by the
suture line
3. Occurs after rupture of
membrane
4. Disappears spontaneously
with in 24 hrs after birth
CEPHAL HEMATOMA
1. Collection of blood in between
the pericranium and the flat bone
of the skull.Due to rupture of a
small emissary vein from the skull
and may be associated with
fracture of the skull bone.
2. Usually unilateral & over a
parietal bone. Swelling is limited
by the suture lines of the skull as
the pericranium is fixed to the
margins of the bone.
3. It develops after birth. Gradually
develops after 12-24 hrs.
4. Take months or weeks to
disappear.

Tentorium cerebelli:
horizontal fold of duramatter & it uses at right
angles to falx cerebri.
It is horse shoe shaped. It contain large veins &
it drains blood from the brain.
Superior sagital sinus
Runs along the upper edge of falx cerebri from
front to back.

Inferior sagital sinus
It is at the lower edge of falx cerebri.
Great cerebral vein of galen
It meets with the inferior sagital sinus at the inner
end of junction between the falx & tentorium.
Straight Sinus
Drains blood from the great cerebral vein & inferior
sagital sinus along the junction between falx &
tentorium.
Lateral sinuses
Carry blood to the internal jugular vein

Ossification
Ossification (or osteogenesis)-
is the process of laying down new bone material by cells called
osteoblasts.
It is synonymous with bone tissue formation.
There are two processes resulting in the formation of normal, healthy
bone tissue:
1. Intramembranous ossification is the direct laying down of bone
into the primitive connective tissue (mesenchyme), while
2. Endochondral ossification involves cartilage as a precursor.
In fracture healing, endochondral osteogenesis is the most commonly
occurring process, for example in fractures of long bones treated
by plaster of Paris,
whereas fractures treated by open reduction and stabilization by
metal plate and screws may heal by intramembranous
osteogenesis.

FETAL SKULL INCLUDING BONES AND DIAMETERS

FETAL SKULL INCLUDING BONES AND DIAMETERS

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FETAL SKULL INCLUDING BONES AND DIAMETERS