Introduction:
Fetal skull is to some
extent compressible, and made mainly of thin pliable tabular (flat) bones
forming the vault. This is anchored to the rigid and incompressible bones at
the base of the skull.
Areas of skull: the skull is
arbitrarily divided into several zones of obstetrical importance.
These are
Vertex: It is a quadrangular area
bounded interiorly by the bregma and
coronal sutures behind by the lambda and labdoid sutures and laterally by lines
passing through the parietal eminences.
Brow: It is an area bounded on one
side by the anterior fontanelle and on
the other side by the root of the nose and supra-orbital ridges of either side.
Face: it is an area bounded on
one side by root of the nose and supra-orbital ridges and on the other, by the
junction of the floor of the mouth with neck.
Sinciput is the area lying in front
of the anterior fontanelle and corresponds to the area of brow and the occiput
is limited to the occipital bone.
Flat bones of the vault are
united together by non-ossified membranes attached to the margins of the bones
these are called sutures and
fontanelles.
Sutures:
1.
Sagittal or
longitudinal suture: Lies between two parietal bones bones
2.
Coronal sutures: Run
between parietal and frontal bones on
either side
3.
Frontal sutures: lies
between two frontal bones.
4.
Lamboid sutures:
separate the occipital bone and the two parietal bones.
Importance:
l. Permits gliding movement
during moulding.
2. Digital palpation of
sagittal suture during internal examinsation during labour.
Fontanelles: Wide gap in the Suture is
called fontanelle.
Anterior fontanelle: It is formed by the
joining of the four sutures in the midplane. The shape is like a diamond,
antero-posterior and transverse diameters measure approximately 3 cm each. The
floor is formed by a membrane and it becomes ossified 18 months after birth.
Importance:
l . Its palpation thought
internal examination denotes the degree of flexion of the head
2. Facilitate moulding of
the head.
3. Palpation of the floor reflects
intracranial status -Depressed in dehydration, elevated in raised intracranial
tension.
Posterior fontanelle: It is formed by junction of
three suture lines –Sagittal suture anteriorly and lambdoid suture on either side. It is triangular
in shape and measures about 1.2x1.2 cm .Its floor is membranous but becomes
bony at term.
Transverse Diameters of the
Fetal Skull:
Biparietal
Diameter
|
9.5 cm
|
Between the 2
parietal eminences
|
Bitemporal
Diameter
|
8 cm
|
It is the
distance between the antero-inferior ends of the coronal suture.
|
Bimastoid Diameter
|
7.5 cm
|
Between the 2
mastoid processes (Not reducible nor destroyable even by destructive
procedures)
|
Super-subparietal
|
8.5cm
|
It extends
from a point placed below one parietal eminence to a point placed above the
other parietal eminence of the opposite side
|
. .
Diameters of skull:
Diameter
|
Length
|
Attitude
|
Presentation
|
Suboccipito-bregmatic
Nape of neck
to centre of bregma
|
9.5 cm
|
Complete
flexion
|
vertex
|
Suboccipito-frontal
Nape of neck
to 2.5-cm. In front of bregma
|
10 cm
|
Incomplete
-flexion
|
Vertex
|
Occipito-frontal
Root of nose
to occipital protuberance
|
11.5 cm
|
Marked
deflexion
|
Vertex
|
Mento-vertical
Point of chin
to above posterior fontanelle
|
14 cm
|
Partial
extension
|
Brow
|
Submento-bregmatic
From below
chin to centre of bregma
|
11.5 cm
|
Incomplete
extension
|
Face
|
Submento-vertical
From below
chin to in front of post. fontanelle
|
9.5 cm
|
Complete
extension
|
face
|
Moulding: It is the
alteration of the shape of the forecoming head while passing through the
resistant during labour.
During normal delivery, an alteration of 4mm
in skull diameter commonly occurs.
Caput succedaneum:
It is the formation of
swelling due to stagnation of fluid in the layers of scalp beneath the gridle
of contact.
Diffuse scalp edema
resulting from venous congestion due to prolonged pressure on the fetal head by
the pelvis bones.
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