Brief description about fetal skull

1. FETAL SKULL
(Annamma Sumon)
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2. FETAL SKULL
(Annamma Sumon)
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3. INTRODUCTION
• The fetal head is large in relation to the fetal body compared with adult.
• Adaptation between the skull and the pelvis is necessary to allow the head to
pass through the pelvis during labour without complication.
• The skull bones encases and protect the brain.
• • Fetal skull is compressible, and made mainly of thin pliable tabular(flat) bones
forming the vault.
(Annamma Sumon)
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4. FETAL SKULL
• The fetal skull has three major parts :
• Vault of the cranium (Roof)
• Face
• Base
(Annamma Sumon)
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5. Continue…
• Vault of the skull:- (made up of thin, pliable, flat bones which are compressible to some
extent)
• There are five main bones:-
1. Two frontal bones in front
2. The two parietal bones in between
3. The occipital bone at the back
• Base of the skull:- (bones are closely knit; hence the base is rigid & incompressible)
• Four bones lie at the base of the skull
1. The sphenoid
2. The ethmoid
3. The two temporal bones
(Annamma Sumon)
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6. SUTURES
• Flat bones of the vault are united together by the non osssified membranes
attached to the margins of the bones. These are called sutures.
• These are membranous lines found at the junction between the bones of the
vault.
• There are four main sutures:-
1. Frontal suture
2. Coronal suture
3. Sagittal or longitudinal suture
4. Lambdoid suture
(Annamma Sumon)
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7. (Annamma Sumon)
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8. IMPORTANCE
• It permits gliding movement of one bone over the other during moulding of the
head.
• Digital palpations 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.
(Annamma Sumon)
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9. FONTANELLES
• A wide gap at the intersection of the sutures is called fontanel
• Six fontanelles exist in the skull at term but only two of these are of obstetrical
significance:-
1. Anterior fontanel or bregma
• Formed by joining four sutures in midplane.
• Anteriorly frontal bone.
• Posteriorly sagittal.
• On either side coronal suture.
• Diamond shape. Measurement- anteroposterior 3 cm., transverse 2 cm.
• Ossifies by 18 months after birth
(Annamma Sumon)
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10. ANTERIOR FONTANEL OR BREGMA
• IMPORTANCE
• Its palpation through internal examination denotes the degree of flexion of the head.
• It facilitates moulding of the head.
• As it remains membranous long after birth, it helps in accommodating the marked
brain growth, the brain becoming almost double its size during first year of life.
• Palpation of the floor reflects intracranial status- depressed in dehydration, elevated in
raised intracranial tension.
(Annamma Sumon)
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11. POSTERIOR FONTANEL OR LAMBDA
• Formed by junction of three sutures.
• Sagittal suture anteriorly
• Lambdoidal suture on either side.
• Triangular shape. Measurement – 1.2x1.2 cm.
• Ossifies by 6 weeks after birth
• Importance:-
• It helps to denote the position of the head in relation to the maternal pelvis
(Annamma Sumon)
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12. PRESENTING PART OF FETAL SKULL
• Vertex
• Face
• Brow
• Sinciput
• Occiput
• Mentum
• Parietal eminences
• Sub-occiput
• Sub-mentum
(Annamma Sumon)
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13. VERTEX
• Quadrangular area
• Bounded
• Anteriorly by bregma & coronal sutures
• Posteriorly by lambda and lambdoidal sutures
• Laterally by arbitrary lines passing through the parietal eminences.
• Fetal head lies in flexion during this presentation
(Annamma Sumon)
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14. FACE
• It extends from the orbital ridges and the roof of the nose to the junction of the
chin and the neck.
• The point between the eyebrows is known as the glabella.
• The fetal head is fully extended during this presentation.
• The chin is termed as mentum & is an important landmark.
• Sub-mentum is the junction between neck and chin.
(Annamma Sumon)
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15. SINCIPUT
• Area in front of anterior fontanel corresponding to forehead
• Sinciput or brow extends from the anterior fontanelle and the coronal suture to
the orbital ridges.
Brow
• It is an area of forehead from the root of nose and supraorbital ridges to the
bregma and coronal sutures.
• The fetal head lies midway between full flexion and a full extension in this
presentation.
(Annamma Sumon)
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16. • Occiput
• Area limited to occipital bone.
• Sub-occiput
• It is the junction of the fetal neck and occiput, also called the nape of the neck.
• Parietal eminences
• These are eminences of parietal bones on either side
(Annamma Sumon)
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17. Diameters Measurement
in Cm (inches)
Attitude of the
Head
Presentation
Suboccipito-
bregmatic
9.5 cm (3 ¾”) Complete fexion Vertex
Suboccipito-
frontal
10 cm (4″) Incomplete fexion Vertex
Occipito-
frontal
11.5 cm (4 ½”) Marked deflexion Vertex
Mento-vertical 14 cm (5 ½”) Partial extension Brow
Submento-
vertical
11.5 cm (4 ½”) Incomplete
extension
Face
Submento-
bregmatic
9.5 cm (3 ¾”) Complete extension Face
DIAMETERS OF SKULL:
The anteroposterior diameters of the head which may engage are:
(Annamma Sumon)
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18. Diameters Measurement in Cm
(inches)
Biparietal 9.5 cm(3 ¾”)
Super-
subparietal
8.5 cm (3 ½”)
Bitemporal 8 cm (3 ¼”)
Bimastoid 7.5 cm (3″)
The transverse diameters:
(Annamma Sumon)
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19. Attitude of the Head Plane of Engagement Circumference
Complete fexion
Biparietal-
suboccipitobregmatic (almost
round shape)
27.5 cm (11″)
Deflexed Biparietal-occipito-frontal
(oval shape)
34 cm (13 ½”)
Incomplete extension Biparietal-mento-vertical
(bigger oval shape)
37.5 cm (15″)
Complete extension
Biparietal-
submentobregmatic (almost
round shape)
27.5 cm (11″)
CIRCUMFERENCES:
Circumferences of the Head in Different Attitudes:
(Annamma Sumon)
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20. MOLDING
• Alteration of the shape of fore-coming head while passing through the
resistant birth passage during labor.
• During normal delivery, an alteration of 4 mm in skull diameter commonly occurs
• Molding disappears within few hours after birth.
• Grading:
• Grade-1: Bones touching but not overlapping
• Grade-2: Overlapping but easily separated
• Grade-3: Fixed overlapping
(Annamma Sumon)
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21. (Annamma Sumon)
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22. Continue…
• Importance:
• Slight molding is inevitable and beneficial.
• Enables head to pass more easily, through birth canal.
• Extreme molding as met in disproportion may produce severe intracranial
disturbance in form of tearing of tentorium cerebelli or subdural hemorrhage.
• Shape of the molding can be a useful information about the position of the head
occupied in the pelvis.
(Annamma Sumon)
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23. CAPUT SUCCEDANEUM:
• Formation of Diffuse, boggy swelling due to
stagnation of sero-sanguineous fluid in the layers
of the scalp beneath girdle of contact crossing
midline suture.
• Localized swelling on the fetal skull due to edema of
tissue beneath the girdle of contact.
• Disappears spontaneously within 24 hrs. after birth.
• Signifies static position of head
• Gives an idea about the position of the head
occupied in the pelvis & degree of flexion achieved
(Annamma Sumon)
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24. MECHANISM OF FORMATION:
Head descends
Press over dilating cervix or vulval ring
Tissues in contact with full circumference of the girdle of contact is compressed
Venous return and lymphatic drainage interrupted
Stagnation of fluid
(Annamma Sumon)
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25. (Annamma Sumon)
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