17-05-2012, 03:16 PM
FETAL SKULL
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FETAL SKULL
The skull is formed of the face , the vault & the base
The bones that form the skull are : two frontal bones, two parietal bones, two temporal bones wings of the sphenoid & occipital bone
The bones of the face & base are heavy & fused
The bones of the vault are 2 frontal ,2 parietal & occipital
The bones of the vault are not joined thus changes in the shape of the fetal head during labor can occur due to molding
FETAL SKULL DEFINITIONS
Bregma
Ant fontanelle
Brow
lies between bregma &root of the nose
Face
lies between root of the nose & suborbital ridges
Occiput
boney prominence behind post fontanelle
Vertex
diamond shaped area between ant & post fontanelles & parietal eminences
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
FETAL SKULL FONTANELLES
Anterior fontanelle
diamond shaped space between
coronal & sagittal suture 3 * 3 cm ,
ossifies at 18 m
Post font (lambda)
triangle shaped space between sagittal &
lambdoid suture
FETAL SKULL DIAMETERS
Suboccipitobregmatic 9.5 cm.
middle of the bregma to undersurface of the occipital bone at the neck
The presenting diameter of the well flexed head in labour
Suboccipitofrontal 10 cm
root of the nose to undersurface of the occipital bone at the neck
The presenting diameter of the partially flexed head.
Submento-vertical 11.5 cm
junction of floor of the mouth and neck to the highest point on the sagittal suture
FETAL SKULL DIAMETERS
Occipitofrontal 11.5 cm
Root of the noose to the most prominent point of the occiput
A defelexed head presents with this diameter
Mentovertical 14cm
Chin to most prominent point of the occiput
The presenting diameter in brow presentation
The largest diameter of the fetal head
Submentobregmatic 9.5 cm
Chin to middle of bregma
The presenting diameter in face presentation
TRANSVERSE DIAMETER
BIPARIETAL 9.5cm
Between 2 parietal eminences
BITEMPORAL 8 cm
Between the antero-inferior ends of the coronal suture
SUPER SUB-PARIETAL 8.5 cm
Extend from a point placed below one parietal eminence to a point placed above the other parietal eminence of the opposite side .
BI-MASTOID DIAMETER 7.5 cm
Distance between the tip of the mastoid process .
MOULDING OF THE HEAD
Occurs with descent of the fetal head into the pelvis to reduce the head circumference
Frontal bones slip under parietal bones
Parietal bones override each other
Parietal bones slip under the occipital bone