Fetal skull

for graduate and undergraduate students

1. FETAL SKULL By: Maj Saminder Malik MSc (N) Obs & Gyn

2. INTRODUCTION Contains delicate brain to prevent any pressure as head passes through birth canal Large in comparison to fetal body and maternal pelvis Require adaptation between fetal skull & maternal true pelvis Most difficult part to deliver Somewhat compressible and made of pliable tubular bones forming vault

3. BONES OF SKULL Total 05 bones in skull 1. Occipital bone (1): at the back of head, at the center of it has occipital protuberance 2. Parietal Bones (2):at the either side of head, ossification center of each is Parietal eminence 3. frontal Bones (2): forms the forehead, center of each is known as frontal eminence. Frontal bones fuses into single by 8 yrs. of age

4. SUTURES OF THE SKULL LAMBDOID: shape like G reek letter Lambda, separates occipital bone from two Parietal bones SAGITTAL: longitudinal suture, lies between two parietal bones CORONAL: separates frontal bones from parietal bones FRONTAL: lies between two frontal bones

5. AREAS OF SKULL VAULT: large dome shaped wall above an imaginary line drawn between the orbital ridges and the nape of neck BASE: comprised of bones which are firmly united to protect the vital centers in the medulla BROW: extends from anterior fontanels and coronal sutures to the orbital ridges FACE: bounded on one side by the root of nose and supraorbital ridges & other side by the junction of the floor of mouth with neck. (composed of 4small bones, firmly united & compressible)

6. FONTANELLES ANTERIOR (BREGMA): POSTERIOR( LAMBDA)

7. ANTERIOR FONTANEL (BREGMA) anteriorly frontal suture, posteriorly sagittal suture and laterally coronal suture Diamond shaped Measures 3-4cm long & 1.5 – 2cm wide Closes by 18months (1.5yrs) Pulsations can be felt through it Help in molding of head, assessing position of head during labor, depressed during dehydration, bulging during increased ICP, collection of CSF from lateral angles

8. POSTERIOR FONTANEL (LAMBDA) Formed by anteriorly sagittal suture and laterally lambdoid suture Triangular in shape Measures 1.2 ˣ 1.2 Floor is membranous Closes by 6weeks (1.5 months) Helps in assessing position and degree of flexion of head of head

9. LANDMARKS BREGMA: anterior fontanel LAMBDA: posterior fontanel VERTEX: bounded anteriorly by Bregma , posteriorly by Lambda and laterally by parietal eminence. Quadrangular in area, considered as a presenting part in labor. BROW: bounded superiorly by b regma & coronal sutures and inferiorly by root of nose & supraorbital ridges. GLABELLA: point between two eyebrows FACE: bounded superiorly by root of nose and supraorbital ridges and inferiorly by the junction of floor of mouth with neck SINCIPUT: area in front of bregma , lined by frontal bone OCCIPUT: between foramen magnum & lambda, lined to occipital bone MENTUM: chin

10. DIAMETERS OF SKULL 1. ANTEROPOSTERIOR/ LONGITUDINAL 2. TRANSVERSE

11. AP /LONGITUDINAL DIAMETERS AP Diameter Extension Clinical Importance SUBOCCIPITOBREGMATIC From below the occipital protuberance to center of bregma , 9.5cm Complete flexion vertex SUBOCCIPIATO FRONTAL From below the occipital protuberance to center of frontal suture, 10cm Partial flexion vertex OCCIPITOFRONTAL From occipital protuberance to the glabella, 11.5cm Deflexion vertex MENTOVERTICAL From midpoint of chin to highest point on vertex, 14cm Partial extension brow SUBMENTOBREGMATIC From junction of floor of mouth & neck to center of bregma , 11.5cm Complete extension, face SUBMENTOVERTICAL From junction of floor of mouth & neck to highest point of vertex, 9.5 cm Partial extension face

12. TRANSVERSE DIAMETERS Transverse Diameter Extension BIPARIETAL Between two parietal eminences , 8 .5cm BITEMPORAL Between two coronal sutures, 8cm BIMASTOID Between tips of mastoid process, 7.5cm

13. CLINICAL CONDITIONS MOLDING OF HEAD CAPUT SUCCEDANEUM CEPHALHEMATOMA

14. MOLDING OF HEAD Occurs with descent of fetal head into pelvis to reduce head circumference Obliteration of sutures Overlapping of the bones of vault (frontal bones slip under parietal bones, parietal bones override each other, parietal bones slip under occipital bones) Reduces the fetal skull diameters by 0.5 -1cm or even more Degree: 0 (suture lines separate) +1 (suture lines meet) +2 (suture lines overlap but can be reduced by gentle digital pressure +3 (suture lines overlap irreducible)

15. CAPUT SUCCEDANEUM Diffuse scalp edema resulting from venous congestion due to prolonged pressure on fetal head by the pelvic bones Soft & boggy to touch Disappears after birth Mostly localized in nature Usually few mm thick but may be large Medico-legal implication: baby was living, difficult labor

16. CEPHALHEMATOMA Swelling due to bleeding between skull bone & periosteum Bleeding occurs due to friction between overriding bones and periosteum during molding Likely to occur during difficult vaginal labor Low prothrombin levels can be contributory Not present at birth but appears after 2-3 days Swelling is limited by periosteum , so doesn't cross the suture line Head appears more red & bruised Swelling can increase & may take 6weeks to disappear