Fetal skull
Download as PPT, PDF35 likes19,550 views
The document discusses the anatomy of the fetal skull. It describes the bones, sutures, fontanelles and regions of the skull. It outlines the ossification process and diameters used to measure the skull. Moulding is explained as the overlapping of skull bones during birth to decrease diameters. Potential injuries like caput succedaneum and cephalhematoma are also summarized.
Fetal skull
- 2. Learning Outcomes By the end of this session and following a period of reflection you will be able to: 1. Identify the external anatomy of the fetal skull 2. Identify the internal structures of the fetal skull 3. Define the diameters of the fetal skull 4. Discuss the relevance of moulding 5. Identify types of injury that can occur to the fetal skull during labour and birth.
- 3. Fetal Skull • Consists of: –Bones –Suture –Fontanelles http://a-s.clayton.edu/biology/biol1151L/lab05/fetal_skull/fetalskull-front.jpg
- 4. Regions of the Skull For purpose of measurement and to describe degrees of flexion and extension the skull is divided into regions • Face: extends from the chin to the orbital ridges • Brow or Sinciput: area of the two frontal bones, extending from the orbital ridges to the anterior fontanelle • Vertx: bounded by the anterior fontanelle, the posterior fontanelle and two parietal eminences • Occiput: the area over the occipital bone, extending from the posterior fontanelle to the nape of the neck (Stables, 2010, p.341)
- 5. Regions of the Fetal Skull Vault Base: Consist of bones that are fixed and protect the base of the brain and medulla Face Face: This area extends from the orbital ridges to the junction of the chin and neck. Vault: The area above an imaginary line drawn from the nape of the neck to the orbital ridges Base (Serci, 2009, p.165)
- 6. Ossification of the Skull 1. Fetal skull formed from membrane 2. Five points called ossification centres – Pregnancy advances and calcium is laid down and these bones develop – Calcification starts as early as 5 weeks gestation 3. Preterm wide gaps of membranes not ossified (texture like a ping pong ball) 4. Full term still narrow areas of membrane between bones – ossification still incomplete (texture like a tennis ball) allows overlapping of bones at delivery 5. Post term ossification continues and areas of membrane decrease reducing overlapping of bones during deliver (Verralls, 1993)
- 7. Ossification of the Skull • Bones of face are made of cartilage and are almost completely ossified from birth • Ossification points on vault appear as a protruberances/boss/eminences e.g. Frontal protruberance/bosses Parietal eminence Occipital eminence (Stables, 2010, p.341; Serci, 2009, p.164)
- 8. Ossification of the Skull 1 32 54 (Verralls, 1993,)
- 9. Anatomy of the Fetal Skull (Wylie, 2005, p.198) MENTUM
- 10. Sutures and Fontanelles (Wylie, 2005, p.199)
- 11. Longitudinal Diameters Suboccipitobregmatic 9.5cm Submentobregmatic 9.5cm Suboccipitofrontal 10cm Occipitofrontal 11.5cm Mentovertical 13.5cm Submentovertical 11.5cm (Serci, 2009, p.166)
- 12. Longitudinal Diameters (Serci, 2009, p.166)
- 13. Fetal Skull – Lateral View http://a-s.clayton.edu/biology/biol1151L/lab05/fetal_skull/fetalskull-front.jpg
- 14. Transverse Diameters Biparietal 9.5cm Bitemporal 8.2cm (Serci, 2009, p.167)
- 16. Fetal Skull – Posterior View http://a-s.clayton.edu/biology/biol1151L/lab05/fetal_skull/fetalskull-front.jpg
- 17. Attitude of Fetal Head • Attitude: the degree of flexion or extension of the head on the neck. The attitude determines which diameters will present in labour (Serci, 2009, p.167) • Flexed: Occurs in the vertex presentation • Military or deflexed: Occurs in the occipitoposterior position • Partially extended: Occurs in the Brow presentation • Extended: Occurs in the face presentation
- 18. Circumferences of the Skull • Suboccipitobregmatic - 33cms – Presents when the head is well flexed – Head engages, fits well on the cervix and labour should be easy • Occipitofrontal - 35cms – Presents when the head is deflexed – Engagement is delayed, membranes may rupture early and labour may be difficult • Mentovertical – 39cms – Presents when the head is fully extended – Head cannot descend into the pelvis and labour is obstructed (Stables, 2010, p.342)
- 19. Moulding • The overlapping of the fetal skull bones at the suture line (Wylie, 2005, p.201) • Bones of vault allow slight bending and override one another at the sutures • Skull changes shape from ovoid to cylindrical • Causes presenting diameter to decrease whilst increasing the diameter at right angles • Rationale: smaller diameter to pass through vaginal canal (Serci, 2009, p.168; Stables, 2010, p.343)
- 20. Principles of Moulding The diameter compressed is decreased and the diameter at right angles is increased (Serci, 2009, p.168)
- 21. Typical Moulding The sutures and fontanelles allow overlap of the bones of the vault in a typical way such as: • Frontal bones are pushed under the anterior edge of the parietal bones • Occipital bone is pushed under the posterior part of the parietal bone • Medial edge of the leading parietal bone is pushed under the other parietal bone (Stables, 2010, pp.343-344)
- 22. Moulding of the Fetal Skull a b c d e Partially flexed Well flexed Partially extended Extended Deflexed (Military)
- 23. Fetal Skull Injuries • External – Caput Succedaneum – Cephalhaematoma – Chignon – Lacerations • Internal – Tentorial tears (Burden and Sapsed, 2011, pp.388-393)
- 24. Caput Succedaneum • Oedematous swelling that occurs on the presenting part • Present at birth • Can cross over the sutures • Soft swelling and will indent with pressure • Decreases following delivery • No treatment is required • Will disappear approximately 24-48hrs after birth • Moulding will also be apparent (Burden and Sapsed, 2011, pp.388-389; Wylie, 2005, p.200)
- 25. Caput Succedaneum (Burden and Sapsed, 2011, p. 390)
- 26. Cephalhaematoma • Bleeding that occurs between the bones of the fetal skull and periosteum • Occurs 12-72 hours after birth • Size increases following delivery • The swelling is restricted to one area and will not indent with pressure • Does not cross over the sutures • Can be bilateral • Can persist for a few weeks and occasionally months • Jaundice may be a problem (Burden and Sapsed, 2011, p.391; Wylie, 2005, p.200)
- 27. Cephalhaematoma Cranium (Burden and Sapsed, 2011, p. 391)
- 28. Internal Structures The main areas of interest within the fetal skull are: • The falx cerebri • The tentorium cerebelli • The superior sagittal sinus • The inferior sagital sinus • The great cerebral vein of Galen • The straight sinus • The two lateral sinuses • The periosteum (Stables, 2010, p.345)
- 29. Internal Structures http://www.is.bangor.ac.uk/images/ets/internalskull.gif Falx cerebri Superior sagittal sinus Inferior sagittal sinus To internal jugular vein Tetorium cerebelli Straight sinus Lateral sinuses Cerebrum Parietal bone Sagittal suture Pons varolii Cerebellum Medulla oblongata Great cerebral vein of Galen
- 30. Self Study • Obtain a definition or explanation from the midwifery textbooks for each of the following internal structures: • The falx cerebri • The tentorium cerebelli • The superior sagittal sinus • The inferior sagital sinus • The great cerebral vein of Galen • The straight sinus • The two lateral sinuses • The periosteum
- 31. Key Points • It is important to know the anatomical structure of the fetal skull and the diameters • The fetal skull diameters influence the presenting part and therefore the delivery outcome • Moulding is a normal occurrence during labour and delivery to decrease the presenting diameter • External and internal injuries can occur to the fetal skull during labour and birth
- 32. References • Burden, B. and Sapsed, M.S. (2011) The Fetal Skull. In: Macdonald, S.,Magill-Cuerden (eds.) Mayes’ Midwifery 14th ed. London: Ballière Tindall. • Serci, I.G,A. (2009) The Fetus. In: Fraser, D.M. and Cooper, M.A. (eds.) Myles Textbook for Midwives. 15th ed. Edinburgh: Churchill Livingstone • Stables, D. (2010) The Nature of Bone – The Female Pelvis and Fetal Skull. In: Stables, D. and Rankin, J. (eds.) Physiology in childbearing with anatomy and related biosciences. 3rd ed. Edinburgh: Elsevier. • Verralls, S. (1993) Anatomy and physiology applied to obstetrics. 3rd ed. Edinburgh: Churchill Livingstone. • Wylie, L. (2005) Essential anatomy and physiology in maternity care. 2nd ed. Edinburgh: Elsevier.
Editor's Notes
- #6: Face- 14 small bones, firmly united & non compressible.