Fetal Skull Anatomy PDF

Fetal skull bones The fetal skull consists of the vault, face and base At term, the bones of the face and base are fused and thus allow little movement At term the vault consists of o 2 frontal bones o 2 parietal bones o 2 temporal bones o 1 occipital bone...

Fetal skull bones The fetal skull consists of the vault, face and base At term, the bones of the face and base are fused and thus allow little movement At term the vault consists of o 2 frontal bones o 2 parietal bones o 2 temporal bones o 1 occipital bone Bones of the fetal skull. Reproduced from Myles Textbook for Midwives by Marshall 1 Fetal skull sutures Vault bones are attached via soft fibrous tissue called sutures which allow movement and overlapping (moulding) o Frontal suture joining the 2 frontal bones o Sagittal suture joining the 2 parietal bones o Coronal suture joining the frontal and parietal bones o Lambdoidal suture joining the posterior margins of the 2 parietal bones and the Fetal skull. Reproduced from Myles Textbook for Midwives by Marshall occipital bone 2 Fetal skull fontanelles Fontanelles formed where 3 or more sutures meet and allow overlapping o Anterior fontanelle (bregma) - found where 2 frontal bones and 2 parietal bones meet - diamond shape - 2-2.5cm width x 2.5-3cm long - ossifies around 18 months old o Posterior fontanelle (lambda) - found where 2 parietal bones and occipital bone meet - triangular shape - ossifies soon after birth and within 1-2 months Palpation of these 4 sutures and 2 fontanelles helps to identify fetal position on vaginal examination Reproduced from Anatomy and Physiology in Healthcare by Marshall et al. ISBN: 97819079042958 © Scion Publishing Ltd, 2017 3 Fetal skull bones – significant landmarks Sinciput (forehead) Mentum (chin) Bregma (anterior fontanelle) Lambda (posterior fontanelle) Vertex (highest point midway between the parietal eminences) Occiput (area over occipital bone) Bones of the fetal skull and significant landmarks. Glabella (bridge of nose) Reproduced from Myles Textbook for Midwives by Marshall 4 Diameters of fetal skull Key transverse measurements o Biparietal diameter – between parietal eminences (~9.5cm). Widest transverse diameter. Crowning of the head occurs once this diameter has passed through the introitus o Bitemporal diameter – between 2 extreme points of coronal suture (~8cm) Key longitudinal measurements o Suboccipital bregmatic (SOB) ~9.5cm o Suboccipital frontal (SOF) ~10cm Diameters of the fetal skull. Reproduced from Physiology in o Occipital frontal (OF) ~11.5cm Childbearing by Rankin o Mentovertical (MV) ~13.5cm o Submentovertical (SMV) ~11cm o Submentobregmatic (SMB) ~9.5cm 5 Diameters of the fetal skull Attitude Presentati Present Average on ing size diamete r Well Vertex SOB ~9.5cm flexed Partially Occipito- SOF ~10cm flexed posterior Erect Cephalic OF ~11.5cm Partially Brow MV ~13.5cm extende d Partially Face SMV ~11cm extende Adapted from Fig. 13.21 (A) Attitude and (B) presentation of the fetus. Reproduced from: Anatomy and physiology for d midwives by Coad et al Extende Face SMB ~9.5cm d 6 Moulding The overlapping of fetal skull bones at the suture lines is called moulding Some degree of moulding is very common at full term. Usually disappear within a a few days Moulding allows a reduction in the dimensions of the presenting part by up to ~1.5cm Dimensions that are not compressed have to compensate The distorted skull shape may be worrying for parents Excessive, rapid and/or abnormal moulding can cause a tentorial tear which may lead to brain damage or death Fig. 13.18 The relationship between the shape of the baby’s head and the moulding of the fetal skull. Reproduced from: Anatomy and 7 physiology for midwives by Coad et al 8 Fetal skull. Reproduced from Mayes’ Midwifery by MacDonald 9