The fetal skull is a compressible part of the fetus to some extent and made of flat bones forming the vault. There is a presence of incompressible bones at the base of the skull.
Flat bones of the vault are united together by non-ossified membranes attached to the margins of the bones. These are called sutures and fontanelles. The following are of obstetric importance, out of many sutures and fontanelles.
Sutures of the Fetal skull
There are four types of sutures present on the fetal skull–
- The sagittal suture also known as longitudinal suture: It lies between two parietal bones.
- The coronal suture: It is present between two parietal and frontal bones on either side.
- The frontal suture: It lies between two frontal bones.
- The lambdoid suture: It separate the occipital bone and the two parietal bones.
Importance- The presence of these sutures on the fetal head has great importance during pregnancy and childbirth.
- Presence of sutures permits gliding movement of one bone over the another during moulding process ( it is the alteration of the shape of the fore-coming head while passing through resistant birth passage during labour).
- When internal examination done during labour, digital palpation of the sagittal suture gives an idea of engagement of head, degree of internal rotation and moulding of the head.
The wide gap in the suture line is called fontanelles. It is 6 in number but only two are of obstetric significance.
Anterior fontanelles- It is diamond-shaped and formed by joining four sutures, i.e, anteriorly frontal, posteriorly sagittal, and on either side, coronal. The floor is formed by the membrane and it gets ossified 18 months after birth. If it fails to close even after 24 months, then it is considered pathological.
- It facilitates moulding of the head.
- Degree of flexion of the head can be identified by palpation through internal examination
- It helps in accommodating the marked brain growth after birth till it gets closed.
- Palpation of the floor gives an idea of depression in dehydration and elevation in raised intracranial tension.
Posterior fontanelles- It is triangular in shape and formed by the junction of three suture lines i.e, sagittal suture anteriorly and lambdoid suture on either side. Its floor is membranous but becomes bony at term or else at 3 months after birth.
Importance- It denotes the position of the head in relation to the maternal spine during labor.
Sagittal fontanelle- It is inconsistent in its presence. When present, it is situated on the sagittal suture at the junction of anterior two-thirds and posterior one-third as shown in the above fig 2. It has got no clinical importance.
In the above post, we have discussed fetal skull sutures and fontanelles, their types, and their importance.