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1. How many different elements, or “parts”, are there to the fetal ?

There are 51 bony elements of the fetal skull. These elements are separated by either cartilage or connective tissue as the newborn skull is only partially ossified at the time of birth.

2. What are sutures? What are fontanels?

Sutures: In the newborn skull, there are gaps between the edges of membranous . These gaps, which are spanned by a flexible bridge of membranous tissue, are called sutures. Sutures allow moulding or movement of the bony plates in labor and they also allow the baby’s brain to grow rapidly after birth.

Fontanels: These are located where sutures intersect. They are membrane and skin- covered openings and spaces. The anterior and posterior are the most important clinically.

3. Explain suture and fontanel locations, shapes, and functions in detail along with their names.

Sutures

• —divides the cranial vault in half, runs between the parietal bones and it originates at the anterior and ends at the .

• Lambdoidal sutures (2)—these run from the posterior fontanelle down and around to the border of the occipital vault. These separate the interparietal portion of the occiput from the two parietal bones.

• Coronal sutures (2)—these run transverse and downward from the to the sphenoid fontanelle on either side. The coronal sutures separate the parietal and frontal bones.

• —this is location between the two frontal bones. It is an anterior continuation of the sagittal suture. It may be mistaken for the sagittal suture in deflexed presentations during an internal exam. It can help to distinguish a face presentation.

• Temporal sutures (2)—these separate the temporal from the . These each extend from the temporal fontanelle. During birth, these sutures allow for some upward and downward mobility of the parietal bones. They also allow the temporal bone to move upward and forward toward the sphenoidal fontanelle. 2

Fontanels

• Anterior fontanelle ()—this is located at the junction point of the sagittal, frontal, and coronal sutures. This is a diamond-shaped opening that is bordered by the two frontal bones and the two parietal bones. This is the largest fontanelle with an average size of 3 cm wide and 2 cm long.

• Posterior fontanelle ()—this is located where the sagittal suture meets the lambdoidal sutures. It is bordered by the interparietal occiput posteriorly and the parietal bones anteriorly. It forms the shape of a Y (or triangle like shape) and is much smaller than the anterior fontanelle.

• Sagittal or interparietal fontanelle (false, Gerdy’s)—this is a developmental fontanelle that usually continues to ossify and by the 5th month, only the parietal foramina remains. Occasionally (5% of babies), a well-developed sagittal fontanelle is present at birth. This is also shaped like a small diamond and so it is sometimes confused for the anterior fontanelle. It is located one-quarter of the distance anterior to the posterior fontanelle in the sagittal suture.

• Anterolateral (sphenoidal) fontanelles (2)—these are formed at the junction of the parietal, frontal, sphenoid and temporal bones on either side of the skull. These fontanelles allow the temporal bone the ability to move upward and forward. These can’t be felt during a normal labor and aren’t a relevant landmark.

• Posterolateral (mastoid) fontanelles (2)—these are rectangular membranous openings that are located at the junction of the parietal, temporal, and occipital bones both laterally and posteriorly. These allow the temporal and occipital bones to move during labor. These normally can’t be felt and they are not relevant directional landmarks.

4. What is the difference in a “membranous bone” and an “endochondral bone”? Why does this matter in regards to labor?

Membranous bone: These bones form by the process of hardening or ossifying outwards from a central location (growth center). Many thin spikes of bone fan out from this central location and are denser at their growth center while being more fragile and flexible near their edges. Membranous bones are more flexible than endochondral bones.

Endochondral bone: The ossification of endochondral bones is more complex than that of membranous bones. The first step is the formation of a cartilaginous template that takes the shape of the bone that will eventually form. Then the cartilage is gradually re- absorbed and then replaced by calcium-filled bone as the newborn continues to develop and mature. These bones are much less flexible than membranous bones at the same stage of development due to the uniformed ossification process. 3

At the point of labor, the endochondral bones are separated by fibrocartilage and meet at the synchodrodial joints, which are slightly flexible, but not as flexible as sutures are. However, the skull bones of the fetal skull at the time of birth are still more flexible and more mobile than is generally taught.

5. How many regions of the fetal skull are there? Name them and their relative locations.

There are 3 regions of the fetal skull. These are:

The face: this region extends from the bridge of the nose (near the orbital sockets) to the junction of the chin and the neck. This region takes up only 1/8 of the newborn skull compared to 1/3 of the adult skull.

The vault: this region extends from the forehead to the back of the head. This is the largest region and is also one of the most important regions in midwifery as this region has the ability to compress, adapt, and mould during labor.

The base: this region is where the skull attaches to the neck. It extends from the face and continues to right below the occiput.

6. What are “parietal” bones? What is their importance in labor and birth?

The parietal bones are 2 bones that make up the majority of the vault of the skull. These bones extend from the center of the top of the head to the ears on either side of the skull. Each of the 2 parietal bones have 4 blunt corners and they are shaped like a shallow bowl. The parietal bones are bordered by the frontal bones in the front, the occiput in the back, and the temporal and sphenoid bones inferiorly.

In labor and birth, the parietal bones can become “dented” due to a hard birth that has excessive pressure. Also, the parietal bones have 3 clinically important landmarks. The first is the parietal eminence. This is the hardest part of this bone and it is located at the highest point on either side of the skull. The distance between the 2 parietal eminences also marks the widest transverse diameter of the fetal skull. The next landmark is the vertex which is bounded by the anterior and posterior fontanelles and on each side by the parietal eminences and it is divided down the middle by the sagittal suture. The last landmark is the crown of the head. This is most protruding part of the vertex and it is located anterior to the posterior fontanelle. This part is included in the presenting circumference of the head when the head is well flexed.

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7. What and where is the “occiput”?

The occiput is a solid bone at the back of the fetal skull. While the occiput is typically described as being a solid bone, there are actually four regions of ossification (the squamous part, two condylar parts, and the basilar part). At birth, the occiput is not fully fused. Synchodrodial joints help to facilitate mobility for during labor.

8. How does the dura (and dura folds) protect the vessels and brain during extreme moulding during labor? Carefully explain the process and, when injury occurs, what the common causes are.

The dura mater is a strong, fibrous membrane that consists of two layers that covers and protects the brain. These two layers are fused in adults, but more easily separated in children and babies. At the time of birth, the newborn’s arterial system in their brain is more developed than the venous system. Because of this, some cerebral veins are more susceptible to be strained and injured during birth. Also, these venous sinuses don’t have the same elastic muscle tissues that are found in other veins, which make them more likely to undergo trauma. During labor, as the baby descends through the pelvis, the intracranial vessels experience tension and pressure as the head moulds and changes shape. When pressure is evenly applied, the fetal head can withstand a good amount of compression because the skull bones are designed so that even pronounced moulding can occur in such a way that minimizes the stress on these structures in the brain. Because of this structure of the head, the brain is protected during the normal stresses of birth.

However, while the fetal skull is designed to protect the brain in most cases, there are some situations that increase the chance of injury. These include: very difficult or obstructed labors, instrument extraction of the head, strong fundal pressure to extract the head, and premature babies. Also, excessive occipitofrontal or oblique distortion can lead to the tearing of veins which bridge the dura or the dural folds. This damage can result in intercranial hemorrhage, which when it is severe, can lead to brain damage or death.

9. What is the “shoulder girdle”? Why does it matter and what important parts are represented in this region/area?

The shoulder girdle consists of three important landmarks: the clavicles (long bones that extend from the sternum to the scapula; cone-shaped at the sternal end and flattened at the outer end), the scapulae (large, thing, flat triangular bony plates that overlay the posterior rib cage), and the acromion (the lateral end of the scapula that articulates with the clavicle and gives attachment to parts of the deltoid and trapezius muscles). The shoulder girdle forms a longer, more narrow axis compared to the oval shape of the head. This is the second most clinically important anatomical feature of the baby during 5 the birth process. The shoulder girdle must rotate within and beneath the pelvic bones during labor without difficulty. The shoulders are designed for mobility rather than stability. Because of this, the soft tissues in this region and the brachial plexus can easily be damaged with inappropriate handling (such as in a breech birth or a shoulder dystocia birth).

10. You should know each of the aforementioned parts and structures and be able to identify them on a drawing. They are all critical to the aspects of normal labor. There will be questions on the final exam with fetal diagrams asking you to note different parts of the fetal skull, etc. It is not required to draw these yourself, but it may be helpful to practice labeling parts of fetal upper-torso and skull anatomy listed in this assignment. For this question, therefore, spend time quizzing yourself on these portions of fetal anatomy. You will find free games and flashcards online to do so or you may create your own. However you study them, however, be sure you know their names and relative locations as well as purposes.

Studied on Purpose Games the fetal skull.