Fetal Skull Anatomy Quiz

Fetal Skull Overview

• Contains a delicate brain, susceptible to pressure during childbirth.
• Earliest bones originate from membranes and cartilage, with variation in ossification timing.

Ossification Process

• Fetal skull bones: some ossified from cartilage (face), others from membranes (vault).
• Ossification centers create protuberances; the process remains incomplete at birth, leading to sutures and fontanelles.

Main Bones of the Vault

• Occipital Bone: Located at the back; contains foramen magnum which protects the spinal cord.
• Parietal Bones: Two bones situated on each side; ossification centers called parietal eminences.
• Frontal Bones: Form the forehead; frontal eminences at the center. Fusion occurs around age 8.
• Temporal Bones: Minor role in the vault structure.

Sutures

• Connective joints between adjacent cranial bones.
• Lambdoidal Suture: Separates occipital from parietal bones.
• Sagittal Suture: Divides two parietal bones.
• Coronal Suture: Connects frontal bones with parietal bones, extending from temple to temple.
• Frontal Suture: Joins two halves of the frontal bones.

Fontanelles

• Areas where multiple sutures converge.

Types of Fontanelles

• Posterior Fontanelle (Lambda): Triangular shape at lambdoidal and sagittal junction; closes by 6 weeks.
• Anterior Fontanelle (Bregma): Kite-shaped, located at the junction of sagittal, coronal, and frontal sutures; closes by 18 months (3-4 cm long, 1.5-2 cm wide).

Regions and Landmarks of the Fetal Skull

• Face: Composed of 14 small bones.
• Vault: Dome-shaped bones, pliable at birth, facilitating skull shape alteration during delivery.
• Base: Firmly united to protect brainstem functions.

Key Skull Regions

• Occiput: Lies between foramen magnum and posterior fontanelle; includes suboccipital region below the occipital protuberance.
• Vertex: Bounded by the anterior fontanelle and two parietal eminences; 95% of babies present head first at this point.
• Sinciput (Brow): Extends from the anterior fontanelle to orbital ridges.
• Face: Smaller at birth; extends from orbital ridges to chin-neck junction; glabella at eyebrow center and mentum at chin.

Diameters of the Fetal Skull

• Important for understanding the relationship between the fetal head and maternal pelvis.

Transverse Diameters

• Biparietal Diameter: 9.5 cm, measured between parietal eminences.
• Bitemporal Diameter: 8.2 cm, from the coronal suture at temples.

Anteroposterior (Longitudinal) Diameters

• Suboccipitobregmatic (SOB): 9.5 cm; crucial in labor.
• Suboccipitofrontal (SOF): 10 cm; from occipital protuberance to frontal suture center.
• Occipitofrontal (OF): 11.5 cm; from occipital protuberance to glabella.
• Mentovertical (MV): 13.5 cm; from chin to vertex.
• Submentovertical (SMV): 11.5 cm; from chin-neck junction to vertex.
• Submentobregmatic (SMB): 9.5 cm; from chin-neck to bregma center.

Conclusion

• The most favorable diameters during labor are SOB and biparietal, both 9.5 cm, indicative of vertex presentation.