1.What is the cranial suture? Cranium includes skull cap and skull base, which are made up of several pieces of skull bones respectively, and the connection between skull bones is called cranial suture. The cranial sutures of the skull cover include two frontal bones symmetrical in front, two parietal bones symmetrical in the side and one occipital bone in the back. There are six main cranial sutures – the frontal suture between the two frontal bones, the sagittal suture between the two parietal bones, the two coronal sutures between the frontal and parietal bones on both sides, and the two herringbone sutures between the parietal and occipital bones on both sides. The area where the cranial sutures meet is fontanelle, the fontanelle is the intersection of the frontal suture, the sagittal suture and the two coronal sutures, and the posterior fontanelle is the intersection of the sagittal suture and the herringbone suture. 2.Why do people need cranial sutures? During delivery, the cranial suture can effectively deform the fetal head to a certain degree of compliance to facilitate passage through the mother’s birth canal. After birth, the cranial suture can adapt to the rapid development of the newborn’s brain. While the relatively hard skull is responsible for protecting the fragile brain tissue inside like armor, the presence of the cranial suture allows the skull to protect the brain without limiting the rapid development of the brain, providing the potential for the cranial volume to continue to increase. 3.When does the normal cranial suture close? In the early stages of fetal and infant development, the cranial suture is covered by soft fibrous tissue. As the brain develops and the volume of the brain gradually increases, several pieces of the skull grow and expand to match the speed of brain development. when the brain develops rapidly up to 1 year old, the skull also develops rapidly. the brain volume at 1 year old is already about 80% of that of an adult. The brain then slows down significantly and the cranial sutures gradually close in sequence. After the age of 6, when the brain basically stops developing in volume, the skull forms a strong structure with tight fiber connections to protect the brain tissue. The long evolutionary process of humans has made this process perfectly coordinated and ultimately seamless. In fact, the six major cranial sutures close at different times, roughly following a sequential order from front to back. The frontal suture is mostly closed at birth, the sagittal and coronal sutures begin to close after 1 year of age, and the herringbone suture closes the latest, gradually after 2 years of age, and is known as the “lazy” suture. The entire process of cranial suture closure continues until about 6-7 years of age, and closes completely at about 12 years of age. The closing of fontanelle and the closing of cranial suture are not synchronized. The posterior fontanelle closes about 2-3 months after birth, while the anterior fontanelle closes from 1.5 to 2.5 years old. 4.What is “early closure of the cranial suture”? Why does it close prematurely? In the process of rapid brain development, in order to match the rapid development of brain tissues in infancy, the bone sutures cannot be closed. If one or more cranial sutures close abnormally early, it will restrict the space for brain tissue development, and this disease is called “premature closure of cranial sutures”. The cause of premature closure of the cranial sutures is not fully understood. During the development of the cranial sutures, the dynamic balance of proliferation, differentiation, and apoptosis of cranial cells is imbalanced due to the alteration of certain specific genes or factors, resulting in premature closure of the cranial sutures. Probably more than 80% of cranial suture premature closure is associated with developmental defects during embryonic development, and less than 10% of cranial suture premature closure has a clear genetic component, i.e. a family history, and may be inherited to the next generation. In other cases without a family history, the presence of the relevant mutated gene can be found in some cases. Some studies have confirmed the association between premature craniosynostosis and some maternal exposure during pregnancy, such as antidepressants and smoking, but the conclusions are not conclusive. In non-syndromic craniosynostosis without a clear mutation, about 7% of siblings have craniosynostosis at the same time. 5. Is craniosynostosis common? Craniosynostosis is a congenital disorder with a prevalence of about 1 in 2500 in Europe, i.e., one case of craniosynostosis in every 2500 births. In general, boys are more common, but the gender predominance of different types of craniosynostosis varies, with an overall male to female ratio of about 2:1. In sagittal, frontal and herringbone sutures, boys are more common, and in coronal sutures, girls are more common. However, this is only a projection based on the prevalence in Europe, and there are no comprehensive and accurate statistics on the overall prevalence in our country and the differences between different ethnic groups and regions. But at least we can understand that craniosynostosis is not a rare disease. For babies with abnormal head shape, do not easily think that it is “sleeping on the wrong side” or “it will be round when it grows up”, but should go to a specialist hospital for consultation as early as possible. 6.What is the performance of premature closure of the cranial suture? After the cranial suture closes prematurely, the local bony structure restricts and obstructs the normal brain development, and the shape of the head changes, so the skull and brain tissue can only grow in other directions, resulting in head deformity, which is called narrow skull. The most prominent manifestation is the abnormal shape of the head. Depending on the closure of the cranial suture, a variety of cranial deformities are produced, including navicular head, triangular head, oblique head, short head, tower head, pointed head deformity, etc. The closed cranial sutures are elevated with bone deposits, forming a prominent “bone ridge” that can often be palpated. In addition to abnormal head shape, different types of premature closure of the cranial suture may cause or combine with other different deformities and signs of neurological impairment. If the coronal suture is involved, it often causes abnormal flattening of the ipsilateral frontal orbit, abnormal and asymmetrical eye position, orbital and facial morphology, and can affect visual development, which can lead to blindness in severe cases. Premature closure of the frontal suture often results in severe bilateral frontal lobe developmental restriction, affecting intelligence and causing ophthalmologic problems such as narrow eye spacing and decreased visual acuity. Children with narrow cranial syndrome are often affected by multiple cranial sutures, and their neurological function and intelligence are more severely affected, and they often have other deformities of the nervous system, jaw, throat, mouth and limbs. 7.Is there any pattern between cranial suture closure and appearance characteristics? There is a clear pattern between the occurrence of premature closure of different cranial sutures, which can cause different appearance of craniosynostosis. A century and a half ago, the famous German Professor Rudolph Virchow, when he was 30 years old, proposed the famous [Virchow’s law] – when the cranial suture is closed, the head grows abnormally towards the long axis of the closed cranial suture, and the growth is limited in the vertical direction. This law is still in use today. For example, if the sagittal suture is closed, the shape of the head grows forward and backward along the closed sagittal suture, and growth is limited in the left and right directions perpendicular to the sagittal suture, forming a navicular head deformity. In the case of bilateral premature closure of the coronal suture, the head grows along the left and right coronal suture and is limited in the anterior and posterior directions perpendicular to the coronal suture, forming a short head deformity in contrast to the navicular head.