Craniosynostosis

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Overview
Craniosynostosis, is a medical condition in which some or all of the sutures in the skull of an infant or child close too early, causing problems with normal brain and skull growth. It can result in craniostenosis, which is the skull deformity caused by the premature closure of the cranial sutures. Also intracranial pressure can be increased.

Normal skull development
In humans, the adult skull is normally made up of 28 bones. The flat bones making up the cranial vault are joined together by sutures: rigid articulations permitting very little movement.

At birth, the human skull is made up of 45 separate bony elements. As growth occurs, many of these bony elements gradually fuse together into solid bone (for example, the frontal bones).

The bones of the roof of the skull are initially separated by regions of dense connective tissue. At birth these regions are fibrous and moveable, necessary for birth and later growth. Larger regions of connective tissue, called fontanelles, occur where certain bony elements meet. As growth and ossification progress, the connective tissue of the fontanelles is invaded and replaced by bone. The posterior fontanelle usually closes by eight weeks, but the anterior fontanelle can remain up to eighteen months.

Pathophysiology
When one or more sutures fuse prematurely, skull growth can be restricted perpendicular to the suture. If multiple sutures fuse while the brain is still increasing in size, intracranial pressure can increase.

Primary craniosynostosis is believed to be a result of primary defect in the mesenchymal layer ossification in the cranial bones. Secondary craniosynostosis is a result of primary failure of brain growth.

Diagnosis
Physicians diagnose craniosynostosis through physical examination, plain x-rays, and CT scans.

Syndromes
Craniosynostosis often occurs alone, however about 20% of cases are associated with syndromes. A syndrome is diagnosed by considering the presence of a variety of features, signs, and symptoms throughout the body. Genetic testing may be available to confirm the diagnosis of a specific syndrome. A family history of abnormal head shape can sometimes be found with genetic syndromes, though many syndromes are caused by new genetic mutations, and there is no family history of the disorder.

The most common causes of syndromic craniosynostosis are Crouzon syndrome and Apert syndrome. However, there are over 150 syndromes associated with craniosynostosis. The following table lists some of the craniosynostosis syndromes, as well as prominent additional symptoms that are found in these syndromes — this is not a comprehensive list of all symptoms that could occur within each syndrome. There is considerable overlap of symptoms between many of these syndromes, and clinical evaluation by a geneticist may be necessary to determine the most appropriate diagnosis.

Differential diagnosis
A separate cause of abnormal head shape is positional plagiocephaly — flattened or misshapen areas on the head that may develop due to sleeping position. While the appearance may look rather similar to craniosynostosis, the distinction is important. Positional plagiocephaly does not require surgery — treatment can be as simple as occasionally repositioning the child's head while sleeping or, in some cases, wearing a cranial band to mold the skull.



Treatment
Surgery is typically used to separate the fused sutures of the skull as well as to reshape the skull. To treat the cosmetic troubles, a combination of orthodontic and orthognathic surgery can be used to relieve some of the midface deficiency.

Typical surgery begins with a zigzag incision from ear to ear across the top of the head. The scar left by this type of incision makes the hair look more natural than that left by a straight incision would. Leroy clips are typically used to curtail bleeding, as cauterization would not result in an aesthetically pleasing result upon healing. Once the scalp is peeled back, pilot holes are drilled through the skull. These pilot holes are then connected, separating the skull into several pieces. Once reshaped, these pieces are placed back on the head (typically in an altered configuration) and held together by a combination of dissolving sutures, plates, and screws. These plates and screws are typically composed of a copolymer comprised of polyglycolic and polylactic acid and will break down into water and carbon dioxide within a year. Demineralized bone matrix or bone morphogenetic proteins are often used to fill gaps left by the expanded skull, encouraging the body to grow new bone in a process called intramembranous ossification. Once the hemostatic scalp clips are removed, sutures are again used to close the incision.

Newer approaches include minimally invasive endoscopic assisted removal of the closed suture followed by treatment with custom made molding helmets. These surgeries are associated with significantly less blood loss, swelling, hospital length of stay and pain. The results have been excellent in the majority of patients treated this way. Endoscopic surgery, however, is indicated only for very young infants(< 6 months of age). Older children require the more extensive surgery described above.

Epidemiology
In the United States, the incidence of craniosynostosis is estimated to be 1 in 2000–3000 live births.