Stenosis - Stenosis

This disease, also known as cranial stenosis, is characterized by the premature closure of the cranial sutures (craniosynostosis), which narrows the anterior-posterior and lateral diameters of the skull, or sometimes both. In the neonatal period, the ossification of the skull that forms the cranial vault is insufficient, and there are several gaps called fontanelles, which are covered by connective tissue membranes. The growth of plate-like bones occurs in the peripheral area, and bone formation at the sutures where the bones join together is actively carried out along with the development (enlargement) of the brain. At 5 or 6 months after birth, the sutures begin to fuse fibrously, and the head circumference grows to 50% of that of an adult at 1 year and 80% at 3 years. However, if for some reason the bones mature (ossification) early and the sutures fuse tightly, bone growth stops even though the brain continues to grow (enlarge). When premature fusion occurs in a part of the brain, the brain grows toward the periphery, resulting in peculiar morphological deformations of the skull, such as scaphocrania, brachycrania, apicocalpism, plagiocrania, and broad cranium. Also, when all sutures fuse tightly prematurely, the development of the skull stops and the head becomes small. At this time, the brain continues to grow and causes significant intracranial pressure increase, which, if left untreated, can cause serious brain damage.

(1) Scaphocrania: This is caused by premature fusion of the sagittal suture and is the most common type, occurring more frequently in boys.

(2) Brachycephaly: This is caused by premature fusion of the bilateral coronal sutures and is frequently accompanied by other morphological abnormalities.

(3) Plagiocrany: caused by premature fusion of one coronal suture.

(4) Apical cranial operculum: This is caused by early fusion of the sagittal, coronal, and sagittal sutures.

(5) Trigonocephaly: This is caused by premature fusion of only the frontal suture. In many cases, this is accompanied by craniofacial dysplasia, which results in deformation of not only the skull but also the face. Syndromes in which craniosynostosis is a part of the skull include Crouzon's disease, which is accompanied by hypertelorism and exophthalmos, and Apelt's syndrome, which is accompanied by syndactyly.

Clinical symptoms include cranial deformation, facial deformation, symptoms of increased intracranial pressure, eye symptoms, delayed psychomotor development, and syndactyly.

Treatment of cranial malformation requires early surgical treatment, and early suture release surgery is performed. When facial deformation is also present, craniofacial plastic surgery is performed to simultaneously reshape the face, such as by moving the frontal bone forward. Microcephaly, in which the brain does not grow larger and the skull is therefore smaller, is treated separately even though the shape is similar.

[Mizuo Kagawa]

Source: Shogakukan Encyclopedia Nipponica About Encyclopedia Nipponica Information | Legend

頭蓋(とうがい)縫合部の早期閉鎖（頭蓋早期癒合症）によって頭蓋の前後径や左右径、ときにはその両者とも狭くなる疾患で、頭蓋狭窄症(とうがいきょうさくしょう)ともいう。新生児期にはまだ頭蓋冠を形成する頭蓋骨の骨化が不十分で、泉門とよばれるいくつかの間隙(かんげき)があり、結合組織性膜で覆われている。板状骨の成長は辺縁部にあり、骨と骨との接合した縫合部で骨の造成が脳の発育（増大）とともに盛んに行われ、生後5、6か月で縫合部が線維性に癒合し始め、1年後には頭囲が成人の50％、3年で80％まで成長する。ところが、なんらかの理由で骨の成熟（骨化）が早期におこって縫合部が固く癒合してしまうと、脳は成長（増大）を続けているのに骨の成長は停止してしまう。一部で早期癒合がおこると、脳はその周辺部に向けて増大する結果、舟状頭蓋、短頭蓋、尖(せん)頭蓋、斜頭蓋、広頭蓋など、頭蓋の特異な形態的変形をおこす。また、すべての縫合部が早期に固く癒合すると、頭蓋の発育はそのまま停止して小さい頭になる。このとき、脳は発育を続けて増大するため著明な脳圧亢進(こうしん)がみられ、放置すれば脳に重大な障害を残すことになる。

(1)舟状頭蓋　矢状縫合の早期癒合によるものでもっとも頻度が高く、男子に多い。

(2)短頭蓋　両側冠状縫合の早期癒合によるもので、ほかの形態異常を合併する頻度が高い。

(3)斜頭蓋　一側冠状縫合の早期癒合による。

(4)尖頭蓋　矢状縫合、冠状縫合、人字縫合のすべてが早期に癒合することによる。

(5)三角頭蓋　前頭縫合のみの早期癒合による。このうちの多くは頭蓋顔面骨形成不全として、頭蓋のみならず顔面の変形を伴う。症候群の一部として頭蓋縫合早期癒合を伴うものに、両眼隔離症、眼球突出などを伴うクルーゾンCrouzon病、合指症を伴うアペルトApelt症候群などがある。

　臨床症状としては、頭蓋の変形のほか、顔面の変形、頭蓋内圧亢進症状、眼症状、精神運動発達遅延、合指症などを伴うことがある。

　狭頭症の治療は早期に手術的治療が必要になり、早期の縫合開放術を行う。顔面の変形を伴うときは、前頭骨の前方移動など顔面形成を同時に行う頭蓋顔面形成術をする。なお、脳が大きくならないため頭蓋も小さくなる小頭症は、形は似ていても別に扱われる。

［加川瑞夫］

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