malformation

Failure of proper or normal development; more specifically, a primary structural defect that results from a localized error of morphogenesis; e.g., cleft lip. Cf.:deformation.

- Arnold-Chiari m. malformed posterior fossa structures associated with caudad traction and displacement of the rhombencephalon as caused by tethering of the spinal cord; may or may not be accompanied by spina bifida and associated anomalies such as meningomyelocele; this m. is usually multifactorial in inheritance; very weak evidence of autosomal recessive inheritance [MIM*207950]. SYN: Arnold-Chiari deformity, Arnold-Chiari syndrome, cerebellomedullary m. syndrome.

- cystic adenomatoid m. a rare developmental lung-bud abnormality which results in stillbirth, acute progressive respiratory disease of newborns, or protracted childhood pneumonias; this m. combines features of a hamartoma, dysplastic growth, and tumorous growth. Three types have been described, based chiefly on cyst diameters: Type I: up to 10 cm; Type II: less than 1.2 cm; Type III: less than 0.5 cm.

- mermaid m. SYN: sirenomelia.

- Michel m. hypoplasia of the petrous pyramid and aplasia of the inner ear.

- venous m. SYN: venous angioma.

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mal·for·ma·tion .mal-fȯr-'mā-shən, -fər- n irregular, anomalous, abnormal, or faulty formation or structure <congenital \malformations>

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n.

any variation from the normal physical structure, due either to congenital or developmental defects or to disease or injury.

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mal·for·ma·tion (mal″for-maґshən) [L. malus evil + formation] 1. a type of anomaly. 2. a morphologic defect of an organ or larger region of the body, resulting from an intrinsically abnormal developmental process.