Imaging spectrum of osteogenesis imperfecta – Pictorial essay

Osteogenesis imperfecta (OI) is a rare genetic disorder caused by the disturbance in the synthesis of Type I Collagen and is divided into several types. Severe form of OI, mainly type II can be diagnosed in utero by ultrasonography during the second trimester of pregnancy. All the other types viz. Type I to Type VIII are diagnosed by conventional radiography. Many authors have classified these into several types. This essay is not meant for a comprehensive review of these types. The main features include fractures, gracile bones, kypho scoliosis, deformities, and wormian bones in skull. These radiologic features are described pictorially.


introduction
Osteogenesis imperfecta (OI) is a genetic disorder and is also known as fragilitas ossium. Armand, in 1716, reported a case of brittle bones of a new born infant. This is said to be the first recorded observation of this condition [1]. It is familial with an autosomal dominant mode of inheritance in many cases. Very few cases are reported to have autosomal recessive mode of inheritance. The quality and quantity of bone is diminished. The skeletal manifestations include a spectrum of findings including osteopenia, multiple fractures, wormian bones in skull, gracile and thinning of bones, bending deformities which are all described with the aid of radiographic images in the following paragraphs. This article deals with 8 types of OI and some of these are quite rare. Great confusion exists in the past and continues to exist in contemporary literature with reference to the classification of brittle and soft bones.

1-13)
The literature is replete with genetic causes and clinical basis of the diagnosis. The estimated incidence is approximately 1 in every 12,000-15,000 births. Osteogenesis imperfecta is the result of a mutation in one of the two genes that carry instructions for making type 1 collagen. Mutations in the COL1A1 and COL1A2 genes, which encode the α2 and α2 polypeptide chains 7, are responsible for more than 90% of all cases. The patient is generally referred for fractures or suspected OI with Blue Sclera. The imaging features although are classical of OI, it is impossible to correlate them with the types that have been described in the literature [3,[15][16][17]. Biphosphonate therapy [19,20] is the choice in the treatment of OI. Corrections of deformities are done by surgery.
The classical radiological features are listed in Table1. Spondylolysis and spondylolisthesis [6,7] There are several synonyms for OI. These are listed in Table 2. Classification by Sillence and Glorieux [2] is listed in Table 3. Type V, VI, and VII have been added to the original classification system (no type I Collagen mutation, but abnormal bone on microscopy and similar phenotype). They are listed in Table 4. Type I is mild and shows few features radiologically and is supported clinically by blue sclera (Picture 1a,b).

Bruck syndrome [18]
OI is associated with several syndromes including Bruck syndrome. It is a rare disorder characterized by association of OI and congenital joint contractures.
They have white sclera. The fractures occur post natally and the contractures are the primary abnormality and not a complication of the fractures ( Figure 14). Also has been reported Osteogenesis Sarcoma in association with OI. Biphosphonate therapy has been introduced and proved to be effective in the treatment of OI ( Figure  15). The proof of this is Zebra lines at the metaphyseal ends of long bones [19,20]. conclusion Osteogenesis imperfecta is a rare congenital genetic disorder and several types of classifications have been described in the literature. The classical findings of OI include osteopenia, multiple fractures, poorly mineralized skull (wormian bones), ribbon bones, hypercallosis, pseudoarthrosis, popcorn calcifications, and spondlolisthesis. It is extremely difficult to categorize them into various types without clinical correlation and genetic testing.