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Osteogenesis Imperfecta

Short-fractured femurs

Calvarial demineralization

Demineralized Skeleton

Fractured rib
Platyspondyly

Findings:

Both femurs are markedly shortened due to multiple fractures. The margin of the bone is irregular. The calvarium demonstrates virtually no evidence of calcification. Fracture and shortening of the ribs are seen. Lastly, marked flattening of the vertebral bodies (arrows) is identified. An x-ray of the fetus demonstrates multiple fractures as well as poor mineralization.

Discussion:

Osteogenesis imperfecta is a heterogeneous disorder, both clinically and genetically, resulting from abnormal collagen maturation. On the basis of clinical, radiographic and genetic features several classifications are utilized to describe the abnormality in an individual patient. Perhaps the two most commonly used are those of Sillence and Maroteaux.

 

Type
Descript.
Inheritance
Bone Shortening
Course
Outcome
I
Blue Sclerae
Autosomal Dominant
None
Usual onset in childhood- >95% walk, 35% deaf
Good / Regressive
IIA
Lethal
Autosomal Dominant
Severe
Perinatal Death
Lethal
IIB
Lethal
Autosomal Recessive
Mod./Femur
Perinatal Death
Lethal
IIC
Lethal
Autosomal Recessive
Mod-All extr.
Perinatal Death
Lethal
III
Deforming
Autosomal Recessive
Mod./Femur

Progressive deformity of limbs and spine-early death

Severe Handicaps
IV
Norm sclerae
Autosomal Dominant
None
Similar to Type I, however w/o Deafness
Good / Regressive
Modified from: Brons JTJ, van der Harten HJ, Wladimiroff JW, van Geijn HP, Dijkstra PF et al. Prenatal ultrasonographic diagnosis of osteogenesis imperfecta. Am J Obstet Gynecol 159:176-181, 1988 and BS Mahony, M.D.

As outlined in the table above, Types I and IV are characterized by little to no bone shorteneing but various levels of bone deformity occurring in childhood. The inheritance of these two types are autosomal dominant. Types II and III are the most severe, with moderate to severe bone shortening, usually lethal and are autosomal recessive, often due to new mutations. The incidence of osteogenesis imperfecta is said to be one in 20,000-30,000 births. Type IIA, which is the most commonly sonographically diagnosed form of osteogenesis imperfecta, occurs with a frequency of 1 in 60,000 births. Most cases of osteogenesis imperfecta which recur are of the same type present historically within the family. The diagnosis has been made as early as 14 weeks gestation but in some cases may not be made until the 3rd trimester or even early childhood.

In the past decade, several groups have attempted to use sonographic criteria to identify osteogenesis imperfecta and distinguish it from other skeletal dysplasias. In 1990 Filly et al utilized three criteria to help identify patients with Type II osteogenesis imperfecta: 1) Femurs measuring more than 3 standard deviations below the mean. 2) Marked demineralization of the fetal skeleton, based upon marked diminution or virtual absence of the usually seen brightly echogenic calvarial margin and marked enhancement of brain visualization. and 3) Multiple fractures, demonstrated by more than one discontinuity along the length of the bone. Another feature often seen is "bone thickening" likely due to callous formation. Rib fractures may occur and may result in the bones never reaching their full length around the thorax. The small thorax and underdeveloped lungs are often cited as the explanation for the lethal nature of this disease. Platyspondyly can be seen, though this is less severe than in thanatophoric dysplasia.

Differential Diagnosis:

Differentiation of the various forms of skeletal dysplasias may often be extremely difficult. Perhaps the two most common entities that can be confused with osteogenesis imperfecta are congenital hypophosphatasia and achondrogenesis Type I. These three lesions are equally severe and are usually fatal during the perinatal period. Fractures should be distinguised from bowing, which may be present in other skeletal dysplasias such as campomelic dysplasia.

References:

Brons JTJ, van der Harten HJ, Wladimiroff JW, van Geijn HP, Dijkstra PF et al. Prenatal ultrasonographic diagnosis of osteogenesis imperfecta. Am J Obstet Gynecol 159:176-181, 1988

Mahony BS. Ultrasound evaluation of the fetal musculoskeletal system. In Ultrasonography in Obstetrics and Gynecology, Ed by Peter W. Callen, 3rd Edition, WB Saunders and Co., Philadelphia, 1994

D'Ottavio F, Tamaro LF and Mandruzzato G. Early prenatal ultrasonographic diagnosis of osteogenesis imperfecta: A case report. Am J Obstet Gynecol 169:384-385, 1993

Sillence DO Senn A, Danks: Genetic heterogeneity in osteogenesis imperfecta. J Med Genetics. 16:101-116 1979

Maroteaux P, Frezal J, Cohen-Solal L, Bonaventure J. Les formes antenatales de l'ostetogenese imparfarite Arch Fr Pediatr 43:235-241, 1986

Munoz C, Filly RA and Golbus MS. Osteogenesis Imperfecta Type II: Prenatal sonogrpahic diagnosis. Radiology 174:181-185, 1990

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Peter W. Callen, M.D.
Professor of Radiology, Obstetrics, Gynecology and Reproductive Science
University of California Medical Center, San Francisco, California