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Neuroradiology Case of the Week

Case 302

Scott Rudzinski, Virendra Kumar, MD, and P-L Westesson, MD, PhD, DDS

Clinical Presentation: The patient is a 9-year-old female with known osteogenesis imperfecta presenting with back pain and progressing scoliosis.

Imaging Findings: The T5, T6 and T8 vertebral bodies show slight decrease in height, approximately 30%. No evidence of any marrow edema seen. These are suggestive of old compression. The T7 vertebral body shows slight decrease in height with focal marrow edema seen as hypointense signals on T1 which appears hyperintense on T2 and fat suppressed images and shows mild enhancement from the post-contrast images especially in the upper part. This is suggestive of acute nature. There is evidence of scoliosis noted in the midthoracic region with slight convexity towards the right.

Diagnosis: Vertebral compression fractures in osteogenesis imperfecta

Discussion: Osteogenesis imperfecta (OI) is an inherited disorder of connective tissue that manifests as osseous fragility, blue sclera, hearing loss, hypermobile joints, and easy bruisability. OI is caused by mutations in the genes that codify for type I procollagen, ultimately producing defective type I collagen. Type I collagen, which is found in the bones, organ capsules, fascia, cornea, sclera, tendons, meninges and dermis, constitutes 30% of the human body by weight. The prevalence of OI is estimated to be 1 per 20,000 live births, but the mild form is underdiagnosed, and the actual prevalence may be higher than this. Patients with OI may present at anytime during their life from in utero to adulthood, depending on severity of disease.

     The most widely used classification system developed by Sillence is as follows:

• Type 1 – Autosomal dominant; most common and mildest form. Patients typically have blue sclera and osseous fragility leading to increased fractures, normal height and do not have bowing deformities.
• Type 2 – Autosomal recessive; extremely severe and often lethal in utero or shortly after birth. All patients have in utero fractures, often have micrognathia, and severe long bone deformity. Death is from pulmonary hypoplasia.
• Type 3 – Autosomal dominant or recessive; severe progressively deforming OI. Rare phenotype in which two-thirds of newborns demonstrate multiple fractures. Deformities of long bones may compromise function and mobility.
• Type 4 – Autosomal dominant; moderate form. About 25 percent of affected individuals are born with bone fractures; others may not have any broken bones until later in childhood or adulthood. Patients may have mild short stature, hearing loss, and dentinogenesis imperfecta.

     Diagnosis is aided by collagen synthesis analysis and DNA mutation analysis after clinical presentation and radiography raises suspicion. There is decreased bone mineral density in OI, but degree varies greatly. Histologically the width of the cortex and the volume of cancellous bone are decreased in all types of OI.
     Initial radiographic survey after birth is recommended. The survey may be normal in mild types or show beaded ribs, broad bones, and numerous fractures with deformities of the long bones in more severe types. Skull manifestations of OI include wormian bones, basilar impression, and various degrees of delayed ossification of the calvarium. Fractures are common throughout development and through adulthood. Vertebral compression fractures are quite common in OI and are a cause of significant pain and physical disability among patients. Scoliosis is a common complication in OI.
     OI patients may be put on oral bisphosphonate treatment as well as cyclic administration of intravenous pamidronate. Intramedullary rod placement corrects bowed long bones to improve weight bearing and physical function. Scoliosis may be treated my spinal fusion, but is difficult due to bone fragility. The literature on the treatment of vertebral compression fractures is limited. One study successfully treated a patient with type 1 OI with percutaneous vertebroplasty.

References:

1. Rami PM, McGraw JK, Heatwole EV, Boorstein JM. Percutaneous vertebroplasty in the treatment of vertebral body compression fracture secondary to osteogenesis imperfecta. Skeletal Radiol. 2002 Mar;31(3):162-5. [Medline]
2. Rauch F, Glorieux FH. Bisphosphonate treatment in osteogenesis imperfecta: which drug, for whom, for how long? Ann Med. 2005;37(4):295-302. [Medline]
3. Sillence DO, Rimoin DL, Danks DM. Clinical variability in osteogenesis imperfecta-variable expressivity or genetic heterogeneity. Birth Defects Orig Artic Ser. 1979;15(5B):113-29. [Medline]