Objectives-To describe the clinical and neuroradiological features of basilar impression in patients with osteogenesis imperfecta type IV. Methods-Four patients with basilar impression were ascertained in a population study of osteogenesis imperfecta. All four had detailed clinical and neuroradiological examination with both CT and MRI of the craniocervical junction andposterior fossa structures. Results-All four showed significant compression of the posterior fossa structures and surgical decompression was performed with relief of symptoms. Conclusion-Symptoms of cough headache and trigeminal neuralgia occurring in patients with osteogenesis imperfecta are indications for detailed clinical and neuroradiological investigation to document basilar impression. (J Neurol Neurosurg Psychiatry 1999;66:357-364) Keywords: basilar impression; osteogenesis imperfecta Basilar impression, the most often occurring malformation of the craniocervical region, is the upward displacement of basilar and condylar portions of the occipital bone causing an infolding of the foramen magnum and leading to a translocation of the upper cervical spine into the brainstem.1 2 This has the potential for severe neurological consequences. Most commonly this condition is due to a congenital developmental anomaly, but it may also occur secondarily to a generalised bone disease such as osteomalacia, Paget's disease, hyperparathyroidism, rheumatoid arthritis, and osteogenesis imperfecta. 3Osteogenesis imperfecta is a clinically and genetically heterogeneous group of heritable disorders of connective tissue characterised by reduced bone mass (osteopenia) with associated bone fragility.4 Skeletal manifestations are due to a generalised deficiency of development of both membranous and endochondral bone and include markedly thinned calvarium with delayed closure of fontanelles and sutures and excessive Wormian bone formation. Until recently, the reported association of osteogenesis imperfecta and basilar impression was considered rare. Furthermore, it was presumed that basilar impression occurs equally in all types of osteogenesis imperfecta. However, the combination of increased awareness coupled with the advent of improved neuroimaging has led to wider screening and detection of the condition. 5 This might have remained an academic exercise were it not for anaesthetic and neurosurgical advances in foramen magnum and posterior fossa decompressive surgery which reduce the morbidity and mortality from intervention. Screening of at risk people is likely to disclose a proportion with subclinical basilar impression. Closer surveillance can then be instituted. However, a craniocervical malformation is likely to be clinically suspected before neuroimaging is performed. The range of clinical symptoms is determined by the particular combination of direct compression and vascular disruption resulting from upward displacement of the floor of the posterior fossa (table 1). Some of these symptoms may be transient, progressive, or catastrophic. The spec...

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