Department of Oral Radiology, Institute of Dentistry, University of Helsinki; Department of Mathematics and Statistics, University of Vaasa; Department of Otorhinolaryngology-Head and Neck Surgery, Vaasa Central Hospital, Vaasa; Department of Otorhinolaryngology-Head and Neck Surgery, Turku University Central Hospital, Turku; Department of Clinical Genetics, Helsinki University Central Hospital, Helsinki; Department of Orthodontics, Institute of Dentistry, University of Helsinki; and Department of Oral and Maxillofacial Diseases, Helsinki University Central Hospital, Helsinki, Finland
Osteogenesis imperfecta (OI), which usually results from mutations in type I collagen genes, causes bone fragility and deformities. The head is often abnormally shaped, and changes in skull base anatomy in the form of basilar impression and basilar invagination have been reported. The authors analyzed the skull base anatomy on standardized lateral cephalograms from 54 patients with OI (Types I, III, and IV) and 108 control volunteers. They were surprised to find that the previously used diagnostic measures for basilar abnormality in patients with OI were exceeded in 6.5 to 7.4% of the controls, and hence needed to be reevaluated.
The authors calculated the distance from the odontoid process to four reference lines, including a novel one, in the controls. The normal mean distances were exceeded by more than two standard deviations (SDs) in 28.3 to 35.2%, and by more than three SDs in 13.2 to 16.6% of the patients with OI. The latter figures reliably reflect the prevalence of basilar impression. As a sign of basilar invagination the odontoid process protruded into the foramen magnum or reached the foramen magnum level in 22.2% of the patients with OI, whereas none of the controls showed this feature. Platybasia (an anterior cranial base angle > 146°) was present in 11.1% of the patients but in none of the controls.
Platybasia, basilar impression, and basilar invagination were often coexpressed, but each was also present as an isolated abnormality. These three abnormalities and wormian bones were predominantly found in OI Types III and IV as well as in patients exhibiting dentinal abnormality.
Abbreviations used in this paper: MR = magnetic resonance; OI = osteogenesis imperfecta; SD = standard deviation.
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ChamberlainWE: Basilar impression (platybasia). A bizarre developmental anomaly of the occipital bone and upper cervical spine with striking and misleading neurologic manifestations Yale J Biol Med11:487–4961939