Friday, October 29, 2010

Platybasia: MR Measurement

Platybasia refers to abnormal flattening of the skull base and can be seen with congenital (craniofacial anomalies, osteogenesis imperfecta, cleidocranial dysplasia, Chiari malformation, etc.), or acquired conditions (Paget disease, osteomalacia, rickets, trauma, etc.)

On radiographs, the Welcher basal angle can be used to diagnose platybasia. Lines are drawn from the nasion to the tuberculum sellae and from the tuberculum sellae to the basion. The angle should be less than 140°.

On MR imaging, the basal angle is measure based on landmarks consistently reproducible on midline sagittal T1 images. The angle is measured between a line extending across the anterior cranial fossa to the tip to the dorsum sellae and another line drawn along the posterior margin of the clivus. Using this technique, the 95% confidence limits of the means were 116°–118° for adults and 113°–115° for children.

The image above shows midsagittal MR images from two different 14-year-old children. The first child has a normal MRI basal angle of 110°, while the second child has an abnormally elevated basal angle of 124° associated with a Chiari I malformation (not shown).


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