Morphometric Measurements of the Cranium in Patients with Chiari Type I Malformation and Comparison with the Normal Population
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To determine the degree of development of the posterior fossa and signs of occipital dysplasia in patients with Chiari type I malformation by morphometric measurements.
In 22 patients with Chiari type I malformation, distance, surface area and angle values reflecting the degree of development of the posterior fossa were measured and compared with the measurements of 21 normal subjects.
In patients with Chiari type I malformation, the depth of the posterior fossa, the length of the clivus reflecting development of the basi-occiput and Klaus' index were significantly shorter than in normal subjects (p<0.001, p=0.007, and p<0.001, respectively). The ratios of the depth of the posterior fossa to the height of the supratentorial region and Twining's line reflecting anteroposterior distance of the posterior fossa were also significantly smaller in the Chiari group (p<0.001 for both). In sagittal section, the surface area of the bony part of the posterior fossa and the ratio of this area to the area of the supratentorial region were significantly smaller than in normal subjects (p=0.038 and p=0.002, respectively). The angle measurements of the cranial base (basal angle, Boogard's angle and nasion-basion-opisthion angle) showed that there was an evident tendency for platibasia in the Chiari group (p=0.04, p=0.004, p<0.001, respectively). In addition, it was shown by measuring tentorium-twining's line angle that the tentorium was steeper in the Chiari group than normal subjects.
These results support the opinion, which claims the existence of underdevelopment of the occipital bone and posterior fossa in patients with Chiari type I malformation.
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