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Cervical characteristics of Noonan syndrome.

BACKGROUND/OBJECTIVES A short neck and low posterior hairline are characteristics of Noonan syndrome (NS) and are hallmarks of basilar invagination/impression. However, it is seldom that NS has been directly linked with this symptom. Thus, this study aimed to investigate basilar impression in NS subjects compared with control subjects and individuals exhibiting Turner Syndrome (TS). SUBJECTS/METHODS The degree of basilar impression and vertical positional differences of the third and fourth cervical vertebrae and hyoid bone in NS (n = 9, mean age: 12.1 years), TS (n = 9, mean age: 12.1 years), and control subjects (n = 9, mean age: 12.0 years) were investigated using lateral cephalometric radiographs. Differences between the three groups were compared using the Steel-Dwass test. Vertical positional differences in the anatomical structures within each group were compared using the Wilcoxon signed-rank test accompanied by a Bonferroni-Holm correction. RESULTS The distance by which the odontoid tip extended past McGregor's line in subjects with NS was significantly greater compared with TS and control subjects. The third and fourth cervical vertebrae were positioned significantly superiorly in subjects with NS compared with TS and control subjects and, in NS, were also significantly superior to the hyoid bone. There was no difference in the position of the hyoid bone itself between the groups. CONCLUSION/IMPLICATION These results suggest that basilar impression may be a frequently found symptom of NS.