The radiological features of rib head protrusion into the spinal canal in patients with scoliosis secondary to neurofibromatosis type 1

English Keywords:Neurofibromatosis  Scoliosis  Rib head  Dislocation  Imaging

English Abstract:

  【Abstract】 Objectives:　To investigate the radiological features of the protrusion of rib head into the spinal canal in patients with scoliosis secondary to neurofibromatosis type 1(NF-1S). Methods:　From August 1998 to March 2011, 142 patients with NF-1S were included in this study. Ninety-one patients with thoracic scoliosis had complete imaging data. Seven boys and four girls with the age ranged from 11 to 21 years old were found rib head protruded into the spinal canal. The magnitude of rib head protrusion into spinal canal, the apex rotation and the ratio of the displaced rib head width between convex and concave side were measured. The features of this phenomenon were concluded and the cause was analyzed. Results: The incidence of this phenomenon was 12.1%. The level of rib head protrusion was from T5 to T11 vertebra. The magnitude of rib head protrusion into the canal was from 11.2% to 50% with an average magnitude of 26.5%. The rib head into the canal behaved sharp and thin. The ratio of the displaced rib head width between convex and concave side was 0.50 to 0.99 with an average ratio of 0.77. The apex where the rib head protruded into the canal rotated significantly and the median of rotation was degree Ⅲ(Ⅰ to Ⅳ degrees). In the axial imaging in MRI, the spinal cord shifted to the concave side. The spinal cord against the medial wall of spinal pedicle in the concave side was found in 5 patients. Paraspinal neurofibromas were found in 4 patients. Conclusions: The rib head protrusion into the spinal canal is found in the convex side of apical area in the patients with NF-1S. The sharpness and thinness of rib, rotation and displacement of apex may contribute to this. CT-scan is a necessary examination around apical area before operation.