Tonsillar Ectopia in AIS - Pathogenic - Prognosis

Scoliosis Journal reported on tonsillar ectopia in adolescent idiopathic scoliosis: does it play a role in the pathogenesis and prognosis or is it only an incidental finding?

Authors: Kasim Abul-Kasim, Angelica Overgaard, Magnus K. Karlsson and Acke Ohlin

Published: 12 November 2009
Abstract (provisional)

Background
There is an ongoing controversy about the significance of tonsillar ectopia among patients with adolescent idiopathic scoliosis (AIS). Aim: To find out if tonsillar ectopia occurs more frequently among patients with AIS and if it plays any etiological or prognostic role in AIS. Study design: Retrospective study.

Methods
Retrospective analysis of 155 consecutive spine MRIs (79 patients with AIS and 76 controls; aged 7-25 years; 55 % were female) with regard to the position of the cerebellar tonsils in relation to foramen magnum and the sagittal diameter of foramen magnum. All images were evaluated independently by two neuroradiologists. Interobserver reliability analysis was performed by calculation of kappa-value, intraclass correlation coefficient, and systematic and random errors. The occurrence of tonsillar ectopia among patients with AIS and controls was estimated and the association of tonsillar ectopia with different predictors has been tested. Statistical significance was set to P [less than or equal to] 0.05.

Results
The interobserver agreement with regard to the occurrence of tonsillar ectopia was almost perfect (kappa 0.84, 95 % CI 0.74-0.93). Tonsillar ectopia was found in 37 % of patients with AIS compared with 13 % among controls (p < 0.001 and odds ratio of 3.8). The occurrence of tonsillar ectopia was not associated with the severity of scoliotic deformity (p=0.85), or rapid progression of scoliosis (p=0.76). Neurological deficit occurs twice as frequently in patients with tonsillar ectopia as in those with no tonsillar ectopia. Two of five patients with tonsillar ectopia showed improvement of their neurological deficit after the surgical correction of scoliosis.

Conclusion
As tonsillar ectopia is significantly more frequent among patients with AIS and may exhibit some prognostic utility in patients with neurological deficit, we conclude that tonsillar ectopia may play a role in the development of the deformity in some patients with AIS. However, occurrence of tonsillar ectopia among 13 % of controls precludes stating a definitive role of ectopia in the pathogenesis of AIS. Some patients with AIS, tonsillar ectopia and neurological deficit showed neurological improvement following the surgical correction of scoliosis.

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