Lateral Semicircular Canal Asymmetry in Idiopathic Scoliosis: An Early Link between Biomechanical, Hormonal and Neurosensory Theories?

<div><p>Introduction</p><p>Despite its high incidence and severe morbidity, the physiopathogenesis of adolescent idiopathic scoliosis (AIS) is still unknown. Here, we looked for early anomalies in AIS which are likely to be the cause of spinal deformity and could also be targeted by early treatments. We focused on the vestibular system, which is suspected of acting in AIS pathogenesis and which exhibits an end organ with size and shape fixed before birth. We hypothesize that, in adolescents with idiopathic scoliosis, vestibular morphological anomalies were already present at birth and could possibly have caused other abnormalities.</p><p>Materials and Methods</p><p>The vestibular organ of 18 adolescents with AIS and 9 controls were evaluated with MRI in a prospective case controlled study. We studied lateral semicircular canal orientation and the three semicircular canal positions relative to the midline. Lateral semicircular canal function was also evaluated by vestibulonystagmography after bithermal caloric stimulation.</p><p>Results</p><p>The left lateral semicircular canal was more vertical and further from the midline in AIS (<i>p</i> = 0.01) and these two parameters were highly correlated (<i>r</i> = -0.6; <i>p</i> = 0.02). These morphological anomalies were associated with functional anomalies in AIS (lower excitability, higher canal paresis), but were not significantly different from controls (<i>p</i>>0.05).</p><p>Conclusion</p><p>Adolescents with idiopathic scoliosis exhibit morphological vestibular asymmetry, probably determined well before birth. Since the vestibular system influences the vestibulospinal pathway, the hypothalamus, and the cerebellum, this indicates that the vestibular system is a possible cause of later morphological, hormonal and neurosensory anomalies observed in AIS. Moreover, the simple lateral SCC MRI measurement demonstrated here could be used for early detection of AIS, selection of children for close follow-up, and initiation of preventive treatment before spinal deformity occurs.</p></div

Scoliosis and controls: Canal paresis is correlated with lateral SCC morphology.

<p>Pearson correlation for parametric distribution, or Spearman Rank.</p><p>*Significant results with <i>p</i>-value < 0.05.</p><p>** Significant results with <i>p</i>-value<0.01.</p><p>Scoliosis and controls: Canal paresis is correlated with lateral SCC morphology.</p

Group characteristics.

<p>Group characteristics.</p

Left lateral SCC and posterior SCC are further from the midline in scoliosis.

<p>(1) Mean (in mm) +/- SD if T Test; or Median (in mm) (Mean Rank) if Mann Whitney U test.</p><p>(2) t value and degrees of freedom (df) if T Test; or U value if Mann Whitney U test.</p><p>*significant results with <i>p</i>-value < 0.05.</p><p>Left lateral SCC and posterior SCC are further from the midline in scoliosis.</p

In scoliosis the orientation of the left lateral SCC is correlated with its position and other left SCC positions.

<p>*Significant results with <i>p</i>-value < 0.05.</p><p>In scoliosis the orientation of the left lateral SCC is correlated with its position and other left SCC positions.</p

Measurement of lateral semicircular canal orientation in the parasagittal plane.

<p>T2 MRI image in the parasagittal plane showing the <b>“</b><i>Vertical Lateral canal Sagittal angle Right</i>” (VLSR) formed between the right lateral semicircular canal and the vertical (represented by the frontal plane).</p

Measurement of the lateral semicircular canal in the frontal plane.

<p>MRI image in the frontal plane showing the “<i>Intercanal Angle</i>”(IA) formed by the axis of the right and left lateral canals; the “<i>Vertical Lateral canal Frontal angle Right</i>”(VLFR) formed between the right lateral SCC and the vertical axis (defined by the sagittal plane); and the” <i>Vertical Lateral canal Frontal angle Left” (</i>VLFL) formed between the left lateral SCC and the vertical axis.</p