Placode rotation in transitional lumbosacral lipomas: are there implications for origin and mechanism of deterioration?

PURPOSE: Rotation of the lipoma-neural placode has been noted in transitional lumbosacral lipomas. The purpose of this study was to confirm this rotation; that this rotation occurs with a preference to the left, and correlates with clinical symptoms. In addition, this study tests the hypothesis that this rotation occurs through local mechanical forces rather than intrinsic congenital malformation. METHODS: Lipomas were classified as per the Chapman classification. Degree of rotation of the placode from the coronal plane was recorded along with the presence of herniation outside of the vertebral canal. Abnormalities on urodynamic testing were recorded, along with neuro-orthopaedic signs picked up on formal neuro-physiotherapy assessment. RESULTS: Placode rotation occurs more frequently in the transitional group. Regardless of lipoma classification, rotation was much more common to the left. Furthermore, when lateralisation of symptoms was present, this strongly correlated with the direct of rotation. There was no difference in rotation of the placode whether it was within (lipomyelocoele) or without the vertebral canal (lipomyelomeningocoele). CONCLUSIONS: Placode rotation is a feature of transitional lumbosacral lipomas and may account for the increase in symptoms amongst this subgroup. Herniation of the placode outside the vertebral canal does not increase the risk of rotation suggesting a congenital cause for this finding rather than a purely mechanical explanation.