The renal axes in spina bifida: issues of confusion and fusion.

The occurrence of horseshoe kidneys in myelodysplasia has been suggested to be overestimated because of the concurrent prevalence of kyphotic spine in the spina bifida population. Pseudohorseshoe kidneys result from the actual medial migration and apposition of the lower renal poles in the deep fossa created by the gibbus deformity. The presence of a lumbosacral kyphosis, however, does not imply there is not a true horseshoe kidney. In our myelodysplasia population of 189 patients, occurrence of true horseshoe kidneys (13 patients) and pseudohorseshoe kidneys (14 patients) was increased. The finding of lumbosacral kyphosis was twice as common in the pseudohorseshoe population as in the true horseshoe population. True horseshoe kidneys were three times more commonly seen in association with congenital vertebral anomalies cephalad to the dysraphic spine. Diagnosis in this study was predominantly based on renal cortical scintigraphy with the posterior pin-hole magnification technique.