Normal bladder functioning depends on intact functioning of the somatic and parasympathetic nerves arising from the second, third and fourth sacral segments of the spinal cord. Structural lesions of the corresponding levels of the spinal cord (the conus medullaris) may result in early and marked bladder involvement, occasionally preceding any other neurological signs or symptoms. In contrast, however, the peripheral component of these fibres in the cauda equina progress centrally closely adjacent to other lumbosacral nerve roots until they exit at the appropriate spinal segment. Therefore, a cauda equina lesion would typically involve a nerve root exiting at the particular level of the lesion and, depending on the size and exact location of the lesion, other nerve roots descending to lower levels will also be involved. In fact, normally, bladder involvement in cauda equina syndrome is quite late, and is accompanied by several other neurological signs. Of course there are rare exceptions. For example, I have seen one patient who had a teratoma of the cauda equina associated with a tethered cord syndrome and thickened filum terminale. AG