True tail dorsal-lumbar: malformation or ancestral remaining?

The case of a healthy newborn presenting a dorsal-lumbar cutaneous appendage is reported. The appendage was excised by ligature. This appendage was not associated with dysraphism or other malformations. It was analysed histologically and then defined as a so called true tail. Although it was been expressed a lot of hypotheses, the etiology of this finding remains disputed. The embryology of malformation and its non identification between known-syndromes is showed. The difference between true tails and not-true tails is discussed. The conclusion is drawn that for its clinical and histological aspect this malformation may be included in true tails.