From small pelvic outlet syndrome to sirenomelia.

We report 5 newborns with a contracted lesser pelvis, imperforate anus (severely stenotic and ectopic anus in 1 case), absent or rudimentary urinary tract, and defective or absent external genitalia, vagina, and uterus but normal gonads. The first 2 patients had small pelvic outlet syndrome (SPOS). The findings in the third patient, a possible transition to sirenomelia, were more severe and included malposition of the penis to the posterior sacral area. The fourth and fifth patients had sirenomelia. The remarkable similarity of many abnormalities observed in these cases and related material in the literature suggests that SPOS and sirenomelia may be part of the same malformation complex (SPOS/sirenomelia complex).