RESUMEN
Caudal regression syndrome is a congenital malformation described by various degrees of developmental failure, which the most extreme and rare form is known as sirenomelia or mermaid syndrome. The associated malformations comprise anorectal, vertebral, urological, genital, and lower limb anomalies. We reported pathological findings of sirenomelia in a female stillborn with breech presentation that was born by normal vaginal delivery at 35 weeks of pregnancy following an uneventful pregnancy of a 31-year-old woman. Physical examination at birth showed normal facies, fusion of the lower limbs with bilateral presence of hip, knee, and ankle joints, sacral meningocele, omphalocele, agenesia of female external genitalia, of anus, and of cervical vertebrae. The sirenomelia etiology is still unknown but there are suggestions of genetic and teratogenic factors involvement that were not identified in the present case. The association with the agenesis of cervical vertebrae is rare and only one case described previously in the literature was reported