Prenatal diagnosis of sirenomelia with anencephaly and craniorachischisis totalis

RATIONALE Sirenomelia and anencephaly are well-defined congenital malformations that usually occur independently. PATIENT CONCERNS We report a case of combined sirenomelia, anencephaly and complete rachischisis, diagnosed in the 16th week of gestation. DIAGNOSES To our knowledge, this is the 7th case in the literature and the first that is diagnosed so early in pregnancy. INTERVENTIONS The final diagnosis is confirmed with radiological examination after the termination of pregnancy. OUTCOMES Prenatal diagnosis of sirenomelia is difficult due to the presence of kidney agenesis and severe oligohydramnios. LESSONS The combination of sirenomelia and craniorachischisis totalis is extremely rare and prenatal ultrasound scan are a challenge, even for experts in the field.