Anencephaly in trisomy 18: Related or unrelated?

A fetus of 20 to 21 weeks of development with the trisomy 18 syndrome has been described. In addition to the phenotypic manifestations usually associated with the syndrome, i.e., low set ears, short neck, omphalocoele, flexion of fingers with the convergence of the second and fifth digits, rocker bottom feet, urinary tract anomalies and intrauterine growth retardation, the fetus also showed left diaphragmatic hernia, anencephaly and aplasia of the squamous part of occipital bone. Since anencephaly has never been described as one of the phenotypic manifestations of trisomy 18, it is reasonable to assume that in the present fetus it is unrelated and resulted from secondary destruction of the neural tube.