In order to improve the detection rate of lesions such as tumors, the fusion of prenatal magnetic resonance imaging (MRI) or CT with navigation has provided a clear benefit in US fusion. This should also be applied in prenatal imaging since poor tissue contrast and/or technical limitations may hinder the ability of the standard US to detect fetal lesions [124].8.1. Patent urachusUltrasonography is typically used when patent urachus is suspected [34]. A tubular connection from the anterosuperior aspect of the bladder to the umbilicus can be detected when using a longitudinal US [125]. In utero, US has the ability for formulating a diagnosis of patent urachus in the first trimester [126,127]. Another study observed a cystic mass in the umbilical cord near the fetal anterior abdominal wall, that was documented to decrease in size through gestation, which may be highly suggestive of a patent urachus [101]. Sinography has also proved useful to confirm patency [5,125]