Which condition presents sonographically as an anechoic mass between the umbilicus and the bladder?

A urachal cyst arises from incomplete closure of the urachus, a remnant of the fetal allantoic duct connecting the bladder to the umbilicus. It appears as a midline, anechoic, nonvascular mass located between the bladder dome and the umbilicus.

According to Rumack’s Diagnostic Ultrasound:

“A urachal cyst is a midline, anechoic structure located between the bladder and umbilicus, resulting from incomplete obliteration of the urachus.”