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Last revised by Dr MT. Niknejad on 17 Jun 2022

The urachus (plural: or urachuses or urachi 6,7) is the fibrous vestigial remnant of the embryonic allantois.

The lumen of the urachus usually obliterates following birth and becomes known as the median umbilical ligament which is in turn covered by a midline linear fibrous fold of parietal peritoneum (the median umbilical fold) 3. This fold extends from the apex of the bladder to the umbilicus. It is located in the retropubic space.

If the lumen does not completely involute, a spectrum of urachal remnants may persist, including 4:

A urachal remnant may transform into an adenocarcinoma 5.

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Cases and figures

  • Figure 1: urachus - indicated by arrows
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  • Case 1: prominent urachus
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  • Case 2: prominent median umbilical ligament
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