Bladder, ureter & renal pelvis

Congenital anomalies

Urachus and patent urachus

Last author update: 1 July 2011
Last staff update: 28 November 2022 (update in progress)

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PubMed Search: Urachus, Patent urachus

Alcides Chaux, M.D.
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Cite this page: Chaux A. Urachus and patent urachus. website. Accessed December 1st, 2022.
Definition / general

    Urachus - definition
  • Vestigial structure, 3-10 cm, located in a preperitoneal pyramid-shaped area formed by the bladder dome (base) and the obliterated umbilical arteries (tip of pyramid is towards umbilicus)
  • Pathology other than patent urachus is described separately in the Table of Contents

Patent urachus - definition
  • Represents 50% of all urachal anomalies
  • Due to failure of obliteration of the urachal canal
  • Rare, because lumen typically closes at week 17 post-conception (Cells Tissues Organs 2010;191:422)
  • May appear later in life due to retubulization secondary to acquired obstructive bladder disease
  • Leads to urination through umbilicus
  • May be associated with infections (Staphylococcus aureus, Escherichia coli, Enterococcus, Citrobacter and, rarely Proteus species)

  • Arises from superior urogenital sinus
  • In fetus, connects bladder dome with allantois (embryonic diverticulum of hindgut, vessels are precursors to those in umbilical cord)
  • Fragmentation occurs post-partum when bladder descends into pelvis; urachus eventually becomes median umbilical ligament
  • Also called persistent urachus
Diagrams / tables

Images hosted on other servers:

Patent urachus

Clinical features
  • Urachal remnants may be found in midline or posterior bladder wall
  • Remnants seen at autopsy in 50% of fetuses, 33% of adults
  • Remnants are associated with urachal cysts, sinus, fistula, diverticulum, infections, adenocarcinoma of bladder; also urothelial carcinoma, villous adenoma, squamous cell carcinoma
Case reports
Microscopic (histologic) description
  • Usually persists as fragmented tubules separated by fibrous cords, but without a desmoplastic tissue response
  • Composed of three layers: epithelium (stratified, columnar or urothelium), connective tissue and an outer smooth muscle layer (in continuity with detrusor muscle)
  • No goblet cells, no atypia in the epithelium
Microscopic (histologic) images

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Urachal remnants

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