Bladder, ureter & renal pelvis

Congenital anomalies

Urachus, benign nonneoplastic lesions



Last staff update: 9 March 2023 (update in progress)

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PubMed Search: Urachus, benign nonneoplastic lesions

Bohdan Zoshchuk, M.D.
Y. Albert Yeh, M.D., Ph.D.
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Cite this page: Zoshchuk B, Morisetti M, Beeter MC, Yeh YA. Urachus, benign nonneoplastic lesions. PathologyOutlines.com website. https://www.pathologyoutlines.com/topic/bladderurachus.html. Accessed March 24th, 2023.
Definition / general
  • The urachus, originated from remnants of allantois, is a fibrous cord connecting the umbilicus to the anterosuperior aspect of the bladder dome; usually obliterates at birth and becomes the median umbilical ligament (Kumar: Robbins & Cotran Pathologic Basis of Disease, 10th Edition, 2020)
  • Urachal pathology results from failure of involution of the embryonic structures, resulting in the formation of a urachal cyst, umbilical urachal sinus, vesicourachal diverticulum or patent urachus ( completely patent, tubular remnant communicating the developing bladder and the umbilical cord) (StatPearls: Patent Urachus [Accessed 29 December 2022])
Essential features
Terminology
  • Congenital malformation of the urachus (Clin Perinatol 2014;41:695)
  • Malformation of urachus
  • Congenital urachal anomaly
  • Urachal anomaly
  • Patent urachus: completely patent tubular lesion communicating the bladder and the umbilical cord
  • Umbilical urachal sinus: tubulocystic lesion with an opening in the umbilicus while the other end is closed (BMJ Case Rep 2016;2016:bcr2016215374)
  • Vesicourachal diverticulum: tubulocystic lesion with an opening in the bladder while the other end is closed
  • Urachal cyst: cystic structure with both the umbilical and bladder ends closed (BMJ Case Rep 2016;2016:bcr2016215374)
  • Urachal remnants within bladder wall: tubulocystic lesion located in the bladder wall
ICD coding
  • ICD-10: Q64.4 - malformation of urachus
    • Urachus, congenital
    • Patent urachus
    • Patent (congenital) urachus
  • ICD-11: LB03.0 - allantoic duct remnants or cysts
Epidemiology
Sites
Pathophysiology
  • At the second week of gestation, the allantois emerges from the posteroinferior yolk sac
  • Allantois: an embryonic remnant with connection between the umbilicus and the cloaca (diagram 1A) (BMJ Case Rep 2016;2016:bcr2016215374)
  • During the fourth to seventh weeks of gestation, the cloaca develops into urogenital sinus and the anal canal
  • The superior part of the urogenital sinus continuous with the allantois develops into the urinary bladder (Differentiation 2018;103:66)
  • During the fourth and fifth weeks of gestation, the urachal lumen (allantois) narrows to form a small tubular structure lined by urothelium (The Developing Human, 8th ed, p256-258, editor Moore et al., Elsevier, 2008)
  • By the twelfth week of gestation, the allantois progressively constricts, resulting in a fibromuscular strand structure known as urachus (Moore: The Developing Human - Clinically Oriented Embryology, 11th Edition, 2019)
  • By the time of birth, the urachus becomes a thin fibrous cord that extends from the umbilicus to the urinary bladder dome (diagram 1B) (BMJ Case Rep 2016;2016:bcr2016215374)
  • If the lumen of the allantois persists, it can develop into urachal anomalies:
Etiology
Diagrams / tables

Images hosted on other servers:
Classification of urachal anomalies

Classification of urachal anomalies

Urachal cysts and fistulas

Urachal cysts and fistulas

Clinical features
Diagnosis
  • Prenatal:
    • Ultrasonography (US): increased thickness of the umbilicus observed as an extra-abdominal cystic mass (Medicina (Kaunas) 2022;58:1621)
    • Early prenatal detection for appropriate counseling for postpartum corrective surgery
  • Postnatal:
  • Ultrasound: diagnostic for 82% of cysts, 100% of sinuses, 100% of patent urachus
  • Voiding cystourethrogram: diagnostic for 100% of patent urachus
  • CT scan: diagnostic for 71% of cysts (J Pediatr Urol 2007;3:500)
Laboratory
  • Check creatinine level if urine in the umbilical drainage is suspected (StatPearls: Patent Urachus [Accessed 10 January 2023])
  • Microorganisms cultured from the umbilical drainage often include Staphylococcus aureus, Escherichia coli, Enterococcus, Citrobacter and rarely, Proteus species
Radiology description
Radiology images

Contributed by Bohdan Zoshchuk, M.D.
Patent urachus, US Patent urachus, US

Patent urachus, ultrasound



Images hosted on other servers:
Hypoechoic mass

Hypoechoic mass

Patent urachus, fistulography

Patent urachus, fistulography

Patent urachus, CT scan

Patent urachus, CT scan

Cyst protruding through umbilicus

Cyst protruding through umbilicus

Prognostic factors
Case reports
Treatment
Clinical images

Images hosted on other servers:
Persistent urachus

Persistent urachus

Before and after surgery

Before and after surgery

Urachal cysts - sinus tract between bladder dome and umbilicus

Urachal cysts - sinus tract between bladder dome and umbilicus

Infected urachal cyst

Infected urachal cyst

Urachal cyst attached to Meckel diverticulum

Urachal cyst attached to Meckel diverticulum

Gross description
Gross images

Images hosted on other servers:
Patent urachus, autopsy specimen

Patent urachus, autopsy specimen

Benign urachal lesion

Benign urachal lesion

Infected urachal cyst and fibrous tract

Infected urachal cyst and fibrous tract

Urachal cyst containing stones

Urachal cyst containing stones

Urachal sigmoid fistula

Urachal sigmoid fistula

Inflamed urachal cyst

Inflamed urachal cyst

Microscopic (histologic) description
  • Tubulocystic lesions of urachal remnants, urachal cyst, patent urachus, vesicourachal diverticulum and urachal sinus are most frequently lined by benign urothelial cells and embedded in fibromuscular tissue
  • Cyst lining epithelial cells with cuboidal cells, flattened epithelial cells or urothelial cells with intestinal (columnar cells with various goblet cells) metaplasia may present (Cheng: Urologic Surgical Pathology, 4th Edition, 2019)
Microscopic (histologic) images

Contributed by Bohdan Zoshchuk, M.D., Manasa Morisetti, M.D., Rosemarie Rodriguez, M.D. and AFIP
Patent urachus Patent urachus

Patent urachus

Patent urachus

Patent urachus

Urachal remnant Urachal remnant

Urachal remnant

Urachal remnant

Urachal remnant


Urachal sinus Urachal sinus

Urachal sinus

Cyst lining Cyst lining

Cyst lining

GATA3

GATA3

Lobulated cystic structure lined by benign epithelium

Lobulated cystic structure lined by benign epithelium

Positive stains
Negative stains
Molecular / cytogenetics description
Sample pathology report
  • Urinary bladder wall lesion, excision:
    • Tubulocystic lesion lined by urothelial epithelium consistent with urachal remnants (see comment)
    • Comment: Sections of the bladder wall lesion show a tubular structure lined by benign urothelium and attached to the muscularis propria. These findings are consistent with urachal remnants.
Differential diagnosis
Board review style question #1
During bladder catheterization in a newborn boy, the tip of the catheter came out through his enlarged umbilical stump. What is the diagnosis?

  1. Patent omphalomesenteric duct
  2. Patent urachus
  3. Umbilical urachal sinus
  4. Urachal cyst
  5. Vesicourachal diverticulum
Board review style answer #1
B. Patent urachus. Patent urachus creates a tubular connection between the umbilicus and the anterosuperior wall of the bladder. Answer A is incorrect because patent omphalomesenteric duct has connection between umbilicus and small intestine. Answers C, D and E are incorrect because umbilical urachal sinus, urachal cyst and vesicourachal diverticulum cannot be probed through.

Comment Here

Reference: Urachus and patent urachus
Board review style question #2

A 50 year old man complained of abdominal pain for several weeks. A noncontrast CT scan of the abdomen was performed. There was a cystic lesion in the anterosuperior bladder wall. No connection between the bladder and the umbilicus was noted. Surgical excision followed by pathological examination was performed. The tubular lesions are lined by benign urothelial cells. The photomicrograph is shown above. What is the diagnosis?

  1. Cystitis cystica
  2. Mesonephric remnant
  3. Omphalomesenteric duct remnant
  4. Urachal remnant
  5. Vitelline duct remnant
Board review style answer #2
D. Urachal remnant. Urachal remnant is usually lined by benign urothelium. Answer A is incorrect because cystitis cystica is found in the bladder mucosa. Answer B is incorrect because mesonephric remnants are composed of small tubules lined by low columnar to cuboidal epithelial cells. The cells are immunoreactive to CK903, CD10 and vimentin. Omphalomesenteric duct remnant is the same as vitelline duct remnant, which is lined by gastrointestinal epithelium.

Comment Here

Reference: Urachus and patent urachus
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