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Urachal remnants

The urachus is the remnant of the embryological allantois.

  • The allantois appears around day 16 – outpoaching of the yolk sac, continuous from cloaca to umbilicus
  • Cloaca separates to the anterior urogenital sinus (-> bladder) and posterior anorectal canal around week 5-6
  • As the embryological bladder/urogenital sinus descends to the pelvis, the attachment to the bladder stretches and narrows (this is 4th – 5th month) and the lumen obliterates to become a thin fibrous cord

 

Anatomy

3 – 10 cm long

Diameter 8 – 10 mm

Located pre-peritoneally between the umbilicus and the dome of the bladder – posterior is peritoneum, anteriorly is transversalis fascia.

In up to 50 % there is no true attachment to the umbilicus – the apex of the urachus is infra-umbilical.

Bordered on each lateral side by the medial umbilical ligaments / obliterated umbilical arteries.

Classically described in 3 histological layers – inner transitional/urothelial or cuboidal, middle connective tissue, outer smooth muscle continuous with detrusor

 

Incidence

1 – 2 % prevalence of urachal anomalies in children – majority asymptomatic.

Slight male predominance.

 

Types of anomalies

  1. Urachal cyst (45 %)
  2. Urachal sinus (37 %)
  3. Patent urachus (16 %)
  4. Vesico-urachal diverticulum (1 %)
  5. Urachal tumour / malignancy

 

 

Urachal cyst

  • Most common in distal third
  • More common in older children – infection
  • May have palpable abdominal mass
  • Usually diagnosed easily with ultrasound
  • Rare reports of perforations into peritoneum

Urachal sinus

  • The lumen of the urachus is obliterated at bladder end, but open at umbilicus
  • Usually presents with umbilical discharge
  • Occasionally presents with granuloma, erythema at umbi
  • Occasionally pain with terminal voiding
  • Diagnosis with contrast study

Patent urachus

  • Typically presents in neonates – clear umbilical discharge
  • Send fluid for creatinine levels for diagnosis
  • DDx – patent omphalo-mesenteric (vitelline) duct – cystogram can delineate
  • May spontaneous close in first year of life
    • Look for distal obstruction – PUV etc – fixing that will aid in spontaneous closure

Vesico-urachal diverticulum

  • Urachus mostly obliterated except at bladder dome end
  • Usually asymptomatic and found incidentally
  • Generally leave alone

 

Clinical presentation and investigation

Typical presenting symptoms include:

  • Umbilical discharge
  • Periumbilical infection or granuloma
  • Palpable mass
  • Pain
  • UTIs, haematuria, dysuria, irritative voiding

Imaging is somewhat bespoke but may include:

  • Ultrasound
  • CT / MRI
  • Contrast study – fistulogram/sinogram, cystogram, MCUG

 

Treatment

EAU guidelines quite clear:

  • Urachal remnants with no epithelial tissue carry little risk of malignancy
  • Asymptomatic / non specific remnants can be managed conservatively
  • Incidental findings of urachal remnants should be observed non operatively
  • Small urachal remnant at birth may be viewed as physiological
  • Remnants in kids < 6 months likely to resolve without surgery
  • Surgical excision of urachal remnants solely as preventative measure against later malignancy has little support in literature
  • Symptomatic urachal remnants can be removed open or laparoscopically
  • MCUG only needed if febrile UTIs

Gleason (2015) – review of 65 000 cases, concluded 5721 remnants would have to be excised to prevent a single case of urachal adenocarcinoma.

 

If presenting with infection – treat infection first (antibiotics +/- drainage)

  • May need no further treatment, or can then proceed to staged excision.

For symptomatic patients – surgical excision of urachal remnant either open or laparoscopically (robotically) is standard treatment.

  • ?Taking a cuff of bladder
  • Can use feeding tube through the umbilical opening

 

Urachal adenocarcinoma

Very rare. 1 % of bladder cancers.

20 – 40 % of adenocarcinomas of the bladder.

 

Typically presents quite late – only when bladder wall has been invaded do symptoms (haematuria, storage symptoms) develop.

Imaging or cystoscopy reveals a tumour at the dome, confluent with distal end of urachus.

Relatively poor prognosis – 55 % 5 year survival, with local recurrence rates quite high of over 20 %

  • Poorer prognosis related to later presentation.

 

Partial cystectomy with wide margins has good oncological outcomes if negative margins achieved.

  • En bloc resection of urachus / dome of bladder +/- umbilicus and posterior sheath
  • Pelvic lymph node dissection should be considered

There is no high level evidence for chemotherapy or radiation therapy.