What are the differences between a urachal cyst and a patent urachus in terms of anatomy, clinical presentation, diagnostic evaluation, and management?

Urachal Cyst vs Patent Urachus: Key Differences

Anatomic Distinctions

A urachal cyst is a closed, fluid-filled cavity located in the midline lower abdominal wall that does not communicate with either the umbilicus or bladder, while a patent urachus is a persistent tubular connection extending from the anterosuperior bladder to the umbilicus. 1

• Urachal cyst: Appears as a noncommunicating, fluid-filled cavity positioned just beneath the umbilicus or above the bladder in the midline anterior abdominal wall 1
• Patent urachus: Demonstrates complete tubular patency connecting the bladder dome to the umbilicus, representing failure of complete obliteration during fetal development 1
• Other urachal remnants include umbilical-urachal sinus (blind-ending tract at umbilical end) and vesicourachal diverticulum (outpouching at bladder end) 1

Clinical Presentation Patterns

The clinical presentations differ markedly: patent urachus typically presents with periumbilical drainage (54% of cases), while urachal cysts present with periumbilical pain (30%) or palpable mass (22%). 2

Patent Urachus:

• Continuous umbilical drainage or "wet umbilicus" is pathognomonic 3, 4
• May be diagnosed prenatally on routine ultrasound screening 4
• Symptoms present earlier in life, often in infancy 4

Urachal Cyst:

• Periumbilical or lower abdominal pain when infected 3, 2
• Palpable midline abdominal mass 3, 2
• Fever and pyuria when complicated by infection 3
• Can achieve massive size with stone formation in rare cases 3
• Often presents later in childhood or adulthood 4

Diagnostic Evaluation Algorithm

For periumbilical drainage, perform a sinogram (100% diagnostic for patent urachus); for periumbilical mass, perform ultrasound (82-100% diagnostic for urachal cyst). 4, 2

First-Line Imaging by Presentation:

Periumbilical drainage:

• Sinogram is diagnostic in 100% of patent urachus cases 4
• Voiding cystourethrogram (VCUG) is diagnostic in 100% of patent urachus but only 6% of sinuses 4

Periumbilical mass or pain:

• Ultrasound is diagnostic in 82-100% of urachal cysts 4, 2
• High-frequency ultrasound shows anechoic structure along the urachus for cysts 5
• Patent urachus appears as tubular connection between umbilicus and bladder on longitudinal ultrasound 1

Second-Line Imaging:

• CT scan correctly diagnoses 71% of urachal cysts when ultrasound is inconclusive 2
• CT shows midline cystic lesion just above the anterosuperior bladder 1
• VCUG has limited utility for cysts (only 6-13% diagnostic) 4

Critical Diagnostic Pitfall:

• Physical examination alone can be diagnostic in many cases; avoid unnecessary imaging when clinical diagnosis is clear 2
• Infected urachal cysts and urachal carcinoma appear similar on imaging (thick-walled, increased echogenicity), requiring percutaneous biopsy for differentiation 1

Management Approach

Complete surgical excision with bladder cuff resection is the definitive treatment for all urachal remnants in adults to prevent recurrent infection and malignant transformation. 6

Surgical Technique:

• En-bloc resection of the entire urachal ligament with umbilicus and bladder cuff excision is recommended for all symptomatic or discovered urachal remnants 6
• For patent urachus: Excision of urachal tract with bladder dome resection 3, 4
• For urachal cyst: Excision with bladder cuff in 50% of cases, or excision without bladder cuff in 50% 4
• Laparoscopic excision is an acceptable alternative approach 4

Critical Management Pitfall:

• Incomplete excision must be avoided, as retained urachal remnants carry risk of malignant transformation 6
• Wound infection occurs in 7-9% of cases postoperatively 4, 2
• Simple incision and drainage of infected cysts is inadequate definitive treatment 4

Timing Considerations:

• Infected cysts may require initial drainage followed by delayed definitive excision after inflammation resolves 3
• All urachal remnants warrant complete excision even if asymptomatic, given malignancy risk 6