Urachal cyst is a cystic dilation of the embryological urachal remnant. The urachus is a tubular structure extending between the bladder dome and umbilicus during fetal life, normally obliterating after birth. A urachal cyst forms when both ends of the urachus close but the middle lumen persists. Usually asymptomatic and detected incidentally; however, when infected, it may present with acute abdominal pain, fever, and suprapubic tenderness. An infected urachal cyst can progress to abscess formation and rarely drain into the bladder lumen or umbilicus. It is imaged as a cystic structure located in midline between the bladder dome and umbilicus. Risk of malignant transformation is low but present — urachal carcinoma should be excluded especially with persistent symptoms or solid component.
Age Range
10-50
Peak Age
30
Gender
Equal
Prevalence
Uncommon
Urachal cyst results from incomplete obliteration of the urachus during embryological development. The urachus is the fetal structure providing the connection between the allantois and bladder. In normal development, the urachal lumen completely closes to become the median umbilical ligament (lig. umbilicale medianum). Urachal anomalies result from failure of this closure at different levels: patent urachus (entire lumen open), urachal sinus (open at umbilical end), vesicourachal diverticulum (open at bladder end), and urachal cyst (both ends closed, middle segment open). The urachal cyst is lined by compatible glandular epithelium (transitional or columnar epithelium) and secretes serous or mucinous fluid. Infection typically develops through hematogenous spread or contamination from adjacent bowel flora. In infected cyst, wall thickening and pericystic inflammation occur — reflected as wall enhancement and surrounding fat stranding on CT. Increased protein and cellular content of cyst fluid due to infection causes density increase on CT and T1 signal increase on MRI.
A cystic structure in midline location in the preperitoneal area of the anterior abdominal wall between the bladder dome and umbilicus is a pathognomonic location for urachal cyst. This specific anatomical position follows the embryological urachal axis and no other cystic lesion is seen in this location with similar frequency. Simple cystic appearance in uncomplicated cyst, wall thickening and enhancement in infected cyst accompany.
Well-defined, low-density (0-20 HU) cystic structure in midline location between bladder dome and umbilicus in portal venous phase. In uncomplicated cyst, the wall is thin (<3 mm) and smoothly contoured. Cyst size is generally between 2-5 cm. Located within the preperitoneal fat tissue of the anterior abdominal wall, posterior to the rectus muscles. A thin soft tissue band (urachal tract remnant) may be seen between the bladder dome and cyst.
Report Sentence
Smooth-walled, simple cystic structure in midline location between bladder dome and umbilicus is observed, consistent with urachal cyst; no solid component or calcification identified.
Homogeneously hyperintense cystic structure in midline location on T2-weighted images. In uncomplicated cyst, signal is homogeneous and very bright, consistent with simple fluid. T2 signal intensity may decrease or become heterogeneous in infected or hemorrhagic cyst (debris, protein increase). Cyst wall is seen as a thin hypointense ring on T2. Sagittal T2 images best demonstrate the position of the cyst along the bladder dome-umbilicus axis.
Report Sentence
Homogeneously hyperintense simple cystic structure in midline location anterior to the bladder dome is observed on T2-weighted images, consistent with urachal cyst.
No diffusion restriction in uncomplicated urachal cyst on DWI — cyst fluid shows low signal on DWI and high value on ADC. In infected cyst, diffusion restriction may be seen due to purulent content (high signal on DWI, low value on ADC). DWI is valuable in distinguishing infected urachal cyst from uncomplicated cyst and abscess formation. Diffusion restriction in the presence of solid component strengthens suspicion of malignant transformation.
Report Sentence
No diffusion restriction is observed in the urachal cyst on DWI, with no findings of infection or malignant transformation.
Anechoic, smooth-walled cystic structure in midline location above the bladder dome on B-mode ultrasonography. Meets simple cyst criteria with thin wall and posterior acoustic enhancement (through transmission). In infected cyst, internal echoes (debris), wall thickening, and increased echogenicity of surrounding fat may be seen. The cyst is in direct contact with the bladder dome and may show connection through a thin neck. US is the most appropriate modality for initial evaluation.
Report Sentence
Anechoic simple cystic structure in midline location above the bladder dome is observed, consistent with urachal cyst.
Prominent enhancement and thickening (>5 mm) of the cyst wall in infected urachal cyst on portal venous phase. Cyst content shows higher density than simple cyst (20-40 HU, due to protein increase). Pericystic fat stranding and reactive inflammation are observed. In advanced cases, signs of peritonitis, bladder or cutaneous drainage may develop. Malignant transformation should be excluded in the presence of solid nodular enhancement or calcification.
Report Sentence
Wall thickening, enhancement, and pericystic inflammatory changes are observed in the urachal cyst, consistent with infected urachal cyst.
Prominent rim enhancement of the cyst wall on contrast-enhanced MRI in infected urachal cyst. Wall enhancement and pericystic inflammatory enhancement are best evaluated on fat-sat T1 post-contrast sequences. In uncomplicated cyst, enhancement is absent or very minimal. Cyst fluid in infected cyst may show higher signal on T1 compared to simple cyst (protein increase).
Report Sentence
Wall rim enhancement and pericystic inflammatory enhancement are observed in the urachal cyst on contrast-enhanced images, consistent with infection.
Criteria
Asymptomatic, simple cystic structure. Thin smooth wall, homogeneous low-density fluid. Incidental detection.
Distinct Features
0-20 HU on CT, homogeneously hyperintense on T2, no restriction on DWI. No enhancement. May not require follow-up or treatment but growing cysts should be monitored due to risk of malignant transformation.
Criteria
Symptomatic — abdominal pain, fever, suprapubic tenderness. Wall thickening, pericystic inflammation. Density/signal changes in cyst content.
Distinct Features
Wall enhancement on CT, high-density cyst content (20-40 HU), pericystic fat stranding. Diffusion restriction on DWI. Treatment with antibiotics and/or percutaneous drainage; surgical excision for definitive treatment.
Criteria
Urachal sinus: opening at umbilical end of urachus — umbilical discharge. Patent urachus: entire urachal lumen open — urine passage between bladder and umbilicus.
Distinct Features
In urachal sinus, tubular structure extending deep from the umbilicus on CT/MRI. In patent urachus, open channel between bladder dome and umbilicus — opacified urine passage on delayed phase CT. Clinically, umbilical discharge is pathognomonic.
Distinguishing Feature
Urachal carcinoma contains solid component, calcification, and heterogeneous enhancement; urachal cyst is simple cystic without solid component or calcification. Carcinoma has solid extension into space of Retzius and tumor enhancement. Risk of malignant transformation is low but present in growing or symptomatic urachal cysts.
Distinguishing Feature
Bladder diverticulum shows open communication with bladder lumen and fills with opacified urine in delayed phase; urachal cyst is in separate location from the bladder lumen and generally has no open communication with the bladder. Diverticulum can arise from any point of the bladder wall; urachal cyst is only in midline location at the dome.
Distinguishing Feature
Bladder endometriosis shows T1-hyperintense (hemorrhagic content) cystic-solid structure; urachal cyst is T1-hypointense (simple fluid). Endometriosis may be at bladder dome but is not limited to midline location. Clinically, cyclic symptoms and menstruation relationship suggest endometriosis.
Distinguishing Feature
Bladder calculus is intraluminal, mobile, hyperdense structure; urachal cyst is extra-luminal, midline, cystic structure. Bladder calculus changes position within bladder lumen; urachal cyst is in fixed location. Both pathologies may coexist but show different imaging characteristics.
Urgency
routineManagement
conservativeBiopsy
Not NeededFollow-up
12-monthUncomplicated urachal cyst generally does not require treatment; annual US follow-up is sufficient. Treatment of infected urachal cyst involves antibiotics and percutaneous drainage if needed first, followed by planned definitive surgical excision (urachal remnant + cyst excision). Surgery can be performed laparoscopically or open. In growing, symptomatic, or cysts showing solid component, urachal carcinoma should be excluded and surgical excision is recommended. Incidence of urachal anomalies in the general population is ~1.6%, with the vast majority being asymptomatic.
Urachal cyst is usually asymptomatic and found incidentally. When infected, it presents with abdominal pain, fever, dysuria, and suprapubic tenderness. Infected urachal cyst requires surgical excision and antibiotic therapy. Uncomplicated cysts may be followed or electively excised. Rarely, malignant transformation (urachal carcinoma) may develop, and careful evaluation is warranted especially in cysts >4 cm.