The urachus revisited: multimodal imaging of benign & malignant urachal pathology (2024)

Abstract

The urachus is a fibrous tube extending from the umbilicus to the anterosuperiorbladder dome that usually obliterates at week 12 of gestation, becoming themedian umbilical ligament. Urachal pathology occurs when there is incompleteobliteration of this channel during foetal development, resulting in theformation of a urachal cyst, patent urachus, urachal sinus or urachaldiverticulum. Patients with persistent urachal remnants may be asymptomatic orpresent with lower abdominal or urinary tract symptoms and can developcomplications. The purpose of this review is to describe imaging features ofurachal remnant pathology and potential benign and malignant complications onultrasound, CT, positron emission tomography CT and MRI.

Introduction

Imaging of urachal remnants

Urachal cysts account for up to 54% of urachal remnant anomalies, arising from thelower third of the urachus and are often asymptomatic and incidentally discovered.Sonography can demonstrate an extraluminal midline fluid-filled structure that doesnot communicate with the umbilicus. CT following intravenous contrast usually reveala fluid-attenuation supravesical lesion (Figure 3). On MRI, urachal cysts usually demonstrate a thin, non-enhancing wall withintrinsic T1 hypointense and T2 hyperintense signal.^1–4

A urachal sinus is a tubular dilatation of the umbilical portion of the urachus thatoccurs three times more frequently in children than adults. Clinical presentation ismost commonly with periumbilical inflammation and purulent discharge. On ultrasound,a urachal sinus may appear tubular and hypoechoic communicating with the umbilicusonly. Fluoroscopic sinography can show a tube-like cul-de-sac. CT may betterdelineate infective complications. MRI can better evaluate for superimposedinfection or developing malignancy.^1,3

The patent urachus is a fistulous communication occuring between the urinary bladderand umbilicus, most commonly presenting with umbilical urine leak. Ultrasound maydemonstrate a tube-shaped anechoic structure communicating with theanterosuperior bladder and umbilicus. Diagnosis can be confirmed on voidingcystourography or fluoroscopic sinogram with instilled contrast media defining theumbilical-vesical tract. CT and MRI can better demonstrate air, fluid or calculiwithin the patent urachus, and evaluate for potential infective complications onpost-contrast imaging.^1–3

A urachal diverticulum is a rare clinical entity accounting for 3–5% ofurachal remnant pathology occurring when the urachus communicates with the bladderdome only. Sonographic evaluation of a urachal diverticulum shows a blind-endingsupravesical hypoechogenic structure arising from the bladder dome. CT candemonstrate an out-pouching from the superior aspect of the bladder (Figure 4) without umbilical communication, andmay demonstrate intraluminal calcification, present in up to 50% of cases. Inchildren, VCUG can show contrast reflux into the diverticulum and help delineate theextent of the involvement of the urachus. On MRI, a protruding midline soft-tissuetract can be seen, demonstrating variable signal intensity and post-contrast enhancement.^1–3

Imaging of benign urachal pathology

Infection of a persistent urachus is the most common benign complication occuring inpatients with a urachal remnant, usually due to Staphylococcusaureus. Patients with infected urachal cysts may be asymptomatic withleukocytosis or present with recurrent urinary tract infections, abdominal pain or fever.^1,2,4

Infected urachal cysts may be difficult to differentiate from non-infected cysts orother pelvic pathology on initial sonographic evaluation in the absence of clinicalsigns and symptoms.⁵ Ultrasound is often the first-line modality for imaging a child presentingwith symptoms of abdominal pathology. Greyscale ultrasound reveals a midlineextraperitoneal structure extending from the bladder dome to the umbilicuscontaining internal echoes (Figure 5) and maymimic other pelvic pathology, such as haematoma. On CT, infected urachal cysts canappear thick-walled and irregular with peripheral enhancment and underlying bladderwall thickening (Figure 6). On MRI, infected urachal cysts can appear as irregular thick-walledsupravesical structures demonstrating variable signal intensity and heterogenouscontrast enhancement. MRI may delineate the infected urachal cyst from adjacentpelvic structures and identify possible rupture and abscess formation.^1,3–5

Urachal abscess can develop if an infected cyst is left untreated. Infected urachalcysts usually discharge into the umbilicus or urinary bladder but may rarely ruptureintraperitoneally from their extraperitoneal location causing sepsis andperitonitis. Given the lack of direct communication with either bladder orumbilicus, clinical asessment may result in misdiagnosis of more commonlyencountered caused of acute abdomen, such as appendicitis or bowel perforation.^5,6 Ultrasound may show a complex cystic mass in the midline above the urinarybladder. CT following intravenous contrast can demonstrate a supravesicalheterogenous collection with a thick enhancing irregular wall and centralnon-enhancing low attenuation (Figure 7), thatmay abut or communicate with the abdominal wall.^1,3,5,6 On MRI, a urachal abscess can appear as a thick-walled, multiloculatedpredominantly T2 hyperintense mass extending into Retzius space demonstratingheterogenous enhancement on post-contrast imaging. (Figure 8)

Benign urachal tumours are rare clinical and radiological entities and includefibroadenomatous lesions, lipoatous tumours and hamartomas.^1,3

Imaging of malignant urachal pathology

Malignant transformation of a urachal remnant is rare, accounting for <0.5% ofbladder cancer and develops twice as often in males, most commonly between the agesof 46 and 56. Adenocarcinoma accounts for 80–90% of cases with up to 75%producing mucin. Sarcomatous neoplasms, squamous cell and transitional cell urachalcancers have also been reported.^1,3,7,8

Clinical presentation is variable and patients may be asymptomatic until local spreador development of metastases. Haematuria is the most common symptom, present in upto 80% of cases. Mucinuria can occur in up to 25% of patients, a rare symptom thatshould raise suspicion and prompt further investigation for a urachal cancer.^3,7–9

On ultrasound, urachal malignancy can appear as a hyperechogenic soft-tissue lesionbetween the urinary bladder and anterior abdominal wall demonstrating internalvascularity on colour doppler imaging. Urachal cancer can demonstrate a variableappearance on cross-sectional imaging. On CT urachal malignancy can appear as asolid-cystic mass extending toward the umbilicus with an irregular, enhancing wall (Figure 9). Up to 90% of cases arise from the juxtavesical urachus, extendingcranially into the space of Retzius. Urachal cancer may also appear as apredominantly cystic mass (Figure 10) or as amidline or paramidline enhancing nodule arising from the anterosuperior aspect ofthe urinary bladder (Figure 11). Urachal cancer appears low attenuation in 60% of cases due to the presenceof mucin or necrosis. CT can also identify central or peripheral calcification,present in almost 75% of urachal cancers.^1,3,8–10 Urachal malignancies may be predominantly cystic demonstrating high T2 signal(Figure 12) or multilobulated with solidand cystic components demonstrating intermediate and high T2 signal representingmucin, cystic change and/or necrosis (Figure 13). On post-contrast T₁ weighted imaging, urachal cancers may demonstrate inhom*ogenousenhancement. MRI may provide addional value by defining local invasion of adjacentsoft-tissue and visceral structures, as well as identifying local nodal metastases.^1,11,12

Assessment of urachal pathology: the role of imaging

Accurate diagnosis of benign from malignant urachal pathology on imaging isimprecise. Meeks et al found that pre-operative imaging with CT had a lowspecificity and negative predictive value of 21 and 43% respectively.¹³ In addition, although the majority of malignant urachal tumours are solid, upto 27% can demonstrate a cystic component.² Similarly, although intrinsic calcification is considered 'pathognomic' ofurachal cancer seen in up to 70% of cases on CT, 'egg-shell' calcification can alsobe seen in ~20% of urachal cysts.^2,3 Fludeoxyglucose positron emission tomography (PET) CT (Figure 14, ^14,15) has been demonstrated as useful in the assessment of urachal cancer¹⁴ However, due to lack of avid fludeoxyglucose uptake in over half of mucinoustumours, diagnostic performance of PET/CT may be unreliable in excluding urachalmalignancy, given that up to three quarters urachal tumours produce mucin. Imagingmay identify a urachal remnant complication but ultimately cystoscopy and biopsy maybe required to confirm the diagnosis of a benign or malignant lesion.^2,7,8,15

Treatment of urachal pathology

Controversy regarding optimal treatment of urachal remnants has become more apparentin recent years. Management strategies also differ between adult and paediatricpatients. While surgery is required for most symptomatic patients, spontaneousregression of urachal anomalies has also been reported. Current series demonstrate a10-year survival rate of only 49% with surgery for urachal cancer while salvagechemotherapy is effective in less than 10% of patients with metastases, suggestingthat the risk of delaying the urachal remnant resection in older adults may exceedthe risk of surgery.^2,7,8

Whereas earlier recommendations favoured surgical intervention for in the majority ofpaediatric patients with a urachal remnant (due to the risk of recurrent infectionand urachal cancer in later life), more recent reports have suggested that between50 and 80% resolve non-operatively. In addition, almost 15% of paediatricpatients develop post-operative complications including iatrogenic bladder injuryrequiring reoperation.^2,13,16

Conclusion

Urachal pathology, although rare, can cause significant morbidity and mortality.Non-specific pelvic symptomatology of urachal disease can potentially result indelayed diagnosis and treatment. Multimodal imaging with ultrasound, CT, PET/CT andMRI can identify and characterise potential complications related to the urachalremnant, however differentiating benign from malignant urachal complications isimprecise with imaging alone and histopathological analysis is usually required toconfidently diagnose urachal cancer from an infectious/inflammatory process.

Footnotes

Contributor Information

Jeeban Paul Das, Dept. of Radiology, Galway University Hospital,Co., Galway,Ireland. Dept. of Oncologic Imaging, Memorial Sloan Kettering CancerCentre, New York,USA. Dept. of Radiology, Beaumont Hospital,Dublin 9, Ireland.

Hebert Alberto Vargas, Dept. of Oncologic Imaging, Memorial Sloan Kettering CancerCentre, New York,USA.

Aoife Lee, Dept. of Radiology, Beaumont Hospital,Dublin 9, Ireland.

Barry Hutchinson, Dept. of Radiology, Galway University Hospital,Co., Galway,Ireland.

Eabhann O'Connor, Dept. of Urology, St. Vincent's UniversityHospital, Dublin,Ireland.

Hong Kuan Kok, Dept. of Radiology, Adelaide & MeathHospital, Dublin,Ireland.

William Torreggiani, Dept. of Radiology, Adelaide & MeathHospital, Dublin,Ireland.

Joe Murphy, Dept. of Radiology, Galway University Hospital,Co., Galway,Ireland.

Clare Roche, Dept. of Radiology, Galway University Hospital,Co., Galway,Ireland.

John Bruzzi, Dept. of Radiology, Galway University Hospital,Co., Galway,Ireland.

Peter McCarthy, Dept. of Radiology, Galway University Hospital,Co., Galway,Ireland. School of Medicine, Clinical Science Institute, NationalUniversity of Ireland, Galway,Ireland.

REFERENCES