The Bladder Stone That Wasn’t: Rare Urachal Calculus Fooled CT Scans and Cystoscopy

A dense white speck sitting squarely inside the bladder outline on a CT scan would seem like the least mysterious finding in urology. Yet for one 54-year-old man in Kunming, China, that seemingly obvious calcification turned out to be something far rarer: a stone lodged in the urachus, a fibrous vestige of the embryonic connection between bladder and umbilicus that most adults never think about again after birth. The case, published in Frontiers in Urology by urologists at the Second Affiliated Hospital of Kunming Medical University, illustrates how a congenital remnant can masquerade as an ordinary bladder stone, fooling both imaging and a first cystoscopy, and why clinicians are being urged to think of the urachus whenever a calcified lesion appears at the bladder dome.

The urachus is a fibromuscular tubular structure that links the dome of the bladder to the umbilicus, derived from the cloaca and allantois during embryonic development. In most people it obliterates in infancy, collapsing into the fibrous median umbilical ligament. When that obliteration fails, a spectrum of anomalies results: a patent urachus accounts for roughly half of all urachal malformations, urachal sinuses about 15 percent, vesicourachal diverticula 3 to 5 percent, and urachal cysts around 30 percent. These remnants are usually silent, but they can become complicated by infection, malignant transformation, or, as in this case, stone formation. Urachal calculi are exceptionally rare, and their clinical and radiological appearances overlap with bladder calculi, vesicourachal diverticula, infected urachal cysts, and calcified urachal tumors, creating what the authors describe as a genuine diagnostic pitfall.

The patient’s story began with more than six months of intermittent, dull lower abdominal pain. The pain did not radiate and bore no relationship to urination. He denied urinary frequency, urgency, dysuria, blood in the urine, lumbar pain, fever, chills, and any discharge from the umbilicus. At a local hospital, cystoscopy had revealed bladder inflammation but no stone, a negative finding that would later prove misleading. On admission, the umbilicus appeared entirely normal, with no discharge, erythema, or visible sinus, and physical examination showed only mild suprapubic tenderness without a palpable mass. Laboratory work was similarly unrevealing: urinalysis showed red blood cells but no pyuria, urine culture was negative, procalcitonin measured just 0.061 ng/mL, and interleukin-6 and C-reactive protein were not elevated.

The turning point came with computed tomography. Non-contrast CT demonstrated a 1.2 by 0.9 centimeter densely calcified nodular lesion at the anterior bladder wall near the dome, with an attenuation of approximately 1112 Hounsfield units, a value firmly in the territory of true calculus rather than soft tissue. The lesion appeared to lie within the bladder outline, and no separate diverticular neck was identified on the available images. That combination, a midline calcification that looked intravesical but lacked any visible tract or neck, initially suggested a bladder diverticular calculus. The authors note that urachal stones are rare, have diverse clinical manifestations, and are easily misdiagnosed or missed entirely.

Definitive answers came only in the operating room. After preoperative evaluation and informed consent, the team performed combined transurethral and laparoscopic surgery under general anesthesia. Repeat cystoscopy systematically evaluated the bladder neck, trigone, ureteric orifices, lateral walls, anterior wall, and dome, and this time identified a calculus at the junction of the bladder dome and anterior wall, with an intravesical component and a residual component embedded in the urachal tract. Holmium laser lithotripsy was used to fragment and remove the visible intravesical portion. Because the residual stone was embedded within the urachus in an inaccessible location, and because of concerns about potential recurrence and malignant transformation, the surgeons converted to laparoscopic resection. A cord-like urachal remnant was identified at the bladder dome, the embedded calculus was palpable within the tract, and the involved remnant, residual stone, and a cuff of the bladder dome were excised en bloc with an ultrasonic device before the bladder was closed.

Histopathological examination confirmed a urachal remnant associated with calculus formation and inflammation, with no intestinal metaplasia, dysplasia, or malignancy, a reassuring result given that urachal remnants carry a recognized risk of cancerous transformation. Recovery was swift: the urinary catheter was removed on postoperative day 2, and the patient was discharged after a 7-day hospitalization. However, the follow-up story is incomplete. The patient was subsequently lost to follow-up, no post-discharge imaging or cystoscopy was available, and his symptom status and recurrence risk could not be assessed, a limitation the authors acknowledge candidly.

To place the case in context, the team conducted a structured search of PubMed updated through 18 July 2026, using combinations of terms including urachal stone, urachal calculus, urachovesical calculus, vesicourachal diverticulum, and urachal calcification, and screening reference lists of relevant reports. Because of heterogeneous terminology and incomplete reporting, they treated the effort as a structured literature review rather than a systematic review. The comparison with previously published cases is instructive. A 1994 report described a 59-year-old man with lower abdominal pain and radiopaque suprapubic shadows whose stone sat in a urachal sac near the anterior bladder; he remained asymptomatic four years after excision. A 2002 case involved a 55-year-old man with irritative voiding symptoms whose CT showed a midline urachal tract containing a cylindrical calculus extending into the bladder as a pedunculated stone, treated with combined endoscopic and laparoscopic removal. Other reports have described an inflamed urachal cyst containing multiple calculi in an adult woman, a vesicourachal diverticulum with a stone in a 24-year-old man, urachal remnant calcification discovered incidentally on trauma imaging, and an infected urachal sinus with a de novo stone presenting with fever and localized peritonitis in a young athlete.

What distinguishes the present case, the authors argue, is the combination of an atypical symptom profile and a misleading anatomical appearance, rather than the surgical technique alone. Unlike the 2002 patient whose CT revealed an obvious midline tract, this patient had isolated intermittent lower abdominal pain with no lower urinary tract or umbilical symptoms, and an initially negative cystoscopic examination. The calcification appeared to lie within the bladder outline without an obvious tubular tract or diverticular neck, creating a realistic risk of misclassification as a bladder diverticular stone. Epidemiologically, urachal abnormalities are rare congenital anomalies with an incidence of approximately 2 per 100,000 hospitalized adults, and while urachal cysts and urachal carcinoma represent the most common urachal pathologies in adults, urachal calculi are exceptionally rare. Their formation is thought to result from prolonged retention of residual urine within the urachal tract, combined with repeated urine reflux, urinary tract inflammation, epithelial cell shedding, and urate deposition; the relatively narrow lumen of urachal remnants and an alkaline urinary environment may further promote stone formation and growth.

The differential diagnosis of a densely calcified lesion at the anterior bladder wall includes several entities that demand careful separation. Bladder diverticular stones share the location and calcified density but sit within a diverticulum that communicates with the bladder lumen, and such stones are typically mobile, changing in size after voiding on CT. Distal ureteral stones produce peri-bladder calcified lesions but are accompanied by proximal ureteral dilatation and hydronephrosis, and lie along the ureteral course rather than in the midline. Urachal carcinoma with calcification presents as a midline supravesical mass with a soft tissue component that enhances, irregular margins, and calcification within the tumor matrix. Urachal cysts or infections produce midline supravesical lesions with cystic or inflammatory components, wall thickening, and surrounding fat stranding. In this case, the key distinguishing features were the midline location at the bladder dome, the very high CT attenuation of 1112 HU consistent with a calculus rather than tumor calcification, the absence of soft tissue enhancement on contrast CT, and intraoperative confirmation that the stone was embedded at the base of the urachus.

For diagnosis, ultrasonography can identify a fixed echogenic focus with posterior acoustic shadowing and may reveal a cystic remnant, while CT provides a broader assessment of the lesion’s relationship to the bladder dome, the median umbilical ligament, surrounding soft tissue, and any enhancing component. Sagittal and coronal reformations are particularly useful when axial images make a lesion appear intravesical, a point the authors emphasize as central to avoiding the misdiagnosis seen here. Cystoscopy remains important for assessing the bladder mucosa and any intravesical component, but a small lesion at the anterior dome can be overlooked, so systematic inspection of the dome and correlation with cross-sectional imaging are essential. Management should be individualized according to symptoms, infection, communication with the bladder, the possibility of malignancy, and the extent of the remnant. Symptomatic or complicated adult urachal remnants are commonly managed by excision, often with a bladder cuff when the lesion involves the dome, and transurethral lithotripsy alone may remove an exposed intravesical component while leaving an embedded calculus and the underlying remnant in place. Published outcomes after removal of the calculus and treatment of the underlying abnormality are generally favorable, though the small number of heterogeneous cases does not permit a reliable recurrence rate. The authors’ conclusion is straightforward: a midline calcification at the bladder dome should prompt consideration of a urachal origin even when it appears intravesical, and a high index of clinical suspicion, careful multiplanar CT evaluation, thorough cystoscopic examination, and histological evaluation of the excised remnant remain essential for accurate diagnosis and complete management.

Subject of Research: Diagnosis and surgical management of a rare urachal calculus with an atypical intravesical CT appearance

Article Title: Case Report: Urachal calculus with an atypical intravesical CT appearance and literature review

Article References: Long, X., Zhi, Y., Zhou, Y., Wang, D., & Guo, H. (2026). Case Report: Urachal calculus with an atypical intravesical CT appearance and literature review. Frontiers in Urology, 6, Article 1899074. https://doi.org/10.3389/fruro.2026.1899074

Image Credits: AI Generated

DOI: 10.3389/fruro.2026.1899074

Keywords: urachal calculus, urachus, bladder dome, computed tomography, cystoscopy, holmium laser lithotripsy, laparoscopic partial cystectomy, urachal remnant, differential diagnosis, urology, case report, congenital anomalies