Xanthogranulomatous inflammation of urachus: A case report.

The urachus is a midline tubular structure that extend between bladder dome and umbilicus which result from incomplete regression during normal development. Defective obliteration of the urachus is rare and can result in urachal abnormalities, most commonly malignant masses. Xanthogranulomatous urachal masses are rare forms of chronic inflammatory processes with only few reported cases. Differentiating malignant from benign urachal lesion is challenging due to lack of typical clinical and radiologic manifestations, coupled with limited diagnostic experience or awareness. We present an initial misdiagnosis of urachal carcinoma, which was revealed to be benign xanthogranulomatous inflammation of urachus on postoperative histopathological examination.

Introduction

The urachus is an embryologic fibrous remnant of the allantois, extending between the bladder dome and the umbilicus. Defective obliteration of the urachus is rare and leads to urachal abnormalities in adulthood, most commonly masses. According to the literature, adenocarcinoma represents the most frequent etiology of urachal masses. Despite concern about malignancy, a possibility of a urachal mass to have a benign etiology should be considered. Urachal xanthogranuloma is an extremely rare benign lesion, with only a few reported cases. A review of the published data found that most of these reported cases are from Japan. We hereby report a case of urachal xanthogranuloma, which was initially presumed to be urachal carcinoma.

Case presentation

A sixty-five-year-old male with a history of Type II Diabetes Mellitus presented to the Emergency Department complaining of right lower quadrant and suprapubic pain. He denied the presence of hematuria, umbilical drainage, or any other urinary tract symptoms. His surgical history included bilateral inguinal and umbilical hernia repair 7 years ago. The patient was hemodynamically stable, afebrile, and nontoxic upon presentation. He was found to have right lower quadrant and mild suprapubic tenderness with suprapubic and paraumbilical fullness on abdominal examination. A well-healed surgical scar was noted from his prior inguinal and umbilical hernia repair. There was no abdominal erythema or umbilical drainage present. A routine blood test showed a normal white blood cell count, and urine culture was negative for bacterial growth. A computed tomography scan (CT) of his abdomen showed necrotic soft tissue mass with irregular thick peripheral enhancement arising from the urinary bladder dome and extending into both inguinal canals and right rectus muscle, concerning for urachal carcinoma (Fig. 1). No evidence was seen of abdominal or pelvic metastases. Further evaluation of the mass with cystourethrogram showed a noncommunicating mass with no evidence of ureterocele or reflux upon voiding or filling defects. He then underwent cystoscopy, which was unremarkable with no evidence of bladder lesion, discoloration, or masses. Based on patient presentation, the etiology of the mass was thought to be urachal carcinoma. Subsequently, he underwent surgical excision of the mass along with partial cystectomy and bilateral pelvic lymph node resection. The final histologic examination was negative for malignancy and showed xanthogranulomatous inflammation of the urachal mass as shown in (Fig. 2).

Fig. 1

CT image of the abdomen shows a supravesicular mass (Headed arrow) measuring 4 × 8 × 6 cm (AP x TR x CC) with thick and irregular peripheral enhancement and central non-enhancing low attenuation area arising from the dome of the urinary bladder. AP, anteroposterior; TR, transverse; CC, craniocaudal.

Fig. 2

Hematoxylin and eosin (H&E) staining image of examined section shows sheets of lipid-laden macrophages, plasma cells and lymphocytes with foamy histocytes which is similar to malakoplakia but without Michaelis-Gutmann bodies.

Discussion

Abnormalities of the urachus, the vestigial remnant of the allantois, result when the embryonic lumen fails to completely obliterate during fetal development. Urachal masses are exceedingly rare in clinical practice and have a low prevalence; most of these masses are caused by adenocarcinoma, accounting for 0.34% of all bladder neoplasms. Although the majority of masses are malignant, benign causes are also seen, as in the above case. One study of 33 cases with urachal masses in China found that 22 cases were caused by carcinoma, most commonly adenocarcinoma, while the remaining 11 cases were due to benign etiologies, including 5 cases of abscess, 3 of cysts, 2 of malacoplakia, and 1 of xanthogranuloma. In our case, postoperative histopathology revealed xanthogranulomatous inflammation of the urachus. A search of published literature revealed about 22 reported cases of urachal xanthogranuloma, nearly half of which were reported in Japan. A few studies suggested that some clinical and radiological findings can assist in formulating a clinical suspicion to distinguish a benign urachal lesion from a malignant lesion. Clinically, based on previously published studies, the presence of gross hematuria was found to be the most significant predictor of malignancy, increasing the risk of urachal cancer seventeen-fold. Thus, the absence of gross hematuria could favor a benign etiology, as seen in our case. Previously reported urachal xanthogranuloma cases also presented with similar symptoms of lower abdominal mass with an absence of gross hematuria. On the other hand, our patient's age and male gender favored urachal carcinoma, according to published studies. One study found that the probability of urachal mass being malignant is tripled when the patient's age is more than 55 years at diagnosis. In addition, men were found to have a significantly higher risk of urachal cancer, more than twice as frequent as women. The accuracy of imaging in distinguishing benign from malignant urachal masses is uncertain. However, the finding of a supravesicular, predominant necrotic mass on the CT scan made us suggest the possibility of a necrotic urachal malignant lesion. Some studies noted a correlation between malignant urachal masses and CT findings of a solid component and calcification of the mass, which were absent in our case. A study by Thali-Swab et al. showed that 72% of proven cases of urachal carcinoma had calcifications. Due to the low prevalence of urachal masses and lack of typical clinical and radiological findings, differentiating benign urachal mass with urachal carcinoma in adults is challenging. In our case, considering the patient's age and the imaging finding of a supravesicular and necrotic mass, urachal carcinoma was considered over a benign lesion. With the aim of preventing the unnecessarily radical treatment of a benign local evolutive urachal process, xanthogranulomatous inflammation of the urachus and other benign etiologies should be considered in the differential diagnoses of urachal masses.

Conclusion

In conclusion, although rare, benign urachal lesion should be considered in the differential diagnoses of urachal masses to prevent radical surgical treatment. This case illustrates a rare case of benign xanthogranulomatous inflammation of the urachus in an elderly patient.