Urachal Malignant Fibrous Histiocytoma: A Case Report and Review of the Literature

The urachus is a vestigial structure located between the dome of the bladder and the umbilicus. In the fetus, the urachus connects the bladder with the allantois. In normal development, the allantois is gradually reduced and obliterated, with the urachus becoming a fibrous band, extending from the anterior bladder dome to the umbilicus. A continuation with the bladder lumen can be identified in the majority of infants, but only in one third of the adult population.1 Nonneoplastic lesions are not infrequently reported in the urachus. The most common nonneoplastic abnormality is incomplete regression giving rise to sinus, fistula, and diverticulum or cyst formation. Despite rarity, neoplastic growths can arise from any portion of the urachus. Among the benign epithelial neoplasms, adenoma and cystadenoma have been identified in this structure. Adenocarcinoma is the most common malignancy of the urachus, and approximately 20% to 40% of adenocarcinomas involving the bladder arise from this location.2 Occasionally sarcomas, such as leiomyosarcomas and rhabdomyosarcomas, have been described within the urachus.3–5 A rare case of primary malignant fibrous histiocytoma (MFH) arising in the urachus was previously described by Bruneton et al.6 

A 66-year-old white man presented with irritative voiding symptoms. His past medical history was remarkable for hypertension and a tubulovillous adenoma of the sigmoid colon that was endoscopically excised 3 years prior to this admission. Imaging studies disclosed a 10-cm mass adjacent to the dome of the urinary bladder (Figure 1). Cystoscopy revealed a submucosal bulge at the urinary bladder dome; however, subsequent biopsies showed no significant histologic findings. The clinical impression at that time was of a tumor probably arising in the urachus. A composite resection of the tumor was performed, including the dome of the bladder, urachal remnants, and umbilicus. Simple prostatectomy was also undertaken at this time. Pathology reported a high-grade pleomorphic sarcoma of the urachus with extension to the bladder dome. The patient recovered uneventfully and was discharged. Eleven months later, a follow-up examination revealed a recurrent tumor involving perivesical soft tissue and abdominal wall. Subsequently, completion cystectomy and ileal conduits were performed. A recurrent mass measuring 8 cm in greatest dimension was removed. Adjuvant postoperative radiation therapy was administered because resection margins were positive. The patient presented with small bowel obstruction 8 months after the second surgery and was found to have intra-abdominal and retroperitoneal metastases. Tumor and bowel were resected. This procedure was followed by wound infection and an intra-abdominal abscess. The patient died shortly after the final surgery, 20 months after the initial presentation. An autopsy was not performed.

The initial resection specimen consisted of an ellipse of umbilical skin, urachal soft tissue containing a bulky tumor (10 × 9.0 × 7.5 cm in greatest dimension) and a portion of the adjacent urinary bladder in continuity. The urachal tumor was a well-circumscribed, white-tan, firm mass with focal areas of hemorrhage (Figure 2). The tumor was confined to the urachus, had a pushing peritoneal border, and extended into the wall of the urinary bladder dome. The bladder mucosa was focally ulcerated. Surrounding fibrotic tissue representing the urachal remnant was also seen attached to the tumor and dome of urinary bladder.

The tumor in the bladder dome involved the submucosa, but did not extend onto the mucosal surface (Figure 3). The tumor was composed largely of spindled cells exhibiting marked nuclear pleomorphism, atypical mitoses, and a high mitotic rate (4/10 high-power fields). The tumor cells were arranged mostly in fascicles within a prominent myxoid background and focally infiltrated into perivesical fat (Figure 3). The tumor cells in this area showed cytoplasmic vacuolation and nuclear indentation suggestive of lipoblasts. All the resection margins were free of tumor, and no angiolymphatic invasion was identified. Sections from the fibroadipose tissue thought to represent urachus showed only fibrous strands with no urachal epithelial remnants. The umbilicus was unremarkable. The prostate specimen showed glandular and stromal hyperplasia.

The recurrent tumors demonstrated greater cellularity with frequent bizarre forms and a higher mitotic rate (10/10 high-power fields) (Figure 4). In the third resection specimen, the metastatic tumor demonstrated the pattern of a high-grade pleomorphic sarcoma with less myxoid background than the primary tumor.

Immunohistochemical stains on the original tumor were positive for vimentin and CD68, and were focally positive for epithelial membrane antigen. CK7 stained only urothelium. Stains for muscle differentiation (desmin and muscle-specific actin), histiocytic differentiation (α₁-antitrypsin, α₁-antichymotrypsin, and Mac-37), nerve/fat/melanocytic differentiation (S100 protein), and epithelial differentiation (low-molecular-weight cytokeratin) were all negative (Table). In light of the clinical, histologic, and immunohistochemical findings, a diagnosis of pleomorphic high-grade MFH of the urachus was rendered.

Diseases of the umbilicus and their relationship to the anatomy of the urachus were described in detail by Cullen7 and Begg.8 To date, much of our understanding of the development, anatomy, and diseases of this vestigial organ has been based on those early studies. The urachus lies hidden in the space of Retzius between the fascia transversalis anteriorly and the peritoneum posteriorly. During the fourth to seventh week of embryologic development, the urorectal septum divides the cloaca into a dorsal anorectal and ventral urogenital sinus. The primitive urogenital sinus is divided into 3 compartments. The lowest part is the vesicle that later becomes the urinary bladder. The second and third parts represent the middle and caudal phallic compartments, respectively. Initially, the bladder is continuous with the allantois. The urachus lies between the urinary bladder and allantois. The lower part of urachus remains attached to the dome of the bladder and is widest at its attachment. Eventually, the urachus is represented only as a fibrous band ranging from 4 to 8 cm in length. The urachus contains one or both of the obliterated umbilical arteries and extends from the anterior bladder dome to the umbilicus. Also, the urachus contains 3 distinct tissues layers: an epithelial canal lined by cuboidal or transitional epithelium, submucosal connective tissues, and an outer layer of smooth muscle. Urachal lesions can arise in any of these 3 layers.

Since the first urachal colloid carcinoma described by Hue and Jacquin in 1863,9 many types of carcinomas have been diagnosed in this location. Sheldon et al reviewed 117 urachal malignancies; 84% of these cases were adenocarcinomas and 8% were sarcomas.1 Among the carcinomas involving the urachus, three quarters of the adenocarcinomas were mucinous adenocarcinomas, with urothelial carcinoma being second most common. A few cases of squamous cell carcinoma, adenosquamous carcinoma, signet ring cell carcinoma, neuroendocrine tumor, primitive yolk sac tumor, and mixed tumors also have been reported.1,2,9,10 

Although soft tissue sarcomas generally arise in the fifth to sixth decades, most sarcomas developing in the urachus occur in young patients, with 67% of cases diagnosed in individuals younger than 20 years.1 The youngest person affected by a urachal sarcoma was a 4-month-old infant who developed a rhabdomyosarcoma.3 The previously documented case of urachal MFH was diagnosed in a 16-year-old girl.6 Most urachal sarcomas described in the literature have not been specifically classified or have not been described in sufficient detail to allow precise classification.

Sheldon et al1 and Mostofi et al10 established the following pathologic criteria for urachal neoplasms: (1) tumor in the dome or superior-anterior wall of the bladder; (2) absence of cystitis glandularis or cystitis cystica; (3) sharp demarcation between the tumor and surface epithelium of the bladder, which is free of glandular or polypoid proliferation or dysplasia; (4) presence of urachal remnants with the tumor; (5) extension of the tumor into the bladder wall with involvement of the space of Retzius, anterior abdominal wall, or umbilicus; and (6) no evidence of a primary neoplasm elsewhere. As early as 1931, Begg8 suggested in his series that sarcomas arising above the junction of the umbilical arteries probably arise from the tissue of obliterated umbilical arteries. He also pointed out that tumors arising away from the bladder might take origin from the fibrous strands or ligaments connecting the urachus to the umbilicus, and suggested the following criteria for urachal sarcomas: (1) the tumor must occupy a site consistent with the anatomical position of the urachus, (2) there must be a demonstrable relationship between the tumor and the urachus, and (3) pathologic and histologic features of a sarcoma must be present.4,8 

Urachal tumors usually remain undiscovered for a long period because of their obscured location. They can be found incidentally or at an advanced stage. The most common clinical presentation of urachal malignancy is hematuria, especially in carcinomas. Other presentations include irritative voiding, discharge of mucous blood or pus from the umbilicus, and obstructive symptoms. Colloid carcinoma arising in the region of the umbilicus often invades the abdominal wall and urinary bladder.2,9 Therefore, presence of mucus in the urine is very suggestive of carcinoma, either in the bladder or arising in the urachus. Urachal sarcomas may also present as a palpable suprapubic mass.1 

Malignant fibrous histiocytoma was well described by Weiss and Enzinger11 after initially being named by O'Brien and Stout in 1964.12 This tumor is the most common soft tissue sarcoma of late adult life and usually presents in the lower extremities, although it can occur at any body site. Since then, there has been an ongoing debate as to whether the tumor arises from fibroblasts or histiocytes. Based on morphology and tissue culture analysis, MFH has both histiocytic and fibroblastic differentiation that manifests a variety of growth patterns.11,13,14 It has been demonstrated that MFH does not represent a true histiocytic tumor, but rather a fibroblastic or myofibroblastic malignancy.13,15 It is now accepted that histiocytic antigens (such as α₁-antitrypsin, α₁-antichymotrypsin, lysozyme, and CD68) play no useful role in the diagnosis of these tumors.14 In the past decade, numerous studies have reported genetic abnormalities in MFH, but conclusive cytogenetic data are not yet available.14,15 

Distinguishing MFH from tumors that mimic it is a common diagnostic dilemma. Pleomorphic liposarcoma, in particular, may have areas that closely simulate MFH. Pleomorphic rhabdomyosarcoma is rare in an adult patient, and most tumors diagnosed as pleomorphic rhabdomyosarcoma in this location are actually MFH. Other sarcomas, including leiomyosarcoma, malignant nerve sheath tumors, anaplastic carcinomas, and even Hodgkin disease, can resemble MFH. Immunohistochemistry can play an important role in resolving these differential diagnoses, and correlation with clinical data is also useful.

The myxoid variant of MFH has been thought to have a better prognosis than the usual form. The diagnosis of this variant requires that at least half the tumor appears myxoid. Local recurrences and distant metastases of MFH usually develop within 12 to 24 months of diagnosis, with the common metastatic locations being lung, bone, and liver. Recurrent tumors are usually more anaplastic than the initial resection specimen, as was seen in this case (Figure 4).

In summary, we report a unique case of urachal MFH that proved fatal within 20 months of diagnosis. Although the great majority of urachal neoplasms are epithelial, it is important to recognize that sarcomas do occasionally develop at this site.

The authors appreciate the excellent photographic assistance from Mr Joseph Samet (Department of Pathology, The Mount Sinai School of Medicine).