We describe a case of urachal adenocarcinoma arising in a 30-year-old woman. The patient underwent partial cystectomy. Three years later, she presented with an isolated metastasis to a thoracic vertebra, which was treated by vertebral corporectomy. Histologic findings are described, and the clinical findings, management, and metastatic patterns of this rare tumor, as well as the differential diagnosis on a biopsy specimen, are discussed.
(Arch Pathol Lab Med. 2004;128:1043-1045)
Adenocarcinoma of the urachus is a rare entity, accounting for less than 1% of all malignant bladder tumors. Although bony metastases are fairly frequent, representing 12.5% of metastases in 1 study,1 they usually occur as part of widespread metastatic disease. To our knowledge, only 1 fully documented case of an isolated bony metastasis has been reported previously.2 We describe a second case, which involved an isolated metastasis to a vertebral body in a young patient.
REPORT OF A CASE
A 30-year-old, previously healthy woman presented with hematuria of 2 months' duration. A cystoscopic biopsy of the midline anterior wall of the bladder revealed a mucinous adenocarcinoma, which was treated by wide partial cystectomy (Figure 1). A bone scan did not reveal any metastatic sites at this stage. The patient remained well for 3 years after surgery, but then developed neck pain, which lasted for 2 months before radiography, a computed tomographic scan, and a bone scan revealed a lesion located in the second thoracic vertebra (Figure 2). A biopsy of this lesion was taken (Figures 3 through 5), and the specimen revealed a metastatic adenocarcinoma of mucinous type; subsequently, a vertebral corporectomy was performed (Figure 6). Six months after surgery, the patient is doing well and shows no other signs of metastatic disease.
On gross examination, the mass located in the second thoracic vertebra was composed of yellowish friable tissue that occupied practically the entire vertebral body, extending as far as the posterior ligament.
On microscopic examination, the bladder tumor was a moderately well-differentiated mucinous adenocarcinoma occupying the submucosa and the inner part of the muscularis propria. The overlying urothelium was intact. No urachal remnants could be identified in the vicinity of the tumor. Surgical margins were negative for tumor.
The spongiosa of the vertebral body contained mucin lakes, in which a few strands of mucin-secreting neoplastic epithelium floated, occasionally forming glandular or cribriform structures. The residual bony trabeculae were sparse and eroded. Some new bone formation was present at the periphery. The cortical bone was destroyed in many places, the tumor having extensively infiltrated the surrounding fatty tissue and skeletal muscle.
Immunohistochemical analysis was performed on the bone metastasis using the following antibodies: cytokeratins (clone MNF; Dako Corporation, Carpinteria, Calif); epithelial membrane antigen, cytokeratin 7, cytokeratin 20, and vimentin (all Dako); and CDX2 (BioGenex Laboratories, San Ramon, Calif). This analysis produced the following results: the neoplastic epithelial cells stained positively for cytokeratins, epithelial membrane antigen, and CDX2, and were focally positive for cytokeratin 7, with only the occasional cell staining for cytokeratin 20. Staining for vimentin was negative.
The urachus is a remnant of allantoic origin, connecting the embryonal cloaca to the allantois during early intrauterine life. It involutes at about the 32nd week of gestation. After birth, it is represented by the median umbilical ligament, which extends from the dome or anterior wall of the bladder to the umbilicus. However, microscopic remains of a patent lumen are identifiable in most adults, and in about one third of cases these remnants are in continuity with the bladder lumen. These rests are usually lined by transitional epithelium, but foci of glandular metaplasia may be found. Various clinical problems may be associated with urachal remnants, including cystic dilatation, infection, and benign and malignant tumors.
The overwhelming majority of urachal carcinomas are adenocarcinomas, usually mucin-secreting, sometimes of signet-ring cell type3; other rare variants include transitional carcinomas, neuroendocrine carcinomas, and mixed tumors. Conversely, one third of bladder adenocarcinomas are of urachal origin. Men are more commonly affected than women; most patients are older than 50 years, although the age range is wide, and 26% of cases occur in patients in their 20s and 30s,1,2,4-8 as in our case. The most common clinical presentation is gross hematuria, although pain, mucinuria, and a palpable mass may also be found.
Because these tumors develop in a clinically silent space-between the bladder and the umbilicus-they often reach an advanced stage before becoming symptomatic; extension beyond the bladder was present at diagnosis in 34% of patients in 1 study.3 Survival is poor, 25% to 45% at 5 years.9,10 Local tumor recurrence occurs in 40% to 50% of cases.1,3
To identify tumors of urachal origin, Wheeler and Hill11 and subsequently Mostofi et al12 put forward several criteria, combining clinical and histopathologic elements. These include tumors centered in the dome or anterior wall of the bladder; bladder wall invasion from the outside in, the bladder mucosa being intact or ulcerated; the absence of cystitis cystica or glandularis; and the presence of urachal remnants. The present case fulfills most of these criteria; however, we agree with Henly et al3 that urachal remnants cannot always be identified because of tumor destruction of underlying structures.
The sites most frequently involved by metastatic spread are lymph nodes, lungs, and the peritoneal cavity, according to an extensive literature review by Kakizoe et al.1 Other frequently reported sites include liver and bone, and less frequently, the brain and ovaries. Metastasis to bone tends to involve the axial skeleton and skull,6,8,13 often with aggressive multiple lesions late in the course of the disease.6,8 A solitary bony metastasis, as in the case under discussion, is very rare; to our knowledge, only 1 fully documented case has been reported to date.2 The presence of disseminated metastatic disease is generally considered a terminal event, but a recent report7 has described longterm survival (10 years) in 2 patients with local recurrence and/or metastatic disease treated by combinations of surgery, radiotherapy, and chemotherapy.
Bone metastasis is an expression of systemic (bloodborne) diffusion of the primary malignant neoplasm. An aggressive surgical procedure, such as vertebral corporectomy, could be deemed overtreatment. However, a bone scan and computed tomographic scan did not reveal any other tumor location. Adequate control could obviously not be achieved by chemotherapy alone. It was therefore decided to opt for vertebral corporectomy, which in this context was not considered overtreatment. Only long-term follow-up will tell if this option was justified.
The origin of a mucinous adenocarcinoma metastatic to bone must be identified essentially on clinical grounds. There is no specific immunohistochemical marker for urachal origin and no panel of antibodies that would, when applied to a distant metastatic deposit, permit a distinction to be made with any certainty; tumors of bladder, urachal, and colonic origin could all be positive for carcinoembryonic antigen and cytokeratin 20, while being negative for cytokeratin 7, for instance.14 A more recently described marker, CDX2, is also unable to discriminate between adenocarcinomas of colonic and bladder origin, as it is positive in both.15 The immunohistochemical profile of the case presented is consistent with, although not specific for, a metastatic urachal adenocarcinoma.
The presence of mucin-rich material in a bone biopsy can be related to metastasis, chordoma, or myxopapillary ependymoma. Occasionally in small needle biopsies of vertebrae, a large amount of mucinous material is present. This stresses the need for a careful search for floating cells to rule out metastatic adenocarcinoma. If present, positive immunostaining for S100 and cytokeratin may help in ruling out chordoma. Soft tissue ependymoma may develop posterior to the sacrum and coccyx or anterior to the sacral region. Immunoreactivity for glial fibrillary acid protein and S100 protein, and lack of cytokeratin expression, are helpful diagnostic hints. Finally, a urachal origin, although rare, must be sought when a mucin-producing metastatic adenocarcinoma is detected, especially in a young patient.
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Sophia Taylor, MD; Patrizia Bacchini, MD; Franco Bertoni, MD
Accepted for publication April 23, 2004.
From the Servizio di Anatomia Patologica, Istituti Ortopedici Rizzoli, Bologna, Italy.
The authors have no relevant financial interest in the products or companies described in this article.
Reprints: Sophia Taylor, MD, Servizio di Anatomia Patologica, Istituti Ortopedici Rizzoli, Via di Barbiano 1/10, 40136 Bologna, Italy (e-mail: firstname.lastname@example.org).
Copyright College of American Pathologists Sep 2004
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