Urachal carcinomas of the nonglandular type: salient features and considerations in pathologic diagnosis

The vast majority of malignant urachal epithelial tumors have a glandular morphology (ie, adenocarcinoma), to which our principal understanding of urachal carcinoma and its prevailing set of diagnostic criteria are largely ascribed. The 2004 World Health Organization classification of genitourinary tumors recognizes other rarer histologic types of urachal carcinomas such as urothelial, squamous cell, and other carcinomas. However, the clinicopathologic data for these nonglandular groups of urachal carcinomas are very limited, being detailed only in sporadic case reports. Some of the criteria recommended for pathologic confirmation of urachal carcinomas were formulated almost exclusively for urachal adenocarcinoma and may not be relevant or applicable for nonglandular tumors. Here, we present 7 examples of pure (5) and mixed predominant (2) nonglandular urachal carcinomas. Patients were 45 to 85 years of age (mean, 64.1) with a male predominance (male-to-female ratio=6:1). Six tumors were related to the bladder [dome (3) or dome/supravesical (3)] and 1 was entirely supravesical. Histologically, 5 were urothelial carcinomas, of pure or mixed histology, all were high grade and invasive, and 2 were small cell carcinomas. Two urothelial carcinomas had focal (<5%) glandular differentiation and signet ring cell change, and 1 had admixed focal malignant squamous cells and high-grade dedifferentiated components. Four of 5 urachal urothelial carcinomas exhibited solid and partly cavitary or luminal growth with papillary structures and a variable amount of necrosis within the cavity. The 2 small cell carcinomas were pure, had classic undifferentiated neuroendocrine histology, were situated at the bladder dome, and were partly cavitary filled with necrotic debris. Urachal remnant was identified in 6 tumors mainly with dysplastic transitional cells in the urachal canal or rudimentary nests and tubules. All 6 bladder-related urachal tumors exhibited reverse invasive front from the surface, including 2 tumors that ulcerated the bladder mucosa. One tumor had concomitant in situ and noninvasive high-grade papillary urothelial carcinomas in the main bladder lumen. Sheldon stages at presentation were IIIA (2), IVA (3), and IVB (2). Follow-up in all 7 cases (<1 to 60 mo; median, 12.5 mo) showed that 6 patients had died of disease, including the 2 patients with small cell carcinoma. In conclusion, nonglandular urachal carcinoma may occur with pure histology or admixed with high-grade dedifferentiated morphologies and a minor adenocarcinoma component. These tumors may arise as deep-seated bladder-related or completely supravesical tumors along the urachal tract and may exhibit reverse invasive spread toward the bladder surface. Cavitary or luminal growth may occur that could be attributed to the intraurachal neoplastic proliferation. Urachal urothelial carcinomas in particular may contain papillary structures within the tumor and urachal cavity. Concomitant primary urothelial carcinoma outside of the urachus and tumor extension to bladder mucosa may occur, which should not negate diagnosis of an urachal primary. Behavior appears poor, as most tumors present with higher stage.