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Malignant lymphoma of the urinary bladder. A case with signet-ring cells simulating urachal adenocarcinoma.

We describe a malignant lymphoma involving the dome and anterior wall of the urinary bladder in an elderly woman. The initial biopsy showed a malignant neoplasm of uncertain cell type. Because the clinical presentation was most compatible with urachal adenocarcinoma, an extensive resection was performed. Microscopically, the excised tumor was composed of large lymphoid cells with isolated and clustered signet-ring cells. Immunohistochemical analysis established the B-cell phenotype of the neoplasm, and electron microscopy of the signet-ring cells revealed endoplasmic reticulum-bound inclusions consistent with immunoglobulin. Primary malignant lymphomas of the urinary bladder are rare, and, to our knowledge, we report the first example with signet-ring cells. We emphasize this histopathologic finding because of the potential for confusion with urachal adenocarcinoma.