Castleman's disease of the urachus.

Castleman's disease (angiofollicular lymphoid hyperplasia) is a rare heterogeneous group of lymphoproliferative disorders of uncertain cause. Most cases occur as mediastinal masses, although extrathoracic involvement has been reported. Castleman's disease involving the genitourinary tract, one of the most infrequent organ systems affected, has so far only been described in pararenal and retroperitoneal locations. We describe a patient with an unusual case of unicentric Castleman's disease that was located in a urachal remnant and bore a malignant appearance. The patient initially presented with abdominal pain and underwent laparoscopic radical excision of the urachal mass. Pathologic examination revealed Castleman's disease, hyaline-vascular type, with atypical lymphoid proliferation and follicular dendritic cell dysplasia. No evidence of concomitant lymphoma or sarcoma was found. Two years after surgical removal of the tumor, no recurrence was evident. To our knowledge, this is the first case of Castleman's disease presenting as a urachal tumor.