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Case Diagnosis and Discussion

Diagnosis:

Diffuse large B-cell lymphoma, germinal center type.

Discussion:

This patient was found to have a left renal mass during workup for hematuria. Since the mass was involving the renal collecting system, a urothelial carcinoma was suspected. Gross pathologic examination showed a large partially necrotic mass, likely due to preoperative left renal artery embolization that was done to control the patient’s hematuria.

Microscopic examination revealed a diffuse infiltrate of small round blue cells with lymphoid morphology, suggesting either a chronic inflammatory condition or a lymphoid neoplasm. Since this patient had no prior history of lymphoma, a high index of suspicion was necessary to arrive at the correct diagnosis. Features consistent with the neoplastic nature of the lymphoid infiltrate in this case were that they were mostly B-cells (as shown by CD20 IHC staining) while  lacking significant numbers of other cells commonly seen in reactive processes (histiocytes, plasma cells, neutrophils, and eosinophils).

Primary renal lymphoma is much less common than secondary renal involvement by systemic lymphoma, and it constitutes less than 5% of all extranodal lymphomas. The most common primary renal lymphoma types are all B-cell non-Hodgkin lymphomas, namely follicular lymphoma, diffuse large B-cell lymphoma, small lymphocytic lymphoma, Burkitt’s lymphoma, and mantle cell lymphoma. Other subtypes of lymphoma very rarely present as a primary renal lymphoma.

This case represented diffuse large B-cell lymphoma arising in the kidney, which was of germinal center type by Hans criteria (positive for CD10 and BCL-6 and negative for MUM-1). The patient was treated with chemotherapy without recurrence at 1 year.

References

Schniederjan SD et al: Lymphoid neoplasms of the urinary tract and male genital organs: a clinicopathological study of 40 cases. Mod Pathol. 22(8):1057-65, 2009‚Äč

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