Diffuse Nephromegaly With Dialysis‐Dependent Acute Kidney Injury as the Initial Presentation of Primary Mediastinal Large B‐Cell Lymphoma

Diffuse renal enlargement is an uncommon manifestation of lymphoma and may mimic primary renal disorders. We report a young woman who presented with acute kidney injury (AKI) and bilateral ballotable flank masses, initially suspected to represent polycystic kidney disease. Chest radiography demonstrated a large mediastinal mass, prompting cross‐sectional imaging that revealed bulky anterior mediastinal disease with widespread nodal and extranodal involvement. Imaging showed asymmetric bilateral renal enlargement, markedly greater on the left, with diffuse hypodense infiltrative lesions radiologically suspicious for lymphomatous involvement. Core biopsy of the mediastinal mass confirmed primary mediastinal large B‐cell lymphoma (PMBCL), and concurrent testing identified newly diagnosed human immunodeficiency virus infection. The patient developed anuric, dialysis‐dependent AKI and died before definitive rituximab‐based chemotherapy could be initiated. This case highlights an atypical and aggressive presentation of PMBCL with presumed diffuse renal involvement, emphasizing the need to consider infiltrative malignancy in patients with unexplained nephromegaly and AKI.