RESUMEN
Key Clinical Message: In the context of lymphoma, it is of paramount importance to perform subsequent Positron Emission Tomography-Computed Tomography (PET-CT) scans to ensure the comprehensive eradication of neoplasms. Abstract: Primary renal diffuse tumors constitute less than 1% of all renal neoplasms. Among these, diffuse renal large B-cell lymphoma is an exceedingly rare extranodal lymphoma. A 64-year-old male presented to the Department of Urology with complaints of persistent left flank discomfort for a duration of 2 weeks. Additionally, he reported generalized weakness, fatigue, and symptoms indicative of lower urinary tract obstruction, such as discomfort in the left testicle and dysuria. Ultrasound imaging revealed an echogenic structure with thickened, reactive walls and a turbid fluid core, located in the left flank, proximal to the lower pole of the kidney. This structure was subsequently identified as diffuse renal large B-cell lymphoma. For the diagnosis of large B-cell lymphomas, it is imperative that a proficient hematopathologist performs a comprehensive examination of the tumor tissue, preferably utilizing an excisional biopsy. The categorization of lymphoma requires specialized tests such as immunohistochemistry, flow cytometry, fluorescence in situ hybridization (FISH), and molecular testing. In instances where a renal mass is detected, healthcare professionals should consider performing a biopsy. In lymphoma cases, follow-up Positron Emission Tomography-Computed Tomography (PET-CT) scans are crucial to confirm the complete eradication of the tumor.