Beyond the Renal Capsule: Unilateral Perinephric Lymphoma in an Immunocompromised Host

Lymphoma rarely involves the kidneys alone (known as PRL; primary renal lymphoma) or with disease elsewhere (secondary renal lymphoma), constituting ∼0.7%¹ and 3%² of Non-Hodgkin’s Lymphoma, respectively. A middle-aged male living with HIV (CD4⁺ = 234 cells/µL), presented with fever and breathlessness for 1.5 months and right flank pain for 15 days. Laboratory evaluation revealed hemoglobin of 10.6 g/dL, leukocytosis of 12,000 cells/μL, creatinine of 2.26 mg/dL, CRP of 124.31 mg/dL, LDH 3347 mg/dL, and uric acid of 13.8 mg/dL.

Contrast-enhanced CT abdomen showed [Figure 1] infiltrative right perinephric soft tissue encasing the right ureter with upstream hydroureteronephrosis (HDUN), along with infiltration of adjacent structures. Mediastinal and abdominopelvic lymph adenopathy, pleural, and pericardial effusion were also noted. ¹⁸FDG-PET/CT revealed intense uptake confined to the perirenal soft tissue and FDG-avid lymph nodes. Ultrasound-guided biopsy [Figure 2] confirmed Diffuse Large B-cell Lymphoma-Germinal Center B-cell type (MUM-1 negative). The patient’s hospital stay was exacerbated by hospital-acquired pneumonia, resulting in his demise on the 5^th day of admission.

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Figure 1:

(a-e) Axial and (f) coronal venous phase CT of abdomen showing perinephric infiltrating soft tissue (red arrows in c and f) extending from the perinephric space into the pelvic retroperitoneum (red arrow in e), invading into the right ureter causing upstream hydroureteronephrosis (yellow arrow in f); there is associated para vertebral lymph adenopathy (green arrow in a), abdominopelvic and pericardiophrenic lymph adenopathy (orange arrow in b), ascites, mesenteric and omental thickening (blue arrows in c and d), pericardial and bilateral pleural effusion.

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Figure 2:

(a) Light microscopy showing atypical lymphoid cells arranged in sheets (hematoxylin and eosin, magnification: 4x); (b) Showing the atypical cells (long black arrows), which are 2-3 times the size of a small mature lymphocyte (small black arrow). These atypical cells demonstrate hyperchromatic nuclei, inconspicuous nucleoli, and brisk mitotic figures. (c-d) Immunohistochemistry done, shows the atypical lymphoid cells are CD20-diffuse positive (c) and CD10-positive in 80% tumor cells with CD3- highlights the reactive T-cells in the background (not shown) (magnification: 40x).

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Differential diagnoses for perinephric masses include tumors (e.g., RCC, lymphoma) and proliferative diseases (e.g., extramedullary hematopoiesis, Rosai-Dorfman disease). Perinephric lymphoma typically appears homogeneous, hypoenhancing, and demonstrates non-obstructive vascular encasement with abdominal lymphadenopathy.³ Six imaging patterns of renal lymphoma include: “multiple lesions, solitary lesion, direct extension from retroperitoneal adenopathy, perinephric disease, nephromegaly, and renal sinus involvement.”⁴ Pain and HDUN occur in 33% and 23% of perinephric lymphoma cases, respectively.⁵

No definitive prevalence of PRL in People living with Human Immunodeficiency virus (PLHIV) has been documented, with only isolated case reports available. Differentiating RCC from lymphoma is crucial, given the management differences (RCC → surgery; lymphoma → R-CHOP). This case highlights the need to consider perinephric lymphoma in the differential diagnosis of flank masses in PLHIV and emphasizes the importance of imaging-guided biopsy for timely diagnosis and initiation of therapy.