Renal lymphoma is the most common hematologic malignancy secondarily involving the kidney. Primary renal lymphoma is extremely rare since the kidney lacks native lymphoid tissue. It usually occurs in the context of non-Hodgkin lymphoma (particularly diffuse large B-cell lymphoma). Bilateral involvement, multifocal lesions, homogeneous hypoenhancement, and retroperitoneal lymphadenopathy are characteristic. Perinephric soft tissue invasion (rind-like infiltration causing nephromegaly) is highly specific for lymphoma.
Age Range
40-80
Peak Age
60
Gender
Male predominant
Prevalence
Uncommon
Renal lymphoma involves the kidney through three pathways: hematogenous spread (most common), direct invasion from retroperitoneal lymphadenopathy, and rarely primary renal lymphoma (on background of chronic inflammation). Lymphoma cells infiltrate the renal interstitium, involving the kidney parenchyma in a diffuse or focal manner. The hypovascular appearance is characteristic due to minimal neoangiogenesis. Bilateral and multifocal involvement reflects the systemic distribution of disease. Perinephric extension occurs through tumor progression along the capsule and Gerota fascia.
Perinephric soft tissue thickening encasing the kidney (rind pattern) is considered pathognomonic for renal lymphoma. This finding results from lymphoma cell infiltration of perinephric fat between the renal capsule and Gerota fascia. This pattern is not seen or is extremely rare in other renal masses (RCC, metastasis).
On non-contrast CT, bilateral, multifocal, homogeneous soft tissue density masses are seen in the kidneys. The masses are mildly hypodense or isodense compared to surrounding renal parenchyma. Calcification and fat content are typically absent. Nephromegaly may be seen in diffuse infiltrative form. Perinephric soft tissue thickening (rind pattern) may accompany.
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Multifocal, homogeneous soft tissue density masses are seen in both kidneys without calcification or fat content.
In nephrographic phase, the masses remain distinctly hypodense against homogeneously and intensely enhancing normal renal parenchyma. The homogeneous hypoenhancement pattern is highly characteristic of lymphoma and differs from heterogeneous enhancement of RCC. Multifocal lesions are best delineated in this phase. Renal sinus and perinephric fat invasion are assessed.
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In nephrographic phase, multifocal masses remaining markedly hypodense compared to surrounding parenchyma with homogeneous enhancement pattern are seen in both kidneys.
In portal venous/delayed phase, perinephric soft tissue thickening (rind pattern) is best evaluated. Smooth or nodular soft tissue thickening encasing the kidney is highly specific for lymphoma. Retroperitoneal lymphadenopathy is seen as conglomerate lymph nodes in para-aortic and paracaval regions. Vascular encasement (aortic/IVC wrapping) may occur but luminal invasion is rare.
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Perinephric soft tissue thickening (rind pattern) encasing both kidneys is observed, with conglomerate retroperitoneal lymphadenopathy.
On T2-weighted images, lymphoma masses demonstrate homogeneous, mildly low-to-intermediate signal intensity. This reflects lymphoma's high cellularity and low water content. Signal is homogeneous since necrosis and hemorrhage are rare. Mildly hypointense appearance compared to normal renal parenchyma is typical. Perinephric infiltration can also be seen on T2.
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On T2-weighted images, homogeneous, mildly hypointense masses are seen in both kidneys.
On diffusion-weighted images, lymphoma masses show marked and homogeneous diffusion restriction (bright signal on high b-value, low signal on ADC maps). ADC values are typically very low (0.6-0.9 × 10⁻³ mm²/s), lower than most other renal tumors. DWI is highly valuable for detection of small lesions and assessment of treatment response.
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On diffusion-weighted images, lymphoma masses demonstrate marked and homogeneous diffusion restriction with low ADC values.
On B-mode ultrasound, lymphoma masses typically demonstrate homogeneous hypoechoic appearance. Masses may be well-defined or infiltrative. Bilateral and multifocal involvement can be demonstrated on ultrasound. Posterior acoustic enhancement may be seen. Perinephric soft tissue thickening may appear as a hypoechoic band different from the echogenic perinephric fat.
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B-mode ultrasound demonstrates homogeneous hypoechoic multifocal masses in both kidneys.
On Doppler ultrasound, lymphoma masses are typically hypovascular or avascular, showing no significant internal vascularity. This is distinctly different from the hypervascular enhancement of RCC. Renal artery and vein flow may be preserved but large masses may displace renal vessels.
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On Doppler examination, the masses show no significant internal vascularity, demonstrating a hypovascular pattern.
On FDG PET-CT, lymphoma masses demonstrate avid FDG uptake. Bilateral renal involvement, retroperitoneal lymphadenopathy, and other extrarenal sites of involvement are assessed in a single examination. PET-CT is the standard imaging modality for staging, treatment response assessment, and recurrence detection. Delayed images are useful for evaluation of renal lesions.
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FDG PET-CT shows avid FDG uptake in masses in both kidneys, with assessment of retroperitoneal lymphadenopathy and additional extrarenal sites of involvement.
Criteria
Multiple discrete, round, homogeneously hypoenhancing masses in bilateral or unilateral kidneys
Distinct Features
Most common form (60%). Each lesion is typically 1-5 cm, homogeneous, well-defined, and hypoenhancing. Bilateral involvement may be seen in up to 50%. Retroperitoneal LAP accompanies.
Criteria
Perinephric soft tissue infiltration surrounding the kidney, renal contours preserved or nephromegaly
Distinct Features
Most specific form for lymphoma. Replacement of perinephric fat by soft tissue seen as a rind encasing the kidney. Renal function is usually preserved. Accompanying nephromegaly may occur.
Criteria
Diffuse lymphomatous infiltration of renal parenchyma without discrete mass formation, prominent nephromegaly
Distinct Features
Characterized by diffuse enlargement of the kidney without focal mass formation and overall hypoenhancement post-contrast. Nephromegaly is prominent. Renal function may be impaired. May be confused with pyelonephritis or renal vein thrombosis.
Criteria
Single, large, homogeneously hypoenhancing renal mass — more common in primary renal lymphoma
Distinct Features
Rarest form. Single large mass may be confused with RCC. Homogeneous hypoenhancement and absence of necrosis distinguish from RCC. Biopsy is usually needed for diagnosis. Exclusion of systemic disease is important when primary renal lymphoma is suspected.
Distinguishing Feature
Renal metastasis can also be bilateral and multifocal but is typically smaller, cortically located, and heterogeneously enhancing. Perinephric rind pattern is not seen in metastasis. Primary tumor history (lung, breast) favors metastasis; lymphoma history favors lymphoma.
Distinguishing Feature
Clear cell RCC is typically solitary, hypervascular with prominent arterial phase enhancement, and heterogeneous (necrosis, hemorrhage). Lymphoma is multifocal, homogeneous, hypovascular, and lacks necrosis. Perinephric rind pattern is not seen in RCC.
Distinguishing Feature
Focal pyelonephritis shows wedge-shaped or round hypoenhancement but the clinical context differs (fever, dysuria, leukocytosis). Perinephric stranding may occur in pyelonephritis but rind pattern is absent. Regression with treatment favors pyelonephritis.
Urgency
urgentManagement
medicalBiopsy
NeededFollow-up
specialist-referralRenal lymphoma diagnosis is usually made in the context of systemic lymphoma staging. In isolated renal involvement, tissue diagnosis via percutaneous biopsy is required. Treatment is chemotherapy (regimens such as R-CHOP); there is no surgical indication. PET-CT is the standard imaging modality for staging and treatment response assessment. Hematology consultation is mandatory. Nephrology consultation is recommended if renal function is affected.
Renal lymphoma responds well to chemotherapy; surgery is generally not indicated. Primary renal lymphoma is extremely rare and must be distinguished from secondary involvement. Histopathological diagnosis via biopsy is required.