Renal lymphoma is usually a part component of multi-systemic lymphoma. Primary renal lymphoma, which is defined as lymphoma involving the kidney exclusively without any manifestation of extra-renal lymphatic disease . Typical imaging findings are multiple bilateral hypodense or infiltrative renal masses.
While renal lymphoma has an autopsy incidence of ~45% (range 30-60%) in lymphoma patients, the incidence by CT evaluation is ~5% .
The kidneys are the most common abdominal organ affected by lymphoma. Most instances are B-cell non-Hodgkin lymphoma; primary renal lymphoma is rare (<1%). Involvement of kidneys in Hodgkin lymphoma is rare (<1%).
Primary renal lymphoma more frequently affects the middle-aged men . Patients with organ transplantation (immunosuppression) and the patients with HIV infection (immunocompromised) are prone to develop renal lymphoma .
Patients present with flank pain (the commonest symptom), weight loss, hematuria, or a palpable mass. Acute renal failure may be seen in infiltrative disease.
Abdominal/flank pain (62%) is the commonest symptom in adult patients (18-50 years), fever (56%) is the commonest symptom in younger patients (<18 years) and weight loss and hematuria (37%) are the common symptoms in the older patients (> 50 years) .
The exact cause or origin of primary renal lymphoma is controversial, as the kidney is an extranodal organ and is devoid of lymphoid tissue normally. It is hypothesized that primary renal lymphoma likely arises from the capsule of the kidney or peri-renal fat (lymphoid rich tissues) and afterwards involves the renal parenchyma. The lymphocytes seen in the region of chronic renal inflammation have also been proposed as a potential causative factor .
Renal lymphoma occurs commonly with non-Hodgkin lymphoma. The majority have intermediate or high-grade lymphomas including Burkitt and histiocytic varieties . Most are B-cell lymphoma.
On gross examination, lesions are fleshy or firm yellow, tan, or grey tumors of 1-20 cm size.
It is the most sensitive imaging for the involvement of the renal collecting system and ureters, as well as provides functional information.
Hypoechoic lesions (single/multiple) within renal parenchyma with very little internal vascularity.
CT is the imaging modality of choice . The following patterns of disease may be seen on CT:
- multiple masses (up to 60%: most common pattern)
- typically 1-3 cm in size
- associated with enlarged retroperitoneal nodes (≥50%)
- single mass (over 20% of cases)
- up to 15 cm
- homogeneous, hypodense without cystic change
- calcium, bleed, or necrosis
- invasion from retroperitoneal nodal mass (over 30% of cases)
- usually >10 cm
- encasement of vessels without thrombosis, +/- hydronephrosis
- diffuse infiltration (up to 20% of cases)
- no discrete mass
- usually bilateral
- seen with Burkitt lymphoma
- perirenal mass (less than 10% of cases)
- perirenal stranding
- thickening of Gerota fascia
- perirenal nodules
- atypical patterns:
- spontaneous hemorrhage
- heterogenous lesion
- cystic changes
- T1: hypointense to renal parenchyma
- T2: iso or hyperintense to renal parenchyma
- poor enhancement compared to renal parenchyma
- delayed enhancement is seen in some lesions
- diffusion-weighted imaging (DWI): restricted diffusion
Renal lymphoma shows intense 18F-FDG uptake. PET-CT is useful in the diagnosis of the disease, in assessing response to the therapy and in the detection of recurrent disease .
Treatment and prognosis
Chemotherapy is the mainstay of treatment . The prognosis of primary renal lymphoma is largely unknown. The 5-year survival rate is ~45%. Younger patients and bilateral primary renal lymphomas are associated with a poorer prognosis (shorter survival time and more rapid progression) .
Imaging differential considerations include: