Primary renal lymphoma (PRL) is extremely rare with an incidence of 0.7% among extranodal lymphomas. Occult renal lymphoma, which mimics medical renal disease and bilateral renal involvement, presents a diagnostic challenge to nephrologists and radiologists as the clinical and radiological findings are mostly non-specific or inconclusive. Acute kidney injury (AKI) is not an uncommon finding in renal infiltration due to malignant lymphoma. However, only 14% of cases are detected before death, and the low diagnostic rate may be due to the non-specific clinical manifestations of renal involvement, with only 0.5% of these cases presenting with AKI. Moreover, PRL is difficult to diagnose based on clinical, biochemical, and radiologic features, especially, in the case of bilateral diffuse involvement.

Herein, we report a 74-year-old woman with primary diffuse large B-cell lymphoma who presented with AKI diagnosed by ultrasound-guided needle biopsy. We also report the clinicopathologic findings of 121 PRL cases reported since 1989, by conducting a literature review of published cases.

A timely renal biopsy provides the most expedient means of establishing the diagnosis. Thus, early identification of the disease by the clinician facilitates early diagnosis toward effective treatment.

Only 20 cases of pediatric primary renal non-Hodgkin's lymphoma have been reported since 1995, rare cases and a variety of imaging manifestations have led to difficulties in its diagnosis and treatment.

Herein, we share in detail a case of primary renal lymphoma (PRL) in a child and summarize the common clinical manifestations, imaging features, and prognostic factors of pediatric PRL by retrospectively analyzing cases reported in the literature. A 2-year-old boy presented to the clinic with a large mass on the right side of his abdomen along with loss of appetite.

Imaging revealed a large right renal mass, nearly replacing the entire renal tissue, along with numerous small nodules in the left kidney. Given no local adenopathy and metastases, the diagnosis was unclear. A percutaneous renal puncture was performed, which proved the diagnosis of Burkitt's lymphoma. Since no bone marrow involvement, this child was diagnosed with pediatric PRL.

This PRL boy was treated with the NHL-BFM95 protocol and supportive care.

Unfortunately, this boy died of multiple organ failure in the fifth month of treatment.

As per literature review, the presentation of pediatric PRL is fatigue, loss of appetite, weight loss, abdominal swelling, or other nonspecific symptoms. Although in 81% of cases it often infiltrates the bilateral kidneys, urine abnormalities caused by pediatric PRL are uncommon. 76.2% of pediatric PRL were boys and 2/3 of all cases presented as diffuse renal enlargement. Those PRL presented as masses could easily be misdiagnosed as WT or other malignancies. Absent of local enlarged lymph node, no necrosis or calcification suggest atypical presentation of renal masses and a percutaneous biopsy is needed in timely establishing the accurate diagnosis for appropriate treatment. Based on our experience, percutaneous renal puncture core biopsy is a safe procedure.

Lymphomas localized in the kidney are a rare entity that may be challenging to diagnose. We analyzed data from 10 patients with renal involvement of lymphoma diagnosed between 2009 and 2019 on fine needle biopsy from our tertiary center, and compared these with findings of 160 cases reported in the literature. Diffuse large B-cell lymphoma was the main histology subtype (40 and 38% in our sample and in the literature, respectively), followed by low-grade B-cell lymphomas, mostly from the marginal zone (MZ). Altogether, 106 patients had urological inaugural symptoms and 64 had general symptoms. Patients with urological presentation more often had renal masses than diffuse infiltration (p < 0.001), unilateral tumors (p = 0.0036) and low-grade B-cell lymphomas (17 vs 6%, p = 0.043). In both groups, nearly one-fourth of patients had diffuse (stage IV) lymphomas. Overall survival did not differ by the presence of urological/systemic symptoms, stage or aggressive lymphoma status. Notably, 3 of 10 patients from our series had MZ lymphomas associated with primary Sjögren syndrome revealed by acute kidney injury, including one where the autoimmune disease was detected. Lymphoproliferative disorders localized in the kidney are a challenging condition that can lead to detection of aggressive or diffuse lymphomas.

Renal involvement by Non-Hodgkin's lymphoma (NHL) is very rare, and involvement of the kidney as the primary site of NHL (PRNHL) is much more uncommon. Gold standard for the diagnosis of PRNHL is histology and imaging modalities although helpful are not specific. Nephrectomy has been mostly recommended for low grade lymphomas, and for high grade PRNHLs, chemotherapy without nephrectomy has been recommended as the treatment of choice. This tumor is aggressive with poor prognosis. This poor prognosis is partly because of delayed diagnosis and partly because of unnecessary surgeries, so it should be kept in mind, especially in bilateral renal tumors with unusual imaging characteristics, to take a tissue biopsy before nephrectomy. In this review, we will discuss all the detailed aspects of clinical, pathologic, and imaging characteristics of 83 cases of PRNHL reported in the last 20 years in the English literature so far. For this purpose, all the published cases of the primary non-Hodgkin's lymphoma of kidney were reviewed via a search in PubMed, Scopus, and Google Scholar, (1999-2019), using the keywords of "Primary renal lymphoma" and "Non-Hodgkin's lymphoma and kidney," "renal Non-Hodgkin's lymphoma," "renal lymphoma," and "lymphoma and kidney." There were 83 cases in the published English literature which were reviewed for this article. There was some missing information in some cases which has been recorded as "not reported."

A 12-year-old boy presented with a prolonged history of headache, fatigue and hypertension. Initial investigations were consistent with presumed non-oliguric end-stage renal disease, leading to a provisional diagnosis of juvenile nephronophthisis. Subsequent imaging demonstrated bilaterally enlarged kidneys without cystic change. Mutation analysis was negative for nephronophthisis, causing diagnostic uncertainty which prompted renal biopsy. Histology revealed a primary renal diffuse large B-cell lymphoma which was highly responsive to chemotherapy, including the anti-CD20 monoclonal agent, rituximab. Renal function improved during lymphoma treatment, with residual chronic kidney disease stage 3a once chemotherapy was completed. Atypical diagnostic features should always prompt re-evaluation of a patient. In this case, the delayed malignancy diagnosis did not have an adverse effect on patient survival or morbidity. The outcome for primary renal lymphoma (PRL) has improved markedly following the introduction of rituximab.

Peripheral T-cell lymphoma (PTCL) is rare in children. Expression of cytotoxic molecules (CM) in nodal PTCL has unique clinicopathologic features, including an Epstein-Barr virus (EBV) association. However, CM+, EBV-associated PTCL is extremely rare in the childhood, with only 1 study having been reported to date, including both pediatric and adult patients. We report a case of CM+ PTCL in a 20-month-old boy with left neck lymphadenopathy as well as multiple visceral lesions. A biopsied lymph node was diffusely infiltrated by atypical lymphoid cells with a CD4/CD8, granzyme B+, perforin+, and TIA-1+ phenotype, and EBV positivity by in situ hybridization. Rearrangements of the TCR γ-chain and β-chain genes were demonstrated by polymerase chain reaction. Ancillary genetic studies detected trisomy 2, trisomy 10, a structurally abnormal 6p, and additional copies of the IRF4 gene. Multiple bone marrow biopsies failed to show any evidence of tumor, histiocytic hyperplasia, or hemophagocytosis. This lesion was therefore diagnosed as "CM+, EBV-associated high-grade peripheral T-cell lymphoma." After 5 cycles of chemotherapy, the patient was in remission 8 months following initial diagnosis. To our knowledge, this represents the youngest child with this rare tumor in the published literature, and showing an unusually favorable initial response to therapy.