(Radiographics. 2000;20:197-212.)
© RSNA, 2000
Renal Lymphoma: CT Patterns with Emphasis on Helical CT1
Bruce A. Urban, MD and
Elliot K. Fishman, MD
1 From the Russell H. Morgan Department of Radiology and Radiological Science, Johns Hopkins Medical Institutions, 600 N Wolfe St, Baltimore, MD 21287. Recipient of a Certificate of Merit award for a scientific exhibit at the 1998 RSNA scientific assembly. Received February 8, 1999; revision requested March 19 and received April 6; accepted April 6. Address reprint requests to B.A.U.
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Abstract
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Renal lymphoma is most often seen in conjunction with multisystemic, disseminated lymphoma or as tumor recurrence. Renal lymphoma may also be seen in immunocompromised patients or, rarely, as primary disease. Computed tomography (CT) is the most sensitive, efficient, and comprehensive examination for evaluation of the kidneys in patients with suspected renal lymphoma. Helical CT in particular improves detection and characterization of lymphomatous renal involvement by optimizing contrast dynamics and data acquisition and is the current modality of choice for accurate staging of lymphoma. Typical CT patterns in renal lymphoma include single and multiple masses, invasion from contiguous retroperitoneal disease, perirenal disease, and diffuse renal infiltration. Atypical CT patterns may also be encountered and provide a diagnostic challenge. These include spontaneous hemorrhage, necrosis, heterogeneous attenuation, cystic transformation, and calcification. Solid renal masses including renal cell carcinoma and metastases are the most commonly encountered entities that mimic renal lymphoma at CT and require biopsy for definitive diagnosis. CT (particularly helical CT) is useful in the evaluation of patients with suspected renal lymphoma, and familiarity with the spectrum of findings in renal lymphoma is important for accurate diagnosis.
Index Terms: Computed tomography (CT), helical, 81.12112, 81.12115 • Kidney neoplasms, 81.34 • Kidney neoplasms, CT, 81.12112, 81.12115 • Lymphoma, CT, 81.12112, 81.12115, 81.34
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Introduction
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Clinical detection of renal involvement in patients with lymphoma is vital whether the kidney is the primary site of disease or a site of disseminated involvement. In autopsy series, estimates of renal involvement in patients with known lymphoma range from 30% to 60% (1,2). However, renal involvement is detected in only 3%–8% of all patients undergoing routine computed tomography (CT) staging for lymphoma (1,3,4). In part, this discrepancy reflects the fact that patients with presumed lymphomatous renal involvement rarely undergo nephrectomy or biopsy, and disease involvement is often poorly documented. In addition, most published studies have made use of older-generation CT scanners, which have relatively low sensitivity for detection of small lesions (1,4). It is anticipated that with continuing improvements in CT technology, notably helical CT, this modality will become increasingly sensitive for detection of renal disease including lymphoma and will allow detection at an earlier stage of involvement (5–7).
In this article, we review typical CT findings in renal lymphoma with emphasis on proper helical CT technique and diagnosis. In addition, we discuss and illustrate CT patterns of disease including single and multiple masses, contiguous retroperitoneal extension, perirenal involvement, and diffuse infiltration. We also discuss atypical manifestations of renal lymphoma and pathologic conditions that can mimic this entity at CT.
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Clinical and Histopathologic Features of Renal Lymphoma
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Clinical Features
Along with the hematopoietic and reticuloendothelial systems, the kidneys are one of the most common extranodal sites of lymphoma (2). Primary renal lymphoma has been described in the literature but is rare (8–10). More commonly, renal lymphoma results from hematogenous dissemination or contiguous extension of retroperitoneal disease (3,9,11). Involvement usually occurs late in the course of the disease and is clinically silent (1,11). Often, an unanticipated diagnosis is made at imaging. Occasionally, patients present with nonspecific signs and symptoms including flank pain, weight loss, hematuria, or a palpable mass (11). Acute renal failure from lymphomatous infiltration has also been described but is quite rare (12–14).
Histopathologic Features
Renal involvement with lymphoma occurs much more commonly with non-Hodgkin disease (3). The kidneys are probably more frequently involved by the diffuse lymphomas than by the nodular forms. The majority of patients have intermediate or high-grade lymphomas including Burkitt and histiocytic types (3). Most of these lymphomas are of B-cell origin (15,16). Gross pathologic examination often reveals fleshy or firm yellow, tan, or gray tumors ranging from 1 cm to 15–20 cm in size (Fig 1).
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Figure 1. Diffuse large cell lymphoma in a 38-year-old woman. Photograph of a gross specimen reveals a large, fleshy yellow tumor arising from the superior pole of the kidney (arrow). Small retroperitoneal and pelvic lymph nodes were also present at surgery. Immunohistochemical analysis of the renal mass demonstrated a staining pattern consistent with a lymphoma of B-cell origin, the most common type of lymphoma involving the kidney.
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Tumor Growth and Mechanism of Spread in Renal Lymphoma
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Understanding of tumor growth and the mechanism of spread in lymphoma at the histologic level is crucial to understanding the resulting imaging patterns of involvement (11). Hematogenous involvement usually results in bilateral distribution of tumor foci within the renal cortex. Tumor proliferation begins within the interstitium, and the underlying nephrons, collecting ducts, and blood vessels provide a framework for tumor growth (11). Infiltrative growth results in preservation of the parenchymal structures with preservation of renal contour (3,11). Consequently, detection is difficult and renal involvement can easily be missed.
As lymphomatous tumors enlarge, the surrounding renal parenchyma is compressed and destroyed, and tumor infiltration results in the formation of expansile masses (11). Nonuniform growth can result in masses that extend beyond the renal contour and displace the collecting system, thereby resembling primary renal neoplasms. More commonly, multiple foci of lymphoma grow at a uniform rate and manifest as multiple parenchymal masses involving both kidneys. Continued growth may result in replacement of the majority of the kidney parenchyma (11).
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Imaging Options in Renal Lymphoma
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Several imaging options exist for the evaluation of renal involvement by lymphoma. These include intravenous urography, ultrasonography (US), nuclear medicine, magnetic resonance (MR) imaging, and CT. Each modality can provide useful information in the detection, characterization, and staging of disease. Intravenous urography is the most sensitive for evaluating involvement of the renal collecting system and ureters and can provide functional information regarding the severity of hydronephrosis in cases involving extensive retroperitoneal disease. US remains the modality of choice for noninvasive imaging of the renal parenchyma and is a useful screening modality. Renal lymphoma is usually hypoechoic at US, a finding that reflects tissue homogeneity (Fig 2) (11,17). US can sometimes depict renal abnormalities that are undetectable with other imaging modalities and is an excellent complementary study for evaluation of the kidneys (1,18). Nuclear medicine provides unique options for functional imaging of the kidney (19). MR imaging allows detailed tissue characterization of complicated renal masses and noninvasive evaluation of the renal vasculature (20). However, CT remains the most sensitive, efficient, and comprehensive examination for evaluation of the kidneys and is the imaging modality of choice in most if not all patients with suspected renal masses including renal lymphoma (1,5,6,21,22). Not only can CT accurately depict renal involvement in most patients, it can also most completely define the extrarenal extent of disease and provide comprehensive staging information (1,21).
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Figure 2. Large cell lymphoma in a 63-year-old man. Sagittal renal US image demonstrates lymphoma with a characteristic hypoechoic appearance in the lower pole of the right kidney (arrow).
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Helical CT of the Kidneys
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Helical CT is universally accepted as the technique of choice in CT of the kidneys (5,6,22). Helical CT offers many advantages and has high sensitivity for the detection of renal lymphoma. Breath-hold images that are essentially free from motion artifact and respiratory misregistration can be quickly obtained during multiple phases of renal enhancement. This allows accurate detection and characterization of most renal masses including very small lesions. Vascular-phase images provide detailed characterization of the renal vasculature and can be used to produce angiographic equivalent images with volume-rendered three-dimensional reconstruction techniques (22). Similarly, helical CT allows evaluation of the surrounding anatomic structures, including the perirenal space and retroperitoneum, which are commonly involved by lymphoma. In addition, helical CT is a reliable method of follow-up in patients with renal lymphoma and is commonly used to determine response to therapy (Fig 3).
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Figure 3a. Recurrent large cell lymphoma in the right kidney in a 28-year-old man. The patient had undergone successful treatment of a large anterior mediastinal mass 7 months earlier. (a) Contrast material-enhanced helical CT scan obtained at the time of recurrence illustrates the sensitivity of this modality for the detection of very small lesions (arrowheads). (b) Contrast-enhanced CT scan obtained 6 weeks later shows that one of the lesions has increased markedly in size (arrow).
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Figure 3b. Recurrent large cell lymphoma in the right kidney in a 28-year-old man. The patient had undergone successful treatment of a large anterior mediastinal mass 7 months earlier. (a) Contrast material-enhanced helical CT scan obtained at the time of recurrence illustrates the sensitivity of this modality for the detection of very small lesions (arrowheads). (b) Contrast-enhanced CT scan obtained 6 weeks later shows that one of the lesions has increased markedly in size (arrow).
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Intravenous administration of contrast material is essential for the diagnosis of renal lymphoma in the majority of patients. Subtle parenchymal involvement, especially with infiltrative forms of the disease, can be missed entirely without the benefit of contrast enhancement (3). Use of contrast material is also important for evaluation of perirenal lymphoma, which can be indistinguishable from the underlying kidney or mistaken for a large primary renal mass on unenhanced images (Fig 4). Following contrast material administration, multiple images can be obtained, each of which can provide useful information regarding diagnosis and extent of involvement (23). These images can be obtained during the corticomedullary or arterial phase, the nephrographic phase, and the excretory phase. Corticomedullary-phase imaging is ideal for evaluating involvement of the renal arteries and veins. Nephrographic-phase imaging is the most sensitive for lesion detection (23). Excretory-phase imaging is important for determining collecting system involvement and extent of hydronephrosis (24). The number of acquisitions required will vary depending on the clinical scenario and extent of disease. Two acquisitions (usually obtained during the corticomedullary or nephrogenic phase and the excretory phase) suffice for most patients (24). Unenhanced images can be helpful for determining baseline attenuation measurements prior to injection. Parameters for helical CT of the kidneys are summarized in the Table.
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Figure 4a. Perirenal lymphoma in a 64-year-old man. Helical CT scans obtained before (a) and after (b) intravenous administration of contrast material show a perirenal soft-tissue mass enveloping the left kidney. The symmetric renal function seen in b reflects the characteristic "soft" nature of lymphomatous tumor.
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Figure 4b. Perirenal lymphoma in a 64-year-old man. Helical CT scans obtained before (a) and after (b) intravenous administration of contrast material show a perirenal soft-tissue mass enveloping the left kidney. The symmetric renal function seen in b reflects the characteristic "soft" nature of lymphomatous tumor.
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Typical CT Patterns in Renal Lymphoma
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Renal lymphoma has a wide variety of CT appearances. In many cases, diagnosis is not difficult because patients present with a known lymphoma at the time of imaging (16). Lymphoma typically involves the kidney in one of several recognizable (albeit somewhat arbitrarily defined) patterns. These patterns include multiple renal masses, solitary masses, renal invasion from contiguous retroperitoneal disease, perirenal disease, and diffuse renal infiltration (3,25). No specific correlation has been found between the exact type of lymphomatous involvement and the pattern or prevalence of renal involvement (7).
Multiple Masses
The most commonly encountered pattern of involvement in patients with renal lymphoma is multiple masses (Fig 5) (1–3,7,25). Involvement is typically bilateral but may also be unilateral. Several studies have retrospectively determined this pattern of renal involvement to be present in approximately 60% of patients (2,7,25). It is likely that this percentage may increase as new, more technologically advanced imaging modalities such as helical CT allow improved detectability of smaller lesions. The presence of multiple masses reflects the widespread, advanced course of disease commonly encountered in patients who present for staging evaluation. Depending on the size and expansile nature of the individual deposits, little mass effect may be seen on renal contour (3). Thus, although there may be extensive renal involvement, imaging findings can be quite subtle, and intravenous administration of contrast material becomes essential for diagnosis.
Masses typically range in size from 1 to 3 cm (1,3). Following intravenous administration of contrast material, there is minimal enhancement, and lesions manifest as areas of decreased enhancement compared with the normal renal parenchyma (1). The masses typically demonstrate homogeneous attenuation (Figs 6, 7) (1,3). A heterogeneous or cystic appearance is rarely seen and is typically a sign of tumor necrosis in patients undergoing chemotherapy (1). Retroperitoneal adenopathy is seen in approximately 50% of affected patients. Calcification is extremely rare (4). Associated enlargement of retroperitoneal lymph nodes is seen in less than 50% of cases (3,4,16).
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Figure 6. Large cell lymphoma in an 11-year-old boy. The patient presented with a large anterior mediastinal mass and renal lesions. Contrast-enhanced helical CT scan demonstrates small, hypoattenuating masses bilaterally (arrows), a typical finding in renal lymphoma. The patient responded well to treatment, and the renal lesions eventually resolved.
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Figure 7. Large cell lymphoma in a 73-year-old woman. Contrast-enhanced CT scan shows bilateral renal masses with characteristic homogeneous attenuation, smooth borders, and low contrast enhancement. Retroperitoneal adenopathy is also present (A).
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Solitary Masses
At CT, a dominant lymphomatous renal mass may resemble other renal neoplasms that grow primarily by expansion, including renal cell carcinoma or metastases (Fig 8). Lymphomatous masses are typically hypovascular and demonstrate minimal enhancement following intravenous administration of contrast material, which may help differentiate lymphoma from the typically enhancing renal cell carcinoma. Moreover, lymphomatous renal masses often demonstrate homogeneous attenuation, unlike the usually heterogeneous renal cell carcinoma. Nevertheless, biopsy is often required for definitive diagnosis (Fig 9). Solitary masses have been reported in up to 48% of patients with renal lymphoma, but series more consistently reflect a frequency of approximately 10%–20% (2–4,11). Solitary lymphomatous masses have been reported to reach 15 cm in diameter and can distort renal contour (Fig 10) (4).
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Figure 9. Renal lymphoma in a 69-year-old man. Contrast-enhanced helical CT scan shows a dominant 5-cm mass in the right kidney (arrow). There is no evidence of retroperitoneal adenopathy.
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Figure 10. Follicular, mixed small cleaved and large cell lymphoma in a 74-year-old man. Contrast-enhanced helical CT scan shows a large mass located in the left kidney and extending into the perirenal space. Small nodes are seen in the retroperitoneum (arrow).
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Contiguous Retroperitoneal Extension
Direct renal invasion from contiguous retroperitoneal disease is another common pattern of involvement in renal lymphoma and is seen in approximately 25%–30% of patients with documented disease (Fig 11) (1,3). These patients typically present with a large, bulky retroperitoneal mass that envelops the renal vasculature and invades the renal hilum. Lymphomatous masses usually demonstrate homogeneous attenuation. In most patients, the renal arteries and veins remain patent despite tumor encasement, a finding that is characteristic for lymphoma (Figs 12, 13). However, contiguous extension of retroperitoneal involvement in the renal collecting system can often cause obstruction, and affected patients will commonly present with hydronephrosis (1,7). Displacement of the kidney can also be seen. Following treatment of larger masses, residual fibrosis is often seen and can be mistaken for recurrent or residual disease.
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Figure 11. Renal lymphoma manifesting as contiguous retroperitoneal extension. Drawing illustrates the characteristic appearance of a bulky retroperitoneal mass invading the renal hilum and enveloping the renal vessels.
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Figure 12. Diffuse lymphocytic lymphoma in a 65-year-old woman. Contrast-enhanced helical CT scan shows a large, homogeneous mass enveloping the retroperitoneum and invading the right kidney. Note how flow is maintained in the renal arteries (straight arrows) and left renal vein (curved arrow) despite the massive tumor burden. These findings are characteristic of retroperitoneal lymphoma.
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Figure 13. Large cell lymphoma in a 51-year-old woman. Contrast-enhanced helical CT scan shows a large tumor mass invading and displacing the left kidney. The tumor also involves the right side of the retroperitoneum.
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Perirenal Disease
Perirenal involvement by lymphoma is usually the result of direct extension from retroperitoneal disease or transcapsular spread of renal parenchymal disease. Less commonly, perirenal disease is isolated from the renal parenchyma, in which case the disease can completely surround the kidney without parenchymal compression or functional impairment (Figs 14, 15) (26). Although this finding in renal lymphoma occurs infrequently, it is virtually pathognomonic. A variety of CT manifestations of perirenal lymphoma have been described, including renal sinus infiltration, thickening of the fascia of Gerota, and perirenal masses (Fig 16) (3). Differentiation of perirenal disease from the underlying parenchyma can be difficult at unenhanced CT, and in most cases of suspected renal lymphoma, intravenous administration of contrast material is vital for detection and accurate staging (3).
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Figure 14. Renal lymphoma manifesting as perirenal disease. Drawing illustrates the characteristic appearance of isolated perirenal lymphoma, which surrounds but does not destroy the underlying kidney.
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Figure 15. Perirenal lymphoma in the same patient as in Figure 4. Sagittal multiplanar reconstruction image from a contrast-enhanced helical CT scan reveals a perirenal soft-tissue mass (arrows) enveloping the left kidney (K). Sp = spleen, St = stomach.
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Figure 16. Large cell lymphoma in a 34-year-old man. Contrast-enhanced helical CT scan demonstrates perirenal masses bilaterally, especially on the right side. The resulting marked compression and deformity of the right kidney are somewhat unusual for perirenal involvement.
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Infiltrative Disease
Because lymphomatous proliferation usually occurs within the interstitium of the kidney, tumor growth often results in nephromegaly with preservation of renal contour (Fig 17) (17). Diffuse infiltration is almost always bilateral and is seen in approximately 20% of patients (4). Diagnosis is often subtle and relies on the appreciation of global enlargement (Fig 18) (4). Detection can be extremely difficult at this stage of involvement, and contrast enhancement may be required for diagnosis (Fig 19) (1). More focal areas of infiltrative disease demonstrate poorly defined interfaces with the normal renal parenchyma (Fig 20) (17). Infiltrated kidneys demonstrate poor function but usually maintain sufficient function to remain clinically silent. In fact, many cases are diagnosed retrospectively following return of the kidneys to normal size following chemotherapy for disease elsewhere in the body. The pelvocaliceal system is usually encased and deformed by the infiltrating tumor (17). Very rarely, a large reniform mass infiltrates and destroys the entire kidney and manifests as a nonfunctioning tumor.
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Figure 17. Renal lymphoma manifesting as infiltrative disease. Drawing illustrates the characteristic appearance of infiltrative lymphoma within the interstitium of the renal parenchyma.
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Figure 18. Infiltrative renal lymphoma in an 80-year-old man. Contrast-enhanced CT scan shows minimal renal enlargement bilaterally, a finding that suggests subtle involvement by lymphoma.
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Figure 19a. High-grade large cell lymphoma in a 35-year-old man. (a) Contrast-enhanced CT scan demonstrates patchy tumor infiltration within the kidneys. The kidneys have retained their normal contour, a finding that is characteristic of infiltrative lymphoma. (b) On an unenhanced CT scan, the infiltration is undetectable, which underscores the importance of contrast-enhanced CT for diagnosis.
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Figure 19b. High-grade large cell lymphoma in a 35-year-old man. (a) Contrast-enhanced CT scan demonstrates patchy tumor infiltration within the kidneys. The kidneys have retained their normal contour, a finding that is characteristic of infiltrative lymphoma. (b) On an unenhanced CT scan, the infiltration is undetectable, which underscores the importance of contrast-enhanced CT for diagnosis.
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Figure 20. Infiltrative renal lymphoma in a 44-year-old woman. Contrast-enhanced CT scan shows the kidneys as diffusely enlarged and replaced by tumor. The lobulated appearance of the tumor reflects the transition to a more focal expansile mass as it compresses and destroys renal parenchyma.
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Atypical CT Patterns in Renal Lymphoma
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The vast majority of patients with renal lymphoma present with characteristic imaging findings and patterns of disease, and diagnosis is usually straight-forward. Rarely, however, the CT findings are quite unusual and the diagnosis of lymphoma is made only in retrospect if at all. Atypical findings include spontaneous hemorrhage, necrosis, heterogeneous attenuation, cystic transformation, and calcification (Figs 21–23) (1). Some of these findings are often the result of prior treatment. However, most lymphomatous kidney masses and nodules disappear following therapy, and the kidney resumes a normal CT appearance (1).
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Figure 21. Non-Hodgkin lymphoma in a 51-year-old man. Contrast-enhanced CT scan shows a cystic retroperitoneal mass (M) invading the left kidney, resulting in hydronephrosis. The attenuation of the mass is similar to that of the dilated collecting system (C).
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Figure 22a. Large cell lymphoma in a 63-year-old man. Contrast-enhanced helical CT scans demonstrate a cystic mass in the right kidney (arrow in a) and cystic or necrotic nodes in the retroperitoneum (arrow in b). These CT findings are highly unusual for lymphoma and are more common in necrotic tumors such as adenocarcinoma or testicular cancer or in infectious diseases such as tuberculosis.
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Figure 22b. Large cell lymphoma in a 63-year-old man. Contrast-enhanced helical CT scans demonstrate a cystic mass in the right kidney (arrow in a) and cystic or necrotic nodes in the retroperitoneum (arrow in b). These CT findings are highly unusual for lymphoma and are more common in necrotic tumors such as adenocarcinoma or testicular cancer or in infectious diseases such as tuberculosis.
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Figure 23a. Diffuse large cell lymphoma in a 56-year-old man who presented with acute abdominal pain. Contrast-enhanced helical CT scans demonstrate retroperitoneal hemorrhage displacing the left kidney anteriorly. Interruption of the enhancing cortical rim (arrow in b) suggests an underlying renal mass as the cause of bleeding. These findings are typical in renal cell carcinoma but very unusual in lymphoma.
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Figure 23b. Diffuse large cell lymphoma in a 56-year-old man who presented with acute abdominal pain. Contrast-enhanced helical CT scans demonstrate retroperitoneal hemorrhage displacing the left kidney anteriorly. Interruption of the enhancing cortical rim (arrow in b) suggests an underlying renal mass as the cause of bleeding. These findings are typical in renal cell carcinoma but very unusual in lymphoma.
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Multisystemic Involvement
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CT is an efficient and accurate procedure for multisystemic imaging of patients with lymphoma and is the modality of choice for staging in virtually all patients (27). Lymphoma that is isolated to the kidney as a primary site of involvement is quite rare, whereas additional sites of extranodal involvement are common and are seen in most patients at the time of diagnosis (3,16). Common extranodal sites include the kidneys, bone marrow, liver, and gastrointestinal tract (Figs 24–26) (4,27), although many other extranodal sites have been reported in the literature. Extranodal involvement, including involvement of the kidneys, is also more common in patients with recurrent disease (Fig 27) (4). The presence of multisystemic disease should always raise suspicion for lymphoma.
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Figure 24. Diffuse large cell lymphoma in a 56-year-old man who presented with a mass in the left kidney and multiple splenic nodules. Contrast-enhanced helical CT scan shows multiple hypoattenuating lesions in the spleen (arrowheads), which is probably the most common site of extranodal lymphoma.
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Figure 25. Diffuse large cell lymphoma in a 76-year-old woman. A contrast-enhanced CT scan obtained earlier (not shown) demonstrated a large retroperitoneal mass infiltrating the right kidney. Subsequent contrast-enhanced CT scan reveals a separate lymphomatous mass (arrow) inferior to the retroperitoneal mass and encasing several small bowel loops in the right lower quadrant.
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Figure 26. Burkitt lymphoma in a 17-year-old boy. Contrast-enhanced CT scan demonstrates masses in the right kidney (straight arrow) and small intestine (curved arrow). The small bowel mass has caused intussusception and bowel obstruction.
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Figure 27. Recurrent diffuse histiocytic lymphoma in a 50-year-old man who presented with bilateral renal masses and lung nodules. Contrast-enhanced CT scan shows multiple pulmonary nodules bilaterally. Parenchymal lung involvement is usually seen only in patients with recurrent disease.
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Lymphoma in Immunocompromised Patients
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An increased prevalence of lymphoma has been described in immunocompromised patients and appears to develop in the setting of impaired immune surveillance from either primary or secondary immunodeficiency (28,29). Lymphoma typically occurs in patients with human immunodeficiency virus (HIV) infection or in secondarily immunosuppressed organ transplant recipients (28–32). Lymphoma is particularly common in patients who have undergone cyclosporine therapy (Fig 28) (28). Lymphoma in immunocompromised patients is typically of small noncleaved cell or immunoblastic origin and has a B-cell phenotype (32). Unlike malignant lymphoma in the general population, immunodeficiency-related lymphoma often has an extranodal origin, with the central nervous system, bone marrow, gastrointestinal tract, lung, heart, and liver being the most common sites (Fig 29) (32).
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Figure 28. Burkitt lymphoma in a 48-year-old woman. The patient had undergone renal transplantation 3 years earlier and was undergoing immunosuppressive steroid and cyclosporin therapy. Contrast-enhanced CT scan shows lymphomatous nodules in the transplanted kidney (arrows). Tumor was also noted within the central nervous system at lumbar puncture.
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Figure 29a. Large cell lymphoma in the same patient as in Figure 16, who tested positive for HIV infection. Multiple sites of involvement included the kidneys and heart. Contrast-enhanced helical CT scans show soft-tissue masses in the perirenal space (a) and within the septum and myocardium of both ventricles (arrows in b). The patient died of acquired immunodeficiency syndrome. Histologic cardiac involvement is common in acquired immunodeficiency syndrome, but bulky lesions as seen in this case are relatively rare.
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Figure 29b. Large cell lymphoma in the same patient as in Figure 16, who tested positive for HIV infection. Multiple sites of involvement included the kidneys and heart. Contrast-enhanced helical CT scans show soft-tissue masses in the perirenal space (a) and within the septum and myocardium of both ventricles (arrows in b). The patient died of acquired immunodeficiency syndrome. Histologic cardiac involvement is common in acquired immunodeficiency syndrome, but bulky lesions as seen in this case are relatively rare.
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Renal involvement in patients with immunodeficiency-related lymphoma is less common but has been reported. Renal lymphoma has also been described in patients with ataxia-telangiectasia (33). Patterns of renal involvement are similar to those seen in malignant lymphoma in the general population. Although the kidney is often just one of many sites of lymphomatous involvement, it may also be the only site (32). At times, differentiation of lymphomatous involvement from infection can be difficult in immunocompromised patients, and biopsy is sometimes needed for definitive diagnosis.
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Entities Mimicking Renal Lymphoma at CT
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CT findings in renal lymphoma are often nonspecific and may be seen with a variety of benign and malignant conditions (9,34). Differential diagnosis is often dictated by imaging findings in conjunction with clinical history because many affected patients already have a diagnosis of lymphoma or primary malignancy at the time of imaging.
Solid renal masses including renal cell carcinoma and metastases are the most commonly encountered entities that mimic renal lymphoma at CT (Fig 30) (11,34). The enhancement pattern of the mass can help differentiate most tumors: Renal cell carcinoma tends to have a more heterogeneous appearance than renal lymphoma (35,36). In addition, vascular invasion is frequently seen with renal cell carcinoma and almost never with lymphoma. Nevertheless, many lesions have overlapping CT features and require biopsy for definitive diagnosis. Metastases from primary tumors such as lung cancer, breast cancer, or synchronous renal cell cancer often manifest as bilateral masses that are indistinguishable from multifocal lymphoma. In such cases, a history of primary malignancy is essential for accurate diagnosis.
An infiltrative growth pattern may be seen with tumors such as transitional cell carcinoma or with inflammatory processes such as acute pyelonephritis or xanthogranulomatous pyelonephritis (Fig 31) (17,34,37). Most transitional cell carcinomas demonstrate expansile growth when they are confined to the renal collecting system; however, they can demonstrate an infiltrative growth pattern with parenchymal renal invasion (37).
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Figure 31. Transitional cell carcinoma in a 72-year-old man. Contrast-enhanced helical CT scan shows a mass infiltrating the left renal hilum. The tumor does not result in vascular occlusion or hydronephrosis. Although these are classic findings in lymphoma, biopsy revealed transitional cell carcinoma.
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Perirenal involvement may be mimicked by direct extension from primary renal cell carcinoma or by metastasis from primary cancers of the lung or breast or from melanoma. Inflammatory and nonneoplastic processes can also extend to the perirenal space and may mimic renal lymphoma. These processes include urinomas, pancreatitis, and retroperitoneal fibrosis (34). Secondary features and clinical history can usually help differentiate perirenal lymphoma from other entities.
Extensive, bulky adenopathy is a hallmark of lymphoma and often involves the kidneys by contiguous extension. Occasionally, very large nodes can be seen with other tumors, most often metastatic adenocarcinoma from the prostate, colon, or an unknown primary site (Fig 32). Adenocarcinoma nodes tend to be "hard" and obstruct the renal vasculature, whereas the "softer" lymphomatous nodes encase and surround the vasculature but do not typically result in occlusion. Furthermore, discrete nodes are often more apparent with metastatic adenocarcinoma, whereas lymphomatous nodes usually manifest as a homogeneous conglomerate mass.
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Figure 32. Adenocarcinoma of unknown primary origin in a 63-year-old man. Contrast-enhanced helical CT scan demonstrates a markedly enlarged, conglomerate nodal mass with homogeneous attenuation enveloping the retroperitoneum. Lymphoma was the most likely diagnosis, but biopsy revealed adenocarcinoma.
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Conclusions
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The kidneys are a frequent site of hematogenous dissemination in patients with lymphoma, and CT is ideally suited for detection and characterization of suspected renal involvement. Several distinct patterns of disease are detectable at CT, and familiarity with the spectrum of findings in renal lymphoma is important for accurate diagnosis. Helical CT optimizes contrast enhancement and improves lesion detection and is the current modality of choice for accurate staging of lymphoma.
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Acknowledgments
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The authors thank Frank Corl for his excellent illustrations.
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Footnotes
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CME FEATURE This article meets the criteria for 1.0 credit hour in category 1 of the AMA Physician's Recognition Award. To obtain credit, see the questionnaire on pp 244-252.
LEARNING >OBJECTIVES After reading this article and taking the test, the reader will be able to:
• Discuss the importance of proper helical CT technique for the detection and characterization of renal disease.
• Enumerate typical and atypical CT findings and patterns in renal lymphoma.
• Recognize the CT appearance of pathologic conditions that may mimic renal lymphoma.
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Top
Abstract
Introduction
