Nguyen, Dustin D. DO; Rakita, Dmitry MD
From the Department of Radiology, Baystate Medical Center, Tufts University, Springfield, MA.
Received for publication July 3, 2013; accepted July 16, 2013.
Reprints: Dustin D. Nguyen, DO, Department of Radiology, Baystate Medical Center, Tufts University, 759 Chestnut St, Springfield, MA 01199 (e-mail: firstname.lastname@example.org).
The authors have no financial disclosures.
Imaging of renal lymphoma on magnetic resonance imaging and diffusion-weighted imaging is not well documented in the literature. We present a case of renal lymphoma in a 61-year-old patient with computed tomography and magnetic resonance imaging correlation. The lymphomatous lesions demonstrate mild enhancement and restricted diffusion. Differential considerations for hypoenhancing masses include papillary or chromophobe renal cell carcinoma, lymphoma, urothelial tumor, or metastasis, all of which have different management pathways. Apparent diffusion coefficient values can be obtained using diffusion-weighted imaging, and may be useful in identifying focal renal lesions, especially on noncontrast imaging. Apparent diffusion coefficient values may be helpful in differentiating between some of these lesions, although more investigation is needed.
A 61-year-old man with no significant medical history presents to the emergency department with a 3-week history of fever, weakness, and fatigue. He did not have upper respiratory symptoms or bladder or bowel incontinence. The patient's laboratory results demonstrated an elevated erythrocyte sedimentation rate of 208 mm/h (normal, ≤ 20 mm/h) and C-reactive protein level of 225 mg/L (normal, < 0.8 mg/L). There was a decreased hemoglobin of 10.0 g/dL and platelet count of 69,000/mm3. The patient's renal function was normal. Earlier blood cultures performed on an outpatient basis were negative. Renal ultrasound performed in the emergency department demonstrated normal-sized kidneys with a right renal cyst. The patient was admitted with a diagnosis of fever of unknown origin and was worked up for possible infectious etiologies, none of which were positive. Peripheral blood smear results, however, demonstrated immature lymphocytes concerning for acute lymphocytic leukemia/lymphoma. Bone marrow aspiration was performed confirming the diagnosis.
Computed tomographic (CT) scan of the chest, abdomen, and pelvis (Fig. 1) was performed for staging purposes. Indeterminate bilateral low attenuation renal lesions were noted and further evaluation with magnetic resonance imaging (MRI) was recommended. An abdominal MRI was performed, revealing numerous bilateral T1 and T2 hypointense lesions (Fig. 2A) demonstrating minimal enhancement (Fig. 2B) and restricted diffusion (Fig. 2C–E). The largest lesion demonstrated an apparent diffusion coefficient (ADC) value of 0.635 (10 − 3 mm2/s). Given the bone marrow findings of lymphoma, the renal findings on MRI were interpreted as representing renal lymphoma. There was diffuse vertebral body bone marrow signal abnormality on the ADC and DWI sequences as well, consistent with lymphoma infiltration.
The patient was subsequently treated with chemotherapy.
Lymphoma is classically categorized into non-Hodgkin or Hodgkin lymphoma.1 The reticuloendothelial and hematopoietic system is the most common organ system affected by lymphoma, followed by the genitourinary system.2 Within the genitourinary system, the organs involved, from the most to least frequent, are the kidneys, adrenal glands, bladder, and testes.2,3 Renal involvement is seen in up to 34% of autopsies of lymphoma patients, but only 5% to 8% of patients have detectable findings on imaging.1,4,5 This discrepancy may be attributed to poor documentation and less-advanced scanner technology at the time these studies were conducted.5
Histology will typically demonstrate a lymphocytic infiltrate containing prominent nucleoli and lacking cytoplasm.5 Non-Hodgkin lymphoma, Burkitt lymphoma, and intermediate to high-grade B-cell tumors are most commonly associated with renal involvement, which is thought to result from hematogenous or direct spread of disease.4,5 Hodgkin lymphoma, on the other hand, less commonly involves the kidneys which is seen in less than 1% of patients.5 Primary renal lymphoma occurs in less than 1% of cases, and the etiology is unknown, since there is no lymphoid tissue in the kidneys.5 The lymphocytic infiltrate will typically spread and proliferate in the renal interstitium, without destruction of the nephrons.1,6 With time, infiltration can eventually lead to diffuse renal enlargement or formation of a discrete mass.1
Middle-aged and older patients, transplant recipients, and immunocompromised individuals are most commonly affected.5 Symptoms of renal lymphoma can include fever, night sweats, flank pain, hematuria, or even acute renal failure in the setting of advanced disease.5
Renal lymphoma can manifest in several ways on imaging. This includes bilateral discrete renal masses (most common), diffusely infiltrated and enlarged kidneys, solitary renal mass, perinephric space involvement, or direct spread of retroperitoneal disease.1,4–7
Multidetector row CT is the preferred imaging modality as it accurately characterizes the kidneys and optimally surveys the adjacent structures for involvement.5 The most important phase of contrast enhancement is the nephrographic phase, as the lesions can be subtle and blend in with the medulla on the corticomedullary phase.5 With the presentation of bilateral masses, there are soft tissue densities that are typically homogeneous (larger lesions can be heterogeneous) and hypoattenuating compared to the renal cortex.5 The lesions are typically hypoenhancing without distorting the renal contours.1,4,5 With diffuse infiltration, there is renal enlargement, diminished renal enhancement, and loss of corticomedullary differentiation in the arterial phase.1,5 There can be concomitant stretching of the collecting system, invasion into the renal sinus, or complete replacement of the renal parenchyma, resulting in an enlarged nonfunctioning kidney.5 Transitional cell carcinoma, medullary carcinoma, or pyelonephritis can have a similar presentation.5 A solitary lesion will usually be hypoenhancing to the renal parenchyma in the corticomedullary phase as opposed to clear cell renal cell carcinoma (RCC).5 It is noted that chromophobe and papillary renal cancers can similarly present as a mildly enhancing solitary mass, which may require a core biopsy to differentiate.5 Direct invasion from the retroperitoneum will appear as a large retroperitoneal mass extending into the kidneys or perinephric space, or as a mass displacing the kidneys.5 Occlusion of the renal arteries, veins, or inferior vena cava is rare.5,8 Isolated perinephric space involvement is less common and may present as a homogeneously enhancing shell of soft tissue compressing the renal parenchyma, as nodules in the perirenal space or as thickening of Gerota fascia.5
Ultrasound is not sensitive in the evaluation of renal lymphoma; nevertheless, it is important to be aware of possible findings, as it may be the first test ordered on the patient.5 Bilateral renal masses may seem homogeneous and hypoechoic, with little vascular flow on color or power Doppler.5 Solitary masses will have a similar appearance with possible posterior acoustic enhancement.5,6 Perinephric involvement will manifest as a varying amount of hypoechoic soft tissue around the kidney.5 With diffuse infiltration, ultrasound will demonstrate renal enlargement, effacement of the echogenic renal sinus fat, and heterogeneous echotexture.5
There is sparse literature regarding the MR appearance of renal lymphoma. We believe MR to be an excellent renal imaging modality, particularly for avoiding ionizing radiation, for patients with an iodinated contrast dye allergy, and for noncontrast examinations in patients with renal insufficiency.5 Lesions will typically be T1 hypointense and T2 isointense to hypointense to the renal cortex.5 Mild enhancement is usually seen in focal lymphoma lesions.5 Diffusion-weighted imaging (DWI) may show restricted diffusion.9,10 Diffusion-weighted imaging measures spontaneous Brownian motion of water molecules, which can be affected by the degree of cellularity and cell membrane integrity.11 In cases such as lymphoma or renal/urothelial tumors, diffusion will be restricted due to the high cellularity.11 In addition, calculated ADC values may be of use in differentiating certain types of tumors.11 In 2 separate studies, the mean ADC values of normal renal parenchyma were 2.18 to 2.30 (× 10 − 3 mm2/s), clear cell RCC was 1.23 to 1.70 (× 10 − 3 mm2/s), papillary RCC was 0.88 to 0.90 (× 10 − 3 mm2/s), and chromophobe RCC was 1.14 to 1.41 (× 10 − 3 mm2/s).12,13 In a study of 38 urothelial tumors by Akita et al,14 the mean ADC was 1.36 (× 10 − 3 mm2/s). Two separate studies state an ADC range of 0.64 to 0.76 (× 10 − 3 mm2/s) for lymphoma.15,16 Our case demonstrated an ADC value of 0.635 (× 10 − 3 mm2/s), which is in the range of reported ADC values for lymphoma and very different compared to renal and urothelial tumors.
Non-Hodgkin lymphoma commonly involves the kidneys and demonstrates focal hypoenhancing masses. Differential considerations include primary renal tumors, of which papillary and chromophobe types can be hypoenhancing, as well as urothelial tumors growing into the renal parenchyma. In presenting our case, we show the potential value of DWI in evaluating focal renal abnormalities. Although ADC values are similar for some primary renal tumors and urothelial tumors, they are reported to be noticeably lower for renal lymphoma, as our case demonstrates. There may still be significant overlap of ADC values in practice. Therefore, these values may be helpful, but should be used in context of all known clinical information in guiding management and further assessment. Tissue diagnosis remains an important consideration. Thus, DWI may facilitate differentiation between lymphoma and primary renal and urothelial tumors, although more studies would have to be performed to validate this.
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