You are in: eMedicine Specialties > Radiology > GENITOURINARY Oncocytoma, KidneyArticle Last Updated: Jul 3, 2007AUTHOR AND EDITOR INFORMATIONSection 1 of 12
  Author: Sanjeeva P Kalva, MD, Assistant Radiologist, Massachusetts General Hospital, Instructor in Radiology, Harvard Medical School, Department of Radiology, Massachusetts General Hospital Sanjeeva P Kalva is a member of the following medical societies: American Roentgen Ray Society and Radiological Society of North America Coauthor(s): Dushyant Sahani, MD, Clinical Instructor of Abdominal Radiology and Intervention, Harvard Medical School; Assistant Radiologist, Department of Abdominal Imaging and Intervention, Massachusetts General Hospital Editors: Steven Perlmutter, MD, FACR, Clinical Associate Professor, Radiology Residency Program Director, Radiology Medical Director, Department of Radiology, University Hospital at Stony Brook; Bernard D Coombs, MB, ChB, PhD, Consulting Staff, Department of Specialist Rehabilitation Services, Hutt Valley District Health Board, New Zealand; Arnold C Friedman, MD, FACR, Professor, Department of Radiology, University of Florida Professor of Radiology, Department of Radiology, Shands-Jacksonville Hospital; Robert M Krasny, MD, Consulting Staff, Department of Radiology, The Angeles Clinic and Research Institute; Eugene C Lin, MD, Consulting Staff, Department of Radiology, Virginia Mason Medical Center Author and Editor Disclosure Synonyms and related keywords: benign renal tumor, renal neoplasms, renal cell carcinomas, RCCs INTRODUCTIONSection 2 of 12
  BackgroundOncocytoma is the most common benign solid renal tumor.1 First described by Zippel in 1942,2 this tumor represents a distinct pathologic entity. In 1976, Klein and Valensi published their case series of patients with oncocytoma; the authors highlighted the benign course of the disease and its discrete pathologic features.3 PathophysiologyOncocytomas originate from the intercalated cells of the renal collecting duct. On gross pathologic examination, the tumors appear spherical and are large (average size, 7 cm),4 with a pseudocapsule. On cut sections, oncocytomas appear homogeneous, with a mahogany color—in contrast to yellow renal cell carcinomas (RCCs). A fleshy central scar, which is a characteristic finding of oncocytomas,5 may be observed in 33-54% of such tumors. Necrosis, hemorrhage, and calcification, however, are rare findings. On histologic examination, oncocytomas are composed of oncocytes, which are large cells with a granular eosinophilic cytoplasm that, on electron microscopy, show abundant mitochondria. The cells are most commonly arranged in sheets, or they can be arranged in a tubulocystic or combined pattern. The nuclei appear smooth and round, with a minimal degree of nuclear atypia. In less than 10% of cases, oncocytoma and chromophobe RCC may coexist.1, 6 A few genetic alterations have been reported in association with oncocytomas. These include a deletion of chromosome 1 and the sex chromosomes, as well as a balanced translocation involving the 11q13 region. FrequencyUnited StatesThe incidence of oncocytoma in the US is not clearly known, but this tumor accounts for approximately 3-7% of all renal neoplasms. About 2-12% of oncocytomas are multifocal, and 4-14% are bilateral.6 Mortality/Morbidity
SexThese tumors are more common in males than females, with a rate of 2-3:1, which is similar to that for RCC. AgeAt the time of resection of the tumor, the mean patient age is 62-68 years. AnatomyThe kidneys are retroperitoneal organs that are enclosed in a fibrous capsule and surrounded by perirenal fat. The anterior pararenal fascia separates the kidneys from the pancreas, and the posterior pararenal fascia demarcates the paraspinal muscles from the kidneys. The adrenal glands are located superomedially. Each kidney is supplied by a main renal artery that arises directly from the aorta. Multiple renal arteries are common, and these play an important role in nephron-sparing surgeries (partial nephrectomy). A single renal vein drains each kidney, and multiple renal veins are uncommon. Lymphatics from the kidney drain into the lymph nodes in the renal hilum, which in turn drain into nodes in the para-aortic region. Clinical DetailsApproximately 56-91% of the oncocytomas are incidentally detected on imaging studies that have been performed for another indication.6, 7, 8 However, 17-21% of affected patients present with symptoms such as hematuria, flank pain, and an abdominal mass. In patients who present with symptoms, hematuria is more common than mass-like findings. Preferred ExaminationComputed tomography (CT) scanning of the abdomen, combined with intravenous administration of iodinated contrast medium, is the examination of choice and the best modality for the evaluation of a solid renal mass. This technique assists in the detection and localization of the tumor, and CT scanning may help in characterizing the mass, especially if fat-containing lesions (eg, angiomyolipomas) are present. Additionally, staging of the tumor can be performed to classify the extent of the lesion, regional lymphadenopathy, vascular involvement, and metastases. CT scanning also helps in the detection of calcifications and in the differentiation of a complex cyst from a solid neoplasm. Limitations of TechniquesThe imaging characteristics of oncocytomas and RCCs overlap, and differentiating an oncocytoma from an RCC and other solid renal neoplasms is not always possible with ultrasonography, CT scanning, or magnetic resonance imaging (MRI). The presence of a central scar on CT scans or MRIs and a spoke-wheel pattern of vessels on angiograms are often suggestive of oncocytoma but are not entirely specific. DIFFERENTIALSSection 3 of 12
Renal Cell Carcinoma Other Problems to Be ConsideredRenal adenoma
RADIOGRAPHSection 4 of 12
FindingsPlain radiographic findings are nonspecific, and images may demonstrate a large, soft-tissue mass in the renal area with displacement of the fat planes. Calcification is rare. Excretory urography shows a large mass with a renal-contour abnormality and compression of the collecting system. Degree of ConfidenceThe degree of confidence is low for detecting oncocytomas with radiographs. False Positives/NegativesFalse-positive results may arise with any lesion that causes a renal-contour abnormality. Examples include renal cysts, any renal mass, and focal infections. In addition, any retroperitoneal tumor may have a similar appearance. False-negative findings are due to the small size of the tumor and the presence of overlapping bowel. CT SCANSection 5 of 12
FindingsOn nonenhanced CT scans, oncocytomas appear isoattenuating or slightly hyperattenuating relative to the kidney parenchyma. On contrast-enhanced CT scans that are obtained during the nephrographic phase, the mass appears less attenuating than the renal parenchyma. Oncocytomas are well encapsulated and have distinct margins, a smooth contour, and a homogeneous appearance. The tumors may range in size from 3 to 10 cm, and in symptomatic patients, the lesions are most often larger than 5 cm. A central hypoattenuating scar may be observed in 33% of cases, but this scar cannot be differentiated from the central necrosis commonly found in RCC. With the advent of multisection CT scanning, high-resolution thin sections through the kidneys may improve detection of the central scar. Calcification, necrosis, and hemorrhage are rare with oncocytomas. Typically, features of a malignant tumor—such as invasion or infiltration into the perinephric fat, collecting system, or vessels—are absent. Likewise, regional lymphadenopathy and metastases are not encountered in patients with oncocytoma. Occasionally, multifocal or bilateral tumors may be found. Degree of ConfidenceThe degree of confidence for detecting this tumor with CT scanning is high. However, the degree of confidence in differentiating an oncocytoma from an RCC is low. False Positives/NegativesDifferentiating an oncocytoma from an RCC and other solid renal tumors is not always possible. The presence of a central scar may help, but necrosis in RCC may mimic this finding. MRISection 6 of 12
FindingsOn nonenhanced T1-weighted MRIs, oncocytomas are well-defined, homogeneous masses. They may appear isointense to hypointense relative to the renal cortex. On T2-weighted images, the tumors are typically isointense to slightly hypointense; however, slight T2 hyperintensity has also been reported. When present, the tumor's scar may be seen as a hypointense, stellate area in the center of the lesion on T1- and T2-weighted MRIs. However, tumor necrosis, a common feature of malignant masses, appears hypointense on T1-weighted images and hyperintense on T2-weighted images. Rarely, the central scar may appear bright on T2-weighted images. After the intravenous administration of gadopentetate dimeglumine contrast material, oncocytomas show homogeneous enhancement, with a nonenhancing central scar. As discussed in the CT section above, features of an invasive tumor are absent. Gadolinium-based contrast agents (gadopentetate dimeglumine [Magnevist], gadobenate dimeglumine [MultiHance], gadodiamide [Omniscan], gadoversetamide [OptiMARK], gadoteridol [ProHance]) have recently been linked to the development of nephrogenic systemic fibrosis (NSF) or nephrogenic fibrosing dermopathy (NFD). For more information, see the eMedicine topic Nephrogenic Fibrosing Dermopathy. The disease has occurred in patients with moderate to end-stage renal disease after being given a gadolinium-based contrast agent to enhance MRI or MRA scans. As of late December 2006, the FDA had received reports of 90 such cases. Worldwide, over 200 cases have been reported, according to the FDA. NSF/NFD is a debilitating and sometimes fatal disease. Characteristics include red or dark patches on the skin; burning, itching, swelling, hardening, and tightening of the skin; yellow spots on the whites of the eyes; joint stiffness with trouble moving or straightening the arms, hands, legs, or feet; pain deep in the hip bones or ribs; and muscle weakness. For more information, see the FDA Public Health Advisory or Medscape. Degree of ConfidenceThe degree of confidence with MRIs for detecting this lesion is high, but this technique's degree of confidence is low for making a specific diagnosis. False Positives/NegativesDifferentiating an oncocytoma from an RCC and other solid renal tumors is not always possible. ULTRASOUNDSection 7 of 12
FindingsOn ultrasonography images, oncocytomas appear as well-defined, homogeneous, and hypoechoic to isoechoic masses. The central scar cannot be confidently identified on sonograms; however, when the scar is seen, especially in large lesions, it may appear echogenic. Color Doppler ultrasonography may show central radiating vessels. As discussed in the CT scanning and MRI sections above, the features of an invasive tumor are conspicuously absent. Degree of ConfidenceUltrasonography has low sensitivity and specificity in the detection and characterization of solid renal masses. However, this modality is useful for differentiating a solid mass from a complex cystic mass. False Positives/NegativesSmall isoechoic lesions may be missed on sonograms. Larger lesions cannot be differentiated from other renal masses. NUCLEAR MEDICINESection 8 of 12
FindingsScintigraphy is not routinely performed in the evaluation of renal tumors. On technetium-99m (99mTc) dimercaptosuccinic acid (DMSA) scans, the oncocytoma appears as a photopenic area that displaces the renal cortex and collecting system. On fluorodeoxyglucose (FDG) positron emission tomography (PET) scans, oncocytomas usually have less FDG uptake than RCCs. The amount of uptake is usually isointense relative to the renal parenchyma. However, oncocytomas can occasionally have uptake in the range similar to that of RCC uptake. Degree of ConfidenceThe degree of confidence with nuclear medicine is low. False Positives/NegativesFalse-positive results are due to renal cysts or other photopenic renal masses. False-negative results occur if the mass is small or if the lesion does not cause a renal-contour abnormality. ANGIOGRAPHYSection 9 of 12
FindingsWith the advent of CT scanning, routine angiography is not performed to diagnose renal masses. However, the classic angiographic findings for oncocytomas include a spoke-wheel arrangement of tumoral vessels, homogeneous tumoral contrast during the capillary phase, sharp demarcation from the kidney and surrounding areas, and a peritumoral halo (lucent-rim sign). Bizarre neoplastic vessels are conspicuously absent, which is in contrast to RCC. Degree of ConfidenceThe degree of confidence with angiography is low. False Positives/NegativesHypovascular lesions may result in false-negative results, and hypervascular lesions may mimic RCCs. INTERVENTIONSection 10 of 12
Percutaneous renal biopsy, fine-needle aspiration cytology, and frozen-section biopsy have been used with variable success for the differentiation of oncocytoma from RCC. Because of these limitations in preoperative pathologic evaluation, the consensus among clinicians is to treat a solid renal mass with a partial or total nephrectomy. Medical/Legal Pitfalls
Special Concerns
MULTIMEDIASection 11 of 12
REFERENCESSection 12 of 12
Article Last Updated: Jul 3, 2007 | ||||||||||||||||||||||||||||||||||||||||||
