FDG PET characterization of renal masses: preliminary experience

Role of positron emission tomography/computed tomography in the evaluation of renal cell carcinoma

Introduction:

Positron emission tomography (PET) is not a standard recommendation in most of the major guidelines for the evaluation of renal cell carcinoma (RCC). Earlier studies evaluating PET scan in patients with RCC have provided discordant results. However, with the advent of newer hybrid PET/computed tomography (CT) scanning systems, this modality has shown increased efficacy in the evaluation of primary renal masses along with the detection of extrarenal metastases, restaging recurrent RCC, and also in monitoring response to targeted therapy. We performed a systematic review of the existing literature on the role of PET scan in the evaluation of RCC.

Methodology:

We systematically searched the databases of PubMed/Medline, Embase, and Google Scholar to identify studies on the use of PET scan in RCC. Using Preferred Reporting Items for Systematic Reviews and Meta-analysis guidelines, 94 full-text articles were selected, of which 54 relevant articles were then reviewed, after a consensus by the authors.

Results:

Several studies have shown similar sensitivity and specificity of fluoro-2-deoxy-2-d-glucose-PET (FDG-PET) scan as compared to conventional CT scan for the initial diagnosis of RCC, and an improved sensitivity and specificity for the detection of metastases and recurrences following curative therapy. The PET scan may also play a role in predicting the initial tumor biology and pathology and predicting the prognosis as well as the response to therapy.

Conclusion:

The current guidelines do not recommend PET scan in the staging armamentarium of RCCs. However, FDG-PET scan is as efficacious, if not better than conventional imaging alone, in the evaluation of the primary and metastatic RCC, as well as in evaluating the response to therapy, due to its ability to pick up areas of increased metabolic activity early on. Newer tracers such as ^Ga68 prostate specific membrane antigen-labeled ligands may help in opening up newer avenues of theragnostics.

[18F-FDG positron emission tomography in non-oncological renal pathology: Current indications and perspectives]

Positron emission tomography combined with computed tomography (PET/CT) is a nuclear imaging technique which provides anatomical and functional information. PET/CT is increasingly used in non-oncological nephrology since conventional radiological approaches after injection of contrast agents are relatively contra-indicated in patients with chronic kidney disease (CKD). PET/CT after i.v. injection of ¹⁸F-fluoro-deoxy-glucose (FDG) is not toxic and is characterized by a high sensitivity. The level of irradiation (∼5mSv) is acceptable. CKD does not significantly influence tissue uptake of ¹⁸F-FDG. The purpose of the present review aims at detailing the non-oncological indications of ¹⁸F-FDG PET/CT in general nephrology and after kidney transplantation. Particularly, ¹⁸F-FDG PET/CT appears useful in the diagnosis of cyst infection in patients with autosomal dominant polycystic kidney disease, as well as in the characterization of retroperitoneal fibrosis. In kidney transplant recipients, ¹⁸F-FDG PET/CT may help in the diagnostic work-up of suspected acute rejection, thereby eventually avoiding unnecessary kidney transplant biopsy. Perspectives in ¹⁸F-FDG PET/CT imaging are discussed, including innovative approaches of image analysis.

Imaging for the diagnosis and response assessment of renal tumours

PURPOSE

Imaging plays a key role throughout the renal cell carcinoma (RCC) patient pathway, from diagnosis and staging of the disease, to the assessment of response to therapy. This review aims to summarise current knowledge with regard to imaging in the RCC patient pathway, highlighting recent advances and challenges.

METHODS

A literature review was performed using Medline. Particular focus was paid to RCC imaging in the diagnosis, staging and response assessment following therapy.

RESULTS

Characterisation of small renal masses (SRM) remains a diagnostic conundrum. Contrast-enhanced ultrasound (CEUS) has been increasingly applied in this field, as have emerging technologies such as multiparametric MRI, radiomics and molecular imaging with 99mtechnetium-sestamibi single photon emission computed tomography/CT. CT remains the first-line modality for staging of locoregional and suspected metastatic disease. Although the staging accuracy of CT is good, limitations in determining nodal status persist. Response assessment following ablative therapies remains challenging, as reduction in tumour size may not occur. The pattern of enhancement on CT may be a more reliable indicator of treatment success. CEUS may also have a role in monitoring response following ablation. Response assessments following anti-angiogenic and immunotherapies in advanced RCC is an evolving field, with a number of alternative response criteria being proposed. Tumour response patterns may vary between different immunotherapy agents and tumour types; thus, future response criteria modifications may be inevitable.

CONCLUSION

The diagnosis and characterisation of SRM and response assessment following targeted therapy for advanced RCC are key challenges which warrant further research.

Role of contrast-enhanced 18F-FDG PET/CT imaging in the diagnosis and staging of renal tumors

PURPOSE

The objectives of this prospective study are to compare intravenous contrast-enhanced (CE) fluorine-18-fluorodeoxyglucose (F-FDG) PET/computed tomography (CE F-FDG PET/CT) with conventional methods (CT/MRI) and to evaluate the relationship of maximum standardized uptake value (SUVmax) with Fuhrman grade in patients with renal tumors.

PATIENTS AND METHODS

A total of 62 patients [35 males and 27 females; mean age 55.8±12.7 (range: 27-81) years] were enrolled in the study. CE F-FDG PET/CT scanning included whole-body (early) and abdominal imaging (late) 1 and 2 h after intravenous F-FDG administration, respectively. SUVmax was calculated for primary tumors. CE F-FDG PET/CT and CT/MRI findings were compared with respect to primary tumors and staging.

RESULTS

The sensitivity of CE F-FDG PET/CT in primary tumor detection was 98%, which was very close to that of CT/MRI (100%). CE F-FDG PET/CT resulted in correct staging in 84% of the cases, compared with 68% of the cases with conventional methods (52 vs. 42 patients). SUVmax values of early PET for the primary tumors were significantly correlated with the Fuhrman grades (P<0.001). CE F-FDG PET/CT enabled the detection of synchronous tumors in four patients, one of which was incorrectly diagnosed as having metastasis by CT. Distant metastases were detected in 16 patients with CE F-FDG PET/CT and in 13 patients with routine conventional methods.

CONCLUSION

CE F-FDG PET/CT showed similar results compared with CT/MRI in the detection of primary tumors, but it was superior to conventional methods in the detection of metastasis and staging. Given the highly significant correlation between SUVmax values and the Fuhrman grading, CE F-FDG PET/CT may play a significant role in the evaluation of patient prognosis.

Imaging the renal mass: a historical review

A matter of months after Roentgen's landmark discovery in 1895, Roentgen's rays were focused on diseases and disorders of the urinary tract, specifically the kidney. At the dawn of the 20th century, urologists in the United States and around the world quickly recognized that by using a variety of metal stylets and radiopaque contrast agents, such as silver salts, the upper urinary tract, namely the ureter, pelvis, and calyces, could be depicted with radiography. Renal cysts and tumors were diagnosed on the basis of deformities in the kidney. Retrograde pyelography dominated the imaging evaluation of the kidney until the discovery of a safe intravenous method for urinary tract imaging (ie, intravenous pyelography). Pioneers and pathfinders in the field of contrast media development and radiologic procedures helped give radiologists the lead role in the work-up of renal masses, an area where urologists once held forth. The subspecialty of uroradiology was born in the middle of the 20th century. Intravenous urography, nephrotomography, and diagnostic angiography with pharmacologic manipulation followed by cyst or mass puncture and biopsy yielded unrivaled specificity for the diagnosis and staging of benign and malignant renal masses. The advent of cross-sectional and multiplanar imaging and the profound effects they had and continue to have on the discovery and characterization of renal masses has been detailed in the pages of Radiology since the 1920s. Ultrasonography, nuclear imaging, computed tomographic scanning, magnetic resonance imaging, and positron emission tomography each have made a claim to a part of the imaging algorithm of modern uroradiologic practice.

Standardized uptake values highly correlate with tumor size and Fuhrman grade in patients with clear cell renal cell carcinoma

BACKGROUND

We investigated the correlation between standardized uptake value (SUVmax), tumor size and Fuhrman grade in patients with renal cell carcinoma (RC).

MATERIALS AND METHODS

We retrospectively analyzed the data of 54 patients with clear cell renal cell carcinoma histopathologically diagnosed who underwent fluorine-18 fluoro-2 deoxyglucose positron emission tomography/computed tomography (F-18 FDG PET/CT) between January 2005 and March 2014.

RESULTS

Avarage tumor sizes were 5.64±1.85, 6.85±2.24 and 7.98±2.45 in low, medium and high SUVmax groups, respectively. The Spearman's correlation coefficient between the tumor size and SUVmax was 0.385 (p=0.004) and between the Fuhrman grade and SUVmax was 0.578 (p<0.001).

CONCLUSIONS

SUVmax appears highly correlated with tumor size and Fuhrman grade in patients with histopathologically confirmed clear cell RC. Multicenter studies are needed to provide larger series for more accurate results.

Diagnosis of complex renal cystic masses and solid renal lesions using PET imaging: comparison of 11C-acetate and 18F-FDG PET imaging

PURPOSE

The study aims to assess the usefulness of PET with C-acetate and F-FDG to differentiate renal cell carcinoma (RCC) from complicated renal cysts.

METHODS

Thirty-one patients were enrolled, 14 patients with complicated renal cysts (12 with Bosniak III and 2 with Bosniak IV) and 17 patients with 19 solid renal tumors. The patients underwent both C-acetate PET and FDG PET. Nephrectomy or partial nephrectomy was performed after the PET scans.

RESULTS

In 29 patients, 32 renal lesions were diagnosed as RCC. Twenty-three of the 32 RCCs (72%) had positive C-acetate PET findings, whereas only 7 FDG PET studies were positive (22%). Considering the relationship between tumor size measured by macroscopic appearance of resected tumors and PET results, 22 of 25 (88%) tumors more than 1.5 cm showed positive C-acetate PET findings. In 12 patients with Bosniak III renal cysts, 10 renal lesions were diagnosed as RCC. In this subgroup, 5 of the 10 RCCs (50%) had positive C-acetate PET findings, whereas 2 RCCs (20%) had positive FDG PET findings. None of the cases with benign findings had positive C-acetate PET or FDG PET scans.

CONCLUSIONS

C-acetate PET demonstrates a pronounced increase in tracer uptake in RCC, especially in renal tumors more than 1.5 cm, and displays a higher sensitivity than FDG PET. These preliminary data show that C-acetate may be a useful PET tracer to exclude RCC in complex renal cysts.

New modalities for evaluation and surveillance of complex renal cysts

PURPOSE

The increased use of abdominal imaging has led to more frequent detection of incidental renal cysts. Since the inception of the Bosniak classification system, management of Bosniak I, III and IV cysts has been clearly defined, while evaluation and management of Bosniak II and IIF cysts have remained a clinical dilemma. Discussions of new imaging modalities are becoming increasingly prevalent in the radiological literature. In this context we performed a comprehensive review of the recent literature on complex renal cysts focusing on new imaging modalities, surveillance strategies and biopsy.

MATERIALS AND METHODS

We performed a comprehensive literature review of articles published from January 1, 1998 through December 31, 2013 via MEDLINE(®), EMBASE and the Cochrane Collection using a predetermined search strategy. All studies included were performed in humans older than 18 years, were written in English and had an abstract available for review. We grouped studies into 1 of 5 categories, ie computerized tomography, magnetic resonance imaging, ultrasound, biopsy and surveillance.

RESULTS

While computerized tomography and magnetic resonance imaging with and without contrast enhancement remain the gold standard to evaluate cystic lesions of the kidney, diffusion-weighted magnetic resonance imaging and contrast enhanced ultrasound have surfaced as new tools for assessment of complex cysts. Comparative effectiveness studies on these new imaging modalities are limited. Image guided biopsy has increasingly been shown to be useful for evaluation of intermediate (Bosniak II and IIF) complex cysts. We found few studies providing guidance on the duration and/or intensity of surveillance required for intermediate complex renal cysts.

CONCLUSIONS

Although new and enhanced techniques are in development and may be useful in the future management of complex renal cysts, there is a paucity of data regarding the value of these new techniques. Future research should focus on surveillance of intermediate complex renal cysts, particularly on the ideal frequency and type of imaging required.

PET/CT appearance of acute pyelonephritis

An 18-year-old male patient with a history of Ewing sarcoma originally involving the right ilium was evaluated with an FDG PET/CT scan to evaluate the effect of salvage therapy after standard treatment failed and disease progressed to involve the right T12 pedicle. Autologous stem cell transplantation and cyberknife therapy resulted in mixed tumor response, with incidental note made of prominent areas of cortical FDG avidity in the right kidney. These regions demonstrated focal hypoenhancement on the corresponding diagnostic contrast-enhanced CT, which additionally demonstrated peripheral enhancement spanning the length of the right ureter. Clinical workup produced a diagnosis of acute pyelonephritis.

Is The Value of FDG PET/CT In Evaluating Renal Metastasis Underestimated? A Case Report And Review of The Literature

Contrast-enhanced CT or MRI are used as a gold standard imaging modalities in the detection and characterization of renal masses. On the other hand, the role of FDG PET/CT in evaluating primary or metastatic cancers of the kidney is limited due to the excretion of FDG through urinary tract. We reported the FDG PET/CT of a lung cancer patient with multiple metastases in both kidneys which were missed in previous PET/CT, and underestimated on sequential diagnostic abdominal CT study.

CONFLICT OF INTEREST

None declared.

Metastatic sarcomatoid carcinoma to liver and bone marrow in renal transplant recipient: due to exacerbation of quiescent renal cancer? A case report

Sarcomatoid carcinoma is a rare tumor with rapid growth and a poor prognosis. A 60-year-old man underwent kidney transplantation. Three months after transplantation, multiple tumors were found in the liver and bone, and the patient died several days later. Pathological examination of liver and bone marrow biopsies revealed metastatic sarcomatoid carcinoma. Pretransplantation, the patient's workup was positive only for mild thrombocytopenia and a complicated cyst with peripheral rim calcification (Bosniak IIF) in the right kidney. Retrospectively, we found the abdominal computed tomography film, which had been examined at another hospital 6 years previously. The calcified complicated cyst was a 3-cm enhancing solid mass in the right kidney, suggesting renal cell cancer. It is possible that the cancer developed from the calcified complicated cyst. In this case, immunosuppressants may have altered malignant cell proliferation, invasion, and the form of metastasis.

Metabolic features of clear-cell renal cell carcinoma: mechanisms and clinical implications

Central to the malignant behaviour that endows cancer cells with growth advantage is their unique metabolism. Cancer cells can process nutrient molecules differently from normal cells and use it to overcome stress imposed on them by various therapies. This metabolic conversion is controlled by specific genetic mutations that are associated with activation of oncogenes and loss of tumour suppressor proteins. Understanding these processes is important as it can lead to the discovery of biomarkers that can predict the aggressiveness of the disease and its response to therapy, and even more importantly, to the development of novel therapeutics. A classic tumour in this respect is clear-cell renal cell carcinoma (RCC). In this review, we will begin with a brief summary of normal cellular bioenergetic pathways, which will be followed by a description of the characteristic metabolism of glucose and lipids in clear-cell RCC cells and its clinical implications. Data relating to the potential effect of dietary nutrients on RCC will also be reviewed along with potential therapies targeted at interrupting specific metabolic pathways in clear-cell RCC.

Role of FDG PET/CT in imaging of renal lesions

Focal incidental renal lesions are commonly encountered on positron emission tomography (PET)/computed tomography (CT) imaging. The vast majority of these lesions are benign. However, the interpretation of renal lesions can be problematic if the imaging criteria of simple cysts are not met. Limited literature exists on the characterisation of renal masses with metabolic imaging. The purpose of this article is to focus on the imaging features of benign and malignant renal masses with PET/CT. The lesions discussed include renal cyst, angiomyolipoma, oncocytoma, renal cell carcinoma, renal metastases and other infiltrating neoplastic processes affecting the kidney. Both the anatomical and metabolic features which characterise these benign and malignant entities are described. We emphasise the importance of viewing the CT component to identify the typical morphological features and discuss how to best use hybrid imaging for management of renal lesions. Metabolic imaging has a promising role in the imaging of renal lesions and can help prevent unnecessary biopsies and ensure optimal management of suspicious lesions.

Functional imaging of renal cell carcinoma

The incidence of early and advanced-stage renal cell carcinoma (RCC) is increasing. Methods of diagnosing, staging and evaluating tumor burden that are more accurate and reliable than the currently available options are needed in order to identify RCC at a stage at which it is curable and to accurately determine the response to treatment. Functional imaging, particularly with combined PET-CT, might improve accuracy of detection and provide essential information that has been unavailable to date. This approach is against a background in which targeted therapies for metastatic RCC have entered clinical practice in the past few years, further highlighting the importance of accurate imaging for patient selection and for monitoring response to treatment. We outline the current clinical status of functional imaging in RCC using PET-CT, which allows simultaneous capture and co-registration of functional and anatomical data. New radiotracers and approaches-including radiolabeled monoclonal antibodies and imaging of tumor hypoxia-are touched on, and areas of future research discussed.

The potential clinical value of FDG-PET for recurrent renal cell carcinoma

PURPOSE

The clinical value of positron emission tomography (PET) using (18)F-fluorodeoxyglucose (FDG) for follow-up or suspected recurrence of renal cell carcinoma (RCC) has not been fully evaluated. The purpose of this study was to assess the diagnostic performance of FDG-PET for postoperative assessment in patients with RCC.

METHODS

We reviewed 28 scans in 23 patients who had undergone FDG-PET scans after surgery for RCC. Diagnostic accuracy of visually interpreted PET was evaluated based on final diagnoses obtained histologically or by clinical follow-up at least 6 months. Also, additional information over CT, influence on treatment decisions, and the accuracy of FDG uptake as a predictor of survival were assessed.

RESULTS

Recurrence of renal carcinoma was histologically (n=15) or clinically (n=6) confirmed in 21 of 28 cases. Overall, the sensitivity, specificity, and diagnostic accuracy using FDG-PET were 81%, 71%, and 79%, respectively. In papillary RCC, the sensitivity was 100%; however, that was 75% in clear cell RCC in patient-basis. PET correctly detected local recurrence and metastases in all cases in the peritoneum, bone, muscle and adrenal gland. Additional information was obtained from scans in 6 cases (21%), which influenced therapeutic management in 3 cases (11%). Cumulative survival rates over 5 years in the PET-positive vs. the PET-negative group were 46% vs. 83%, respectively (p=0.17).

CONCLUSIONS

FDG-PET would be useful for postoperative surveillance in patients with RCC, although its impact on treatment decisions may be limited. Further investigations are necessary to conclude whether PET has a prognostic value.

Molecular imaging of renal cell carcinoma

The recent identification of agents that have significantly influenced the therapy of clear cell renal carcinoma and the decreasing size of renal masses, usually detected serendipitously, have led to a resurgence in imaging for this condition. Although structural methods continue to be used routinely for identification of renal masses, functional and molecular techniques are showing considerable promise in their ability to characterize unique features of the renal cancer phenotype. This article discusses the evolving role of molecular imaging in the evaluation of renal cancer, including current and future applications.

Molecular Positron Emission Tomography and PET/CT Imaging in Urological Malignancies

OBJECTIVES

Positron emission tomography (PET) provides unique insights into molecular pathways of diseases. PET using [F-18]-fluorodeoxyglucose (FDG) has gained increasing acceptance for the diagnosis, staging, and treatment monitoring of various tumour types. The aim of this review is to provide an update on the current status of molecular PET and PET/CT imaging in urological malignancies.

METHODS

The current literature on PET and PET/CT imaging was reviewed and summarized for prostate cancer, bladder cancer, renal cell carcinoma, and germ cell tumours.

RESULTS

Depending on the radiotracer used, PET offers diagnostic information based on glucose, choline or amino acid metabolism and has also been applied to imaging tumour cell proliferation and tissue hypoxia in urological malignancies. The diagnostic performance of FDG-PET is hampered by the renal excretion of FDG and by the low metabolic activity often seen in tumours such as prostate cancer. However, new PET tracers including radiolabelled choline and acetate may offer an alternative approach. There is consistent evidence that FDG-PET provides important diagnostic information in detecting metastatic and recurrent germ cell tumours and it might offer additional information in the staging and restaging of bladder and renal cancer.

CONCLUSIONS

Although PET imaging has been shown to be a clinically useful tool, its application in urological malignancies still needs to be fully determined by larger prospective trials. The introduction of novel PET radiopharmaceuticals along with the new technology of PET/CT will likely change the future role of molecular imaging in urological malignancies.

Imaging of kidney cancer

Advances in molecular genetics have expanded the understanding of renal cell tumors. Now it is understood that renal cortical tumors are a family of neoplasms with distinct cytogenetics and molecular defects, unique histopathologic features, and different malignant potentials. Imaging contributes to clinical management of patients with renal tumors in providing diagnostic information for tumor detection, characterization, staging, treatment planning, and follow-up.

2-Deoxy-2-[F-18]fluoro-D-glucose-Positron Emission Tomography in Characterization of Solid Renal Masses

The present study was aimed to evaluate the ability of 2-deoxy-2-[F-18]fluoro-D -glucose (FDG)-positron emission tomography (PET) in characterization of solid renal masses visualized by computed tomography (CT)/magnetic resonance imaging (MRI) in patients with suspected or known malignancies.

METHODS

Twenty-eight solid renal masses (20 unilateral and four bilateral, Size ranges, 1.0-8.4 cm) were evaluated in 24 patients. The results were correlated with histopathology in 15 patients, and clinical follow-up and conventional imaging in all patients.

RESULTS

Of the 28 solid renal masses, 10 were primary (nine malignant, one benign) and 18 were metastatic renal tumors. FDG-PET accurately depicted 23 of 27 (85%) malignant renal masses. Of the 10 primary renal tumors, FDG-PET was true positive in eight of nine (89%), true negative in one and false negative in one. The maximum and average standardized uptake values (SUVs) for FDG positive primary renal malignant tumors were 7.9 +/- 4.9 and 6.0 +/- 3.6, respectively. In addition to the characterization of primary tumors, FDG-PET was valuable in primary staging and altered treatment in 30% of patients (three of 10). Of the 18 metastatic renal masses, FDG-PET was positive in 15 (83%) masses. The maximum and average SUVs of metastatic renal masses were 6.1+/- 3.4 and 4.7+/- 2.8, respectively. There was no significant difference in maximum and average SUVs between primary and metastatic renal masses (p=0.3 and p=0.3).

CONCLUSION

Despite the physiological excretion of FDG by the kidneys, FDG-PET can be employed effectively in characterization of solid renal masses in patients with suspected or known malignancies. We propose that FDG-PET could be useful as a complimentary modality to conventional imaging in these patients.

Noninvasive in vivo measurement of vascular inflammation with F-18 fluorodeoxyglucose positron emission tomography

BACKGROUND

Fluorine 18 fluorodeoxyglucose (FDG) has been shown to accumulate in inflamed tissues. However, it is not known whether vascular inflammation can be measured noninvasively. The aim of this study was to test the hypothesis that vascular inflammation can be measured noninvasively by use of positron emission tomography (PET) with FDG.

METHODS AND RESULTS

Inflamed atherosclerotic lesions were induced in 9 male New Zealand white rabbits via balloon injury of the aortoiliac arterial segment and exposure to a high cholesterol diet. Ten rabbits fed standard chow served as controls. Three to six months after balloon injury, the rabbits were injected with FDG (1 mCi/kg), after which aortic uptake of FDG was assessed (3 hours after injection). Biodistribution of FDG activity within aortic segments was obtained by use of standard well gamma counting. FDG uptake was also determined noninvasively in a subset of 6 live atherosclerotic rabbits and 5 normal rabbits, via PET imaging and measurement of standardized uptake values over the abdominal aorta. Plaque macrophage density and smooth muscle cell density were determined by planimetric analysis of RAM-11 and smooth muscle actin staining, respectively. Biodistribution of FDG within nontarget organs was similar between atherosclerotic and control rabbits. However, well counter measurements of FDG uptake were significantly higher within atherosclerotic aortas compared with control aortas (P < .001). Within the upper abdominal aorta of the atherosclerotic group (area of greatest plaque formation), there was an approximately 19-fold increase in FDG uptake compared with controls (108.9 +/- 55.6 percent injected dose [%ID]/g x 10(3) vs 5.7 +/- 1.2 %ID/g x 10(3) [mean +/- SEM], P < .001). In parallel with these findings, FDG uptake, as determined by PET, was higher in atherosclerotic aortas (standardized uptake value for atherosclerotic aortas vs control aortas, 0.68 +/- 0.06 vs 0.13 +/- 0.01; P < .001). Moreover, macrophage density, assessed histologically, correlated with noninvasive (PET) measurements of FDG uptake (r = 0.93, P < .0001). In contrast to this finding, FDG uptake did not correlate with either aortic wall thickness or smooth muscle cell staining of the specimens.

CONCLUSION

These data show that FDG accumulates in macrophage-rich atherosclerotic plaques and demonstrate that vascular macrophage activity can be quantified noninvasively with FDG-PET. As such, measurement of vascular FDG uptake with PET holds promise for the noninvasive characterization of vascular inflammation.

Positron emission tomography in uro-oncology

Positron emission tomography (PET) in uro-oncology has been one of the slowest areas to develop. There are problems because of the excretion of tracer through the renal tract. Its use in prostate cancer has generally being disappointing, with PET being unable to differentiate malignancy from benign prostatic hypertrophy. In more advanced disease and in the search for the site of recurrence, PET can be of more use. Also, new tracers may prove to be more effective. PET has been shown to be of value in testicular cancer, particularly in defining recurrent disease in residual masses and in patients with raised markers. There is a clear place for PET in some of these cases. Early studies at staging are promising but more work is required to define its exact place. In renal and bladder cancer, PET may be a useful adjunct to conventional imaging in difficult cases and may assist in local staging. In all tumours it is valuable to differentiate fibrosis from recurrent disease in the treatment bed, an area of difficulty for CT/MR.

PET in the management of urologic malignancies

FDG-PET has a limited role in diagnosis of prostate cancer mainly because of the low uptake of FDG in the tumor and normal excretion of FDG through urine. FDG-PET has shown some promise in the assessment of lymph nodes and bone metastases. There is a large degree of variability when FDG-PET is compared with bone scintigraphy. New C11-labeled radiotracers (acetate, choline, and methionine) have shown promising initial results but further studies are required to determine their role in such settings. These radiotracers provide a unique opportunity for dynamic, multitracer, and quantitative studies, which improve the sensitivity and specificity on PET in this population. Short half-lives and of C-11, however with the limits to their use requires an on-site cyclotron. Recent synthesis schemes with [18F]-labeling, however, may overcome this limitation. FDG-PET has a significant potential to assist with the diagnosis and management of testicular cancer. PET has been most useful in defining the presence or absence of disease in patients with residual masses. PET has shown promising results for the initial diagnosis of this cancer, but further for studies ar required to determine its role in the management of this malignancy. PET can be used in conjunction with conventional imaging techniques to diagnose retroperitoneal masses in patients with primary testicular cancer. FDG-PET has shown very encouraging results in a limited number of studies, and has also demonstrated a good sensitivity for initial staging. FDG-PET seems to be superior to conventional imaging modalities for detecting local disease and recurrence, and distant metastases.

Positronenemissionstomographie (PET) zur Diagnostik und zum Therapiemonitoring bei urologischen Tumoren

Positron emission tomography (PET) using ((18)F)2-fluoro-D-2-desoxyglucose (FDG) has been shown to be a highly sensitive and specific imaging modality in the diagnosis of primary and recurrent tumors and in the control of therapies in numerous non-urologic cancers. It was the aim of this review to validate the significance of PET as a diagnostic tool in malignant tumors of the urogenital tract. A systematic review of the current literature concerning the role of PET for malignant tumors of the kidney, testicles, prostate, and bladder was carried out. The role of FDG PET for renal cell cancer can be seen in the detection of recurrences after definitive local therapy and metastases. The higher sensitivity of PET in comparison to other therapeutic modalities (CT, ultrasound, MRI) in recurrent and metastatic renal cell cancer suggests a supplemental role of this diagnostic procedure to complement other imaging modalities.The clinical value of PET is established for the identification of vital tumor tissue after chemotherapy of seminomatous germ cell tumors. This diagnostic method has little significance for primary tumor staging and diagnosis of non-seminomatous germ cell tumor because of the high probability of false-negative results in adult teratomas. FDG PET is not sensitive enough in the diagnosis of primary or recurrent tumors in prostate or bladder cancer. Also PET did not prove to be superior to conventional bone scintigram in the detection of mostly osteoblastic metastases in prostate cancer. The recent use of alternative tracers, which are partly not eliminated by urinary secretion (acetate, choline) has increased the sensitivity and specificity of PET also in this tumor entity so that further clinical investigations are needed to validate these technical modifications in their significance for this imaging modality. PET appears to be sufficiently evaluated only for the diagnostic follow-up of patients with seminomatous germ cell tumors after chemotherapy to regard it is the diagnostic tool of first choice. For all other tumors of the urogenital tract this proof is still awaited.

Clinical use of fluorodeoxyglucose F 18 positron emission tomography for detection of renal cell carcinoma

PURPOSE

We evaluate the role of fluorodeoxyglucose F 18 positron emission tomography (PET) in patients with renal cell carcinoma (RCC) by retrospective review. To our knowledge this series is the largest reviewing the use of PET in patients with RCC.

MATERIALS AND METHODS

A total of 66 patients who underwent 90 PET scans for suspected or known RCC were identified. Dictated reports of PET, chest computerized tomography (CT), abdominal/pelvic CT and bone scan were examined with confirmation of results by histopathology or followup of at least 1 year. The accuracies of PET and conventional imaging modalities were compared.

RESULTS

PET exhibited a sensitivity of 60% and specificity of 100% for primary RCC tumors (abdominal CT demonstrated 91.7% sensitivity and 100% specificity). For retroperitoneal lymph node metastases and/or renal bed recurrence, PET was 75.0% sensitive and 100.0% specific (92.6% sensitivity and 98.1% specificity for abdominal CT). PET had a sensitivity of 75.0% and a specificity of 97.1% for metastases to the lung parenchyma compared to 91.1% and 73.1%, respectively, for chest CT. PET had a sensitivity of 77.3% and specificity of 100.0% for bone metastases, compared to 93.8% and 87.2% for combined CT and bone scan. In 39 scans (32 patients) PET failed to detect RCC lesions identified by conventional imaging.

CONCLUSIONS

The role of fluorodeoxyglucose F 18 PET in the detection of RCC is limited by low sensitivity. With superior specificity PET may have a complementary role as a problem solving tool in cases that are equivocal on conventional imaging.

PET Radioimmunoscintigraphy of Renal Cell Cancer Using 89Zr-Labeled cG250 Monoclonal Antibody in Nude Rats

INTRODUCTION

With the introduction of positron-emitting radionuclides with half-lifes in days, such as 89Zr and 124I, radioimmunoscintigraphy (RIS) with positron-emitter-labeled monoclonal antibodies (moAbs) becomes feasible. RIS, using positron emission tomography (immuno-PET), combines the specific localization of an antibody with the high resolution of a PET camera. In the present study, scintigraphic tumor imaging using chimeric moAb G250 labeled with 89Zr (immuno-PET) or 111In (RIS), and [18F]FDG-(PET) was explored in rats with s.c. renal cell carcinoma (RCC) tumors.

METHODS

Nude rats (6-8 rats per group) with s.c. SK-RC-52 tumors were i.v. injected with 4 MBq 111InDTPA-cG250, 20 MBq 89Zr-Df-cG250 or 4 MBq [18F]FDG. Planar 111In-DTPA-cG250 images were obtained 5 minutes, and 24, 48, and 72 hours postinjection (p.i.). 3D PET imaging was performed 5 minutes, and 24, 48, and 72 hours after a 89Zr-Df-cG250 injection and 1 hour after a [18F]FDG injection using a Siemens ECAT EXACT PET camera. Rats were killed after the last imaging session, and the uptake of the radiolabel in the dissected tissues was determined.

RESULTS

Both radiolabeled antibody preparations were stable during 4 days of incubation in serum at 37 degrees C, and the immunoreactivity was preserved. Two (2) days after injection, s.c. tumors (100 mg) were clearly visualized, both with 89Zr-Df-cG250 and 111In-DTPA-cG250. Tumors were not visualized with [18F]FDG (uptake in tumor of 0.5 +/- 0.1 %ID/g, 1 hour p.i.). The biodistribution experiments showed an identical uptake in the tumor for both 89Zr-Df-cG250 and 111In-DTPA-cG250 at 3 days p.i. (5.0 +/- 2.4 and 4.9 +/- 2.9 %ID/g, respectively). Blood levels at 3 days p.i. were also identical (1.4 +/- 0.4 versus 1.7 +/- 0.7 %ID/g), and no significant differences were found in the biodistribution of normal tissues between the two radiolabeled cG250 preparations.

CONCLUSION

The cG250 antibody can be stably labeled with the positron-emitter 89Zr, while preserving the immunoreactivity of the moAb. In this rat model, the in vivo biodistribution of 89Zr-Df-cG250 was identical to that of 111In-DTPA-cG250. Immuno-PET of RCC is feasible with 89Zr-cG250, and relatively small tumors could be visualized, even without a dedicated PET camera for small animals.

CT/MRI in staging renal cell carcinoma

Renal cell carcinoma (RCC) is the eighth most common malignancy. It accounts for approximately 3% of newly diagnosed cancers and has been reported to occur in 11 out of 100000 individuals. The incidence of RCC has increased by 40% in the USA from 1974 to 1990. There appears to be a true increase in the incidence of RCC over and above that attributable to the increased number detected by abdominal cross-sectional imaging. This increase has been accompanied by improved 5-year survival as the tumors detected by imaging are diagnosed at an earlier stage when they are still resectable. The male to female ratio is approximately 2:1; the majority present in the fifth to seventh decade of life and the racial distribution is equal. The majority of cases occur sporadically, but predisposing factors can sometimes be identified. RCC occurs in about 36% of patients with von Hippel–Lindau disease and invasive RCC is three to six times more common among long-term dialysis patients than in the general population.

Efficiency of [(18)F]FDG PET in characterising renal cancer and detecting distant metastases: a comparison with CT

The purpose of this study was to assess the efficiency of fluorine-18 fluoro-2-deoxyglucose (FDG) positron emission tomography (PET) in the characterisation and primary staging of suspicious renal masses, in comparison with computed tomography, the current standard imaging modality. Fifty-three FDG PET studies were performed within the framework of a prospective study: 35 for both characterisation and staging of a suspicious mass, and 18 for staging early after surgical removal of a renal cancer. In the characterisation of renal masses, a high rate of false negative results was observed, leading to a sensitivity, specificity and accuracy of 47%, 80% and 51% respectively, versus 97%, 0/5 and 83% respectively for CT. FDG PET detected all the sites of distant metastasis revealed by CT, as well as eight additional metastatic sites, leading to an accuracy of 94% versus 89% for CT. However, 36/53 patients (68%) did not have any distant metastasis on either CT or on PET. All but one of these patients had a low Fuhrman histological grade and a limited local stage (< or =pT2). We conclude that FDG PET does not offer any advantage over CT for the characterisation of renal masses but that it appears to be an efficient tool for the detection of distant metastasis in renal cancer. However, our data suggest that a selection process could be implemented to determine which patients should undergo PET. FDG PET could be performed in the event of a solitary metastasis or doubtful images on CT. Selection could also be based on adverse histological findings from nephrectomy specimens in order to perform staging early after nephrectomy.

Positron emission tomography for urological tumours

For urological tumours, positron emission tomography (PET) is currently most useful in testicular cancer. In patients with residual masses or raised marker levels after treatment, PET is both sensitive and specific for detecting recurrent disease, at suspected and unsuspected sites. Although fewer studies are available it also appears to be useful for staging at diagnosis, although this requires further investigation. Prostate cancer imaging has been more variable, with studies showing that PET cannot reliably differentiate between tumour and hypertrophy. It is not as good as a bone scan for defining bone metastases. In renal cancer, PET can be used to define the primary tumour, providing better staging of local recurrence than computed tomography (CT), and to define metastatic disease. There are few studies in bladder cancer, and despite excretion of the tracer via the bladder in early studies, it has better results than CT or magnetic resonance imaging for local staging; again it can detect metastases. Overall, the place of PET in urological tumours is developing, with the strongest areas undoubtedly being testicular and renal cancer. Tracers other than fluorodeoxyglucose are being examined and are providing further information.

131 I-cG250 monoclonal antibody immunoscintigraphy versus [18 F]FDG-PET imaging in patients with metastatic renal cell carcinoma: a comparative study

The aims of this study were to establish the percentage of metastatic renal cell carcinoma (RCC) lesions detected by radioimmunoscintigraphy (RIS) with the chimeric monoclonal antibody 131I-cG250 versus positron emission tomography (PET) with 18F-labelled deoxyglucose ([18F]FDG), and to evaluate the use of these radionuclide imaging modalities compared with routinely used imaging techniques. Twenty patients with metastatic RCC disease were examined with [18F]FDG-PET and 131I-cG250 RIS within 1 week. Total body gamma camera images were obtained up to 120h after injection of 232MBq 131I-cG250. Total body PET scanning was performed 45-60 min after intravenous injection of 370MBq [18F]FDG. Nuclear medicine techniques were compared to routine imaging procedures. Routine imaging modalities revealed a total of 79 metastases. [18F]FDG-PET and 131I-cG250 RIS detected 33 previously unknown metastases, of which 32 were [18F]FDG positive and seven were 131I-cG250 positive. Of the 112 tumour lesions that were documented, [18F]FDG-PET detected 69% (77 out of 112), whereas 131I-cG250 RIS detected only 30% (34 out of 112). In conclusion, [18F]FDG-PET is superior to 131I-cG250 RIS in detecting metastases in patients with metastatic RCC, and therefore seems a promising tool for (re)staging patients with RCC. The usefulness of RIS with a diagnostic dose of 131I-cG250 seems to be restricted to selecting patients for radioimmunotherapy with 131I-cG250.

Positron emission tomography in urological malignancy

Positron emission tomography is a unique imaging modality with the capability of studying regional metabolism. The major clinical applications of positron emission tomography have been in the detection of brain, breast, cardiac, lung and colorectal tumours, as well as the evaluation of coronary artery disease by imaging the metabolism of heart muscle. In the field of urology, positron emission tomography has been evaluated in the relevant malignancies with promising results in certain areas and disappointing results in others. This article attempts to summarize recent advances in positron emission tomography scanning with regards to urological malignancy. At this stage positron emission tomography scanning is capable of visualizing urological tumours and associated lymph nodes and distal metastatic sites. However, its use is severely limited by the excretion of the most commonly used radioisotope via the urinary tract, making pelvic imaging particularly unrewarding. It is, however, undoubtedly capable of diagnosing malignancy in soft tissue masses or lymph nodes before these changes become apparent on conventional cross-sectional imaging modalities (computerized tomography or magnetic resonance imaging). Larger studies are required before it can be advocated for clinical use in the field of urology.

Imaging renal masses

Imaging plays a crucial role in the detection, characterization, and post-operative follow-up of renal masses. With rapidly advancing technology, imaging techniques are continuously evolving. This review will discuss the current modalities and techniques available for renal imaging, and recent developments.

Evaluation of pseudoenhancement of renal cysts during contrast-enhanced CT

OBJECTIVE

The purpose of our study was to evaluate renal cyst pseudoenhancement during helical CT in a phantom model and in patients.

MATERIALS AND METHODS

Iodine baths containing water-filled spheres and cylinders were constructed to simulate cysts in enhancing renal parenchyma. Iodine concentration, cyst size and location, collimation, and peak kilovoltage were varied and cyst attenuation was measured. Data were analyzed with the mixed linear models and Mantel-Haenszel tests. Subsequently, a paired t test compared CT attenuation values before and after contrast material enhancement in 40 patients with 68 renal cysts (radiographic stability >3 months).

RESULTS

The attenuation values of phantom cysts increased when placed in a contrast media bath (p = 0.001). The increase in attenuation values became more pronounced with increasing iodine concentrations, decreasing peak kilovoltage, and smaller sphere sizes. In patients, mean cyst attenuation increased 3.4 +/- 6.2 H after administration of contrast material (p = 0.00002). The attenuation did not increase more than 10 H in any of the 37 cysts larger than 2 cm found in patients. Eight (26%) of the 31 cysts smaller than 2 cm found in patients increased by at least 10 H.

CONCLUSION

In a phantom model, at simulated physiologic levels of renal enhancement, cysts may pseudoenhance by more than 10 H. Similarly, in patients, cysts may also pseudoenhance; however, most pseudoenhancement does not exceed 10 H. In patients, pseudoenhancement of at least 10 H is more likely in cysts smaller than 2 cm.