Percutaneous Ablation of T1 Renal Masses: Comparative Local Control and Complications after Radiofrequency and Cryoablation.

The efficacy and complication rates of percutaneous radiofrequency ablation (RFA) and cryoablation (CA) in the treatment of T1 renal masses in two Northern Italy hospitals were retrospectively investigated. Eighty-two patients with 80 T1a tumors and 10 T1b tumors treated with thermal ablation from 2015 through 2020 were included. A total of 43 tumors in 38 patients were treated with RFA (2.3 ± 0.9 cm), and 47 tumors in 44 patients were treated with CA (2.1 ± 0.8 cm). The mean follow-up observation period was 26 ± 19 months. The major complications and efficacy, as measured using the technical success and local tumor recurrence rates, were recorded. There were three (6.9%) technical failures with RFA and one (2.1%) with cryoablation (p = 0.30). Among the 40 tumors that were successfully treated with RFA, 1 tumor (2.5%) developed local tumor recurrence; 5/46 tumors that were treated with cryoablation (10.8%) developed local tumor recurrence (p = 0.17). T1b lesions (4.0 ± 0.7 cm) resulted in 1/6 technically unsuccessful cases with RFA and 0/4 with CA. No recurrent disease was detected in the T1b lesions. Major complications occurred after 2.3% (1/43) of RFAs and 0/47 of cryoablation procedures. RFA and cryoablation are both effective in the treatment of renal masses. Major complications with either procedure are uncommon.

Small Renal Masses: Developing a Robust Radiomic Signature.

(1) Background and (2) Methods: In this retrospective, observational, monocentric study, we selected a cohort of eighty-five patients (age range 38-87 years old, 51 men), enrolled between January 2014 and December 2020, with a newly diagnosed renal mass smaller than 4 cm (SRM) that later underwent nephrectomy surgery (partial or total) or tumorectomy with an associated histopatological study of the lesion. The radiomic features (RFs) of eighty-five SRMs were extracted from abdominal CTs bought in the portal venous phase using three different CT scanners. Lesions were manually segmented by an abdominal radiologist. Image analysis was performed with the Pyradiomic library of 3D-Slicer. A total of 108 RFs were included for each volume. A machine learning model based on radiomic features was developed to distinguish between benign and malignant small renal masses. The pipeline included redundant RFs elimination, RFs standardization, dataset balancing, exclusion of non-reproducible RFs, feature selection (FS), model training, model tuning and validation of unseen data. (3) Results: The study population was composed of fifty-one RCCs and thirty-four benign lesions (twenty-five oncocytomas, seven lipid-poor angiomyolipomas and two renal leiomyomas). The final radiomic signature included 10 RFs. The average performance of the model on unseen data was 0.79 ± 0.12 for ROC-AUC, 0.73 ± 0.12 for accuracy, 0.78 ± 0.19 for sensitivity and 0.63 ± 0.15 for specificity. (4) Conclusions: Using a robust pipeline, we found that the developed RFs signature is capable of distinguishing RCCs from benign renal tumors.

Impact of modifiable lifestyle risk factors for prostate cancer prevention: a review of the literature.

Introduction: Although prostate cancer (PCa) is one of the most common cancers among men, the impact of modifiable risk and protective factors is still being debated. This review aims to qualitatively summarize the most recent studies related to potential healthy lifestyle factors affecting the development of PCa. Methods for data acquisition: The literature focusing on modifiable risk factors for prostate cancer was reviewed. Medline and Embase via the Ovid database were searched, and all relevant and inherent articles were analyzed. Non-eligible publications, such as review articles, editorials, comments, guidelines, or case reports, were excluded. Synthesis of the evidence obtained from data analysis: This review confirms that there is strong evidence that being overweight or obese increases the risk of advanced prostate cancer (assessed by body mass index (BMI), waist circumference, and waist-hip ratio), particularly considering central adiposity and ethnicity as contributing factors. The possible contribution of smoking still seems not entirely clear, while alcohol seems to affect PCa prevention in patients taking 5α-reductase inhibitors (5-ARIs). Dietary fibers may have anti-inflammatory properties and improve insulin sensitivity by reducing IGF bioactivity. In particular, dietary fiber intake like insoluble and legume fibers may be inversely associated with prostate cancer risk. Also, hyperglycemia and hyperinsulinemia, with untreated diabetic fasting blood glucose levels, could be modifiable prostate cancer risk factors. In two studies, aspirin was associated with a lower risk of lethal PCa and overall mortality. Concerning the role of vitamins, despite conflicting and divergent results, serum retinol concentration seems to be associated with an increased risk of prostate cancer and high-grade prostate cancer. Some studies resulted in disagreement about the role of selenium and vitamin E. We found inconsistent and controversial findings about the association between vitamin D and prostate cancer risk. Conclusion: Far from being conclusive evidence, our findings confirm some strong evidence already found in the previous literature and highlight the need to clarify the role of some risk factors whose role is not yet completely known. This effort would facilitate the cultural and social change that may allow the shift from the treatment of prostate cancer when diagnosed to the real efforts needed for systematic prevention.

Lymph node staging with 68Ga-PSMA PET in patients with intermediate and high-risk prostate cancer suitable for radical prostatectomy managed in a prostate cancer unit.

BACKGROUND: Prostate-specific membrane antigen (PSMA) positron emission tomography/computed tomography (PET/CT) is coming up as a superior imaging tool for prostate cancer (PCa). However, its use in primary staging is still debated. The aim of this study was to assess accuracy of 68Ga-PSMA PET/CT in staging patients with intermediate and high risk PCa candidates to radical prostatectomy managed in the Prostate Cancer Unit of our institution. METHODS: We retrospectively evaluated patients with biopsy-proven PCa staged through PSMA PET/CT before undergoing radical prostatectomy (RP) with extended pelvic lymph node dissection (ePLND). PET findings were categorized with respect to primary tumor (T), nodal (N) and distant metastasis (M). We analyzed the correspondence between PSMA PET/CT and final histopathological examination. RESULTS: We evaluated 42 men with high and intermediate risk PCa submitted to RP with ePLND. Mean age was 65.5 years (range, 49-76 years) and median preoperative prostate-specific antigen (PSA) was 13 ng/mL (IQR, 8.1-20 ng/mL). Patients in the high-risk group were 23 (54.7%), and the remainders were in the intermediate risk group. The mean risk of lymph node involvement (LNI) using the Memorial Sloan Kettering Cancer Center (MSKCC)-nomogram was 20%. The most common International Society of Urological Pathology (ISUP) grade was 3 (26.19%) after prostate biopsy. PSMA PET/CT showed focal prostatic uptake in 28 patients [mean value of maximum standardized uptake value (SUVmax) 18.5] and detected pelvic lymph node metastases in 6 cases (14.3%) with a median value of SUVmax 4.5 (IQR, 2-6.9). Histopathological examination detected lymph node metastases in seven patients (16.6%). In the only patient with negative PSMA PET/CT pathology revealed the presence of micrometastasis. After histopathological confirmation, sensitivity, specificity, positive and negative predictive values of pre-operative 68Ga-PSMA PET/CT were 85.7%, 100%, 100% and 97%, respectively. CONCLUSIONS: In our series, 68Ga-PSMA PET/CT holds high overall diagnostic value for lymph node staging in patients with intermediate and high risk PCa. Accuracy may depend on lymph node size.

Robotic transposition and ureteroureterostomy of type 1 retrocaval ureter.

Retrocaval ureter (RCU) is a rare malformation of the inferior vena cava. We report a case of a 60-years-old female presented with right flank pain and computed tomography scan diagnosis of (RCU). She underwent robotic transposition and ureteroureterostomy of RCU. No complications were recorded. After 1 year of follow-up the patient remains asymptomatic and without signs of obstruction. Robotic repair of RCU with preservation of the retrocaval segment is a safe procedure with the advantages of the vision and dexterity in dissection and suturing.

Safety profile of treatment with greenlight versus Thulium Laser for benign prostatic hyperplasia.

OBJECTIVE: The major strengths of surgical treatment of benign prostatic hyperplasia with laser are reduced morbidity compared to endoscopic resection. No studies analysed the different risk of intra/peri-operative events between patients undergoing Thulium and GreenLight procedures. MATERIALS AND METHODS: We retrospectively reviewed 100 consecutive cases undergoing GreenLight vaporization and Thulium procedures performed during the learning curve of two expert endoscopic surgeons. Pre-operative data, intra and post-operative events at 90 days were analysed. RESULTS: Patients on antiplatelet/anticoagulant therapy were pre-dominant in the Green group (p < 0.0001). Rates of blood transfusion (p < 0.0038), use of resectoscope (p < 0.0086), and transient stress urinary incontinence were statistically higher in the Thulium group. On the contrary conversions to TURP (p < 0.023) were more frequent in GreenLight patients. Readmissions were more frequently necessary in GreenLight group (24%) vs. Thulium group (26.6%). The overall complication rate in GreenLight and Thulium groups were 31% and 53% respectively; Clavien 3b complications were 13% in Thulium patients versus 1% in GreenLight patients. CONCLUSIONS: GreenLight and Thulium treatments show similar safety profiles. Randomized controlled trial are needed to better clarify the rate of major complications in Thulium group, and the incidence of post-operative storage symptoms in these patients' populations.

The Role of CT Imaging in Characterization of Small Renal Masses.

Small renal masses (SRM) are increasingly detected incidentally during imaging. They vary widely in histology and aggressiveness, and include benign renal tumors and renal cell carcinomas that can be either indolent or aggressive. Imaging plays a key role in the characterization of these small renal masses. While a confident diagnosis can be made in many cases, some renal masses are indeterminate at imaging and can present as diagnostic dilemmas for both the radiologists and the referring clinicians. This review focuses on CT characterization of small renal masses, perhaps helping us understand small renal masses. The following aspects were considered for the review: (a) assessing the presence of fat, (b) assessing the enhancement, (c) differentiating renal tumor subtype, and (d) identifying valuable CT signs.

Radiofrequency Ablation, Cryoablation, and Microwave Ablation for the Treatment of Small Renal Masses: Efficacy and Complications.

Over the last two decades the detection rate of small renal masses has increased, due to improving diagnostic accuracy, and nephron-sparing treatments have become the first-choice curative option for small renal masses. As a minimally invasive alternative, thermal ablation has increased in popularity, offering a good clinical outcome and low recurrence rate. Radiofrequency ablation, Cryoablation, and Microwave ablation are the main ablative techniques. All of them are mostly overlapping in term of cancer specific free survival and outcomes. These techniques require imaging study to assess lesions features and to plan the procedure: US, CT, and both of them together are the leading guidance alternatives. Imaging findings guide the interventional radiologist in assessing the risk of complication and possible residual disease after procedure. The purpose of this review is to compare different ablative modalities and different imaging guides, underlining the effectiveness, outcomes, and complications related to each of them, in order to assist the interventional radiologist in choosing the best option for the patient.

MR-based simplified extraprostatic extension evaluation: comparison of performances of different predictive models.

OBJECTIVES: To test reproducibility and predictive value of a simplified score for assessment of extraprostatic tumor extension (sEPE grade). METHODS: Sixty-five patients (mean age ± SD, 67 years ± 6.3) treated with radical prostatectomy for prostate cancer who underwent 1.5-Tesla multiparametric magnetic resonance imaging (mpMRI) 6 months before surgery were enrolled. sEPE grade was derived from mpMRI metrics: curvilinear contact length > 15 mm (CCL) and capsular bulging/irregularity. The diameter of the index lesion (dIL) was also measured. Evaluations were independently performed by seven radiologists, and inter-reader agreement was tested by weighted Cohen K coefficient. A nested (two levels) Monte Carlo cross-validation was used. The best cut-off value for dIL was selected by means of the Youden J index to classify values into a binary variable termed dIL*. Logistic regression models based on sEPE grade, dIL, and clinical scores were developed to predict pathologic EPE. Results on validation set were assessed by the main metrics of the receiver operating characteristics curve (ROC) and by decision curve analysis (DCA). Based on our findings, we defined and tested an alternative sEPE grade formulation. RESULTS: Pathologic EPE was found in 31/65 (48%) patients. Average κw was 0.65 (95% CI 0.51-0.79), 0.66 (95% CI 0.48-0.84), 0.67 (95% CI 0.50-0.84), and 0.43 (95% CI 0.22-0.63) for sEPE grading, CLL ≥ 15 mm, dIL*, and capsular bulging/irregularity, respectively. The highest diagnostic yield in predicting EPE was obtained by combining both sEPE grade and dIL*(ROC-AUC 0.81). CONCLUSIONS: sEPE grade is reproducible and when combined with the dIL* accurately predicts extraprostatic tumor extension. KEY POINTS: • Simple and reproducible mpMRI semi-quantitative scoring system for extraprostatic tumor extension. • sEPE grade accurately predicts extraprostatic tumor extension regardless of reader expertise. • Accurate pre-operative staging and risk stratification for optimized patient management.

Role of Renal Biopsy in the Management of Renal Cancer: Concordance between Ultrasound/CT-Guided Biopsy Results and Definitive Pathology, Adverse Events, and Complication Rate.

(1) Background: In the last decade, the number of detected renal cancer cases has increased, with the highest incidence in Western countries. Although renal biopsy is reported as a safe procedure, it is not adopted in all centres. As it is not possible to accurately distinguish benign tumours using imaging, this may lead to overtreatment. Most of the cancer detected on imaging is treated by surgery, radiofrequency ablation (RFA), or cryotherapy. (2) Methods: This was a single-centre retrospective study of 225 patients studied preoperatively with ultrasound (US)/CT-guided renal biopsy, with the aim of supporting clinical management. Decisions regarding the biopsy were based on either MDT indication or physician preference. US-guided renal biopsy was the first option for all patients; CT-guided biopsy was used when US-guided biopsy was not feasible. The efficacy of renal biopsy in terms of diagnostic performance and the concordance between biopsy results and definitive pathology were investigated. Additionally, adverse events related to the biopsy were recorded and analysed. Data collected throughout the study were analysed using binary logistic regression, Fisher's exact test, and Pearson's chi-square test to investigate possible correlations between post-procedural complications and the size of the lesion. (3) Results: Renal biopsy was not diagnostic in 23/225 (10.2%) patients. A CT-guided approach was necessary in 20/225 patients after failure of US-guided biopsy. The complication rate of renal biopsy was 4.8% overall-all Clavien grade I and without any serious sequelae. Interestingly, complications occurred in patients with very different sizes of renal cell carcinoma. No correlation between complications and anticoagulant/antiplatelet drugs was found. No seeding was reported among the patients who underwent partial/radical nephrectomy. (4) Conclusions: Renal biopsy was shown to be safe and effective, with a high concordance between biopsy results and definitive pathology and a low rate of complications. The use of a CT-guided approach whenever the US-guided approach failed improved the diagnostic performance of renal biopsy.

Percutaneous Radiofrequency Ablation (RFA) in renal cancer. How to manage challenging masses. A narrative review.

In the last decades, the refinements in the imaging techniques led to an increased number of detected renal tumors. If radical and partial nephrectomy remain the gold standard for the treatment of renal cancer, Radio-Frequency Ablation (RFA) has emerged as a therapeutic option for renal masses. Even if this technique is minimally-invasive, it requires a proper preoperative anatomic study and in some cases RFA treatment is technically challenging. To date, there is no standardization for studying challenging cases before treatment and to plan a safe and effective procedure when intervening organs are in the trajectory of the needle. In this study we searched the literature focusing on the challenging cases and strategy applied to manage the treatment safely and effectively. MATERIALS AND METHODS: MedLine and Embase via Ovid database were searched, using the following key words: Percutaneous RFA, radiofrequency, renal ablation, kidney ablation, renal thermoablation, kidney thermoablation, hydrodissection, heat sink. The difficulties found in the literature while performing the ablation procedure were grouped and a categorization of the strategies applied to perform a safe and effective procedure was proposed, in the aim to standardize the approach for treatment of challenging cases. Literature was analyzed according with selection criteria agreed by the Authors. RESULTS: The literature review showed four groups of lesions requiring an experienced approach. Group 1: Lesions close to the bowel. Group 2: Lesions close to the urinary tract. Group 3: Lesions close to intervening organs. Group 4: Lesions close to large vessels (heat-sink phenomenon). CONCLUSION: When planning a RFA treatment, a standardized approach to challenging masses is possible. This review make the treatment of these masses more systematic and safe.

Factors predicting prolonged glucocorticoid therapy in patients with adrenal insufficiency after laparoscopic adrenalectomy.

Introduction and importance: Adrenal insufficiency (AI) is common after adrenalectomy for Primary Adrenal Cushing's syndrome (PACS), due to the inhibition of the Hypothalamic-Pituitary-Adrenal Axis (HPAA) by the functioning adrenal mass. The treatment of post-surgical AI is based mainly on glucocorticoid supplementation therapy. To date, however, there is no known predicting factor of the duration of supplementation therapy in patients treated with laparoscopic adrenalectomy for PACS. Case presentation: We report the case of a 22-year-old Caucasian female who presented with dyspnea, osteoporosis, vertebral collapses and fractures of the pelvis. The diagnosis of ACTH-independent Cushing's syndrome was provided. Abdominal MRI revealed a left adrenal mass suggestive for adrenal adenoma, highly suggestive for PACS. The patient underwent left laparoscopic adrenalectomy. After surgery, glucorticoid supplementation therapy was started. More than A-year steroid replacement therapy was necessary before the patient completely recovered the function of the HPAA. During this period the patient was strictly followed up in order to adjust pharmacologic treatment, thus allowing to investigate the possible causes of such a slow and hard recover of the contralateral adrenal gland function. Conclusion: AI is common after adrenalectomy for PACS due to HPAA suppression. The duration of steroid replacement therapy may be vary depending on patient's characteristics and may be uncommonly long, as in our case. We concluded the not only cortisol and ACTH level, but also radiological findings, such as the size of the mass, its functional activity as well as the hypotrophy or atrophy of the contralateral adrenal gland may be predictive of the duration of the steroid therapy. These factors, if correctly studied before surgery, may be of help in tailoring the postoperative management of the patients after adrenalectomy.

PSA-IgM and iXip in the diagnosis and management of prostate cancer: clinical relevance and future potential. A review.

The Prostate Specific Antigen (PSA) is the first filter in the diagnosis of prostate cancer. Unfortunately, it is organ-specific but not cancer-specific. In addition, some prostate cancers are not clinically-significant and their diagnosis and treatment may lead to overdiagnosis and overtreatment. For these reasons, other markers have been proposed in the last years, such as PCA3 and PHI, but none of these are currently used in the clinical practice on large scale. In the last decade, PSA-IgM and the algorithm iXip have emerged for the diagnosis of prostate cancer and showed to perform well in decreasing the detection of clinically-insignificant prostate cancer and in reducing the number of unnecessary prostate biopsies. This review focuses on data reported in the literature on PSA-IgM and iXip as well as on the future perspectives of their usage in the clinical practice on large scale.

Metastatic Clear Cell Renal Cell Carcinoma: The Great Pretender and the Great Dilemma.

Metastatic renal cell carcinoma (mRCC) may present with a wide range of clinical pictures. Reportedly, paraneoplastic syndromes are the first sign in 20% of cases and only 15% of cases show the classic triad (flank pain, gross hematuria, and palpable abdominal mass) at presentation. The remaining cases present with signs and symptoms related to the site of distant metastases. These data may explain the reason why about 20-30% of patients are metastatic at presentation. We report the case of a 63-year-old woman who came to our attention for lower back pain. After imaging studies, we detected a left kidney mass of 86 × 61 × 79 mm, multiple right pulmonary nodules and six bone lesions. She underwent left radical nephrectomy. After 1 month, she developed signs of spinal cord compression with neurological deficits and she underwent emergency spinal decompression. In order to allow complete motor recovery, the subsequent stereotactic body radiation therapy was not performed, and she is currently taking combination immunotherapy regimens. Management of mRCC is in a continuous evolution due to availability of new target therapies and the possibility of a multimodal approach with surgical, focal and radiotherapy treatments. However, the ideal treatment algorithm is yet to come. This is why mRCC diagnosis and management are still challenging for the clinicians.

Oncologic outcome of salvage high-intensity focused ultrasound (HIFU) in radiorecurrent prostate cancer. A systematic review.

INTRODUCTION: External Beam Radiation Therapy (EBRT) is one of the option available for the treatment of clinically localized prostate cancer. In patients with radiorecurrent localized prostate cancer, Androgen Deprivation Therapy (ADT) is one of the most common therapeutic strategies. However, in the last decades, other salvage treatment options have been investigated, such as brachytherapy, cryoablation and High Intensity Focused Ultrasound (Hifu). MATERIAL AND METHODS: The oncologic outcome of Hifu in a salvage setting after EBRT failure was investigated. We reviewed the literature from 2005 to 2020 in order to report the oncologic outcome of the technique. RESULTS: A total of 1241 patients were analyzed, with a mean age of 68.6 years and a PSA value of 5.87 ng/mL before treatment. Mean follow-up was 24.3 months after treatment, ranging from 3 to 168 months. CONCLUSION: Our review of the literature revealed that salvage Hifu is effective in the treatment of radiorecurrent clinically localized prostate cancer, with an overall survival of 85.2% at 5 years.

CT-guided percutaneous drainage of abdominopelvic collections: a pictorial essay.

CT-guided percutaneous drainage is a safe and effective procedure that allows minimally invasive treatment of abdominopelvic abscesses and fluid collections. This technique has become an alternative for surgery with lower morbility and mortality rates. In this pictorial essay, we aim at providing an overview of the technical approaches, the main clinical indications and complications of CT-guided percutaneous drainage, in order to provide a practical guide for interventional radiologists, with a review of the recent literature. The focus will be the CT-guidance, preferred when the interposition of viscera, vascular and skeletal structures, counteracts the ultrasound guidance.

Müllerianosis of the urinary bladder may simulate a bladder cancer: a case report.

Müllerianosis is an extremely rare entity consisting of an admixture of 2 or more müllerian tissues. We report the case of a 61 years old woman who came to our attention with hypogastric pain and dysuria. She was in menopause and had a previous history of cesarean section. Ultrasound and CT-scan of the abdomen showed a proliferative bladder lesion close to the left ureteric orifice. Transurethral resection of the bladder (TUR-B) was performed. Histopathological examination of the specimens was negative for bladder cancer and revealed the presence of endosalpingeal tissue. Postoperative course was unremarkable as well as follow up at 12 months. A proper knowledge and awareness of this disease, even if rare, is necessary for an accurate differential diagnosis and to perform an appropriate treatment.

Imaging guided percutaneous renal biopsy: do it or not?

Since its first reported application, renal biopsy became an important part of the diagnostic algorithm, considered advantages and risks, to better manage therapeutic options. The biopsy can be performed with different techniques (open, laparoscopic, transjugular, transurethral and percutaneous). Currently, the percutaneous approach is the modality of choice. Percutaneous biopsy can be performed under CT or US guidance, but critical benefits and disadvantages have to be considered. Core needle biopsy is usually preferred to fine-needle aspiration because of the sample quality, usually obtaining multiple cores, especially in heterogeneous tumors. Principal complications are hematuria (1-10%), perinephric hematoma (10-90%), pneumothorax (0,6%), clinically significant pain (1,2%).

Oncologic outcome, side effects and comorbidity of high-intensity focused ultrasound (HIFU) for localized prostate cancer. A review.

INTRODUCTION: Prostate cancer is considered one of the most important health problems. Due to the increased number of diagnosed patients and the inability to distinguish aggressive tumors, minimally-invasive procedures have become increasingly interesting. High-intensity focused ultrasound (HIFU) is an alternative option to radical surgery to treat prostate cancer. To date, however, data on side effects and comorbidities of this technique are still not conclusive. METHODS AND RESULTS: We reviewed the literature to concentrate on side effects and comorbidities of HIFU treatment of prostate cancer with the following key words: hifu, high intensity focused ultrasound, ultrasonic therapy, transrectal hifu, prostate ablation, side effects, comorbidities. MedLine and Embase via Ovid database were searched. Selection criteria were: English language, articles published between 2001 and 2015, case series including at least 100 participants and reported data on side effects and comorbidities. Sixteen uncontrolled studies were identified. No randomized controlled trials (RCT) were found in the literature comparing side effects and comorbidities of HIFU to other routine approaches to prostate cancer treatment. CONCLUSION: HIFU seems to be a promising minimally-invasive treatment for low- and intermediate-risk prostate cancer, especially for patients who are unfit for radical surgery. Prospective studies with longer follow-up periods and RCT are required to properly assess the impact of side effects and comobidities related to the HIFU technique in comparison with other therapies to treat prostate cancer.

Small renal masses (≤ 4 cm): differentiation of oncocytoma from renal clear cell carcinoma using ratio of lesion to cortex attenuation and aorta-lesion attenuation difference (ALAD) on contrast-enhanced CT.

PURPOSE: We investigate the use of ratio of lesion to cortex (L/C) attenuation and aorta-lesion attenuation difference (ALAD) on multiphase contrast-enhanced CT to help distinguish oncocytoma from clear cell RCC in small renal masses (diameter < 4 cm). METHODS: We retrospectively identified 76 patients that undergo CT before surgery for a suspicious small renal mass between January 2014 and December 2018 with pathological diagnosis of 21 oncocytomas (ROs), 25 clear cell RCCs, 7 chromophobe RCCs, 7 papillary RCCs, 7 multilocular cystic RCCs, 7 angiomyolipomas and 2 leiomyomas. CT attenuation values were obtained for the tumor, the normal renal cortex and the aorta, placing a circular region of interest (ROI) in the same slice by two radiologists, independently. RESULTS: In the corticomedullary phase, ROs showed isodense enhancement to the renal cortex (ratio L/C 0.92 ± 0.12), while clear cell RCCs appeared hypodense to the renal cortex (ratio L/C 0.69 ± 0.20; p < 0.01) with an accuracy of 80% for diagnosing RO. In nephrographic phase, the ratio L/C attenuation was lower than the corticomedullary phase in ROs (0.78 ± 0.11) showing an early washout pattern, while the ratio L/C was similar to the corticomedullary phase in clear cell RCCs (0.69 ± 0.13; p = 0.025, with an accuracy of 65% for diagnosing RO). The ratio L/C attenuation showed considerable overlap between ROs and clear cell RCCs in the excretory phase (p = 0.27). Mean ALAD values in the nephrographic phase were 21.95 ± 16.24 for ROs and 36.96 ± 30.53 for clear cell RCCs (p = 0.049). CONCLUSION: The ratio L/C attenuation in corticomedullary phase may be useful to differentiate RO from clear cell RCC.