Imaging of Renal Infections and Inflammatory Disease

Imaging features of perinephric myxoid pseudotumors of fat

OBJECTIVE

Retrospectively evaluate multimodality imaging features of perinephric myxoid pseudotumor of fat (PMPTF).

METHODS

Institutional cases of PMPTF with CT, MRI and/or ultrasound evaluation from 1/1/2020 to 9/1/2023 were retrospectively reviewed. Patient demographics and clinical history were reviewed, and imaging features recorded.

RESULTS

14 patients with pathologically-proven PMPTF were identified (11 M, 3 F; mean age 66.7 ± 17.0 years; range 40-87 years). Three patients (18%) had bilateral lesions; a total of 17 PMPTFs were reviewed. 15/17 (88%) were biopsy-proven; two cases were diagnosed by imaging only in patients with a contralateral biopsy-proven PMPTF. All evaluable specimens were negative for MDM2 amplification. 11/17 (65%) occurred in patients with renal disease, including 4/17 (24%) in patients with renal transplant. 100% (17/17) had CT, 11/17 (65%) MRI, and 6/17 (35%) ultrasound. The mean largest lesion dimension was 10.9 ± 4.6 cm (range 4.3-17.0 cm). Of cases involving native kidneys, 7/13 (54%) presented as multifocal perinephric masses and 5/13 (38%) as a solitary perinephric mass. All four transplant cases presented as infiltrative-appearing masses involving the renal sinus with lesser perinephric involvement. 14/17 (82%) lesions contained macroscopic fat on CT and MRI and 3/17 (18%) showed no macroscopic fat, all involving renal transplants. All cases with MRI demonstrated T2 hyperintensity with signal dropout on opposed-phase imaging. 11/13 (85%) PMPTF showed no or equivocal CT enhancement. Enhancement was better seen on MRI in all cases evaluated by both CT and MRI. Of the six PMPTFs imaged by ultrasound, four (67%) were heterogeneously hypoechoic and two (33%) had mixed regions of hypo-, iso- and hyperechogenicity relative to adjacent renal parenchyma.

CONCLUSIONS

PMPTF is a rare, benign, and underrecognized lesion that may mimic malignancy, particularly retroperitoneal well-differentiated liposarcoma. The imaging features of this unusual pseudosarcoma differ in native and transplanted kidneys. Improved awareness of this entity will facilitate appropriate patient management and avoid unnecessary intervention.

Machine learning constructs a diagnostic prediction model for calculous pyonephrosis

In order to provide decision-making support for the auxiliary diagnosis and individualized treatment of calculous pyonephrosis, the study aims to analyze the clinical features of the condition, investigate its risk factors, and develop a prediction model of the condition using machine learning techniques. A retrospective analysis was conducted on the clinical data of 268 patients with calculous renal pelvic effusion who underwent ultrasonography-guided percutaneous renal puncture and drainage in our hospital during January 2018 to December 2022. The patients were included into two groups, one for pyonephrosis and the other for hydronephrosis. At a random ratio of 7:3, the research cohort was split into training and testing data sets. Single factor analysis was utilized to examine the 43 characteristics of the hydronephrosis group and the pyonephrosis group using the T test, Spearman rank correlation test and chi-square test. Disparities in the characteristic distributions between the two groups in the training and test sets were noted. The features were filtered using the minimal absolute value shrinkage and selection operator on the training set of data. Auxiliary diagnostic prediction models were established using the following five machine learning (ML) algorithms: random forest (RF), xtreme gradient boosting (XGBoost), support vector machines (SVM), gradient boosting decision trees (GBDT) and logistic regression (LR). The area under the curve (AUC) was used to compare the performance, and the best model was chosen. The decision curve was used to evaluate the clinical practicability of the models. The models with the greatest AUC in the training dataset were RF (1.000), followed by XGBoost (0.999), GBDT (0.977), and SVM (0.971). The lowest AUC was obtained by LR (0.938). With the greatest AUC in the test dataset going to GBDT (0.967), followed by LR (0.957), XGBoost (0.950), SVM (0.939) and RF (0.924). LR, GBDT and RF models had the highest accuracy were 0.873, followed by SVM, and the lowest was XGBoost. Out of the five models, the LR model had the best sensitivity and specificity is 0.923 and 0.887. The GBDT model had the highest AUC among the five models of calculous pyonephrosis developed using the ML, followed by the LR model. The LR model was considered be the best prediction model when combined with clinical operability. As it comes to diagnosing pyonephrosis, the LR model was more credible and had better prediction accuracy than common analysis approaches. Its nomogram can be used as an additional non-invasive diagnostic technique.

Ultrasonography of acute retroperitoneum

The retroperitoneum is an important space in the human body that is often implicated in a range Epub ahead of print of acute medical conditions, some of which can be life-threatening. Ultrasonography may serve as a pivotal first-line imaging technique when assessing patients with suspected retroperitoneal abnormalities. Effective ultrasonography of the retroperitoneum requires a comprehensive grasp of its anatomy, adjacent structures, and potential pathologies. Being well-acquainted with the imaging characteristics of acute conditions can meaningfully assist in an accurate diagnosis and guide subsequent management. This review article summarizes and illustrates the acute conditions involving the retroperitoneum through the lens of ultrasound imaging.

Tumefactive Nonneoplastic Proliferative Pseudotumors of the Kidneys and Urinary Tract: CT and MRI Findings with Histopathologic Correlation

A diverse spectrum of pathologically distinct, nonneoplastic, proliferative conditions of the kidneys and urinary tract demonstrate a expansile growth pattern similar to that of neoplasms. The renal pseudotumors include myriad causes of infections as well as rare noninfectious causes such as sarcoidosis, amyloidosis, and immunoglobulin G4-related disease (IgG4-RD). Rare entities such as cystitis cystica, endometriosis, nephrogenic adenoma, and pseudosarcomatous myofibroblastic proliferation and distinct types of prostatitis comprise tumefactive nontumorous disorders that affect specific segments of the urinary tract. The pseudotumors of the kidneys and urinary tract demonstrate characteristic histopathologic and epidemiologic features, as well as protean clinical manifestations, natural history, and imaging findings. Many patients present with genitourinary tract-specific symptoms or systemic disease. Some cases may be incidentally discovered at imaging. Some entities such as perinephric myxoid pseudotumors, IgG4-RD, fibroepithelial polyp, and nephrogenic adenoma display specific anatomic localization and disease distribution. Imaging features of multisystem disorders such as tuberculosis, sarcoidosis, and IgG4-RD provide supportive evidence that may allow precise diagnosis. Fungal pyelonephritis, xanthogranulomatous pyelonephritis, IgG4-RD, actinomycosis, and endometriosis show markedly low signal intensity on T2-weighted MR images. Although some pseudotumors exhibit characteristic imaging findings that permit correct diagnosis, laboratory correlation and histopathologic confirmation are required for definitive characterization in most cases. A high index of suspicion is a prerequisite for diagnosis. Accurate diagnosis is critical for instituting optimal management while preventing use of inappropriate therapies or interventions. Surveillance CT and MRI are frequently used for monitoring the response of pseudotumors to therapy. ©RSNA, 2023 Quiz questions for this article are available in the supplemental material.

What do we see when we do not see the bladder? Review of the main urinary diversion techniques and their complications

OBJECTIVE

To review the different types of urinary diversion surgeries (UDS) in order to recognize the expected findings in a postoperative study, using different imaging techniques. To recognize the main postoperative complications, both early and late.

CONCLUSION

UDS are surgical procedures whose purpose is to redirect urine flow after cystectomy, generally in an oncologic context. The imaging evaluation of urological surgeries is often a radiological challenge, with CT being the most commonly used image modality. Therefore, it is essential to know the main surgical techniques, the expected postoperative findings and the optimization of imaging techniques for early diagnosis and correct evaluation of postoperative complications.

Association between the imaging characteristics of renal abscess and vesicoureteral reflux

INTRODUCTION

Renal abscesses are rare in pediatric populations. We aimed to highlight the differences in the computed tomography (CT) imaging characteristics of renal abscesses in patients with and without vesicoureteral reflux (VUR).

MATERIALS AND METHODS

Thirteen children with renal abscesses were included and categorized into those with and without VUR. Blood and urine culture results were recorded as positive or negative. Imaging characteristics were recorded: with/without subcapsular fluid collection, with/without upper/lower pole involvement, and with single/multiple lesions in kidneys. Fisher's exact test was used for intergroup comparisons of the rate of positive pathogens and imaging characteristics.

RESULTS

Nine patients had VUR (45.9%). Blood and urine culture were positive in two (15.4%) and seven cases (53.8%), respectively. There was no significant difference in the rate of pathogen-positive blood and urine cultures (blood culture positive/negative status with VUR vs. that without VUR = 2/7 vs. 0/4, p > 0.999, urine culture positive/negative status with VUR vs. that without VUR = 4/5 vs. 3/1, p = 0.559). The two groups differed significantly regarding subcapsular fluid collection presence (with/without subcapsular fluid collection with VUR vs. that without VUR = 9/0 vs 1/3, p = 0.014). There was no significant difference in upper/lower pole involvement (with/without involving upper/lower pole with VUR vs. that without VUR = 8/1 vs 2/2, p = 0.203). Patients with VUR were non-significantly more likely to have multiple lesions compared to those without VUR.

CONCLUSIONS

VUR was associated with subcapsular fluid collection and possibly with multiple lesions, indicating the need for prompt detection of and specific treatment for VUR in cases with these findings.

Complications after Nephron-sparing Interventions for Renal Tumors: Imaging Findings and Management

The two primary nephron-sparing interventions for treating renal masses such as renal cell carcinoma are surgical partial nephrectomy (PN) and image-guided percutaneous thermal ablation. Nephron-sparing surgery, such as PN, has been the standard of care for treating many localized renal masses. Although uncommon, complications resulting from PN can range from asymptomatic and mild to symptomatic and life-threatening. These complications include vascular injuries such as hematoma, pseudoaneurysm, arteriovenous fistula, and/or renal ischemia; injury to the collecting system causing urinary leak; infection; and tumor recurrence. The incidence of complications after any nephron-sparing surgery depends on many factors, such as the proximity of the tumor to blood vessels or the collecting system, the skill or experience of the surgeon, and patient-specific factors. More recently, image-guided percutaneous renal ablation has emerged as a safe and effective treatment option for small renal tumors, with comparable oncologic outcomes to those of PN and a low incidence of major complications. Radiologists must be familiar with the imaging findings encountered after these surgical and image-guided procedures, especially those indicative of complications. The authors review cross-sectional imaging characteristics of complications after PN and image-guided thermal ablation of kidney tumors and highlight the respective management strategies, ranging from clinical observation to interventions such as angioembolization or repeat surgery. Work of the U.S. Government published under an exclusive license with the RSNA. Online supplemental material and the slide presentation from the RSNA Annual Meeting are available for this article. Quiz questions for this article are available in the Online Learning Center. See the invited commentary by Chung and Raman in this issue.

Importance of the hounsfield unit value measured by computed tomography in the differentiation of hydronephrosis and pyonephrosis

Background

Acute or chronic obstruction of the urinary tract can be due to a lot of different causes. Patients with pyonephrosis usually complain of a triad of fever, loin pain and elevated white blood cell count in cases of acute obstruction; and they may also have hypotension in severe cases of the disease. These patients have to be treated with appropriate decompression, or they may develop septic shock. The urgency of the need for treatment greatly depends on the differentiation between hydronephrosis and pyonephrosis.

There is a lack of reliable clinical prognosticators of pyonephrosis in patients with obstructive hydronephrosis. Hounsfield unit (HU) measurement is considered as an adequate predictor of pyonephrosis and may aid in the diagnosis and management of this disease that may be fatal.

The use of HU values in differentiation between pyonephrosis from hydronephrosis depends on the fact that the pyonephrotic fluid contains infected material, urine, cellular particles and microorganisms, which when combined can increase the HU values on a computed tomography (CT) study.

This study was done to assess the diagnostic value of the HU measured CT in differentiation between hydronephrosis and pyonephrosis.

Results

Thirty-nine patients were included in this study. All patients had loin pain and were diagnosed with pelvicalyceal dilatation by ultrasonographic examination. They then underwent non-contrast CT examination.

Using CT scan, the degree of PC dilatation was significantly higher among hydronephrosis group as hydronephrosis group had 63.1% severe dilatation of PCs versus 30.8% in pyonephrosis group with p value 0.0001.

Pelvic wall thickness > 2 mm was reported in 10 (76.9%) patients of pyonephrosis group versus in three (7.9%) patients among hydronephrosis group with p value 0.0001.

The mean Hounsfield units were significantly higher among pyonephrosis group compared to hydronephrosis group (16 ± 5.2 versus 1.7 ± 5.5) with p value 0.0001.

Sensitivity analysis showed that Hounsfield units can significantly diagnose pyonephrosis using the cutoff point 6.2 units, with sensitivity 92.3%, specificity 93.3%, area under the curve (AUC) 96.9% and p value 0.0001.

Conclusions

Measuring HU in a NCECT scan of the kidney might be helpful for differentiating between hydronephrosis and pyonephrosis especially upon considering 6.2 HU as a cutoff point.

Nomogram for diagnosing acute pyelonephritis in pediatric urinary tract infection

BACKGROUND

For risk stratification and individualized treatment for children with urinary tract infection (UTI), they must be assessed for the presence of acute pyelonephritis (APN). Our study aimed to combine variables that can predict APN and establish a nomogram for clinical use.

METHODS

In total, 111 children <5 years old hospitalized at Kaohsiung Veterans General Hospital for UTI were classified into APN and simple UTI groups based on a technetium-99 m dimercaptosuccinic acid scan. Their demographic, laboratory test, and renal and urinary bladder sonography (RUBS) data were compared.

RESULTS

Fever peak of >39 °C, serum procalcitonin (PCT) ≥ 0.52 pg/mL, C-reactive protein (CRP) ≥ 2.86 mg/dL, and abnormal RUBS findings were independent variables for predicting APN in children. The nomogram established using the aforementioned variables had an area under the receiver operating characteristic curve (AUC) of 0.89, which was higher than those of PCT and CRP alone (0.776 and 0.774, respectively).

CONCLUSION

The combination of four variables had the highest power in predicting APN in children with UTI. The established nomogram is practical for clinical use.

Value of noncontrast computer tomography in predicting the characteristics of obstructive uropathy

OBJECTIVE

To explore the diagnostic value of noncontrast computed tomography (NCCT) in differentiating pyonephrosis from nonpyogenic hydronephrosis on the basis of CT values (in Horsfield unit [HU]).

METHODS

Data from patients diagnosed with obstructive uropathy at the First affiliated hospital of University of South China from November 2017 to January 2021 were subjected to retrospective analysis. In accordance with the gold standard-the presence of pus during the operation-all patients were divided into the nonpyogenic hydronephrosis group and the pyonephrosis group. The relationship between CT values and the presence or absence of pyonephrosis was performed using binary logistic regression. A receiver operating characteristic (ROC) curve was constructed to determine threshold values for classification on the basis of mean HU.

RESULTS

A total of 207 patients, including 100 males and 107 females, were enrolled. Out of the 207 cases, 124 cases of obstructive uropathy were nonpyogenic hydronephrosis and 83 cases were of pyonephrosis. The CT values of the pyonephrosis group were significantly higher than that of the nonpyogenic hydronephrosis group (t = 9.15, P < 0.05). The CT values were dependent on the presence or absence of pyonephrosis (P < 0.05). A HU threshold value of 9.75 could be applied to diagnose the presence of pyonephrosis.

CONCLUSION

The CT values of hydronephrosis might predict the presence of pyonephrosis in the kidney, and the CT value of 9.75 HU might be the appropriate threshold for its prediction.

Basic principles and new advances in kidney imaging

Over the past few years, clinical renal imaging has seen great advances, allowing assessments of kidney structure and morphology, perfusion, function and metabolism, and oxygenation, as well as microstructure and the interstitium. Medical imaging is becoming increasingly important in the evaluation of kidney physiology and pathophysiology, showing promise in management of patients with renal disease, in particular with regard to diagnosis, classification, and prediction of disease development and progression, monitoring response to therapy, detection of drug toxicity, and patient selection for clinical trials. A variety of imaging modalities, ranging from routine to advanced tools, are currently available to probe the kidney both spatially and temporally, particularly ultrasonography, computed tomography, positron emission tomography, renal scintigraphy, and multiparametric magnetic resonance imaging. Given that the range is broad and varied, kidney imaging techniques should be chosen based on the clinical question and the specific underlying pathologic mechanism, taking into account contraindications and possible adverse effects. Integration of various modalities providing complementary information will likely provide the greatest insight into renal pathophysiology. This review aims to highlight major recent advances in key tools that are currently available or potentially relevant for clinical kidney imaging, with a focus on non-oncological applications. The review also outlines the context of use, limitations, and advantages of various techniques, and highlights gaps to be filled with future development and clinical adoption.

Pyonephrosis Ultrasound and Computed Tomography Features: A Pictorial Review

Urinary tract infections (UTIs) are the most frequent community-acquired and healthcare-associated bacterial infections. UTIs are heterogeneous and range from rather benign, uncomplicated infections to complicated UTIs (cUTIs), pyelonephritis and severe urosepsis, depending mostly on the host response. Ultrasound and computed tomography represent the imaging processes of choice in the diagnosis and staging of the pathology in emergency settings. The aim of this study is to describe the common ultrasound (US) and computed tomography (CT) features of pyonephrosis. US can make the diagnosis, demonstrating echogenic debris, fluid/fluid levels, and air in the collecting system. Although the diagnosis appears to be easily made with US, CT is necessary in non-diagnostic US examinations to confirm the diagnosis, to demonstrate the cause and moreover to stage the pathology, defining extrarenal complications. In emergency settings, US and CT are differently used in the diagnosis and staging of pyonephrosis.

Imaging Characterization of Renal Masses

The detection of a renal mass is a relatively frequent occurrence in the daily practice of any Radiology Department. The diagnostic approaches depend on whether the lesion is cystic or solid. Cystic lesions can be managed using the Bosniak classification, while management of solid lesions depends on whether the lesion is well-defined or infiltrative. The approach to well-defined lesions focuses mainly on the differentiation between renal cancer and benign tumors such as angiomyolipoma (AML) and oncocytoma. Differential diagnosis of infiltrative lesions is wider, including primary and secondary malignancies and inflammatory disease, and knowledge of the patient history is essential. Radiologists may establish a possible differential diagnosis based on the imaging features of the renal masses and the clinical history. The aim of this review is to present the contribution of the different imaging techniques and image guided biopsies in the diagnostic management of cystic and solid renal lesions.