Are There Ultrasound Features to Distinguish Small (<3 cm) Peripheral Renal Angiomyolipomas From Renal Cell Carcinomas?

BACKGROUND

Small echogenic renal masses are usually angiomyolipomas (AMLs), but some renal cell carcinomas (RCCs) can be echogenic and confused with an AML.

OBJECTIVES

This is a study to evaluate any distinguishing demographic and sonographic features of small (<3 cm) peripheral AMLs versus peripheral RCCs.

METHODS

This is a HIPAA-compliant retrospective review of the demographics and ultrasound features of peripheral renal AMLs compared with a group of peripheral RCCs. All AMLs had confirmation of macroscopic fat as noted on thin-cut CT or fat-saturation MRI sequence images. All RCCs were pathologically proven. Statistical analysis was used to compare findings in the two groups.

RESULTS

There were a total of 52 patients with 56 AMLs, compared with 42 patients with 42 RCCs. There were 42 females in the AML group versus 10 females in the RCC group (P < .0001). The AML diameters (15.7 mm × 12.0 mm) were statistically significantly smaller (Plargest  = .0085, Psmallest  < .001) than the diameters of the RCCs (19.9 mm × 18.5 mm). Ultrasound features found to be statistically different between the two groups were the ratio of the largest dimension to the smallest dimension (P < .001), a lobulated versus smooth margin of the AML (26 vs 30) compared with the RCC group (3 vs 39) (P = .0012), and an "unusual" versus a round shape (P < .001) of the AML group (45 vs 11) compared with the RCC group (9 vs 33). In the multivariable model, the patient sex, margin, and mass shape were predictive of AML, with an area under the receiver operating characteristic curve of 0.92.

CONCLUSION

For a small (<3 cm) peripheral echogenic mass in a female patient, a lobulated lesion with an unusual shape is highly predictive of being an AML.

Etiology of Small Echogenic Renal Masses

OBJECTIVES

There has been controversy on how frequently small echogenic masses are angiomyolipomas (AMLs) versus renal cell carcinoma (RCC) and how best to manage these echogenic masses. We performed this study to determine the etiologies of echogenic renal masses and compare them with prior publications to reach possible management decisions.

METHODS

This is a retrospective chart review of all consecutive renal ultrasound examinations performed at our institution between January 2015 and December 2016, with an ultrasound report finding containing the wording "echogenic" and "mass." This yielded 6462 total examinations. A total of 107 echogenic lesions met inclusion and exclusion criteria with correlative computed tomography, pathology, or long-term (>5 years) follow-up ultrasound. These lesions were stratified into those that were ≤2 cm and those that were >2 cm.

RESULTS

Almost all masses were benign, with the majority (79/107) being AMLs (73.8%); 64 of the 79 (81%) of the AMLs were in female patients. Two of the 107 masses were RCCs, and 1 mass was an oncocytic neoplasm. There were 77 of the masses that were ≤2 cm and these masses were benign except for one lesion of an oncocytic neoplasm. There were 30 of the 107 masses >2 cm, with 2 of the 30 (6.7%) being RCCs.

CONCLUSIONS

Incidental echogenic renal masses are most commonly AMLs. However, some masses may be RCCs. In comparing our results with the prior literature, we feel that small echogenic renal masses ≤1 cm usually require no further evaluation, while masses greater than that size require other imaging.

Differentiation of renal masses with multi-parametric MRI: the de Silva St George classification scheme

Purpose

To develop a system for multi-parametric MRI to differentiate benign from malignant solid renal masses and assess its accuracy compared to the gold standard of histopathological diagnosis.

Methods

This is a retrospective analysis of patients who underwent 3 Tesla mpMRI for further assessment of small renal tumours with specific scanning and reporting protocol incorporating T2 HASTE signal intensity, contrast enhancement ratios, apparent diffusion coefficient and presence of microscopic/macroscopic fat. All MRIs were reported prior to comparison with histopathologic diagnosis and a reporting scheme was developed. 2 × 2 contingency table analysis (sensitivity, specificity, positive predictive value (PPV) and negative predictive value (NPV)), Fisher Exact test were used to assess the association between suspicion of malignancy on mpMRI and histopathology, and descriptive statistics were performed.

Results

67 patients were included over a 5-year period with a total of 75 renal masses. 70 masses were confirmed on histopathology (five had pathognomonic findings for angiomyolipomas; biopsy was therefore considered unethical, so these were included without histopathology). Three patients were excluded due to a non-diagnostic result, non-standardised imaging and one found to be an organising haematoma rather than a mass. Therefore 72 cases were included in analysis (in 64 patients, with seven patients having multiple tumours). Unless otherwise specified, all further statistics refer to individual tumours rather than patients. 52 (72.2%) were deemed ‘suspicious or malignant’ and 20 (27.8%) were deemed ‘benign’ on mpMRI. 51 cases (70.8%) had renal cell carcinoma confirmed. The sensitivity, NPV, specificity and PPV for MRI for detecting malignancy were 96.1%, 90%, 85.7% and 94.2% respectively, Fisher’s exact test demonstrated p < 0.0001 for the association between suspicion of malignancy on MRI and histopathology.

Conclusion

The de Silva St George classification scheme performed well in differentiating benign from malignant solid renal masses, and may be useful in predicting the likelihood of malignancy to determine the need for biopsy/excision. Further validation is required before this reporting system can  be recommended for clinical use.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12894-022-01082-9.

Hyperechoic Renal Masses: Differentiation of Angiomyolipomas from Renal Cell Carcinomas using Tumor Size and Ultrasound Radiomics

A retrospective single-center study was performed to assess the performance of ultrasound image-based texture analysis in differentiating angiomyolipoma (AML) from renal cell carcinoma (RCC) on incidental hyperechoic renal lesions. Ultrasound reports of patients from 2012 to 2017 were queried, and those with a hyperechoic renal mass <5 cm in diameter with further imaging characterization and/or pathological correlation were included. Quantitative texture analysis was performed using a model including 18 texture features. Univariate logistic regression was used to identify texture variables differing significantly between AML and RCC, and the performance of the model was measured using the area under the receiver operating characteristic (ROC) curve. One hundred thirty hyperechoic renal masses in 127 patients characterized as RCCs (25 [19%]) and AMLs (105 [81%]) were included. Size (odds ratio [OR] = 0.12, 95% confidence interval [CI]: 0.04-0.43, p < 0.001) and 4 of 18 texture features, including entropy (OR = 0.09, 95% CI: 0.01-0.81, p = 0.03), gray-level non-uniformity (OR = 0.12, 95% CI: 0.02-0.72, p = 0.02), long-run emphasis (OR = 0.49, 95% CI: 0.27-0.91, p = 0.02) and run-length non-uniformity (OR = 2.18, 95% CI: 1.14-4.16, p = 0.02) were able to differentiate AMLs from RCCs. The area under the ROC curve for the performance of the model, including texture features and size, was 0.945 (p < 0.001). Ultrasound image-based textural analysis enables differentiation of hyperechoic RCCs from AMLs with high accuracy, which improves further when combined with tumor size.

Evidence-based protocol-led management of renal angiomyolipoma: A review of literature

Renal angiomyolipomas (R-AMLs) are rare benign tumors, which occur sporadically and in association with genetic conditions such as tuberous sclerosis complex (TSC) and lymphangioleiomyomatosis (LAM). The key clinical concern is life-threatening hemorrhage. There is uncertainty about the optimal management strategy for patients with R-AMLs. We aim to review the evidence and provide a protocolled approach for the management of R-AMLs. A literature search of R-AML was conducted using MEDLINE and EMBASE for articles published between January 1990 and March 2020. Patient with TSC and sporadic cases were included. Treatment strategies, including active surveillance, surgery, selective arterial embolization (SAE), ablation, and systemic therapies, were reviewed. Outcomes from contemporary case series of active surveillance, surgery, and SAE were collated. There were no randomized controlled trials on this topic. The retrospective case series reviewed showed that many R-AMLs can be managed safely with active surveillance. Tumor size is the most important predictor of bleeding, and other factors such as rate of growth, women of child-bearing age, aneurysm size, and symptoms should be considered when deciding on prophylactic treatment. There is limited evidence for the traditional 4-cm cutoff for treatment, which may lead to overtreatment. The primary intervention options are SAE and surgery; whereas SAE is a less invasive option, nephron sparing surgery offers a lower risk of recurrence. Both appear to have similar morbidity, and the current evidence does not recommend one over the other in most cases. Thermal ablation has promising results but has only been trialed in small case series. Patients with TSC can be offered mammalian target of rapamycin inhibitors of which everolimus appears to cause the greatest shrinkage of tumors with an acceptable side-effect profile. R-AMLs should be assessed for their risk of bleeding. Low-risk tumors should be treated with active surveillance. High-risk tumors should be treated with SAE or surgery. Systemic treatments are the first-line of treatment for patients with TSC to preserve renal parenchyma.

Chemical shift imaging in the identification of those renal tumours that contain microscopic fat and the utility of multiparametric MRI in their differentiation

INTRODUCTION

The aim of this study was to assess the qualitative and MRI findings of renal tumours, to determine which lesions contain microscopic fat, one of the potential differentiating factors between tumour types.

METHODS

73 patients who underwent 3 Tesla MRI including chemical shift imaging, with subsequent biopsy or excision for histopathological diagnosis, were included in the study. The images were reviewed for a decrease in signal intensity (SI) on the opposed phase compared with the in-phase gradient echo T1 images, indicating the presence of microscopic fat. The chemical shift index was then calculated as a percentage of SI change and compared with the pathological diagnosis.

RESULTS

In total, 38 (52%) of lesions demonstrated a decrease in SI, consistent with microscopic fat. Microscopic fat was found in 28 (80%) clear cell renal cell carcinomas (RCCs), 6 (66.7%) angiomyolipomas, 2 (20%) papillary RCCs, 1 (20%) chromophobe RCC and 1 (9.1%) oncocytoma. Pairwise comparison of means indicated that the amount of microscopic fat was significantly larger only for angiomyolipomas compared with clear cell RCCs (P < 0.001) and other renal lesions (P < 0.001).

CONCLUSIONS

A decrease in SI on opposed phase compared with in-phase chemical shift imaging favours the diagnosis of either clear cell RCC or an angiomyolipoma. When combined with other parameters in mpMRI, this may aid differentiation of benign from malignant tumours and differentiation of aggressive from indolent RCC subtypes. This may be of value where biopsy is non-diagnostic, not feasible due to location or in high-risk patients.

Can subcentimetre ultrasound detected angiomyolipomas be safely disregarded?

AIM

To optimise follow-up by dismissing lesions on baseline ultrasound (US) if renal lesions conform to US criteria of an angiomyolipoma (AML).

METHOD AND MATERIALS

The present study was a 10-year retrospective review of patients who were found to have incidental hyperechoic renal lesions on US to ascertain the outcome from subsequent imaging, clinical encounters, and cancer registrations. Exclusions included renal calculi, tuberous sclerosis, Von-Hippel-Lindau, or a known cancer.

RESULTS

After excluding 39 patients, 1,493 patients were identified. One hundred and sixty had more than one lesion with 87 patients having bilateral lesions. Regardless of indication, 889 patients had subsequent imaging within 5 years (59.5%). The average size of all AMLs was 13.2 mm. In the group with lesions that were <10 mm (807), 438 had imaging follow-up with an average follow-up time of 1.5 years. Mean lesion size in this group was 7 mm, with an average increase of <0.5 mm on follow-up. No lesions were found to be malignant on subsequent imaging nor did any of these patients have a subsequent renal cancer diagnosis registered at local multidisciplinary team meetings.

CONCLUSION

No incidental subcentimetre hyperechoic renal lesion with imaging characteristics of an AML demonstrated significant growth or developed into a malignancy on follow-up.

The value of surveying the kidneys during pelvic ultrasound examinations

INTRODUCTION

Pelvic ultrasounds are commonly performed for various clinical indications in female patients presenting to the hospital. A survey of the kidneys is routinely included as part of the examination, but there is limited justification for their inclusion in the assessment of every female presenting for a pelvic ultrasound.

METHOD

We examined the utility of surveying the kidney ultrasound during pelvic ultrasonography by reviewing the records of 1009 pelvic ultrasound examinations in 1000 women.

RESULTS

In total, 46 incidental findings were identified, but 91% of these were clinically inconsequential. Only four patients had incidental findings of high clinical priority requiring specialist treatment. Of these, two patients were symptomatic and had urinary tract obstruction due to stones. The other two patients harboured asymptomatic renal cell carcinomas. The overall incidence of renal incidental findings of high clinical priority in asymptomatic patients was two in 1009 examinations (1999 kidneys).

CONCLUSION

Indiscriminate uncritical screening of the kidneys in women presenting for pelvic ultrasound is not evidence-based and represents a low-yield examination with extremely low rate of incidental findings of clinical significance.