Minimal-fat Angiomyolipoma Research Articles

Discordance about the Use of the TermMinimal Fat Angiomyolipoma

Discordance about the Use of the Term<i>Minimal Fat Angiomyolipoma</i>

Small solid renal masses: Characterization by diffusion-weighted MRI at 3 T

To describe the appearance of small solid renal lesions (≤3 cm) on diffusion-weighted magnetic resonance imaging (MRI) and to determine whether ADC measurements may help to differentiate benign from malignant small solid renal masses. Thirty-five patients with 47 small renal masses (23 malignant, 24 benign) who underwent 3 T MRI of the kidney using diffusion-weighted sequences (b values of 0 and 1000 s/mm(2)) were retrospectively evaluated. Qualitative and quantitative analysis of diffusion-weighted images was performed. Most lesions were hyperintense to kidney on high b-value diffusion-weighted images and hypointense on apparent diffusion coefficient (ADC) map. The mean ADC of the lesions was significantly lower than that of kidney (1.22 ± 0.3 versus 1.85 ± 0.12 mm(2)/s; p < 0.005). The mean ADC was significantly different between renal cell carcinomas (1.2 ± 0.01 mm(2)/s), metastases (1.25 ± 0.04 mm(2)/s), angiomyolipoma (1.07 ± 0.3 mm(2)/s) and oncocytomas (1.56 ± 0.08 mm(2)/s; p < 0.05). The mean ADC of clear cell renal cell carcinomas was significantly different from that of non-clear cell renal cell carcinomas (1.38 ± 0.34 versus 0.83 ± 0.34 mm(2)/s; p < 0.005). No significant difference was found between mean ADC of fat containing and minimal fat angiomyolipomas (1.06 ± 0.48 versus 1.11 ± 0.33 mm(2)/s). Small solid renal masses are hyperintense on high b value and have different ADC values.

Angiomyolipoma with Minimal Fat: Can It Be Differentiated from Clear Cell Renal Cell Carcinoma by Using Standard MR Techniques?

To retrospectively assess whether magnetic resonance (MR) imaging with opposed-phase and in-phase gradient-echo (GRE) sequences and MR feature analysis can differentiate angiomyolipomas (AMLs) that contain minimal fat from clear cell renal cell carcinomas (RCCs), with particular emphasis on small (<3-cm) masses. Institutional review board approval and a waiver of informed consent were obtained for this HIPAA-compliant study. MR images from 108 pathologically proved renal masses (88 clear cell RCCs and 20 minimal fat AMLs from 64 men and 44 women) at two academic institutions were evaluated. The signal intensity (SI) of each renal mass and spleen on opposed-phase and in-phase GRE images was used to calculate an SI index and tumor-to-spleen SI ratio. Two radiologists who were blinded to the pathologic results independently assessed the subjective presence of intravoxel fat (ie, decreased SI on opposed-phase images compared with that on in-phase images), SI on T1-weighted and T2-weighted images, cystic degeneration, necrosis, hemorrhage, retroperitoneal collaterals, and renal vein thrombosis. Results were analyzed by using the Wilcoxon rank sum test, two-tailed Fisher exact test, and multivariate logistic regression analysis for all renal masses and for small masses. A P value of less than .05 was considered to indicate a statistically significant difference. There were no differences between minimal fat AMLs and clear cell RCCs for the SI index (8.05%±14.46 vs 14.99%±19.9; P=.146) or tumor-to-spleen ratio (-8.96%±16.6 and -15.8%±22.4; P=.227) when all masses or small masses were analyzed. Diagnostic accuracy (area under receiver operating characteristic curve) for the SI index and tumor-to-spleen ratio was 0.59. Intratumoral necrosis and larger size were predictive of clear cell RCC (P<.001) for all lesions, whereas low SI (relative to renal parenchyma SI) on T2-weighted images, smaller size, and female sex correlated with minimal fat AML (P<.001) for all lesions. The diagnostic accuracy of opposed-phase and in-phase GRE MR imaging for the differentiation of minimal fat AML and clear cell RCC is poor. In this cohort, low SI on T2-weighted images relative to renal parenchyma and small size suggested minimal fat AML, whereas intratumoral necrosis and large size argued against this diagnosis.

Histogram Analysis of Small Solid Renal Masses: Differentiating Minimal Fat Angiomyolipoma From Renal Cell Carcinoma

The objective of our study was to retrospectively determine whether minimal fat renal angiomyolipoma can be differentiated from clear cell or papillary renal cell carcinoma (RCC) in small renal masses using attenuation measurement histogram analysis on unenhanced CT. Twenty minimal fat renal angiomyolipomas were compared with 22 clear cell RCCs and 23 papillary RCCs using an institutional database. All masses were histologically confirmed and all minimal fat renal angiomyolipomas lacked radiographic evidence of macroscopic fat. Using attenuation measurement histogram analysis, two blinded radiologists determined the percentage of negative pixels within each renal mass. The percentages of negative pixels below attenuation thresholds of 0, -5, -10, -15, -20, -25, and -30 HU were recorded. Sensitivity, specificity, positive predictive value, negative predictive value, and receiver operator characteristic curves for the diagnosis of minimal fat renal angiomyolipoma were generated for each threshold. The Student t test was used to compare radiologists and cohorts. Previously published attenuation and pixel-counting thresholds reported as having a specificity of near 100% for discriminating between minimal fat renal angiomyolipomas and RCCs were analyzed. The mean maximal transverse lesion diameter was 1.8 cm for minimal fat renal angiomyolipomas (SD, 0.5 cm; range, 1.1-3.0 cm), 2.1 cm for clear cell RCCs (SD, 0.5 cm; range, 1.0-2.9 cm), and 2.1 cm for papillary RCCs (SD, 0.7 cm; range, 1.3-3.9 cm). No significant difference in the percentage of negative pixels was found between minimal fat renal angiomyolipomas and clear cell RCCs or between minimal fat renal angiomyolipomas and papillary RCCs at any of the selected attenuation thresholds for either radiologist (p = 0.210-0.499). Radiologist 1 and radiologist 2 used significantly different region-of-interest sizes (p < 0.001), but neither radiologist could differentiate minimal fat renal angiomyolipoma from RCC. No previously published threshold allowed discrimination between minimal fat renal angiomyolipoma and RCC with 100% specificity. Attenuation measurement histogram analysis cannot reliably differentiate minimal fat renal angiomyolipoma from RCC.

Off-clamp laparoscopic partial nephrectomy for a fat-poor angiomyolipoma arising from the renal capsule: a case report.

Renal function can be significantly preserved after nephron-sparing surgery by decreasing the intraoperative ischemic duration or by performing off-clamp surgery. We report the case of a 56-year-old woman diagnosed with a minimal-fat angiomyolipoma arising from the renal capsule, which was successfully treated by retroperitoneoscopic partial nephrectomy without hilar clamping. Computed tomography revealed a 16 × 13 mm homogenous lenticular mass protruding from the lateral aspect of the left kidney. On both T1- and T2-weighted magnetic resonance images, the mass exhibited homogenous low-signal intensity and well-defined margins. Laparoscopic magnification indicated that the exophytic tumor was attached to the renal cortex by a small peduncle. The tumor was resected completely with negative surgical margin. The estimated glomerular filtration rate after surgery was nearly equal to that before surgery. Off-clamp laparoscopic partial nephrectomy is a feasible surgical option to prevent ischemic renal damage in select patients presenting with small, exophytic, and peripheral renal masses.

Low T2 signal intensity on magnetic resonance imaging: A feature of minimal fat angiomyolipomas

International Journal of UrologyVolume 19, Issue 1 p. 90-91 Low T2 signal intensity on magnetic resonance imaging: A feature of minimal fat angiomyolipomas Gavin Low M.B.Ch.B., M.R.C.S., F.R.C.R., Gavin Low M.B.Ch.B., M.R.C.S., F.R.C.R. Department of Radiology and Diagnostic Imaging, University of Alberta Hospital, Edmonton, Alberta, Canada. timgy@yahoo.comSearch for more papers by this authorKamal Sahi M.D., Kamal Sahi M.D. Department of Radiology and Diagnostic Imaging, University of Alberta Hospital, Edmonton, Alberta, Canada. timgy@yahoo.comSearch for more papers by this authorHarold Dhliwayo M.B.Ch.B., M.Sc., M.R.C.P.C.H., F.R.C.R., Harold Dhliwayo M.B.Ch.B., M.Sc., M.R.C.P.C.H., F.R.C.R. Department of Radiology and Diagnostic Imaging, University of Alberta Hospital, Edmonton, Alberta, Canada. timgy@yahoo.comSearch for more papers by this author Gavin Low M.B.Ch.B., M.R.C.S., F.R.C.R., Gavin Low M.B.Ch.B., M.R.C.S., F.R.C.R. Department of Radiology and Diagnostic Imaging, University of Alberta Hospital, Edmonton, Alberta, Canada. timgy@yahoo.comSearch for more papers by this authorKamal Sahi M.D., Kamal Sahi M.D. Department of Radiology and Diagnostic Imaging, University of Alberta Hospital, Edmonton, Alberta, Canada. timgy@yahoo.comSearch for more papers by this authorHarold Dhliwayo M.B.Ch.B., M.Sc., M.R.C.P.C.H., F.R.C.R., Harold Dhliwayo M.B.Ch.B., M.Sc., M.R.C.P.C.H., F.R.C.R. Department of Radiology and Diagnostic Imaging, University of Alberta Hospital, Edmonton, Alberta, Canada. timgy@yahoo.comSearch for more papers by this author First published: 03 November 2011 https://doi.org/10.1111/j.1442-2042.2011.02885.xCitations: 10Read the full textAboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat No abstract is available for this article.Citing Literature Volume19, Issue1January 2012Pages 90-91 RelatedInformation

IJU this issue

This issue contains two Editorials, one Review article, three Original articles, one Case Report, three Short Communications, and two Letters to the Editor. This issue starts with an Editorial by Professor Razack (Kuala Lumpur, Malaysia). Professor Razack, of the University of Malaya, describes the history and current status of urology in Malaysia. The Malaysian Urological Association (MUA) was founded in 1974, and aims to strengthen closer links within Asia and rest of the world's urological communities. Urology in Malaysia had made great strides since its humble start in the late 1960s to its current status, in which most of the latest equipment and facilities are available within the country. There are three da Vinci robots in the country and many laser machines for both treatment of stones and prostate diseases. MUA continues to look for opportunities to host international conferences and meetings. The review by Kitajima et al. (Kobe, Japan) describes recent issues in contrast-induced nephropathy (CIN). CIN is a serious complication among patients undergoing contrast-enhanced computed tomography with potentially high morbidity and mortality. Patients with pre-existing renal insufficiency appear to be at higher risk of CIN. To prevent CIN, every effort is required, including the routine identification of at-risk patients, the use of appropriate hydration regimens, the withdrawal of nephrotoxic drugs, the selection of a low-osmolality or iso-osmolar contrast medium (CM), and using the minimum volume of CM possible Cao et al. (Qingdao, China) determine whether steroidogenic enzyme expression is associated with the steroid secretory pattern of subclinical Cushing's syndrome (SCS) by investigating the mRNA and protein expression of CYP17 and CYP11B1 in SCS adenomas. They found that CYP11B1 and CYP17 are overexpressed in subclinical cortisol-producing adenomas (CPA) and their overexpression accounts for the increased production of cortisol that is characteristic of CPA. Gacci et al. (Florence, Italy) report factors predicting the recovery of continence after a radical prostatectomy (RP). They found that preoperative erectile function can predict post-prostatectomy incontinence, and bladder neck preservation has a significant effect on early continence recovery after RP. Kobayashi et al. (Sapporo, Japan) report an animal model for erectile dysfunction (ED) following lower urinary tract symptoms (LUTS) and bladder outlet obstruction (BOO). Male Sprague–Dawley rats with partial BOO are an experimental model of LUTS and ED. The partial-BOO rats show decreased erectile function due to endothelial dysfunction induced by impaired eNOS function. Sugimoto et al. (Saga, Japan) report a rare case of a ureterosciatic hernia successfully treated by a ureteral placement. Non-enhanced computed tomography reveals left hydroureteronephrosis and obstruction of the distal left ureter with herniation into the sciatic foramen. After 2 months with treatment with the stent, there was no recurrence. The three Short Communications are of great interest. Suzuki et al. (Tokyo, Japan) analyze the results of direct decompressive surgery plus stabilization of the vertebrae involved in six non-ambulatory patients with metastatic extradural spinal cord compression due to renal cell carcinoma. Tanaka et al. (Tokyo, Japan) evaluate diffusion-weighted magnetic resonance imaging in differentiating between minimal fat angiomyolipoma and clear cell renal cell carcinoma. Kozyrakis et al. (Athens, Greece) report on their experience with six patients diagnosed with lymphoepithelioma-like bladder carcinoma over the past 15 years. The Letter to the Editor from Nomiya et al. (Tokyo, Japan) report the first Japanese case of interstitial cystitis (IC) symptoms associated with ketamine abuse. Ketamine abuse should be included in the differential diagnoses for those presenting with LUTS suggestive of IC. The Letter to the Editor from Adam (Pretoria, South Africa) describes a message about an article by Ochiai et al. (International Journal of Urology 2011; 18: 200–5). He points out importance of combination threshold values for the PCA3 assay and prostate-specific antigen (PSA) levels, or a normal digital rectal examination (DRE), or both, to identify the presence of cancer. In their cohort study, a PCA3 score <60 associated with a PSA level <4 ng/mL and a normal DRE excluded the presence of cancer on histology. None declared.

Diffusion‐weighted magnetic resonance imaging in the differentiation of angiomyolipoma with minimal fat from clear cell renal cell carcinoma

The aim of the present study was to evaluate diffusion-weighted (DW) magnetic resonance imaging (MRI) in differentiating between minimal fat angiomyolipoma (MFAML) and clear cell renal cell carcinoma (CCRCC). Forty-one solid renal tumors without visible macroscopic fat on unenhanced computed tomography images were evaluated by MRI, including DW-MRI, and were diagnosed pathologically as CCRCC (n = 36) or MFAML (n = 5). To evaluate the heterogeneity of diffusion in each tumor, the signals of the tumors on DW-MRI were analyzed subjectively and the apparent diffusion coefficient (ADC) values and histograms assessed objectively. Thirty-three of 36 CCRCC (92%) exhibited a heterogeneous signal on DW-MRI and several peaks in the ADC value histogram, whereas four of five MFAML exhibited a homogeneous signal on DW-MRI and a single prominent peak in the histogram. The standard deviations of the ADC values were significantly smaller for MFAML than for CCRCC (P = 0.0015). In conclusion, DW-MRI can be considered a useful and noninvasive addition to the preoperative differentiation of CCRCC and MFAML.

Imaging

OBJECTIVE. The purpose of this study was to determine whether counts of pixels with subzero attenuation on CT scans can aid in the diagnosis of renal angiomyolipoma with minimal fat.MATERIALS AND METHODS. Of 33 angiomyolipomas identified among 719 renal masses resected from 702 patients over 4 years, 15 masses in 15 patients were prospectively diagnosed on the basis of the presence of fat at MDCT. The 18 patients with minimal-fat angiomyolipoma and a matched (age, sex, tumor size) cohort of patients with renal cell carcinoma were included in this study. Three radiologists independently counted the number of pixels with attenuation less than –10, –20, and –30 HU. Receiver operating characteristic analysis of the number of pixels at each cutoff was used to calculate sensitivity, specificity, and positive predictive value with the following criteria: 1, more than 10 pixels less than –20 HU; 2, more than 20 pixels less than –20 HU; 3, more than 5 pixels less than –30 HU.RESULTS. Using criterion 1, reader A id...

Angiomyolipoma with Minimal Fat on MDCT: Can Counts of Negative-Attenuation Pixels Aid Diagnosis?

The purpose of this study was to determine whether counts of pixels with subzero attenuation on CT scans can aid in the diagnosis of renal angiomyolipoma with minimal fat. Of 33 angiomyolipomas identified among 719 renal masses resected from 702 patients over 4 years, 15 masses in 15 patients were prospectively diagnosed on the basis of the presence of fat at MDCT. The 18 patients with minimal-fat angiomyolipoma and a matched (age, sex, tumor size) cohort of patients with renal cell carcinoma were included in this study. Three radiologists independently counted the number of pixels with attenuation less than -10, -20, and -30 HU. Receiver operating characteristic analysis of the number of pixels at each cutoff was used to calculate sensitivity, specificity, and positive predictive value with the following criteria: 1, more than 10 pixels less than -20 HU; 2, more than 20 pixels less than -20 HU; 3, more than 5 pixels less than -30 HU. Using criterion 1, reader A identified six angiomyolipomas; reader B, five; and reader C, two. The combined sensitivity was 24%; specificity, 98%; and positive predictive value, 69%. Using criterion 2, reader A identified three angiomyolipomas; reader B, four; and reader C, two. The combined sensitivity was 17%; specificity, 100%; and positive predictive value, 100%. Using criterion 3, reader A identified four angiomyolipomas; reader B, four; and reader C, two. The combined sensitivity was 18%; specificity, 100%; and positive predictive value, 100%. CT findings of more than 20 pixels with attenuation less than -20 HU and more than 5 pixels with attenuation less than -30 HU have a positive predictive value of 100% in detection of angiomyolipoma, but most angiomyolipomas with minimal fat cannot be reliably identified on the basis of an absolute pixel count.

Imaging characteristics of minimal fat renal angiomyolipoma with histologic correlations

ObjectivesTo review our experience with minimal fat angiomyolipomas (AMLs) and correlate the confirmed pathologic diagnosis with preoperative radiologic features to evaluate the feasibility of an accurate diagnosis preoperatively. On rare occasions, renal AMLs contain minimal amounts of fat that are not identified on cross-sectional imaging. MethodsFrom November 1998 to August 2003, 6 patients (seven lesions) underwent renal surgery with the preoperative diagnosis of renal cell carcinoma as determined by preoperative imaging studies, and the finding of AML was unexpected. A single pathologist and radiologist reviewed all pathologic specimens and radiologic examinations. The characteristic findings were recorded and compared with those in published reports. ResultsPathologic review of the specimens demonstrated microscopic amounts of mature adipocytes, abnormally thickened blood vessels, and smooth muscle cells in all seven lesions. The mean estimated fat content was 4.1% (range 3% to 10%). Hounsfield unit measurement of the lesions on unenhanced computed tomography images revealed all lesions to be hyperdense relative to the normal kidney parenchyma and enhanced by at least 90 Hounsfield units or more with the administration of intravenous contrast. Enhancement was homogenous throughout each of the seven masses. ConclusionsMinimal fat renal AML tumors are typically hyperdense relative to the normal kidney parenchyma and demonstrate homogenous enhancement with the administration of intravenous contrast on computed tomography. These results may have important implications when planning partial versus radical nephrectomy by open or minimally invasive techniques.

Tuberose sclerosis complex: analysis of growth rates aids differentiation of renal cell carcinoma from atypical or minimal-fat-containing angiomyolipoma

To study the radiological characteristics of renal masses in individuals with tuberous sclerosis complex (TSC) using serial CT, and to examine how renal cell carcinoma (RCC) may be differentiated from indeterminate cysts or masses. This was a retrospective study of 12 cases of TSC in which dedicated renal CT followed after US had demonstrated cystic or sonographically unusual renal masses. The CT density of all masses was measured and the masses categorized as simple cysts, complex cysts, angiomyolipomas or indeterminate solid masses. Subjects were maintained on regular follow-up with repeat CT or MRI and interval renal US. Indeterminate masses that showed rapid growth were considered suspicious for renal cell carcinoma and biopsy or nephrectomy followed. Comparative data were available for a median of 4 years. In each case the renal masses were multiple and bilateral; mean mass diameter was 3.6 cm. Among a total of 206 masses, 18 were simple cysts and 3 were complex cysts. Of the complex cysts, 1 proved to be an angiomyolipoma on histology and the other 2 showed no growth. Of the solid masses, 133 were typical angiomyolipomas (AMLs) and 52 were indeterminate. On follow-up, only 3 indeterminate masses showed rapid growth (>0.5 cm/year), of which only 1 proved to be an RCC on biopsy. The other 2 were minimal-fat AMLs, and the remainder of the masses showed no or slow growth. Many renal masses associated with TSC are radiologically indeterminate. A growth threshold of >0.5 cm/year identified the only RCC in this study (0.5% of all masses). Yearly radiological follow-up of indeterminate renal masses is recommended for individuals with TSC.