Primary and secondary diseases of the perinephric space: an approach to imaging diagnosis with emphasis on MRI.

The perinephric space is the middle compartment of the retroperitoneum, containing the kidneys and adrenal glands. Differential considerations for diseases involving primarily the perinephric space differ from those arising from the kidney itself, show variant imaging features, and require identification and characterisation by interpreting radiologists-an imaging diagnosis can be suggested in many cases. Lymphangiomas are congenital cystic lesions that may contain lipid-laden chyle, which may be detectable on magnetic resonance imaging (MRI). Retroperitoneal fibrosis, Erdheim-Chester disease, and lymphoma may present as a perinephric soft tissue rind. Osseous findings favour Erdheim-Chester, ureteric obstruction favours retroperitoneal fibrosis, and associated lymphadenopathy with mass-effect, but without invasion of adjacent structures favours lymphoma. Extramedullary haematopoiesis and brown fat stimulation are both characterised by signal drop on opposed-phase T1-weighted (W) images, the former resulting from severe anaemia and the latter in the context of elevated serum catecholamines, especially in the setting of phaeochromocytoma. Liposarcoma is the most common primary sarcoma of the retroperitoneum. Metastases are uncommon; however, they can be seen in melanoma, among other primary malignancies. Increased T1W signal hyperintensity is typical of melanoma metastases and haematomas. Abscesses show non-enhancing fluid centrally with marked diffusion restriction. This article presents a review of the perinephric space, pathological conditions of the perinephric space, and an approach towards imaging and diagnosis using cross-sectional imaging, with emphasis on MRI. MRI provides better tissue characterisation, assessment of enhancement kinetics, and detection of intralesional fat in comparison to CT. Clinical and laboratory correlation or tissue sampling may be required for definitive diagnosis in some cases.

Contemporary update on imaging of cystic renal masses with histopathological correlation and emphasis on patient management.

This article presents an updated review of cystic renal mass imaging. Most cystic renal masses encountered incidentally are benign and can be diagnosed confidently on imaging and require no follow-up. Hyperattenuating masses discovered at unenhanced or single-phase enhanced computed tomography (CT) measuring between 20-70 HU are indeterminate and can be further investigated first by using ultrasound and, then with multi-phase CT or magnetic resonance imaging (MRI); as the majority represent haemorrhagic/proteinaceous cysts (HPCs). Dual-energy CT may improve differentiation between HPCs and masses by suppressing unwanted pseudo-enhancement observed with conventional CT. HPCs can be diagnosed confidently when measuring >70 HU at unenhanced CT or showing markedly increased signal on T1-weighted imaging. Although the Bosniak criteria remains the reference standard for diagnosis and classification of cystic renal masses, histopathological classification and current management has evolved: multilocular cystic renal cell carcinoma (RCC) has been reclassified as a cystic renal neoplasm of low malignant potential, few Bosniak 2F cystic masses progress radiologically during follow-up; RCC with predominantly cystic components are less aggressive than solid RCC; and Bosniak III cystic masses behave non-aggressively. These advances have led to an increase in non-radical management or surveillance of cystic renal masses including Bosniak 3 lesions. Tubulocystic RCC is a newly described entity with distinct imaging characteristics, resembling a pancreatic serous microcystadenoma. Other benign cystic masses including: mixed epithelial stromal tumours (MEST) are now considered in the spectrum of cystic nephroma and angiomyolipoma (AML) with epithelial cysts (AMLEC) resemble a fat-poor AML with cystic components.

CT imaging of solid renal masses: pitfalls and solutions.

Computed tomography (CT) remains the first-line imaging test for the characterisation of renal masses; however, CT has inherent limitations, which if unrecognised, may result in errors. The purpose of this manuscript is to present 10 pitfalls in the CT evaluation of solid renal masses. Thin section non-contrast enhanced CT (NECT) is required to confirm the presence of macroscopic fat and diagnosis of angiomyolipoma (AML). Renal cell carcinoma (RCC) can mimic renal cysts at NECT when measuring <20 HU, but are usually heterogeneous with irregular margins. Haemorrhagic cysts (HC) may simulate solid lesions at NECT; however, a homogeneous lesion measuring >70 HU is essentially diagnostic of HC. Homogeneous lesions measuring 20-70 HU at NECT or >20 HU at contrast-enhanced (CE) CT, are indeterminate, requiring further evaluation. Dual-energy CT (DECT) can accurately characterise these lesions at baseline through virtual NECT, iodine overlay images, or quantitative iodine concentration analysis without recalling the patient. A minority of hypo-enhancing renal masses (most commonly papillary RCC) show indeterminate or absent enhancement at multiphase CT. Follow-up, CE ultrasound or magnetic resonance imaging (MRI) is required to further characterise these lesions. Small (<3 cm) endophytic cysts commonly show pseudo-enhancement, which may simulate RCC; this can be overcome with DECT or MRI. In small (<4 cm) solid renal masses, 20% of lesions are benign, chiefly AML without visible fat or oncocytoma. Low-dose techniques may simulate lesion heterogeneity due to increased image noise, which can be ameliorated through the appropriate use of iterative reconstruction algorithms.

Multiparametric MRI of the anterior prostate gland: clinical-radiological-histopathological correlation.

Anterior prostate cancer (APC) is defined as a tumour in which more than half of malignant tissue is located anterior to the urethra. APCs are increasingly recognized as clinically important, particularly in patients undergoing active surveillance and for patients with negative non-targeted systematic transrectal ultrasound (TRUS)-guided biopsies but with persistent clinical suspicion of cancer. Multiparametric (mp) MRI has a crucial role for the diagnosis of anterior tumours, eventual histological sampling of suspicious lesions using image-guided targeted biopsy techniques, and potentially, to improve local staging of disease. mpMRI is accurate for the detection of APC and for differentiation of tumour from other anterior prostatic structures including benign prostatic hyperplasia (BPH) and the anterior fibromuscular stroma (AFMS). Characterization and reporting of APC should rely on the recently revised Prostate Imaging and Data Reporting System (PI-RADS) version 2.0 document. T2-weighted (T2W) imaging is emphasized as the determining sequence for assessment of the anterior prostate and specific features for APC on T2W imaging include: ill-defined/spiculated margin, lenticular shape, anterior/inferior location, and growth pattern (invasion of urethra or AFMS and crossing midline). Functional imaging, mainly with diffusion-weighted imaging, is also contributory and improves the sensitivity for detection of APC compared to T2W imaging alone. APCs commonly show positive surgical margins after radical prostatectomy and staging of disease extent using conventional clinical parameters is limited. mpMRI may have a future role to improve local staging of APC. This review illustrates the importance of mpMRI in APC using a clinical-radiological-histopathological approach.

Assessing the utilization of functional imaging in multiparametric prostate MRI in routine clinical practice.

AIM: To evaluate the utilization of functional imaging tests in multiparametric (mp)-MRI of the prostate in routine practice and to assess whether education improves usage. MATERIALS AND METHODS: With research ethics board approval, 254 patients underwent mp-MRI [diffusion-weighted imaging (DWI) and dynamic contrast enhancement (DCE)] over a 1-year period at a single tertiary-care referral centre for prostate disease. All studies were reported by fellowship-trained abdominal radiologists. To determine to what extent parametric tests were used, radiology reports were searched for terms indicating usage of DWI/DCE and studies were reviewed to determine whether post-processing of DCE was performed. Midway through the study, an internal continuing medical education (CME) programme was instituted (consisting of lectures, electronic reading material, intra- and inter-departmental prostate rounds) and a standardized reporting template was introduced. Utilization of functional imaging was compared between radiologists by years of experience and by number of examinations interpreted, by study indication, and before and after CME. RESULTS: Overall, both DWI and DCE were used in 50.7% of examinations. DWI (67.3%) was more frequently used than DCE (56.3%). DCE contrast curves were generated in 33.5% of studies, and quantitative analysis was performed in only one patient. Use of parametric tests was higher after CME (60.6% versus 40.4%), p = 0.009. There was no correlation between the use of parametric tests and years of experience, (p = 0.94), and there was no association with the number of examinations interpreted (p = 0.19-0.97). There was no association between the use of parametric tests and study indication, (p = 0.16); however, contrast curves were produced more frequently in non-staging studies, (p = 0.027). CONCLUSION: Parametric tests were underutilized in routine practice. DWI was used more commonly than DCE. CME was associated with increased utilization of mp-MRI.

Multiparametric MRI of solid renal masses: pearls and pitfalls.

Functional imaging [diffusion-weighted imaging (DWI) and dynamic contrast enhancement (DCE)] techniques combined with T2-weighted (T2W) and chemical-shift imaging (CSI), with or without urography, constitutes a comprehensive multiparametric (MP) MRI protocol of the kidneys. MP-MRI of the kidneys can be performed in a time-efficient manner. Breath-hold sequences and parallel imaging should be used to reduce examination time and improve image quality. Increased T2 signal intensity (SI) in a solid renal nodule is specific for renal cell carcinoma (RCC); whereas, low T2 SI can be seen in RCC, angiomyolipoma (AML), and haemorrhagic cysts. Low b-value DWI can replace conventional fat-suppressed T2W. DWI can be performed free-breathing (FB) with two b-values to reduce acquisition time without compromising imaging quality. RCC demonstrates restricted diffusion; however, restricted diffusion is commonly seen in AML and in chronic haemorrhage. CSI must be performed using the correct echo combination at 3 T or T2* effects can mimic intra-lesional fat. Two-dimensional (2D)-CSI has better image quality compared to three-dimensional (3D)-CSI, but volume averaging in small lesions can simulate intra-lesional fat using 2D techniques. SI decrease on CSI is present in both AML and clear cell RCC. Verification of internal enhancement with MRI can be challenging and is improved with image subtraction. Subtraction imaging is prone to errors related to spatial misregistration, which is ameliorated with expiratory phase imaging. SI ratios can be used to confirm subtle internal enhancement and enhancement curves are predictive of RCC subtype. MR urography using conventional extracellular gadolinium must account for T2* effects; however, gadoxetic acid enhanced urography is an alternative. The purpose of this review it to highlight important technical and interpretive pearls and pitfalls encountered with MP-MRI of solid renal masses.

Ten uncommon and unusual variants of renal angiomyolipoma (AML): radiologic-pathologic correlation.

Classic (triphasic) renal angiomyolipoma (AML) is currently classified as a neoplasm of perivascular epithelioid cells. For diagnosis of AML, the use of thin-section non-contrast enhanced CT (NECT) improves diagnostic accuracy; however, identifying gross fat within a very small AML is challenging and often better performed with chemical-shift MRI. Although the presence of gross intra-tumoural fat is essentially diagnostic of AML; co-existing intra-tumoural fat and calcification may represent renal cell carcinoma (RCC). Differentiating AML from retroperitoneal sarcoma can be difficult when AML is large; the feeding vessel and claw signs are suggestive imaging findings. AML can haemorrhage, with intra-tumoural aneurysm size >5 mm a more specific predictor of future haemorrhage than tumor size >4 cm. Diagnosis of AML in the setting of acute haemorrhage is complex; comparison studies or follow-up imaging may be required. Not all AML contain gross fat and imaging features of AML without visible fat overlap with RCC; however, homogeneity, hyperdensity at NECT, low T2-weighted signal intensity and, microscopic fat are suggestive features. Patients with tuberous sclerosis often demonstrate a combination of classic and minimal fat AML, but are also at a slightly increased risk for RCC and should be imaged cautiously. Several rare pathological variants of AML exist including AML with epithelial cysts and epithelioid AML, which have distinct imaging characteristics. Classic AML, although benign, can be locally invasive and the rare epithelioid AML can be frankly malignant. The purpose of this review is to highlight the imaging manifestations of 10 uncommon and unusual variants of AML using pathological correlation.

Low b-value (black blood) respiratory-triggered fat-suppressed single-shot spin-echo echo-planar imaging (EPI) of the liver: comparison of image quality at 1.5 and 3 T.

AIM: To compare echo-planar imaging (EPI) of the liver at 1.5 and 3 T. MATERIALS AND METHODS: Under a waiver from the institutional review board, 46 patients underwent respiratory-triggered fat-suppressed b = 50 s/mm(2) EPI at 1.5 or 3 T between 2010-2013. Thirty liver lesions were included with no therapy performed between studies. Signal- and contrast-to-noise ratios (SNR/CNR) were compared using a paired t-test. Two blinded readers independently assessed EPI at 1.5 and 3 T in two separate reading sessions for image quality by hepatic region and the presence and severity of artefacts. Results were compared using the Wilcoxon sign rank test. Interobserver agreement was assessed using Cohen's kappa statistic. RESULTS: There was no difference in mean SNR/CNR at 3 T (20.26 ± 10.25/9.55 ± 15.78); compared to 1.5 T (21.96 ± 9.75/5.35 ± 7.89); p = 0.43 and p = 0.09, respectively. Image quality was better at 1.5 T for all hepatic regions (p < 0.001). Image quality was poor or suboptimal at 3 T in 57% of regions studied, compared to 5.6% at 1.5 T. With the exception of image blur (p = 0.27), all artefacts were more prevalent at 3 T with higher rates of image distortion (p < 0.001), failed fat suppression (p = 0.002), ghosting (p < 0.001), parallel imaging artefact (p < 0.001), and shading (p < 0.001). Interobserver agreement was moderate (κ = 0.43-0.53). CONCLUSION: Fat-suppressed low b-value EPI of the liver is significantly better at 1.5 T compared to 3 T.

Pitfalls of adrenal imaging with chemical shift MRI.

Chemical shift (CS) MRI of the adrenal glands exploits the different precessional frequencies of fat and water protons to differentiate the intracytoplasmic lipid-containing adrenal adenoma from other adrenal lesions. The purpose of this review is to illustrate both technical and interpretive pitfalls of adrenal imaging with CS MRI and emphasize the importance of adherence to strict technical specifications and errors that may occur when other imaging features and clinical factors are not incorporated into the diagnosis. When performed properly, the specificity of CS MRI for the diagnosis of adrenal adenoma is over 90%. Sampling the in-phase and opposed-phase echoes in the correct order and during the same breath-hold are essential requirements, and using the first echo pair is preferred, if possible. CS MRI characterizes more adrenal adenomas then unenhanced CT but may be non-diagnostic in a proportion of lipid-poor adenomas; CT washout studies may be able to diagnose these lipid-poor adenomas. Other primary and secondary adrenal tumours and supra-renal disease entities may contain lipid or gross fat and mimic adenoma or myelolipoma. Heterogeneity within an adrenal lesion that contains intracytoplasmic lipid could be due to myelolipoma, lipomatous metaplasia of adenoma, or collision tumour. Correlation with previous imaging, other imaging features, clinical history, and laboratory investigations can minimize interpretive errors.

Multiparametric Magnetic Resonance Imaging in the Diagnosis of Clinically Significant Prostate Cancer: an Updated Systematic Review.

There has been growing utilisation of multiparametric magnetic resonance imaging (MPMRI) as a non-invasive tool to diagnose and localise clinically significant prostate cancer (CSPCa). This updated systematic review examines the use of MPMRI in patients with an elevated risk of CSPCa who have had a prior negative transrectal ultrasound systematic biopsy (TRUS-SB) and who were biopsy naïve. MEDLINE, EMBASE and the Cochrane Database of Systematic Reviews were searched for existing systematic reviews published up to September 2020. The literature search of the electronic databases combined disease-specific terms (prostate cancer, prostate carcinoma, etc.) and treatment-specific terms (magnetic resonance, etc.). Studies were included if they were randomised controlled trials (RCTs) comparing MPMRI to template transperineal mapping biopsy (TPMB) or to TRUS-SB. Thirty-six RCTs were eligible. For biopsy-naïve men, accuracy of diagnosis of CSPCa showed sensitivities from 87 to 96% and specificities ranging from 29 to 45%. Meta-analyses for CSPCa showed increased detection favouring MPMRI-targeted biopsy over TRUS-SB by 3% (95% confidence interval 0-7%, P = 0.03) and decreased detection of clinically insignificant prostate cancer (CISPCa) favouring MPMRI by 8% (95% confidence interval -11 to 5%, P < 0.00001). Accuracy of MPMRI for men with prior negative biopsy showed sensitivities of 78-100% and specificities of 30-100%. Meta-analyses comparing MPMRI to TRUS-SB showed increased detection of 5% (95% confidence interval 3-7%, P < 0.0001) with a reduction of CISPCa detection of 7% (95% confidence interval 4-9%, P < 0.00001). The growing acceptance of MPMRI utilisation internationally and the recent publication of several RCTs regarding MPMRI in reducing CISPCa detection rates, particularly in biopsy-naïve men, without loss of sensitivity for CSPCa necessitates the synthesis of updated evidence examining MPMRI in the diagnosis of CSPCa.

Characterization of small (<4cm) solid renal masses by computed tomography and magnetic resonance imaging: Current evidence and further development.

Diagnosis of renal cell carcinomas (RCC) subtypes on computed tomography (CT) and magnetic resonance imaging (MRI) is clinically important. There is increased evidence that confident imaging diagnosis is now possible while standardization of the protocols is still required. Fat-poor angiomyolipoma show homogeneously increased unenhanced attenuation, homogeneously low signal on T2-weighted MRI and apparent diffusion coefficient (ADC) map, may contain microscopic fat and are classically avidly enhancing. Papillary RCC are also typically hyperattenuating and of low signal on T2-weighted MRI and ADC map; however, their gradual progressive enhancement after intravenous administration of contrast material is a differentiating feature. Clear cell RCC are avidly enhancing and may show intracellular lipid; however, these tumors are heterogeneous and are of characteristically increased signal on T2-weighted MRI. Oncocytomas and chromophobe tumors (collectively oncocytic neoplasms) show intermediate imaging findings on CT and MRI and are the most difficult subtype to characterize accurately; however, both show intermediately increased signal on T2-weighted with more gradual enhancement compared to clear cell RCC. Chromophobe tumors tend to be more homogeneous compared to oncocytomas, which can be heterogeneous, but other described features (e.g. scar, segmental enhancement inversion) overlap considerably between tumors. Tumor grade is another important consideration in small solid renal masses with emerging studies on both CT and MRI suggesting that high grade tumors may be separated from lower grade disease based upon imaging features.