Elliot K. Fishman M.D.
Johns Hopkins Hospital

“In patients less than 35 years old, ostensibly at much lesser risk of developing renal malignancies, we acquire only noncontrast, arterial, and delayed phase images, because the odds of the patient having either a renal parenchymal lesion or a significant abnormality in the other parenchymal organs of the upper abdomen are much less, making venous phase acquisitions of less value.”
Upper and Lower Tract Urothelial Imaging Using Computed Tomography Urography
Raman SP, Fishman EK
Radiol Clin North Am 2017 Mar;55(2):225-241. 

The AUA guidelines for performing PN include the following: (a) PN should be a priority for management of cT1a renal masses when intervention is indicated. (b) Nephron-sparing approaches should be a priority for patients with an anatomic or functionally solitary kidney, bilateral tumors, known familial RCC, preexisting CKD, or proteinuria. (c) Nephron-sparing approaches should be considered for patients who are young, have multifocal masses, or have comorbidities that are likely to affect renal function in the future. 
2017 AUA Renal Mass and Localized Renal Cancer Guidelines: Imaging Implications 
Ward RD et al.
Radiographics. 2018 Nov-Dec;38(7):2021-2033

“The AUA guideline for performing RN stipulates that physicians should consider RN in cases in which tumor size, RMB results, and/or imaging characteristics suggest increased oncologic potential. In this setting, RN is preferred when all of the following criteria are met: (a) there is high tumor complexity and PN would be challenging, even in experienced hands; (b) there is no preexisting CKD or proteinuria; and (c) the contralateral kidney is normal and the new baseline estimated glomerular filtration rate will likely be greater than 45 mL/min/1.73 m2.”
2017 AUA Renal Mass and Localized Renal Cancer Guidelines: Imaging Implications 
Ward RD et al.
Radiographics. 2018 Nov-Dec;38(7):2021-2033

“ In current practice, most renal masses are discovered serendipitously. As the size of these newly discovered renal lesions decreases, the proportion of benign lesions increases. However, while great strides have been made in lesion detection, lesion characterization has lagged.”
Simplified Imaging Approach for Evaluation of the Solid Renal Mass in Adults
Dyer R et al.
Radiology 2008;247:331-343

“ In a study of 2770 surgical resections of solid renal masses, investigators found that 25% of the masses smaller than 3 cm were benign.”
Solid Renal Tumors: An Analysis of pathological Features Related to Tumor Size
Frank I et al.
J Urol 2003;170:2217-2220

“ In general, large (>3cm) solid renal masses are likely malignant; similarly, the smaller a solid mass, the more likely it is benign. In addition, a small renal cell carcinoma is more likely to be low grade and indolent behaving than a larger one.Therefore we have suggested that solid masses <1cm be observed.”
Managing Incidental Findings on Abdominal CT: White Paper of the ACR Incidental Findings Committee
Berland LL et al.
J Am Coll Radiol 2010;7;754-773

“ A homogeneous renal mass measuring greater than 70 HU at unenhanced CT has a greater than 99.9% chance of representing a high attenuation renal cyst rather than a renal cell carcinoma.”
Can High-Attenuation Renal Cysts Be Differentiated from Renal Cell Carcinoma at Unenhance CT?
Jonisch AI et al.
Radiology 2007; 243:445-450

Mean is 67 HU ± 13

Mean is 68 HU ± 12

Mean is 69 HU ± 14

86HU

“ All provens RCCs in this series contained substantial noncalcified regions that measured 20-70 HU in ROI attenuation on unenhanced CT. Indeterminate renal lesions on unenhanced CT measuring within this 20-70 HU danger zone warrant further workup, whereas lesions that fall entirely outside this range may be considered benign.”
Renal Cell Carcinoma: Attenuation Values on Unenhanced CT
Pooler BD et al.
AJR 2012; 198:1115-1120

“ The average maximum unenhanced ROI attenuation for all lesions was 39.7 ± 10.6 HU (range 21-80 HU), and the average minimum ROI attenuation was 27.5 ± 10.4 HU (range 4-67 HU).”
Renal Cell Carcinoma: Attenuation Values on Unenhanced CT
Pooler BD et al.
AJR 2012; 198:1115-1120

“An incidental renal mass is considered to be a benign cyst if it is both homogeneous and less than 20 HU and is considered indeterminate if it measures above 20 HU on either unenhanced or contrast-enhanced CT.”
Prevalence of Low-Attenuation Homogeneous Papillary Renal Cell Carcinoma Mimicking Renal Cysts on CT 
Corwin MT et al.
AJR 2018; 211:1259–1263

“Most renal angiomyolipomas are asymptomatic. However, patients can present with flank pain, hematuria, hemorrhage, or a tender abdominal mass. Renal angiomyolipomas are the second most common cause of morbidity and mortality among patients with tuberous sclerosis. This risk can be attributed to an increased risk of rupture or hemorrhage of angiomyolipomas larger than 4 cm and aneurysms larger than 5 mm occurring within these tumors. If either of these criteria is met, treatment consists of resection or embolization. Tumors smaller than 4 cm are followed conservatively.”
Comprehensive imaging manifestations of tuberous sclerosis.
Manoukian SB, Kowal DJ.
AJR Am J Roentgenol. 2015 May;204(5):933-43

Multiple Septations in AML