1. Imaging of Small Renal Masses
Mark E. Lockhart, MD, MPH
University of Alabama at Birmingham
July 28, 2012

2. Objectives
Discuss basic imaging findings associated with small renal masses
Highlight recent radiology recommendations of incidental renal lesions

3. Konnak JW, J of Uro 1985; Ozen H, Br J Uro 1993
Renal “Masses”
Most are now incidental on US, CT and MRI
Most are simple cysts and require no action
Incidental RCC have lower stage of malignancy (82% stage 1) than symptomatic (37%)
Konnak JW, J of Uro 1985; Ozen H, Br J Uro 1993

4. Column of Bertin Actually a septum rather than a column
Junction of interpolar region and pole
May be slightly echogenic relative to adjacent cortex

5. How to evaluate a renal mass
Is it fatty?
Gross fat is less than -20 HU
Consider angiomyolipoma or liposarcoma
Is it cystic?
Is it fluid density (-10 to 20 HU)
Use Bosniak criteria
Does it enhance?
Borderline is HU change
Metastases, IVC clot, lymphadenopathy?

6. Angiomyolipoma 10% of patients with tuberous sclerosis
80% of TS have AML
If exophytic then look for wedge of fat in cortex

7. Bosniak Classification
Bosniak MA. The current radiological approach to renal cysts. Radiology 1986;158:1 -10
Type 1 – simple cyst
Type 2 – mildly complex; likely benign
Type 3 – complex; worrisome
Type 4 – cystic neoplasm
Bosniak MA, Rad Curry NS, AJR 2000

8. Bosniak II: Small hyperdense
Cannot show enhancement
Evaluation for de-enhancement can be useful if same scanner on same day

9. Bosniak IIF
Slightly more complex cysts that cannot be neatly classified as category II or III lesions.
Perceived but nonmeasureable septal enhancement
stable on f/u

10. Bosniak III Indeterminate cystic masses
Thickened irregular walls or septa with measureable enhancement
25-59% chance malignancy
Recent work at UAB suggests lower rate
Percutaneous biopsy is controversial
Curry NS, AJR 2000; Berland 2012

11. Bosniak MA, Rad 1986 Curry NS, AJR 2000
Bosniak IV
Malignant cystic masses.
80-100% likelihood of malignancy
Findings similar to Bosniak III but also have enhancing soft-tissue components adjacent to, but independent of, the wall or septum.
Bosniak MA, Rad Curry NS, AJR 2000

12. Bosniak IV: Thick enhance septa
Multilocular cystic nephroma
Look for extension into collecting system
No venous extension

13. Renal Cell Carcinoma Most common renal malignancy More common in males
Arises in renal cortex – often disrupts renal contour even when small
Bilateral in only 2%
Calcifications in 25-30%

14. Oncocytoma mimics RCC Both are solid and disrupt cortical margin
Both can enhance
Both can have central scar

15. Urothelial Carcinoma Central renal mass with mild ehancement
Rarely calcified
Extension into collecting system
Nodal metastases

16. Lipid-Poor AML Mildly hyperdense on CT
Low T2 signal. Does not drop signal on opposed phase MRI
Enhances similar to RCC

17. Renal Lymphoma Focal mass(es) Infiltrative mass Renal hilar mass
Perinephric rind
Rarely only site of involvement

18. Management ACR white paper on incidental renal masses
Cystic based on Bosniak criteria
Solid based on size
>3cm, surgery
1-3cm, surgery (may biopsy if hyperdense, homogenously enhancing)
<1cm, observe until 1cm
Berland JACR 2010

19. Management
Slight different criteria if high risk patient or limited life expectancy
Small mass more likely benign
Still rare risk of metastases in small mass
Lack of morphologic change over 5 years suggests benign
Berland JACR 2010

20. Management different for VHL
Lower malignant potential
Resect when largest 3 cm

21. Acquired Cystic Renal Disease
Much higher risk of RCC development
Consider any solid mass as suspicious

22. Summary Small renal masses are a common diagnostic challenge
A few have characteristic features that can help the diagnosis
Know the imaging criteria