Imaging of Small Renal Masses
Mark E. Lockhart, MD, MPH
University of Alabama at Birmingham
July 28, 2012
Objectives

Discuss basic imaging findings
associated with small renal masses

Highlight recent radiology
recommendations of incidental renal
lesions
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
Column of Bertin

Actually a septum
rather than a column

Junction of interpolar
region and pole

May be slightly
echogenic relative to
adjacent cortex
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 15-20 HU change
 Metastases, IVC clot, lymphadenopathy?
Angiomyolipoma
10% of patients
with tuberous
sclerosis
 80% of TS have
AML
 If exophytic then
look for wedge of
fat in cortex

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 1986
AJR 2000
Curry NS,
Bosniak II: Small hyperdense

Cannot show
enhancement

Evaluation for
de-enhancement
can be useful if
same scanner on
same day
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
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
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 1986
Curry NS, AJR 2000
Bosniak IV: Thick enhance septa

Multilocular cystic
nephroma

Look for extension
into collecting
system

No venous extension
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%

Oncocytoma mimics RCC

Both are solid and
disrupt cortical margin

Both can enhance

Both can have central
scar
Urothelial Carcinoma

Central renal mass
with mild
ehancement

Rarely calcified

Extension into
collecting system

Nodal metastases
Lipid-Poor AML

Mildly hyperdense on
CT

Low T2 signal. Does
not drop signal on
opposed phase MRI

Enhances similar to
RCC
Renal Lymphoma





Focal mass(es)
Infiltrative mass
Renal hilar mass
Perinephric rind
Rarely only site
of involvement
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
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
Management different for VHL
Lower malignant potential
Resect when largest 3 cm
Acquired Cystic Renal Disease

Much higher risk of
RCC development

Consider any solid
mass as suspicious
Summary
Small renal masses are a common
diagnostic challenge
 A few have characteristic features that can
help the diagnosis
 Know the imaging criteria
