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GU 2 -- Renal Masses


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How are 50% of renal cell carcinomas diagnosed?
Incidentally on imaging studies performed for other reasons
What is true of lesions diagnosed incidentally versus those diagnosed after symptoms are present?
Most of them are stage T1 or T2, and amenable to surgical treatment
Why has survival in RCCa improved over the past 40 years?
Earlier diagnosis directly attributable to imaging
What is a ball?
Renal mass that grows circumferentially, expanding the contour of the kidney as it comes into contact with the capsule.
What is a bean?
Renal lesion that is infiltrative. May swell the involved area, but the bean shape of the kidney is maintained.
What masses are in the “ball” category?
Most common renal masses: Cysts, renal cell CA, angiomyolipoma, oncocytoma, most metastases, and abscess.
What masses are in the “bean” category?
The three “I”s.
What are the three “I”s
Infiltrating neoplasms

Inflammatory lesions

What are the infiltrating neoplasms?
Transitional cell CA

Squamous cell CA

Infiltrating renal cell CA

Renal medullary CA



Some metastases
What are the common “balls”?

Renal cell carcinoma
What are the uncommon balls?


Most metastases
What are the rare balls?
Oncocytoma, Multilocular cystic nephroma, Focal XGP
What are the common beans?
Transitional cell CA, Pyelonephritis
What are the uncommon beans?
Squamous cell carcinoma, Infiltrating renal cell carcinoma, Lymphoma, Some metastases, Infarct
What are the rare beans?
Renal medullary carcinoma, Collecting duct carcinoma, Leukemia
What is the sensitivity of US for renal mass?
What is the sensitivity of CT for renal mass?
Greater than 95%
Where may a renal mass be first identified?
Plain film
What makes a renal mass suspicious?
What is an old urology adage?
“A calcified renal mass is a surgical renal mass”
What pattern of calcification in the area of the kidney is suspicious on plain film?
Rim calcification.
What percent of patients with rim calcification have malignancy?
What are the other 80% due to?
Rim calcification in renal cysts
What percent of renal cysts have rim calcification?
What percent of renal cell CA has calcification?
What percent of renal masses that have calcification visible on plain film are due to renal cell CA?
What are other frequently calcified renal lesions?
Complex renal cysts, XGP, Hemangiomas, Chronic perirenal hematomas, Aneurysms/vascular malformations
What is ultrasound particularly crappy at finding?
Infiltrating renal lesions (beans)
What are the phases of nephrogram after IV contrast on CT?
Portal venous phase correlates to corticomedullary phase, 120 seconds correlates to tubular (nephrographic) phase, Delayed imaging is in the equilibrium phase
When are renal lesions most commonly missed on MDCT?
When the kidneys are imaged only in the corticomedullary phase
When is the optimal phase for renal mass detection?
Tubular/nephrographic phase, when the cortex and medulla are contrast opacified, and contrast is starting to pour into the renal pelvis.
How will almost all renal tumors appear in this phase?
How are all renal lesions classified from the most basic imaging appearance standpoint?
Expansile versus geographic infiltrating
How are lesions further classified?
Solitary versus multiple
What is seen in 50% of patients over 50?
Renal cysts
When is the only time renal cysts are worrisome?
In a child.
What may they signal in a child?
May signal inheritable cystic disease.
What about in young patients?
Not uncommon in young adults.
How is diagnosis of cyst confirmed?
What is acceptable for simple cyst?
Anechoic, with augmented through transmission and well demarcated back wall.
What can simple cyst contain?
1 or 2 delicate internal septations (of course without flow).
What should any lesion with any variance from these criteria have done to it?
Be analyzed with CT to exclude a neoplasm.
What are Bosniak class I cysts?
Simple cysts
What is criteria for Bosniak I?
Water density mass, No enhancement, Imperceptible or barely perceptible margin
What are characteristics of Bosniak II renal cystic lesions?
Multiple (3 or more) septations, Thin peripheral calcification, High density contents
What other lesion falls into Bosniak II category?
Cysts with appearance consistent with infection
What is the suspected cause of the septations, rim calcification, and/or high density contents seen in Bosniak II lesions?
Prior infection
What is the “BIRADS” for these lesions?
Probably benign lesions. Follow up recommended.
When is the follow-up to be done?
Repeat CT scanning in 6-12 months to exclude progression of disease.
What is the most problematic Bosniak II lesion?
The hyperdense cyst.
What is the appearance of hyperdense cyst on unenhanced CT?
Hyperdense relative to renal parenchyma.
What is appearance of hyperdense cyst on enhanced CT?
Hypodense relative to renal parenchyma.
What happens to the cyst in the interval?
NOTHING. No part of the lesion can enhance, otherwise it is Bosniak IV and is a surgical candidate.
If a hyperdense cyst is problematic, what can be done for further evaluation?
Ultrasound, to confirm its nature as a benign cyst.
What if the lesion cannot be confirmed as simple cystic?
Short term follow up or surgical removal.
What are Bosniak class III lesions?
More complex characteristics than those typically explained by postinfectious sequelae.
What are the characteristics?
Dense thick calcification, Numerous septae or loculations, Nodularity of septa(e), Unenhancing solid components
What is the “BIRADS” of Bosniak III lesions?
50% are cystic renal cell carcinoma, 50% are benign
What are the typical etiologies of the benign Bosniak III lesions?
Cysts complicated by infection, Cysts complicated by hemorrhage, Multilocular cystic nephroma
How is presurgical differentiation of benign versus malignant Bosniak III lesions performed?
It isn’t done. Bosniak III lesions are excised.
What are characteristics of Bosniak IV lesions?
Any area of solid enhancing tissue. Irregular margins.
Where is the enhancing solid tissue typically?
At the periphery of the cystic lesion.
How should apparently benign cystic lesions be evaluated on CT?
With careful attention to the lesion periphery. Any peripheral enhancement, even rim enhancement, is consistent with Bosniak IV lesion.
What is the presumed diagnosis in a Bosniak IV lesion?
Cystic renal cell CA.
What percent of RCCA has cystic areas?
What is true in 75% of these RCCAs with cystic contents?
The cystic areas represent central necrosis
What is the largest component of the other 25%?
Truly cystic RCCAs, which represent the papillary variety of RCCA.
What is the appearance of papillary RCCA?
Cystic lesion with frond-like tissue protruding into the cyst from the periphery
What is true of these lesions?
How is their papillary nature best evaluated?
What is in the rest of the 25%?
RCCA that occurred adjacent to an already present cyst.
What can a renal cyst represent?
It can signal the presence of a renal mass, which it formed by obstructing renal tubules. Thus renal cysts can herald the presence of a RCCA.
What is the rarest RCCA/cyst combination?
RCCA that originated in the wall of an already present cyst.
What is renal cell carcinoma also called?
Renal adenocarcinoma
What is the appearance of RCCA on cross sectional imaging?
Expansile, with solid components
What excludes RCCA?
Intratumoral fat.
What is the exception to this rule?
If the mass has grown to engulf renal sinus or perirenal fat. This can usually be discerned from true intrinsic tumor fat.
What is the typical density of RCCA precontrast on CT?
Is this always true?
No. Sometimes hypodense. Sometimes hyperdense due to hemorrhage.
What is the typical density of RCCA postcontrast on CT?
May be transiently hyperdense during initial bolus. All are hypodense during infusion phase. ? Appearance on delayed images (5 min)—probably mildly enhancing, like with gado.
What percent of RCCA are expansile?
What percent of RCCA are inflitrative?
What percent of RCCA are calcified on CT?
What percent exhibit transient hyperdensity during bolus?
How often is percutaneous renal biopsy performed?
What is one of the few indications for percutaneous renal biopsy?
Patient with renal mass and known primary tumor elsewhere.
AMLs smaller than 4 cm are very unlikely to hemorrhage.
How do infiltrating RCCAs differ in appearance?
May not bulge renal contour. Homogeneous internal architecture (like small masslike RCCAs)
How are infiltrating RCCAs detected?
Hypodensity versus surrounding parenchyma
What is a clinical presentation in which RCCA may be the underlying cause, but will not be suspected?
Renal abscess.
How does this occur?
Necrotic center of RCCA becomes infected.
How are renal abscesses managed?
1) Send drainage fluid for cytology. 2) FOLLOW UP IMAGING TO EXCLUDE UNDERLYING MASS
When is the follow up imaging performed?
After symptoms have resolved.
What is another presentation of RCCA in which the diagnosis is often missed?
Nontraumatic subcapsular/perirenal hemorrhage
What does nontraumatic subcapsular/perirenal hemorrhage mean until proven otherwise?
Underlying malignant tumor.
What percentage of subcapsular/perirenal hemorrhage is due to RCCA?
Why is the underlying diagnosis missed?
The hemorrhage, which can be extensive, obscures the underlying tumor
What should be done in all cases of subcapsular or perirenal hemorrhage where a mass is not detected on the initial diagnostic study as the underlying cause?
What is being searched for on the arteriogram?
Vasculitis, vascular malformation, or other vascular lesion to explain the presence of hemorrhage.
If one is detected, what is done?
The lesion can be assumed the cause of the bleed.
What if no such lesion is identified (i.e. normal arteriogram)
CT or MRI should be repeated to look for an underlying mass.
When is the repeat study performed?
1 Month after the hemorrhage, to allow time for the blood to clear.
What does the follow up scan often reveal?
A mass, which may be benign or malignant.
What benign mass often bleeds?
How are they treated?
Nonsurgically or with renal sparing surgery if possible.
What is the treatment for RCCA?
Usually nephrectomy
What is the advantage of this approach?
Minimize nephrectomy for benign lesions.
What is the appearance of RCCA on US?
Solitary expansile mass
What is the echogenicity?
Variable. May be hyper, iso, or hypoechoic versus normal renal parenchyma
What is the sonographic appearance of most small (< 5 centimeter) RCCAs?
Mildly hyperechoic
What is sometimes seen?
Marked hyperechogenicity.
What lesion is this imaging appearance the same as?
In what percent of <5 cm RCCAs does this appearance occur?
What does this mean?
You can’t diagnose an AML based on US appearance alone. Must exclude RCCA with CT.
What should all renal masses detected on US have done to them?
A CT (or MRI) for further evaluation.
What percentage of RCCA can be accurately staged on imaging?
What is stage I?
Tumor confined within renal capsule
What is stage II?
Invasion of perirenal fat without lymph node mets
What is stage III divided into?
a, b and c
What is stage IIIa?
Tumor invasion into renal vein or IVC
What is stage IIIb?
Lymph node mets
What is stage IIIc?
Renal vein or IVC invasion AND lymph node mets
What is stage IVa disease?
What is stage IVb disease?
Distant metastases
What is the best way to diagnose renal vein or IVC tumor invasion?
High-rate infusion CTA of the renal veins/IVC.
What is the most reliable finding?
Thrombus visualized in the vessel.
What finding is unreliable?
Enlargement of the renal vein, as it may be enlarged simply secondary to increased flow related to hypervascular RCCA.
What is the most practical method to confirm tumor thrombus in the renal vein or IVC and determine its extent?
Ultrasound with doppler
What size nodes are pathologic?
1.5 cm in short axis
What size nodes are suspicious?
1.0 or greater
What are common sites for distant mets of RCCA?
Liver, bone, lung, brain
What must be done to detect RCCA liver mets?
Unenhanced imaging and ARTERIAL PHASE imaging as they are hypervascular.
What is the importance in differentiating stage I from stage II?
No practical importance, as both can be treated with partial nephrectomy.
What is the most important thing to note in stage II disease?
Whether the ipsilateral adrenal is involved or not.
What is the most reliable indicator of perinephric tumor spread?
Discrete perinephric soft tissue mass.
What are unreliable signs?
Perinephric stranding, fat obliteration, or enlarged perinephric vessels
When should MRI be performed in evaluation of RCCA?
Only when CT is inadequate for staging.
What is T1W and T2W appearance of RCCA?
Variable and unreliable. Just look for contour disrupting mass.
What is appearance post contrast on MR?
Hypointense on infusion phase. Mildly hyperdense on delayed imaging (3-5 min).
What percent enhancement is considered highly suspicious for malignancy?
How is tumor extension into renal vein/IVC detected on MR?
Absence of flow void on black blood. More sensitively diagnosed with bright blood images as a filling defect, however.
What is the most important thing to tell surgeon about IVC extension?
Whether it extends above the hepatic vein inflow.
What is the most important reason that suspected RCCA is not biopsied for confirmation before excision in surgical cases?
RCCA can contain elements that appear like oncocytoma.
What is oncocytoma?
Benign renal tumor with no metastatic potential
What are the diagnostic imaging findings of an oncocytoma?
There are none.
How is the diagnosis made preoperatively?
It is NOT made preoperatively, because as mentioned before, even if the pathology comes back as oncocytoma, this STILL does not rule out RCCA, because RCCA can contain elements resembling oncocytoma.
What is the best thing that suggesting a diagnosis of oncocytoma can do for a patient/surgeon?
Can suggest that the lesion may be benign, and a renal sparing approach may be considered.
How does the surgeon decide whether to do renal sparing or more aggressive surgery?
Based on frozen section biopsies taken intraoperatively.
What are the typical features of oncocytoma on CT or MR?
Well circumscribed. Homogeneous enhancement. Central stellate scar.
What may be seen around the edge of the lesion?
A pseudocapsule.
What is a pseudocapsule?
Normal renal tissue compressed around the lesion.
What is the ultrasound echogenicity?
Isoechoic to renal parenchyma.
What do oncocytomas that exceed 6 cm often contain?
Central areas of necrosis.
What is the angiographic appearance of oncocytoma?
Spoke-wheel pattern.
What is spoke wheel pattern?
There is a prominent rim of vessels at the periphery of the lesion, with (somewhat difficult to visualize) centrally radiating vessels.
When a multilocular cystic nephroma is suspected by imaging, how is the surgical approach handled differently?
If the patient is in the first peak (boys under 3 y.o.), I am not sure how it is handled.
What if the multicystic tumor is seen herniating into the renal pelvis?
Consistent with MLCN, but still not good enough to exclude RCCA.
What percentage of MLCN hemorrage?
They do not hemorrhage. If hemorrhage is seen in a multicystic mass, it is another diagnosis, probably RCCA.
What is the DDx for a multiloculated cystic renal mass?
Cystic RCCA Cystic Wilms Multilocular cystic nephroma Segmental multicystic dysplastic kidney Localized renal cystic disease Renal abscess Rare forms of renal inflammatory disease (echinococcus, segmental XGP, renal malakoplakia)
Of these lesions, which is the most common when a multicystic renal mass is identified?
What is segmental multicystic dysplastic kidney?
MCDK involving only part of the kidney.
Where is it seen?
Only in cases of renal duplication.
What suggests it?
Presence of duplication with unenhancing solid components.
What is localized renal cystic disease?
Rare disease of a collection of simple cysts in one part of one kidney. They look like individual cysts that just happen to be close together. They have normal enhancing renal tissue between them.
What is the usual cause of renal abscess?
Untreated or improperly treated pyelonephritis.
What is the clinical setting of renal abscess?
Persistent infection symptoms despite antibiotic treatment (i.e. at least 72 hours after treatment commencement)
What confirms the diagnosis of renal abscess in the right clinical setting?
What is the enhancement pattern?
Peripheral enhancement
What is the treament for renal abscess?
IV Abx and percutaneous drainage.
What else must be treated if present?
Ureteral obstruction.
Why must this be treated?
Ureteral obstruction impairs blood flow and limits antibiotic delivery to the parenchyma.
What is the clinical history with focal XGP?
Recurrent UTI
In what demographic group?
Middle aged women
What is the appearance?
Nonspecific. See nonfunctional mass which may exhibit minimal contrast enhancement. Usually perinephric stranding.
What is seen in 80% of cases of focal XGP?
What are the common causes of multilocular cystic renal masses?
RCCA Septated renal cyst Renal abscess
What are the uncommon causes of multilocular cystic mass?
Multilocular cystic nephroma Cystic Wilms Segmental multicystic dysplastic kidney
What are the rare causes of multilocular cystic mass?
Focal XGP Localized renal cystic disease Echinococcus Malakoplakia AVM or AV fistula
In a patient with known extrarenal malignancy, what is the differential diagnosis of a solitary renal mass?
Renal metastasis RCCA
How is the diagnosis made?
This is the one time percutaneous biopsy is indicated, as it dictates whether patient has surgical disease or not.
What tumors metastasize to kidney commonly?
Breast. Lung GI Malignant melanoma
What other lesion commonly metastasizes to the kidney?
In what percent of patients with lymphoma is there renal involvement?
1/20 (5%).
What is special about these patients?
They usually have known lymphoma, and they usually have extensive disease, which secondarily involves the kidney.
What is true about primary renal lymphoma?
Exceedingly rare.
What is the characteristic pattern of lymphoma (i.e. not always seen, but when seen suggestive of it)?
Extensive retroperitoneal mass, which spreads directly into the renal sinus, OR into the perinephric space, encasing the kidney. These features are IN ADDITION to its parenchymal involvement of the kidney.
How many patterns of renal parenchymal involvement in lymphoma are there?
What is the most common pattern?
Multiple homogeneous nodules
What is the parenchymal displacement pattern?
Infiltrating, not exerting mass effect
What is the second most common pattern of renal parenchymal involvement in lymphoma?
Diffuse infiltration.
What is this pattern usually typified by?
Bilateral involvement. Renal enlargement, sometimes massive, with loss of renal architecture
What occurs functionally?
Decreased function
In what condition is this pattern seen even more commonly than in lymphoma?
What is the least common parenchymal involvement pattern in lymphoma?
Solitary lesion
What does this pattern mimic?
What would be useful if this pattern is seen in a patient with known lymphoma?
Percutaneous biopsy, as lymphoma is not a surgical lesion
With all patterns of involvement, what are the common features of the parenchymal lesions?
Homogeneous Minimal enhancement (hypodense versus normal renal parenchyma)
What is the appearance of lymphoma on ultrasound?
Since lymphoma is from a monoclonal line of cells which are densely packed, there is little internal echo generation, and lesions appear hypoechoic to anechoic.
What differentiates this from cyst?
No significant posterior acoustic augmentation.
When a focal renal mass is present, RCC is the most likely diagnosis. What additional finding suggests that the lesion is not RCC?
Marked retroperitoneal lymphadenopathy, which would suggest lymphoma.
What is important about angiomyolipoma and imaging of it?
It is one of the few renal masses that can be definitively diagnosed by imaging
In what group of patients do most angiomyolipomas occur?
Middle age
Is there a sex predilection?
What is characteristic of lesions in these patients?
Small, asymptomatic
A significant percentage of angiomyolipomas occur in another demographic group. Which?
Patients with tuberous sclerosis
What percentage of patients with angiomyolipoma have tuberous sclerosis?
What percentage of patients with tuberous sclerosis will develop angiomyolipoma?
What are the characteristic features of angiomyolipoma in tuberous sclerosis patients?
Multiple tumors

Bilateral invovement

Large symptomatic lesions
When do AMLs occur in patients with TS?
Detectable before patient reaches 30, in most cases, which is much younger than patients in the general population who get AMLs.
What is an angiomyolipoma?
A renal hamartoma. A totally benign lesion.
What is angiomyolipoma pathologically?
A lesion composed of varying proportions of angioid, myoid, and lipoid components.
What occurs in AMLs with a higher proportion of angioid component?
They are hypervascular, and due to this, some of the feeding arteries develop small aneurysms.
What do these aneurysms do?
Predispose to spontaneous hemorrhage.
What is important about AML hemorrhages?
Can be massive and life threatening.
Otherwise, what symptoms do AMLs cause?
Just those related to mass effect.
How are AMLs treated?
Depends on their size.
What is the size cutoff for treatment?
4 cm
How are these smaller AMLs managed?
F/U sonogram every 6-12 months.
What is the treatment for AMLs over 4 cm?
Embolization or renal sparing surgery.
What if the lesion is not amenable to renal sparing surgery or embolization?
Sonographic follow-up evaluation can be used to look for enlargement or other features that would necessitate nephrectomy.
What are the diagnostic criteria for AML?
Only one criteria: Fat within a mass arising in the kidney.
What is one additional unnecessary but nevertheless supporting finding for diagnosing AML?
Enlarged or aneurysmal vessels within the tumor
What if you are unsure of intratumoral fat?
Do thinner sections


Do CT pixel mapping


How is the diagnosis made with pixel mapping?
Three contigous pixels between -20 and -100
How is the diagnosis made on MRI?
Do T1W imaging with and without fat saturation; should see bright signal on T1W and dark on T1W with fat saturation.
What is true of 10% of AMLs?
Contain minimal fat, so that definitive diagnosis cannot be made on imaging. These lesions will appear to be RCCAs, and will be treated as such.
What are rare findings that can occur with AML?
Tumor extension into renal vein/IVC

Lymph node spread
What is the differential diagnosis for common causes of multiple renal masses?
1) Simple cysts

2) Autosomal dominant polycystic kidney disease

3) Acquired cystic disease of dialysis
What is the differential diagnosis for uncommon causes of multiple renal masses?
1) Von Hippel-Lindau

2) Tuberous sclerosis


4) Lymphoma

5) Mets
What is the differential diagnosis for rare causes of multiple renal masses?
1) Medullary cystic disease

2) Multiple oncocytomas

3) Multiple abscesses
When do patients with ADPCKD present?
20s to 30s
What do they present with?
Flank pain, hematuria, urolithiasis, pyelonephritis, renal insufficiency, or HTN
Where are the cysts anatomically?
Can develop anywhere along the nephron
What is the best way to diagnose ADPCKD?
What does ADPCKD have genetically?
High penetrance
All patients with the genetic abnormality will develop clinical symptoms.
How is it inherited?
Autosomal dominant
So a parent with ADPCKD can expect that half of his/her children will develop the disease.
What is the typical appearance?
Bilateral renal enlargement due to parenchymal replacement with large number of renal cysts
What is the increased risk of malignancy in ADPCKD?
No increased risk
What do 50% of patients with ADPCKD have in addition to renal findings?
Liver cysts
What do 15% of patients with ADPCKD have?
Berry aneurysyms of the CNS
Where are other places that cysts can occur in ADPCKD?



What other condition do patients with ADPCKD have increased risk for?
Heart disease
What types of heart disease?
Valvular disease

Aortic coarctation
What are suggests ADPCKD in patients with a parent with the disease?
Depends if under 30, 30-60, or 60+ years old

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