Benign

1. BENIGN RENAL TUMORS
Dr. Muhammad Z. Z. Khan

2. GENERAL FACTS
Benign renal tumors are a common entity in the urology clinic because of the
widespread use of abdominal imaging.
Among suspected RCC cases, 20% of resected masses are benign.
Management is based on the perceived risk of RCC, and can vary widely, from
“no management for the simple renal cyst to selective embolization for larger
AMLs and surgical extirpation for solid renal masses.”

3. CONTD…
Symptoms are flank pain, a palpable mass, and hematuria;
however, most diagnoses result from an incidental renal mass.
Certainly there are clues to a benign entity, such as thin, unenhanced walls in
simple cyst disease or macroscopic fat in an AML;
smaller mass size, lack of growth in serial imaging, female sex, & older age.

4. LEARNING OBJECTIVES
1. Renal Cysts
2. Oncocytoma
3. Angiomyolipoma
4. Papillary Adenoma of Kidney
5. Metanephric Adenoma
6. Mixed Mesenchymal & Epithelial Tumors
 Cystic Nephroma
 Mixed Epithelial & Stromal Tumors [MESTs]
8. Leiomyoma
9. Other Benign Renal Tumors
 Hemangiomas
 Lymphangiomas
 Juxtaglomerular Cell Tumors
 Renomedullary Interstitial Cell Tumor
 Intrarenal Schwannoma
 Solitary Fibrous Tumor

5. 1. RENAL CYSTS
Up to 10% of the population may harbor a renal
cyst, with putative risk factors of increasing age,
male gender, hypertension, and worsening renal
function.
Renal cysts can be sporadic, acquired, or genetic
(polycystic kidney disease) in their origin.

6. GENETIC…
Autosomal Dominant Polycystic Kidney Disease (ADPKD) is an inherited renal
cystic disease related to alterations in cilia function; primarily through mutation of
PKD1.
PKD1
Transmembrane
Complex
(mechanosensor to
urine flow)
Regulating
Intracellular
Calcium Levels
Mutation in
PKD1,
Reduction in
Calcium Levels
Amplification
in CAMP
Typical Cystic
Epithelial
Histology
There is a diverticulum on the tubular epithelium that ultimately detaches
from the tubule to form a true cyst in the interstitium of the kidney.

7. CONTD...
Growth of cysts is asynchronous but persistent and radially oriented, with gradual
development of large kidneys, renal insufficiency, and mortality based on growth
kinetics.
Criteria of ADPKD:
at least 2 unilateral or bilateral renal cysts before age 30
at least 2 cysts in each kidney between ages 30 and 59
or 4 cysts in each kidney in patients 60 years or older.
In addition, patients with ADPKD tend to develop hepatic and pancreatic cysts.

8. ACQUIRED…
Acquired cystic kidney disease (ACKD) is a disease in which renal cyst
development is preceded by the development of chronic and end-stage renal
disease.
Development of cysts is dependent on the length of time on dialysis, with up to
80% of patients developing cysts after 10 years.
Unlike the cysts in sporadic and genetic renal cyst disease, ACKD is associated with
the development of RCC, with almost 7% developing RCC after 10 years of dialysis.
Mechanistically, the cysts of ACKD arise from the proximal convoluted tubule (as in
clear cell RCC), unlike the cysts of ADPKD and sporadic renal cyst disease, which
arise from the distal tubule.

9. EVALUATION OF RENAL CYSTS
Diagnosed incidentally; experience pain from local expansion, a palpable mass,
and hematuria.
The goal of imaging in cystic renal disease is evaluation of malignancy risk as
defined by increasing complexity.
Simple renal cysts are characterized by smooth walls, sharp outlines, and the
absence of internal echoes on ultrasonography.
Meanwhile, on CT and MRI the hallmark of simple cyst disease is the absence of
enhancement

10. BOSNIAK CLASSIFICATION
Bosniak Classification is a commonly
used method to characterize cysts, risk
of malignancy and their managment.
Bosniak Class I

11. CONTD…
Bosniak Class II
Note internal calcification

12. CONTD…
Bosniak Class IIF
Note several thin irregular septations are
present within the cyst.

13. CONTD…
Bosniak Class III
Note thick, irregular septations are
present within the cyst.

14. CONTD…
Bosniak Class IV
Note a solid enhancing nodule.

15. CONTD…
More recently, the concept of active surveillance of cystic renal masses (Bosniak
III/IV) has been evaluated.
Although most Bosniak III/IV lesions are malignant, they are overwhelmingly low
grade and small and associated with excellent cancer-specific survival.
Outside of malignant risk, renal cysts require treatment because of local symptoms
such as pain, infection, hypertension, hemorrhage, or traumatic cyst rupture.
Management can include aspiration, cyst decortication, cyst resection,
sclerotherapy, arterial embolization, and even nephrectomy depending on the
cause and symptom.

16. 2. ONCOCYTOMA
Oncocytoma is the most common benign enhancing
renal mass.
Up to 25% of renal masses smaller than 3 cm represent
oncocytomas, making them a challenging diagnostic
entity in clinical practice.
 Overlapping features with eosinophilic chromophobe RCC
 Mahogany brown surface, similar to the appearance of
normal renal parenchyma, with a variably present central
scar
 Arising from the distal tubule

17. CONTD…
Interestingly, oncocytoma can be associated with perirenal fat invasion and renal
vein invasion— findings that carry prognostic significance in RCC but do not in
oncocytoma and should not be interpreted as an aggressive pathology.
CK7 is rarely positive in oncocytoma, whereas chromophobe RCC tends to be
diffusely positive and is recommended by the ISUP to distinguish these entities
Oncocytoma is typically associated with Cyclin D-1 mutation and genetically exists
in patients with Birt-Hogg-Dube (BHD) syndrome and renal oncocytosis.
International Society of Urologic Pathology (ISUP)

18. EVALUATION
Asymptomatically as an unilateral incidental renal mass (5% occur bilaterally).
Certain imaging clues to the diagnosis are hypervascularity and a central scar on
axial imaging.
When suspicion of oncocytoma is high based on imaging, renal mass biopsy has
been used with some success.

19. MANAGEMENT
As most renal oncocytomas are diagnosed after surgical resection (because of
perceived risk of RCC), the mainstay of management is postsurgical observation.
In evaluation of 90 patients initially managed with active surveillance, only one-
third received intervention (either surgery or ablation), mainly because of growth
on surveillance, with 100% 5-year cancer-specific survival.
When oncocytoma is suspected but uncertainty exists or treatment is indicated,
nephron-sparing approaches (such as ablation or partial nephrectomy) should be
the standard when technically feasible given the benign nature of this disease.

20. 3. ANGIOMYOLIPOMA
Angiomyolipoma (AML) is a benign renal entity composed of dysmorphic blood
vessels, smooth muscle, and adipose tissue.
It occurs sporadically or as part of genetic syndromes: most commonly tuberous
sclerosis complex (TSC) and lymphangioleiomyomatosis (LAM).
Prevalence of 0.13%; female predisposition; a peak in the fourth and fifth decade.
Among TSC patients, the prevalence has been reported from 55% to 90%.

21. CONTD…
Grossly, tumors are well circumscribed with yellow
surface; vessels are thick-walled and spindle cells around
the vessels. Adipocytes are mature and without atypia.
Atypia within the epithelioid cells with less fat denote
aggressive course. Indeed, metastatic disease has been
reported in one-third of reported cases.
AMLs stain strongly for estrogen, progesterone and
androgen receptor, which may mechanistically explain
the postpubertal female preponderance.

22. DIAGNOSIS
up to 15% of patients have Wunderlich syndrome (spontaneous retroperitoneal
hemorrhage).
Pregnancy has been identified as a risk factor for hemorrhage, likely because of
the hormonal receptor positivity of these tumors.
Contrary to other benign renal masses, the diagnosis of AML can be made on
imaging.
The presence of macroscopic fat on CT or MRI is diagnostic of AML.
Ultrasonographically, masses are hyperechoic, similar to some RCCs, making
ultrasound less reliable in the diagnosis.

23. CONTD…
On CT the presence of intralesional fat
15 to -20 Hounsfield units [HU]) on
nonenhanced series is diagnostic

24. CONTD…
Non–contrast-enhanced T1 MRI with
hyperintensity of lesion secondary to
macroscopic fat.
Post-contrast, fat-suppressed T1 image with
signal dropout of mainly fat containing lesion,
all consistent with classic angiomyolipoma.

25. CONTD…
Fat-poor AML, fat-containing RCC, and liposarcoma are unique situations in which
the diagnosis can be problematic on imaging.
Very large AMLs may have the appearance of retroperitoneal liposarcomas,
As AML arises from the parenchyma, an indentation in the parenchyma can be
observed from this site of origination, whereas liposarcomas begin in the
retroperitoneum and subsequently envelop and compress the renal parenchyma.

26. MANAGEMENT
Once the diagnosis is made, the management of patients with an AML should be
individualized on the presence of symptoms and the perceived risk of
hemorrhage.
AML less than 4 cm in size are expected to be asymptomatic and unlikely to
bleed, and therefore active surveillance is an option.
Flum et al. (2016) outlined an algorithm for management of AML that summarizes
the mainstays of management.

27. ALGORITHM
NSS
nephron sparing surgery;
RFA,
radiofrequency ablation

28. CONTD…
When a lesion is more than 4 cm in size, assessment of intralesional aneurysm size
with a thin-slice CT angiogram may improve the risk stratification.
Selective arterial embolization is often reserved for the management of acute
hemorrhage in AML, but it usually results in total nephrectomy.
When therapeutic embolization to surgery is considered, it is important to note
that embolization obligates the patient to continued surveillance (based on
recurrence risk), whereas surgery is curative in most sporadic AML cases.
Therefore the burden of post-treatment follow-up is different between the two
approaches.

29. 4. PAPILLARY ADENOMA OF
KIDNEY
Papillary adenoma, controversially benign is a low-grade, well circumscribed
cortical lesion measuring less than 0.5 cm.
Incidence increases with age, male sex, end-stage renal disease, acquired renal
cystic disease, sporadic RCC, and hereditary papillary RCC.
Papillary adenomas are associated with papillary RCC (47%), raising concerns
about the potential that papillary adenomas are a premalignant lesion.
They are often diagnosed pathologically as a concomitant finding with RCC and
therefore require no further directed therapy

30. 5. METANEPHRIC ADENOMA
Metanephric adenomas of the kidney is a rare benign epithelial lesion in the
kidney (0.2% of renal masses).
Present at any age; in the fifth decade; more in females (2 : 1 female:male ratio).
50% patients are diagnosed incidentally. Others have symptoms i.e flank pain,
gross hematuria, a palpable mass, and polycythemia (due to the production of
erythropoietin).
Differentials are Wilm’s Tumor and Papillary RCC; can be differentiated on the basis
of histology and immunohistochemistry.

31. CONTD…
Notably, enhancement is uniformly less than that of
the renal parenchyma; a finding in contrast to RCC,
in which rapid hyperenhancement is common.
When the suspicion is high, renal mass biopsy may
be considered, perform immunohistochemical
staining.
Once diagnosed, management is often nephron sparing (such as partial nephrectomy or
thermal ablation), because metastatic Metanephric adenoma has rarely been described.

32. 6. MIXED MESENCHYMAL &
EPITHELIAL TUMORS
CYSTIC NEPHROMA
It is a rare benign tumor that occurs in youth
(boys predominately, 2–3 years of age) and
adults (females predominately; fourth and fifth
decades).
Radiographically, tumors are often solitary,
central cystic masses with calcifications,
extension to the collecting system, and septal
enhancement.

33. CONTD…
Because of the inability to rule out Wilms tumor radiographically, children should be
managed as per the Children’s Oncology Group Renal Tumor Committee guidelines,
with initial radical nephrectomy.

34. CONTD…
Mixed Epithelial & Stromal Tumors
(MESTs)
MESTs are benign tumors of the kidney that are
most often identified in perimenopausal women,
often with a history of estrogen replacement, with
a peak incidence in the fifth decade.
In men this has been reported after long-term
hormonal deprivation for prostate cancer

35. CONTD…
On radiologic evaluation, MESTs often appear as a
complex cystic mass, such as a Bosniak III-IV lesion,
similar to RCC.
Mean size of 6 cm; encapsulated with solid and
cystic components that often extend into the renal
pelvis.
A nephron-sparing approach with partial
nephrectomy is the preferred management strategy
as malignant transformation has been observed.

36. 7. LEIOMYOMA
Leiomyoma is a rare renal tumor of smooth muscle differentiation. These tumors
can arise anywhere in the urinary tract; the bladder is the most common site
Within the kidney, the renal capsule is the most often described location.
They are found more often in women (2 : 1 predominance), and account for 0.29%
of primary renal mass.
As leiomyomas arise from the capsule, radiographically
they appear as small exophytic masses that are
hyperdense on noncontrast CT with hypoenhancement
on intravenous contrast administration.

37. CONTD…
Microscopic examination demonstrates spindle cells
that form intersecting fascicles without evidence of
hypercellularity, pleomorphism, mitotic figures, or
necrosis
Management, as with most benign renal masses,
depends on the certainty of the diagnosis before
intervention, with nephron sparing approaches
preferred when treatment is considered.

38. 8. OTHER RENAL TUMORS
Hemangioma
Hemangiomas are vascular lesions that are more often identified in young
patients.
When identified they are often singular, associated with the renal pyramids and
pelvis. There is no capsule and on histologic evaluation there are irregular vascular
spaces.
Most are diagnosed incidentally at nephrectomy, no specific treatment is required
or suggested.

39. CONTD…
Lymphangioma
Renal lymphangiomas are rare tumors that arise from a developmental
abnormality in which the perirenal lymphatics do not communicate with the rest of
the lymphatic system, resulting in dilated, cystic masses around the renal capsule,
renal sinus, or peripelvic fat.
Treatment depends on presence of symptoms and can include aspiration/sclerosis
or surgical excision.

40. CONTD…
Juxtaglomerular Cell Tumor
Juxtaglomerular cell tumor (also known as reninoma or JGCT); arising from the JG cells
of the kidney; common in women in their second and third decade; causing
overproduction of renin.
Imaging typically reveals a small renal mass that is solid and can be hypoechoic on
ultrasound and nonenhancing on CT.
Such small lesions; a young hypertensive patient; high plasma renin levels; hypokalemia
Once diagnosed, surgical resection resolves the symptoms in majority; however, up to
10% have persistent hypertension because of the development of hypertensive
angiopathy.

41. CONTD…
Renomedullary interstitial cell tumor
It is a tumor that arises within the renal medullary tissue.
It synthesize prostaglandins; it was therefore thought to be the result of
hypertension.
Tumors are small (mean 1.7 mm), with spindle/stellate cells in a fibrous background
with increasing collagen as age increased.

42. CONTD…
Intrarenal Schwannomas
They are exceptionally rare benign renal masses arising from nerve sheath tissue in the
renal parenchyma.
Solitary Fibrous Tumor
It is a rare benign tumor of Mesenchymal origin that tends to occur with hematuria, flank
pain, and an enlarging mass.
Masses are large with heterogenous enhancement, calcifications, and necrosis on CT that
are hard to distinguish from RCC.

43. TAKE HOME MESSAGE
They are Benign tumors but some have malignant potential and they need to be
followed.
Very few are diagnostic on radiology, so patients undergo surgery in doubt of
malignant tumors, however surgery would not be need if precise diagnosis would
have established.
Careful evaluation of the lesion using theoretical knowledge and available
radiological modalities is required to deliver the best management option.
For Postgraduates Trainees:
Every tumor is not an RCC and every cystic lesion is not a simple cyst.

44. THANK YOU