BENING RENAL TUMORS

Dept of Urology
Govt Royapettah Hospital and Kilpauk Medical College
Chennai 1

Professors:
 Prof. Dr. G. Sivasankar, M.S., M.Ch.,
 Prof. Dr. A. Senthilvel, M.S., M.Ch.,
Asst Professors:
 Dr. J. Sivabalan, M.S., M.Ch.,
 Dr. R. Bhargavi, M.S., M.Ch.,
 Dr. S. Raju, M.S., M.Ch.,
 Dr. K. Muthurathinam, M.S., M.Ch.,
 Dr. D. Tamilselvan, M.S., M.Ch.,
 Dr. K. Senthilkumar, M.S., M.Ch.
Dept of Urology, GRH and KMC, Chennai. 2

 Large and heterogenous group of renal lesions
 15-20% of renal masses <7cm are benign
 Management varies widely
◦ Some have clear radiographic features to suggest benign etiology
◦ Majority are diagnosed after definitive therapy
◦ Management continues to evolve
3
Dept of Urology, GRH and KMC, Chennai.

4

 Cystic lesions
◦ Simple cyst
◦ Hemorrhagic cyst
 Solid lesions
◦ Angiomyolipoma
◦ Oncocytoma
◦ Renal adenoma
◦ Metanephric adenoma
◦ Cystic nephroma
◦ Mixed epithelial stromal tumor
◦ Reninoma
◦ Leiomyoma
◦ Fibroma
◦ Hemangioma
5

 Most common benign renal lesions
 More than 70% of asymptomatic renal masses
 Can be solitary or multiple
 Unilateral or bilateral
 Presentation – Asymptomatic, pain, HTN, hemorrhage,
infection
 Risk factors
◦ Increasing age
◦ Male
◦ Hypertension
◦ Renal insufficiency
◦ Familial syndromes – ADPKD, ARPKD
6

 USG
◦ Simple cyst – smooth wall, fluid filled with no internal echoes, posterior
wall enhancement
◦ Complex cyst – internal echoes, calcifications or nodularity in the wall
or internal septa
7

8

 Thin walled
 No septa / calcifications /
solid components
 Water density
9

 Cyst with internal
calcification
10

 Several thin irregular
septations within the cyst
11

 Thick irregular septations
within the cyst
12

Solid Enhancing nodule Cyst with solid component - RCC 13

 Tends to exaggerate
◦ Septa – appear thicker which could make enhancement of cyst walls
and septa more obvious
 Advantage
◦ In hemorrhagic lesions or other lesions that have high intensity on CT
14

For symptomatic benign cystic lesions
 Aspiration
 Surgical resection
 Cyst decortication
 Sclerotherapy
15

 Small, solid cortical lesions
 Renal adenoma – Tumor with nuclear grade I and a
diameter of at least 1 cm (Thoenes and collegues)
 Risk factors
◦ Inreasing age (40% over 70 years of age)
◦ Male gender
◦ Acquired renal cystic diseases
◦ ESRD
 These lesions may be linked to the development of
papillary RCC and represent a biologic link and
continuum as a premalignant precursor
16

 Gross
◦ 5mm or smaller
◦ Well circumscribed
 Microscopic
◦ Uniform basophilic or eosinophilic cells
◦ Arranged in papillary, tubular or tubulopapillary architecture
17

 Papillary adenomas in the setting of papillary RCC –
multiple
 Associated with other renal tumors – one / two in
number
 Similar IHC to Papillary RCC - + for AMACR
 Similar cytogenetic profile – Loss of Y chromosome,
trisomy of chromosomes 7&17
 The diagnosis of papillary adenoma remains
controversial; many believe that all solid renal
epithelium derived masses are potentially malignant
& should undergo treatment.
18

 Rare tumor
 Symptomatic presenation
◦ Flank pain, gross hematuria, palpable mass, polycythemia,
hypercalcemia
 Large tumor size – upto 15cm with mean size 5.5cm
 Female predominance (2:1)
 Peak – 5th decade
 Because of lack of highly predictive clinical or radiographic
criteria, metanephric adenoma remains primarily a pathologic
diagnosis
19

◦ Peripheral or central
calcifications
◦ Hypovascular on CECT
◦ Solitary, hypodense or
isodense with poorly defined
margin
◦ Less enhancement than the
medulla and cortex
◦ Hyperechoic on USG
20

 MICROSCOPIC
◦ Highly basophilic epithelial cells
◦ Forms small acini and occasionally tubular or papillary
structures within a predominantly acellular stroma
 Metanephric adenoma might be histologically related
to epithelial Wilms tumor because it exhibited
histologic similarities to the metanephric,
hamartomatous elements of nephroblastomatosis.
 Many of these tumors exhibit evidence of regression
in the form of scarring or calcifications.
21

Highly basophilic epithelial cells with
Relatively acellular stroma
22

 Positive staining for the Wilms tumor protein WT1 suggests a
histogenetic relationship to Wilms tumor
 Gain of chromosomes 7 and 17 - suggest a clonal neoplastic
disorder potentially related to papillary RCC
 Gain of chromosome 19
 Tumor suppressor gene for metanephric adenoma at
chromosome 2p13
 90% had BRAF V600E mutations
23

Metanephric adenoma Papillary RCC
 Wilms tumor marker WT1
frequently expressed
 AMACR – poorly expressed
 S-100 protein expression is
very high (weak in Wilms
tumors)
 Alpha methylacyl co-A
racemase highly expressed
 WT1 & S-100 - absent
24

 Only one case of metastasis has been described in association
with classic metanephric adenoma into a regional lymph node,
and death related to this entity has not been reported
 Single case of malignant stromal elements associated with a
metanephric neoplasm of the kidney in a 21-year-old woman
who died of progressive cancer → there may be a spectrum of
metanephric tumors that includes rare, aggressive variants.
 Atypical histologic features and multifocality in childhood
have also been reported
25

 If radiographic findings raise the index of suspicion, then
percutaneous core biopsy may prove helpful in establishing a
diagnosis for nephron-sparing treatment or observation
 But most patients will require surgical excision because of
concern for malignancy
26

 Most common benign tumor that appears as an enhancing
renal mass on cross-sectional imaging
 Presumed to be RCC until surgical excision, representing one
of the ultimate challenges in preoperative diagnosis for the
urologist.
 Accounts for 3% to 7% of kidney tumors
 Derived from distal renal tubules
 Oncocytoma was initially described by Zippel in 1942
 Peak incidence – 7th decade
 Male to female – 2:1
27

 Gross
◦ Mahogany or tan
◦ Homogenous, well circumscribed
◦ Pseudocapsule
◦ Central stellate scar
 Microscopic
◦ Round or polygonal cells arranged in nested growth pattern
◦ Cells – large, uniform, highly eosinophilic, owing to an abundance of
mitochondria
◦ Upto 1/3rd of patients – hemorrhage, extension into perinephric fat,
vascular invasion, cellular atypia, prominent nucleoli, plemorphism
28

Large, uniform, highly eosinophilic arranged in distinct nests
Well circumscribed with central stellate scar
29

 Most common genetic abnormality – loss of heterozygosity at
chromosome 1 and /or 14
 Other
◦ Loss of Y chromosome
◦ Loss of chromosome 14q
◦ Rearrangements of 11q13
The chromosomal abnormalities typically seen in RCC are not seen in
renal oncocytomas, further reinforcing the concept that these tumors
are genotypically distinct from RCC
30

 Histologically, the greatest dilemma arises from distinguishing chromophobe and
clear cell RCC with eosinophilic characteristics from oncocytoma
◦ Hale colloidal iron stain – classic differentiating marker for oncocytoma; but nonspecific and
difficult to interpret.
◦ Expression of cytokeratin-7 is seen in 66% of chromophobe RCC and only 5% of oncocytomas,
and parvalbumin is expressed in 100% of chromophobe RCC and 47% of oncocytomas
◦ Other markers – Pax2, Claudin 7&8, tight junction proteins, vimentin, c-KIT, S-100, NPM
(nucleophosmin/B23)
◦ Immunohistochemistry to study the expression of BCA2 → RCC were negative for BCA2
expression while oncocytomas were positive
An “optimal” panel for distinguishing between chromophobe and clear cell RCC and
oncocytoma was recommended by Liu and colleagues in 2007, consisting of a
combination of three markers
◦ vimentin,
◦ glutathione-S-transferase-α
◦ epithelial cell adhesion molecule
31

 CT
◦ High peak HU attenuation - similar to RCC
◦ More frequently during nephrogenic phase (RCC- more often in
corticomedullary phase)
◦ Stellate scar
 Angiography
◦ “Spoke-wheel” appearance of tumor arterioles,
◦ “Lucent rim sign” of the capsule
◦ Homoogeneous capillary nephrogram phase.
◦ Unfortunately, these findings are not invariable, and similar findings
have been reported in patients with RCC
 MRI
◦ Complete late enhancement in the central area of the mass
◦ Absence of T2 signal intensity inversion or presence of signal drop on
chemical shift imaging → rules out oncocytoma
32

33

 Multicentric, bilateral, metachronous – 4 – 13%
 Oncocytosis – Renal oncocytomatosis (Warfel and Eble)
 Familial renal oncocytomas – young age, multicentric, bilateral
& recurrent tumors
34

 Observation
◦ Particulary for older or sicker patients
 Thermal ablation
◦ Long term radiographic surveillance
◦ Lower success rates
 Laparoscopic/ open partial or even radical nephrectomy
 If oncocytoma is suspected preoperatively, a percutaneous core
biopsy in addition to fine-needle aspiration may reliably provide a
diagnosis when core tissue is available for additional
immunohistochemical studies.
 If oncocytoma is highly suspected and surgery is indicated, a nephron
sparing approach is preferred, given the benign nature of these
lesions and the very low probability of recurrence.
 Frozen section analysis is usually not sensitive enough to differentiate
the eosinophilic appearance of oncocytomas from eosinophilic RCC
and should not be used to guide surgical strategy.
35

 Originally described in 1900 by Grawitz
 Accounts for less than 10% of renal tumors, with autopsy series
and ultrasound-screened populations showing incidences of 0.3%
and 0.13%, respectively, in the general population
 Initially considered to be a form of hamartoma, but recent evidence
suggests a neoplastic origin with evidence of a monoclonal, rather
than polyclonal, source
 Angiomyolipoma is now considered to be derived from perivascular
epithelioid cells, therefore belonging to a group of tumors referred
to as PEComas (perivascular epithelioid cell tumors)
36

 Strongly expresses estrogen receptor β, progesterone
receptor, and androgen receptor
 Predominantly found in females
 Rare before puberty, suggesting a potential hormonal
influence
 Genetic studies in patients with tuberous sclerosis complex
(TSC) resulted in discovery of two genes associated with
angiomyolipomas:
◦ TSC1 on chromosome 9q (encoding for hamartin protein)
◦ TSC2 on chromosome 16p (encoding for tuberin protein)
37

 SPORADIC FORM
◦ Middle aged woman
◦ Single asymptomatic tumor – detected incidentally
◦ Slow growth rate
 TSC – ASSOCIATED
◦ Younger age (mean 30 years)
◦ Less female to male predominance 2:1
◦ Multiple, bilateral, symptomatic tumors
◦ Associated with renal cysts, risk of RCC,
lymphangioleiomyomatosis
 WUNDERLICH SYNDROME
◦ Massive retroperitoneal hemorrhage
◦ Most significant complication – occurs in 10%
◦ Increased risk in pregnancy
38

 Only benign renal tumor that is confidently diagnosed on
cross-sectional imaging
 The presence of fat (confirmed on nonenhanced thin-cut
CT by a value of −20 HU or less) within a renal lesion is
considered the diagnostic hallmark
 USG
◦ Well circumscribed
◦ Highly echogenic lesion with shadowing
 CT Angiography – Aneurysmal dilatation in 50% of cases
 MRI
◦ Used in difficult cases when lesion has minimal fat
◦ Appears hypointense on fat-suppressed T1 sequencing
◦ Hyperintense on T1 & T2 – because of the fat content
39

 A, Computed tomography scan
demonstrating large bilateral
renal angiomyolipomas in a
patient with tuberous sclerosis.
 B, Renal angiogram shows
increased vascularity and
aneurysmal dilation
characteristic of
angiomyolipoma.
 C, Typical microscopic
appearance of angiomyolipoma
with admixture of mature
adipose tissue, smooth muscle,
and thick-walled blood vessels
40

 Retroperitoneal Liposarcoma
◦ Angiomyolipoma – small
indentation of renal parenchyma
even when the tumor envelops
the kidney
◦ Liposarcomas – compress or only
extrinsically push the renal
parenchyma
 Fat containing RCC
◦ These extreme rare cases also
contains calcifications, which is
almost never seen in AML
41

 Classic form - Thick-walled poorly organized bloodvessels,
smooth muscle, and varying levels of mature adipose tissue
 Many angiomyolipomas exhibit regions of cellular atypia, and
the pathologic differential diagnosis can include a number of
subtypes of sarcoma, including fibrosarcoma, leiomyosarcoma,
and liposarcoma, depending on the relative amounts of
adipose, vascular, or smooth muscle tissue present.
 Positive immunoreactivity for HMB-45 (human melanoma black
45), a monoclonal antibody raised against a melanoma-
associated antigen, is characteristic for angiomyolipoma and
can be used to differentiate this tumor from sarcoma and other
tumors
42

43

 Fat poor angiomyolipoma resembling RCC
◦ Commonly single, smaller, and found in older patients
◦ On CT many appear to have hyperattenuation on noncontrast imaging
and have a homogeneous and prolonged enhancement pattern
◦ Percutaneous biopsy can play an important role in diagnosis in these
patients because a core biopsy should be eminently accurate in the
diagnosis of angiomyolipoma when supplemented with
immunohistochemical staining for HMB-45 protein
◦ Epithelial markers should be negative in a typical angiomyolipoma
 Extrarenal occurrences are occasionally seen and have been
reported in the hilar lymph nodes, retroperitoneum, and liver,
with direct extension into the venous system
◦ Even in these patients a benign clinical course follows, indicating
multicentric origin rather than malignancy with metastasis
44

 Epithelioid angiomyolipoma
◦ Angiomyolipoma with a predominant epithelioid component
◦ Malignant epithelioid variant of angiomyolipoma that can metastasize
has been further described in patients with and without TSC
◦ This phenotype is characterized by epithelioid cells that are cytokeratin
negative and HMB-45 positive.
◦ Whether this extremely rare variant represents malignant degeneration
of a preexistent angiomyolipoma or a de novo tumor without a benign
precursor remains unknown.
45

 The management should take into account
◦ size of the tumor,
◦ presence of symptoms
◦ patient factors
◦ the risk of hemorrhage
46

 Asymptomatic, smaller tumors, which by convention have
been those with a diameter less than 4 cm, can be observed
expectantly
 Repeat initial imaging at 6 to 12 months to define the growth
rate and clinical significance.
 Repeat imaging can be lengthened once stability has been
established, with follow-up performed only annually or
biannually for smaller tumors.
47

 Intervention should be considered for larger tumors, particularly if
the patient is symptomatic, taking into account the patient’s age,
comorbidities, and other related factors.
 In women of childbearing age and patients with limited access to
surveillance or to emergency care, a proactive approach should
also be considered.
 A nephron-sparing approach, by either selective embolization or
open or laparoscopic or robotic partial nephrectomy, is clearly
preferred to radical nephrectomy in patients with angiomyolipomas
requiring intervention.
 Preservation of renal tissue remains a priority in those with TSC or
multicentric angiomyolipoma and particularly in patients with
underlying renal insufficiency.
48

 Selective embolization
◦ First-line therapy in patients with acute or potentially life-threatening
hemorrhage, because surgical exploration in this setting is often
associated with total nephrectomy
◦ Complications - hemorrhage, abscess formation,or sterile liquefaction
of the tumor requiring percutaneous drainage or surgical intervention.
◦ Substantial proportion of patients experienced persistent or recurrent
symptoms or hemorrhage, and most of these required repeated
procedures, including embolization or surgery
49

 Radiofrequency ablation and cryoablation
 Evaluation of success remains poorly defined
 Duration for continued radiographic surveillance is unknown
 Committing the patient to multiple, long-term imaging
 Best role for the treatment of patients with TSC who have
multicentric angiomyolipomas or older patients with
comorbidities who require treatment and are not ideal
candidates for embolization or surgery
50

 Research into the molecular aspects of renal
angiomyolipomas in patients with TSC showed a link between
loss of TSC2 protein as a result of TSC2 mutation and
activation of the mammalian target of rapamycin (mTOR)
pathway (by demonstrating presence of S6K and phosphor-
S6K in angiomyolipoma tissues)
 mTOR inhibitors(under clinical trials)
◦ Sirolimus
◦ Everolimus
◦ Used in a neoadjuvant fashion → tumor shrinkage in tumors → partial
nephrectomy become feasible
51

 CYSTIC NEPHROMA
 MIXED EPITHELIAL AND STROMAL TUMORS (MEST)
 Rare benign renal neoplasms that have overlapping clinical,
morphologic, and immunohistochemical characteristics
 Striking similarities between global gene expression profiles
→ Spectrum of the same biologic process
 Female predilection and history of hormonal ablation therapy
in male patients, combined with the frequent expression of
estrogen and progesterone receptors, suggest that the sex-
steroid hormones might play a role in the pathogenesis of
these rare lesions
52

 Bimodal age distribution
◦ Diagnostic peaks occur primarily in the first 2 to 3 years of life,
predominantly in boys,
◦ Again in the fourth and fifth decades with a significant (8 : 1) female
prevalence
 Presentation - abdominal mass, pain, and hematuria, majority
are incidental findings
 Radiologically - solitary, centrally located, and widely variable
in size (mean size 9 cm) and commonly demonstrate
curvilinear calcifications, herniation into the renal collecting
system, and septal enhancement.
 Reliable radiologic differentiation between cystic nephroma and
cystic RCC in adults or Wilms tumor in children is not possible!
53

 Histology
◦ Well encapsulated by a thick fibrous pseudocapsule and are composed
of
◦ Cysts lined by flattened, cuboidal, or hobnail epithelium
◦ Stromal component can range from dense paucicellular collagen to
markedly cellular fascicles of spindle cells, closely resembling ovarian
stroma.
 Immunohistochemical studies reveal
◦ affinity of the epithelial component for cytokeratins, whereas
◦ stromal components frequently stain positive for CD10, calretinin,
inhibin, estrogen, and progesterone receptors
54

Computed tomography (A) and magnetic resonance imaging (B) scans do not allow
reliable distinction from cystic renal cell carcinoma or cystic Wilms tumor
55

The variably sized cystic
spaces are lined by flattened
epithelium
56

 Most children with cystic nephromas continue to be managed
by radical nephrectomy (Because of concern for cystic Wilms
tumor)
 Nephron-sparing approach with partial nephrectomy, if
feasible, is an attractive option in adults.
57

 Rare benign adult renal neoplasm with a variable admixture of
epithelial and mesenchymal components
 Previously - congenital mesoblastic nephroma,
leiomyomatous renal hamartoma, solid and cystic biphasic
tumor, cystic hamartoma, solitary multilocular cyst, and adult
metanephric stromal tumor
 Female predominance
 Diagnostic peak in the fifth decade
 Only male patient in the largest MEST series had a long
history of androgen deprivation therapy for prostate cancer
58

 Radiologic appearance of MEST is of a complex cystic renal
mass, typically classified as Bosniak class III to IV lesions,
indistinguishable from cystic RCC
 recently a case of malignant transformation to a sarcomatoid
carcinoma and several cases of local recurrence of a
malignant stromal component with a dismal clinical course
have been described
59

Computed tomography scan
characteristics are not
distinguishable from renal
cell carcinoma
60

 Grossly, MEST appears encapsulated and ranges from 2 to 24 cm
(mean 6 cm).
 Involvement of renal hilum and compression of the pelvicalyceal
system is common
 The mesenchymal component is characterized by spindle cells
showing variable degrees of smooth muscle, fibroblastic, or
myofibroblastic differentiation with interspersed collagen bundles.
 The epithelial components vary from regular tubules to complex
tubulopapillary structures with or without cystic dilatation, lined by
cuboidal to flattened epithelium that may show clear cell changes and
have a characteristic hobnail appearance
 Epithelial components stain positive for cytokeratins whereas estrogen
and progesterone receptor staining has been observed in the majority
of the mesenchymal elements of MEST
61

Gross photograph of a partial
nephrectomy specimen
demonstrating a well-
circumscribed mass composed
of variably sized cysts separated
by thick white septa.
Medium-power
magnification shows cysts
lined by hobnailed cells and
spindle cell stroma.
62

 A preoperative diagnosis of MEST should be considered in
perimenopausal women receiving hormone therapy
 Since radiologic differentiation from RCC is not reliable,
surgical intervention, preferably with a nephron-sparing
approach, should be offered to appropriately selected patients
63

 Rare, benign tumors that may arise from smooth muscle cells
anywhere along the genitourinary tract
 Most commonly arise from the renal capsule
 Renal pelvis and renal vein sites of origin have been reported
 Leiomyomas are found at autopsy with a frequency of 4.2% to
5.2%, but only a minority are discovered clinically,
representing approximately 1.5% of all benign renal tumors
treated surgically
 Vast majority - incidental
64

 Renal leiomyomas have a characteristic appearance of a small
exophytic renal mass with or without enhancement arising
from renal capsule
 Conclusive radiologic differentiation from RCC is not possible
 Grossly, leiomyomas are firm, well encapsulated solid lesions.
 Histologic examination reveals intersecting fascicles of smooth
muscle with no evidence of hypercellularity, pleomorphism,
mitotic activity, or necrosis
 Immunohistochemical stains confirm the smooth muscle nature
of the tumor
◦ strong diffuse positive staining for smooth muscle markers desmin and
caldesmin
◦ Some leiomyomas positively stain for HMB-45, suggesting a possible
link to angiomyolipoma and other PEComas
65

Small renal mass arising from
the renal capsule.
Medium-power magnification shows
uniform spindle cells with thin cigar-
shaped nuclei, without any
pleomorphism
Strong positive immunohistochemical
staining with smooth muscle actin in
the leiomyoma. Lack of smooth-
muscle actin staining in the normal
renal tubules on the right.
66

 Large lesions have traditionally been managed with radical
nephrectomy
 Nephron-sparing approaches should be considered for
peripherally located small lesions.
67

68

 Affect young adults
 No gender predilection
 Typically single and unilateral and for the
 Most part occur close to the renal pyramids and pelvis.
 They do not have a capsule
 Appear spongy red, with irregular vascular spaces lined by a
single-cell endothelial layer
 Renal hemangiomas are commonly sporadic but can also
occur with syndromes such as Klippel-Trenaunay, Sturge-
Weber, and systemic angiomatosis.
69

 Lymphangiomas are rare benign tumors arising from the renal
capsule
 Grows as a renal sinus mass or peripelvic mass.
 Some patients exhibit genetic abnormalities such as trisomy
7, monosomy X, and VHL abnormalities
 Lymphangiomas are encapsulated, diffusely cystic, with
communicating cysts composed of fibrous septations lined by
flat endothelium.
70

 Juxtaglomerular cell tumor (also known as reninoma) is a
benign tumor of the renal juxtaglomerular cell apparatus
 Women in the third and fourth decades
 Clinical presentation is dominated by hypersecretion of renin
and includes hypertension and hypokalemia and associated
symptoms such as polydipsia, polyuria, myalgia, and
headaches
 Laboratory testing - elevated plasma renin activity, secondary
hyperaldosteronism, hypokalemia, and a solitary renal lesion.
 Radiology - Small (<3 cm) solid hypovascular renal mass
71

 HISTOLOGY: Sheets of polygonal to spindle-shaped cells with
indistinct cell borders, abundant eosinophilic cytoplasm, and
minimal atypia
 IHC:
◦ Strong immunostaining for factor VIII and factor VIII–related antigens is
characteristic and confirms derivation from endothelial cell lineage.
◦ Cells will also stain for renin, CD34, vimentin, and actin
 Although a benign clinical course is expected, one case of
malignant reninoma has been documented in the literature
 Surgical excision, preferably sparing the remaining renal
parenchyma, results in rapid decline of plasma renin levels,
normalization of blood pressure, and resolution of the
associated symptoms
72

 Commonly seen at autopsy
 Measure less than 5 mm in size
 Asymptomatic, without any effect on blood pressure.
 Cells are polygonal or stellate in a basophilic stroma and
contain minimal collagen
73

 Intrarenal schwannoma is very rare, with fewer than 20 cases
reported.
 Tumors cause nonspecific signs and symptoms
 Well encapsulated, and are composed of spindle cells in a
palisading format
74

 Solitary fibrous tumor is a clinically important entity, as it
tends to manifest as a
◦ large mass with gross hematuria
◦ could be mistaken for RCC or sarcoma.
 Rare tumor reported in fewer than 50 patients to date
 Tumors arise from the renal parenchyma
 Well circumscribed, and consist of bland spindle cells and
collagenous bands.
 Typically, staining for CD34, CD99, and BCL-2 ascertains the
diagnosis of solitary fibrous tumor
75

 Benign renal tumors cover a wide spectrum and show
characteristic histology, histogenesis and anatomic distribution
 Some tumors like angiomyolipoma show characteristic imaging
findings that permit their diagnosis preoperatively.
 Most benign tumors appear as solid enhancing masses
indistinguishable from malignant tumors
 Biopsy & IHC may help establish the definitive diagnosis and
may obviate aggressive treatment.
76

77

BENING RENAL TUMORS

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