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Kidney tumor - cysts, children, adult benign

Benign (usually) adult tumors


Reviewers: Mandolin Ziadie, M.D. (see Authors page)
Revised: 23 July 2015, last major update January 2012
Copyright: (c) 2003-2015, PathologyOutlines.com, Inc.


● Usually benign neoplasm composed of thick-walled vessels, smooth muscle and adipose tissue with spindle and epithelioid cells
● The amount of each component varies
● May occur outside of the kidney
● May be sporadic but is associated with tuberous sclerosis and with TSC2 / PKD1 contiguous gene syndrome


● Usually diagnosed in adults
● < 1% of all renal tumors


● Member of perivascular epithelioid cell (PEC) tumor family (Arch Pathol Lab Med 2001;125:751), which includes pulmonary lymphangioleiomyomatosis; clear cell “sugar” tumors of pancreas, lung and uterus; also cardiac rhabdomyomas
● Tumors are neoplasms, not hamartomas
● Many cases have loss of heterozygosity of TSC2 gene
● Adipose tissue and smooth muscle cells are monoclonal but may arise independently (Am J Surg Pathol 2001;25:1231)
● Tumors stain positively with HMB45

Clinical features

● Characteristic radiologic appearance, benign behavior (almost always)
● Also occurs in liver (dominant epithelioid smooth muscle cell component), lungs, lymph nodes and retroperitoneal soft tissue
● May co-exist with renal cell carcinoma in non-tuberous sclerosis patients, particularly clear cell carcinoma, which is HMB45 negative (Mod Pathol 2001;14:157)
● Usually benign but may be complicated by hemorrhage, invasion of contiguous organs or non-contiguous involvement of other organs

Radiologic images

CT scan shows tumor has same radiodensity as subcutaneous fat

Tuberous sclerosis

● Autosomal dominant neurocutaneous disorder in 1 per 6-11,000 individuals
● Characterized by hamartomas / tumors of brain (subependymal giant cell tumor), retina, skin (cutaneous angiofibromas), heart (rhabdomyomas), bone, lung (lymphangioleiomyomatosis, multifocal micronodular pneumocyte hyperplasia) and kidney (angiomyolipoma in 40-80%, cysts, renal cell carcinoma [but some epithelioid tumors may be misclassified]); also mental retardation and infantile / childhood seizures
● Caused by alterations of TSC1 gene (9q34, encodes hamartin) and TSC2 gene (16p13.3, encodes tuberin, which interacts with hamartin)
● 60-70% of cases are tuberous sclerosis cases are sporadic (OMIM #191100); patients with tuberous sclerosis present at younger age, tumors are usually larger and more often bilateral (Urology 2008;72:1077)
● TSC2 / PKD1 contiguous gene syndrome: both kidneys are enlarged and cystic, have classic angiomyolipomas and rare intraglomerular microlesions (Am J Surg Pathol 2002;26:198)

Case reports

● 21 year old woman with tuberous sclerosis and intraglomerular microlesions composed of smooth muscle and adipose cells (Hum Pathol 2000;31:1325)
● 21 year old post-partum woman with spontaneous tumor rupture (Arch Gynecol Obstet 2009;280:643)
● 26 year old woman with 4 cm renal mass-AML with epithelioid cysts (Case of the Week #359)
● 44 year old woman with tuberous sclerosis and locally destructive tumor (Arch Pathol Lab Med 2005;129:676)
● 49 year old woman with tumor invading liver and lung metastases (Am J Surg Pathol 1991;15:1083)
● Two patients with lung and pancreatic tumors metastatic to angiomyolipoma (Arch Pathol Lab Med 2008;132:1016)


● Tumors may be embolized (Eur Urol 2009;55:1155); also excision
● Rarely recurs locally
● May cause death due to blood vessel invasion or retroperitoneal hemorrhage

Gross description

● Red (vascular component), gray-white (smooth muscle component) and yellow (adipose component) tumor that resembles clear cell carcinoma
● May invade local lymph nodes and renal vein even though benign (Arch Pathol Lab Med 1990;114:65); capsular invasion in 25%
● Tumors usually unilateral and unifocal
● Multiple (1/3) or bilateral (15%) tumors suggest underlying tuberous sclerosis
● Occasionally gross or microscopic cysts (Mod Pathol 2006;19:669)

Gross images

Solitary tumors:

Gray-white well circumscribed tumor

Tumor is composed predominantly of adipose

Tumor compresses and distorts renal pelvis

Massive intratumoral hemorrhage

Tumor resembles yellow fat,  fatty tissue, necrosis and prominent vessels #1,  #2,  #3

Multiple tumors:

Hemorrhagic tumor and smaller tumors,  yellow tumor nodules in parenchyma and renal pelvis,  gray tumor nodules in renal cortex

With clear cell renal cell carcinoma #1, #2

51 year old woman with right lumbar pain had USG, showing a kidney mass

Micro description

● Triphasic with myoid spindle cells, islands of mature adipose tissue and dysmorphic thick walled blood vessels without elastic lamina
● Smooth muscle component appears to originate from vessel walls and may be hypercellular, atypical, pleomorphic or epithelioid
● May resemble a high grade sarcoma if it metastasizes
Epithelioid variant: pure or predominant population of large, epithelioid cells with clear or eosinophilic cytoplasm, large hyperchromatic bizarre nucleus and possibly multinucleation, including an intimate relationship with vessel wall
● Hemorrhage and necrosis are common
● Adipose tissue may be scanty or dominant, and resemble well-differentiated liposarcoma
● Small mesenchymal nodules (< 2 cm) are precursors of angiomyolipoma (Mod Pathol 1996;9:1081)
● May have epithelial cysts (Am J Surg Pathol 2006;30:593, Mod Pathol 2006;19:669), prominent stromal sclerosis (Pathol Int 2008;58:306)

Micro images-general

Tumor extends into main renal vein

Triphasic: adipose, smooth muscle and thick walled blood vessels,  #6,  #7,  #8

Smooth muscle cells appear to arise from outer walls of blood vessels

Myomatous foci

Tumor consists principally of smooth muscle

Immature smooth muscle cells (leiomyoblasts) may be abundant

Bizarre and atypical changes in smooth muscle component

Tumor consists principally of adipose tissue

Thick-walled blood vessels resembling arterialized veins are characteristic

Abnormal tumor vessels may form aneurysms

Trapped renal tubules

Entrapped renal tubule has dilated to form a cyst

Tumor largely replaces a renal hilar lymph node

Spindle cells with cigar shaped nuclei and granular cytoplasm

51 year old woman with right lumbar pain had USG, showing a kidney mass

Micro images-cystic tumors

Epithelial lined cyst

Cambium-like layer

Cysts with AML type vessels

Large and small cysts with prominent lymphatics

Lymphatic rich smooth muscle

Prominent lymphatics and D2-40 staining

Tumor is present within liver parenchyma

Case of the Week #359:

H&E images

Left to right: CD10; HMB45; ER; PAX8

Micro images-with other tumors

Clear cell carcinoma

Pancreatic neuroendocrine carcinoma metastatic to angiomyolipoma

Lung adenocarcinoma metastatic to angiomyolipoma

Micro images-stains

    , spindle cells are focally HMB45+

Melanocytic stains in various components

S100+ (hepatic tumor)

Various stains (liver / kidney tumors)

PR+ subepithelial cells

Spindle cells are smooth muscle actin+

Cytology description

● Oval to spindled cells and cohesive stromal fragments, adipose tissue and branching blood vessels in a hemorrhagic background
● No mitotic figures (Cytopathology 2007;18:250)

Positive stains

In adipose, myoid and epithelioid cells:
● HMB45 (100%, Arch Pathol Lab Med 2002;126:49), MART1 / MelanA, muscle specific actin (HHF35, 100%), calponin (100%) and NKI-C3 (70-100%)
● Also CD117 (Am J Surg Pathol 2002;26:493), desmin, estrogen receptor (20%, Am J Surg Pathol 1999;23:1011), HMB50 (100%), microphthalmia transcription factor (50%, Am J Surg Pathol 2001;25:65), progesterone receptor (28%, usually women < age 50 with tuberous sclerosis), smooth muscle actin, tyrosinase (20-50%) and vimentin
● Also evidence of lymphatic differentiation (podoplanin and D2-40, Hum Pathol 2009;40:374), S100 (fat component)
Note: HMB45 and MelanA are positive in fat > smooth muscle > blood vessel components (Arch Pathol Lab Med 2007;131:122)

Negative stains

● Keratin, renin

Molecular description

● 5q- (Hum Pathol 1999;30:295), monoclonal (Hum Pathol 1998;29:1063)

Electron microscopy description

● Premelanosomes

Electron microscopy images

Various images

Differential diagnosis

Leiomyoma: usually no prominent vascular or adipose component, negative for melanocytic markers
Leiomyosarcoma: prominent atypia, infiltrative, usually no prominent vascular or adipose component, negative for melanocytic markers
Melanoma: marked atypia, no prominent adipose or vascular component
Oncocytoma: oncocytes are prominent; no prominent adipose or vascular component, negative for melanocytic markers
Pleomorphic rhabdomyosarcoma: smooth muscle component is markedly atypical, tumor is infiltrative, no prominent adipose or vascular component, negative for melanocytic markers
Renal cell carcinoma: usually marked atypia and infiltrative margins, not triphasic, negative for melanocytic markers

Additional references


End of Kidney tumor - cysts, children, adult benign > Benign (usually) adult tumors > Angiomyolipoma

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