Kidney tumor - adult malignancies
Benign (usually) adult tumors
Angiomyolipoma

Author: Pallav Gupta, M.D. (see Authors page)

Revised: 21 January 2016, last major update January 2016

Copyright: (c) 2003-2016, PathologyOutlines.com, Inc.

PubMed Search: Angiomyolipoma [title] kidney
Definition / General
  • Usually benign neoplasm composed of admixture of blood vessels, smooth muscle and adipose tissue
  • The amount of each component is variable
  • Apart from kidney, can occur in extrarenal sites such as liver, lungs, retroperitoneal soft tissue
  • May be sporadic but is associated with tuberous sclerosis and with TSC2 / PKD1 contiguous gene syndrome
Epidemiology
  • Usually diagnosed in adults
  • < 1% of all renal tumors
Pathophysiology
  • 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 and cardiac rhabdomyoma
  • More than 50% occur in patients without tuberous sclerosis
  • About 80% cases of tuberous sclerosis patients develop angiomyolipoma with loss of heterozygosity of TSC2 gene
  • Tumor adipose tissue and smooth muscle cells are monoclonal but clones may arise independently (Am J Surg Pathol 2001;25:1231)
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

    Tuberous sclerosis:
    • Autosomal dominant neurocutaneous disorder in 1 per 6 to 11,000 individuals
    • Characterized by hamartomas / tumors of brain (subependymal giant cell tumor), retina, skin (cutaneous angiofibromas), heart (rhabdomyoma), 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 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)
Prognostic Factors
  • Benign course
  • Tumors with pleomorphic features can have a more aggressive course
  • Sarcomatous transformation with distant metastasis is extremely rare
  • Retroperitoneal hemorrhage is important complication
  • Patients with bilateral disease can have renal failure
  • Death can occur due to invasion of contiguous organs particularly blood vessels
Case Reports
Treatment
Clinical Images
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CT, radiodensity same
as subcutaneous fat

Gross Description
  • Circumscribed, non encapsulated with pushing border
  • Cut surface can have red (vascular component), gray-white (smooth muscle component) or yellow (adipose component) appearance
  • Tumor ranges from 0.5 - 25cm with a mean of 6cm
  • May invade local lymph nodes and renal vein even though benign (Arch Pathol Lab Med 1990;114:65)
  • Capsular invasion in 25%
  • Tumors are 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

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Predominantly adipose

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Compresses and distorts renal pelvis

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Massive intratumoral hemorrhage



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Superior pole, right kidney

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Resembles yellow fat

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Fatty tissue, necrosis and prominent vessels

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With clear cell renal cell carcinoma

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51 year old woman with right lumbar pain

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
  • Vascular component is in the form of thick walled hyalinized vessels
  • Fat component is in the form of mature adipose tissue and is seen in >90% tumors
  • Epithelioid variant:
    • Pure or predominant population of polygonal cell with clear or densely eosinophilic cytoplasm, large hyperchromatic bizarre nucleus
    • Multilobated nuclei and multinucleation is common
    • Hemorrhage and necrosis are common
Micro Images

General

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Tumor extends into main renal vein

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Thick walled blood vessels

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Smooth muscle component

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Immature smooth muscle cells (leiomyoblasts)

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Bizarre and atypical changes

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Principally adipose tissue

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Thick-walled blood vessels

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Abnormal tumor vessels

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Trapped renal tubules

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Cyst

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Renal hilar lymph node



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Adipose tissue

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Smooth muscle component

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Adipose, smooth muscle and thick walled blood vessels

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Spindle cells

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51 year old woman with right lumbar pain had kidney mass



Cystic tumors

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Within liver parenchyma

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Case of the Week #359, H&E images

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CD10

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HMB45

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ER

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PAX8



With other tumors

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Pancreatic neuroendocrine carcinoma

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Lung adenocarcinoma



Stains

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HMB45+

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Melanocytic stains

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S100+ (hepatic tumor)

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Various stains (liver / kidney tumors)

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SMA+

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
Negative Stains
Molecular / Cytogenetics Description
Electron Microscopy Description
  • Premelanosomes
Electron Microscopy Images

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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