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Kidney tumor - cysts, children, adult benign

Benign (usually) adult tumors

Solitary fibrous tumor

Reviewers: Mandolin Ziadie, M.D. (see Reviewers page)
Revised: 30 March 2012, last major update March 2012
Copyright: (c) 2003-2012, PathologyOutlines.com, Inc.


● Benign (90%) tumor of patternless or storiform spindle cells with bland nuclear features, mixed with dense collagen
● See also Soft tissue tumor chapter


● Rare in kidney, arises from serosal surfaces of pleura and other sites

Clinical features

● May be associated with hypoglycemia (Eur Urol 2009;55:739, Ann Thorac Surg 2007;84:292)

Case reports

● 26 year old man (Can J Urol 2007;14:3583)
● 39 year old woman with giant (20 cm) tumor (Hinyokika Kiyo 2010;56:435)
● 48 year old woman with capsular tumor (Am J Surg Pathol 1996;20:1288)
● 50 year old woman with malignant component (Diagn Pathol 2011;6:96)
● 52 year old woman (Urol Ann 2011;3:158)
● 76 year old man with malignant tumor (Arch Pathol Lab Med 2006;130:857)
● 85 year old woman (Arch Pathol Lab Med 2006;130:117)


● Excision
● Almost always benign behavior

Gross description

● Large (up to 14 cm, Am J Surg Pathol 2001;25:1194), well-circumscribed
● Slightly nodular, gray-tan firm cut surface with hemorrhage / cystic change

Gross images

Various images

Malignant tumor

Micro description

● Patternless, hemangiopericytomatous or storiform pattern of bland spindle cells mixed with dense collagenous bands that may entrap renal tubules
● Variable lymphoplasmacytic infiltrate, variable myxoid change
● Usually no necrosis, no cystic change and no mitotic figures

Micro images

Patternless pattern of bland spindle cells

Various images-malignant tumor

Entrapped renal tubules

Malignant tumor with atypia and mitotic figures

Left: CD34+, right: vimentin

Top to bottom: CD34+, CD99+, Ki-67

Positive stains

● CD34, bcl2 and CD99 (these three confirm the diagnosis)
● Also vimentin, type IV collagen

Negative stains

● Cytokeratin, S100, p53, CD117, muscle markers and melanocytic markers

Electron microscopy description

● Fibroblast-like cells (irregular nuclei, prominent Golgi, branching rough endoplasmic reticulum, variable mitochondria and intermediate filaments, no thin filaments with focal densities, no tonofilaments and no cell-cell junctions)
● No myoepithelial or epithelial differentiation

Differential diagnosis

Cellular mesoblastic nephroma: congenital tumor of myofibroblasts with thin collagen fibers, smooth muscle actin+; has t(12;15)
Fibroepithelial polyp of renal pelvis: very rare, smooth glistening external surface, polyp covered by urothelium, collagen is present, but is not a tumor of spindle cells
Fibroma: no dense collagen, usually not CD34+, bcl2+ or CD99+
Fibrosarcoma (on needle biopsies): storiform pattern of atypical spindle cells
Gastrointestinal stromal tumor: kidney is a very unusual site, no dense collagenous bands and is CD117+
Inflammatory myofibroblastic tumor: tumor of myofibroblasts, actin+, desmin+, EBV+ by ISH, often keratin+ and usually CD34-
Neurofibroma: CD99-, CD34-, bcl2- (J Cancer Res Ther 2010;6:388)
Sarcomatoid renal cell carcinoma: infiltrative, atypical spindle cells, usually typical renal cell carcinoma component also present, keratin+ or vimentin+
Smooth muscle tumor: spindle cells have smooth muscle features, usually no dense collagen and positive for muscle markers
Synovial sarcoma: infiltrative, more atypical spindle cells, CD99+ but CD34-

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

Ref Updated: 3/12/12

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