Kidney tumor - cysts, children, adult benign
Benign (usually) adult tumors
Inflammatory myofibroblastic tumor

Author: Mandolin Ziadie, M.D. (see Authors page)

Revised: 19 January 2017, last major update January 2012

Copyright: (c) 2003-2017,, Inc.

PubMed Search: "Inflammatory myofibroblastic tumor" kidney

Cite this page: Inflammatory myofibroblastic tumor. website. Accessed March 28th, 2017.
Definition / General
  • Rare spindle cell tumor in kidney with an inflammatory component
  • Rare; presents at a median age of 57 years, range 21 - 76 years, no gender preference
  • In GU, usually occurs in bladder but also reported in kidney, renal pelvis, ureter
Clinical Features
  • Patients may present with hematuria, flank pain or hydronephrosis
Case Reports
Gross Description
  • 4 - 13 cm, unencapsulated, partially circumscribed, firm white tumor in renal pelvis / adjacent soft tissue with a gelatinous / myxoid appearance
  • No hemorrhage, no necrosis
Gross Images

Images hosted on other servers:

Polypoid lesion of renal pelvis and calyces

Micro Description
  • Varies; patterns include myxoid vascular (similar to nodular fasciitis), compact spindle cell with lymphoplasmacytic aggregates and hypocellular keloid-like areas of fibrosis
  • Spindle cells are bland and uniform
  • Occasional foam cells, osseous metaplasia or mild nuclear atypia may be present
  • No / rare mitoses
Micro Images

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Spindle cells and inflammatory cells in myxoid stroma

Ill defined spindle cell proliferation of renal pelvis

Spindle cells in loose fascicular pattern

Various images

Various stains: smooth muscle actin+, vimentin+, CD34 stains some spindle cells and vessels

Positive Stains
Negative Stains
Differential Diagnosis
  • Fibromatosis: culture-like fibroblasts, infiltrative border, usually no inflammatory infiltrate
  • Fibrous histiocytoma: storiform pattern of fibrohistiocytic cells, possibly giant cells
  • Spindle cell sarcoma: spindle cells exhibit atypia