Kidney tumor
Benign adult tumors
Inflammatory myofibroblastic tumor

Topic Completed: 1 January 2012

Revised: 20 September 2019

Copyright: 2003-2019,, Inc.

PubMed Search: "Inflammatory myofibroblastic tumor" kidney

Mandolin S. Ziadie, M.D.
Page views in 2018: 649
Page views in 2019 to date: 719
Cite this page: Ziadie MS. Inflammatory myofibroblastic tumor. website. Accessed December 6th, 2019.
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

Microscopic (histologic) 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
Microscopic (histologic) images

Images hosted on other servers:

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
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