Nonurothelial benign tumors
Inflammatory myofibroblastic tumor (IMT)

Author: Monika Roychowdhury, M.D. (see Authors page)

Revised: 8 June 2016, last major update December 2014

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

PubMed Search: Inflammatory myofibroblastic tumor bladder
Cite this page: Inflammatory myofibroblastic tumor (IMT). website. Accessed October 22nd, 2018.
Definition / general
  • Rare myofibroblastic spindle cell neoplasm of bladder with unknown neoplastic potential, more common at other sites (lung most common followed by soft tissue, bone)
  • Similar to postoperative spindle cell nodule, but without a history of surgery
  • Characterized by spindle cell proliferation with characteristic fibroinflammatory and pseudosarcomatous appearance
  • Inflammatory myofibroblastic tumor (IMT) is terminology for neoplastic lesions
  • Inflammatory lesions are often called pseudotumors
  • Also known as pseudosarcoma, atypical myfibroblastic tumor, atypical fibromyxoid tumor, plasma cell granuloma
  • More common in children and young adults
  • More common in females
  • Bladder is most common site in genitourinary tract
  • Idiopathic, no known predisposing conditions
Clinical features
  • Pain, fever, weight loss, anemia, thrombocytosis, increased erythrocyte sedimentation rate and elevated gamma globulins are more common with IMTs arising at sites other than bladder
  • IMTs in bladder present with painless hematuria
  • Benign, but frequently misinterpreted as leiomyosarcoma or rhabdomyosarcoma
  • May recur locally, but doesn’t metastasize (Am J Surg Pathol 2006;30:1502)
Case reports
Gross description
  • Polypoid mass with pale, firm cut surface
  • May be very large
  • Often gelatinous
Gross images

White, gelatinous mass with cystic
change and hemorrhage

Microscopic (histologic) description
  • Essential criteria: spindled myoepithelial cell proliferation and lymphocytic infiltrate
  • Patterns include:
    (1) loose stellate cells with myxoid background containing scattered inflammatory cells (nodular fasciitis-like)
    (2) spindle cells with a compact fascicular pattern (fibrohistiocytoma-like)
    (3) sparse cellular, collagenous areas (desmoid-like)
    (4) mixed

  • Cells are stellate myofibroblasts with abundant eosinophilic cytoplasm, elongated nuclei
  • May be cellular and infiltrative with mucosal ulceration, necrosis, cytologic atypia
Microscopic (histologic) images

Images hosted on Pathout server:

AFIP (3rd Series) Fig. 2-71: abundant
thin walled vessels

Images hosted on other servers:

ALK1 expression

Focal inflammatory cells

Myofibroblastic cells and inflammatory
cells in edematous stroma

Spindle cells within fibromyxoid matrix and inflammatory cells

Comparison with leiomyosarcoma
and embryonal rhabdomyosarcoma

Electron microscopy description
  • Myofibroblasts: bipolar cells with eosinophilic, elongated, tapering cytoplasmic processes without striation, central oval nuclei with smooth contours, open chromatin, occasional nucleoli
  • No evidence of smooth muscle or skeletal muscle differentiation
Molecular / cytogenetics description
Differential diagnosis