Bladder & urothelial tract
Other tumors
Inflammatory myofibroblastic tumor
Author: Monika Roychowdhury, M.D.
Last author update: 1 December 2014
Last staff update: 28 May 2024
Copyright: 2003-2025, PathologyOutlines.com, Inc.
PubMed Search: Inflammatory myofibroblastic tumor bladder
Table of Contents
Definition / general | Terminology | Epidemiology | Sites | Etiology | Clinical features | Case reports | Treatment | Gross description | Gross images | Microscopic (histologic) description | Microscopic (histologic) images | Positive stains | Negative stains | Electron microscopy description | Molecular / cytogenetics description | Differential diagnosis | Additional referencesCite this page: Roychowdhury M. Inflammatory myofibroblastic tumor. PathologyOutlines.com website. https://www.pathologyoutlines.com/topic/bladderIMT.html. Accessed April 2nd, 2025.
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
Terminology
- 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
Epidemiology
- More common in children and young adults
- More common in females
Sites
- Bladder is most common site in genitourinary tract
Etiology
- 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
- 2 year old with sclerosing tumor that massively infiltrated bladder wall (Am J Surg Pathol 1992;16:1233)
- 27 year old woman with coexisting lupus (Int J Urol 2008;15:182)
- 30 year old man (Urol Ann 2010;2:78)
- 36 year old woman with abdominal pain and gross hematuria (Diagn Pathol 2008;3:11)
Treatment
- Conservative surgical excision, including in children (Pediatr Surg Int 2007;23:815)
Gross description
- Polypoid mass with pale, firm cut surface
- May be very large
- Often gelatinous
Gross images
Images hosted on other servers:
White, gelatinous
mass with cystic
change brand
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
AFIP images
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
Positive stains
- Smooth muscle actin, desmin, ALK1 (75-89%, (Am J Surg Pathol 2001;25:1364), vimentin, calponin
- Variable keratin (Hum Pathol 1994;25:181, Am J Surg Pathol 2006;30:787)
Negative stains
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
- Usually ALK+ or ALK gene rearrangements by FISH (Mod Pathol 2007;20:592, Am J Surg Pathol 2004;28:1609)
Differential diagnosis
