Bladder - Inflammatory myofibroblastic tumor (IMT)

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Bladder

Nonurothelial benign tumors

Inflammatory myofibroblastic tumor (IMT)

Reviewer: Monika Roychowdhury, M.D., University of Minnesota Medical Center (see Reviewers page)
Revised: 25 April 2011, last major update April 2011
Copyright: (c) 2003-2011, PathologyOutlines.com, Inc.

Definition
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● 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
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● 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
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● More common in children and young adults
● More common in females

Sites
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● Bladder is most common site in genitourinary tract

Etiology
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● Idiopathic, no known predisposing conditions

Clinical features
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● 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
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● 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 Mar 13;3:11)

Treatment
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● Conservative surgical excision, including in children (Pediatr Surg Int 2007;23:815)

Gross description
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● Polypoid mass with pale, firm cut surface
● May be very large
● Often gelatinous

Gross images
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White, gelatinous mass with cystic change and hemorrhage

Micro description
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● 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

Micro images
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Spindle cells and inflammatory cells in myxoid stroma

Resembles post-operative spindle cell nodule


Highly cellular spindle cell tumor with moderate atypia

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


Myofibroblastic cells and inflammatory cells in edematous stroma

Focal inflammatory cells


Spindle cells within fibromyxoid matrix and inflammatory cells

Various images

Inflammatory myofibroblastic tumor composed of spindle cells and inflammatory cells with no atypia and no necrosis

Comparison with leiomyosarcoma and embryonal rhabdomyosarcoma


ALK1 expression

Other images

Positive stains
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● 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
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● EMA, myogenin, p53 (Mod Pathol 2001;14:1043), h-caldesmon (Hum Pathol 1999;30:392)

Electron microscopy description
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● 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

EM images
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Myofibroblastic features of rough endoplasmic reticulum, peripheral smooth muscle myofilaments (long arrows), fibronectin fibrils (short arrows)

Molecular description
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● Usually ALK+ or ALK gene rearrangements by FISH (Mod Pathol 2007;20:592, Am J Surg Pathol 2004;28:1609)

Molecular images
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ALK translocation is indicated by separation of green and orange probes of ALK gene in inflammatory myofibroblastic tumor (a), but not leiomyosarcoma (b)

FISH analysis

Differential diagnosis
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● Leiomyosarcoma: smooth muscle morphology, strong desmin staining, keratin negative (Am J Surg Pathol 1989;13:480)
● Neurofibroma: neural morphology, strong S100+
● Rhabdomyosarcoma in children: necrosis or myxoid degeneration, moderate/severe nuclear atypia, more mitotic figures, no myofibroblastic differentiation; myoD1+, myogenin+ (Arch Pathol Lab Med 2001;125:1070, Am J Surg Pathol 1995;19:1224)
● Sarcomatoid (spindle cell) carcinoma

Additional references
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● Hum Pathol 1993;24:1203, Am J Surg Pathol 1993;17:264, Am J Surg Pathol 1985;9:366
● Am J Clin Path 1986;86:583, eMedicine

End of Bladder > Nonurothelial benign tumors > Inflammatory myofibroblastic tumor (IMT)

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