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Bladder

Bladder tumors - benign

Inflammatory myofibroblastic tumor (IMT)

Author: Nat Pernick, M.D. (see Authors page)

Revised: 28 February 2010, last major update February 2010

Copyright: (c) 2002-2010, PathologyOutlines.com, Inc.

Definition

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● Rare myofibroblastic spindle cell neoplasm of bladder, more common at other sites (lung, soft tissue, bone)

● Similar to postoperative spindle cell nodule, but without a history of surgery

Terminology

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● IMT is terminology for neoplastic lesions

● Inflammatory lesions are often called pseudotumors

● Also called pseudosarcomatous fibromyxoid tumor

Epidemiology

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● Usually middle-aged women

Sites

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Etiology

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Clinical features

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● Pain, fever, weight loss, anemia, thrombocytosis, increased erythrocyte sedimentation rate, elevated gamma globulins

● Benign, but frequently misinterpreted as leiomyosarcoma or rhabdomyosarcoma

● May recur locally, but doesn’t metastasize (Am J Surg Pathol 2006;30:1502)

Prognostic factors

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●

Case reports

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● 2 year old child with sclerosing inflammatory pseudotumor that massively infiltrated bladder wall (AJSP 1992;16:1233)

● 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)

Clinical images

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Gross description (Macroscopy)

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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 (Histopathology)

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● 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 (J Clin Pathol 2008;61:428)

● 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                      Resembles post-operative spindle

cells in myxoid stroma                                     cell nodule

Highly cellular spindle cell tumor                   AFIP Fig 2-71: abundant thin walled vessels

with moderate atypia

Myofibroblastic cells and inflammatory cells in edematous stroma

Focal inflammatory cells                  Spindle cells within fibromyxoid

                                                                matrix and inflammatory cells

Resembles low grade myxoid leiomyosarcoma                                                    ALK1+

Fig a/b: compact fascicles of spindle cells with inflammatory cells

Fig c: looser spindled cells in myxoid background

Fig d: diffuse ALK1+ in cytoplasm

Inflammatory myofibroblastic tumor composed       Comparison with leiomyosarcoma

of spindle cells and inflammatory cells with no         and embryonal rhabdomyosarcoma

atypia and no necrosis;

tumor extends into muscularis propria

ALK1 expression

Other images: #1

Cytology description

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Cytology images

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Positive stains

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● Smooth muscle actin, desmin, ALK1 (also by FISH, Mod Path 2004;17:765, AJSP 2004;28:1609), vimentin, calponin

● Variable keratin (Hum Path 1994;25:181, Am J Surg Pathol 2006;30:787), h-caldesmon (Hum Pathol 1999;30:392)

Negative stains

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● EMA, myogenin, p53 (Mod Path 2001;14:1043)

Electron microscopy descriptions

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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

Electron microscopy images

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Myofibroblastic features of rough endoplasmic reticulum,

peripheral smooth muscle myofilaments (long arrows),

fibronectin fibrils (short arrows)

Molecular / cytogenetics description

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● Usually ALK+ or ALK gene rearrangements (Mod Pathol 2007;20:592)

Molecular / cytogenetics images

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ALK translocation is indicated by separation             FISH analysis

of green and orange probes of ALK gene in

inflammatory myofibroblastic tumor (a),

but not leiomyosarcoma (b)

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+ (Archives 2001;125:1070, Am J Surg Pathol 1995;19:1224)

● Sarcomatoid (spindle cell) carcinoma

Additional references

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● Hum Path 1993;24:1203, AJSP 1995;19:1224, AJSP 1993;17:264, AJSP 1985;9:366, AJCP 1986;86:583, eMedicine

End of Bladder > Benign tumors > Inflammatory myofibroblastic tumor (IMT)

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