Inflammatory Myofibroblastic Tumor
Definition
- Tumor composed of cytologically bland spindled myofibroblasts with admixed inflammatory cells, predominantly occurring in infants and children
Alternate / Historical Names
- Inflammatory fibrosarcoma
- Inflammatory myofibrohistiocytic proliferation
- Inflammatory pseudotumor
- Omental-mesenteric myxoid hamartoma
- Plasma cell granuloma
- Plasma cell pseudotumor
Diagnostic Criteria
- Virtually all patients under 30 years
- Most under 14
- Grossly circumscribed
- Microscopically usually infiltrative
- May be multinodular
- May have associated reactive lymphadenopathy
- Composed of spindled myofibroblasts and inflammatory cells
- Spindle or stellate cells bland to mildly atypical
- Large vesicular oval nuclei
- No hyperchromasia
- Small nucleoli
- Variable amounts of pale eosinophilic cytoplasm
- Mitotic figures variable
- May be numerous but not atypical
- Large vesicular oval nuclei
- Ganglion-like cells may be seen
- Abundant eosinophilic to amphophilic cytoplasm
- Prominent large nucleoli
- May be numerous
- Prominent inflammatory cells, predominantly lymphocytes and plasma cells
- May include neutrophils and eosinophils
- May form germinal centers
- Foamy histiocytes occasionally present
- Spindle or stellate cells bland to mildly atypical
- Three patterns of cell mixtures described:
- Patterns may vary within the same tumor
- Pattern 1: Loose or myxoid stroma with prominent vascularity
- Pattern 2: Compact spindle cells
- Pattern 3: Densely collagenous with fewer spindle cells and inflammatory cells
- The following have been proposed as predictors of malignant behavior
- Aneuploidy by flow cytometry
- Frequent ganglion like cells
- p53 positivity by immunohistochemistry
- The utility of such grading has not been confirmed
- Rare reports of transformation to high grade malignant pattern
- Increased cellularity, atypical mitotic figures, necrosis
- Calcifying fibrous pseudotumor has been proposed to represent a sclerosing stage of inflammatory myofibroblastic tumor
Richard L Kempson MD
Robert V Rouse MD
Department of Pathology
Stanford University School of Medicine
Stanford CA 94305-5342
Original posting: May 15, 2008
Last update: June 15, 2008
