Inflammatory Fibroid Polyp

Definition

Gastrointestinal tract tumor characterized by spindle and stellate cells set in an inflammatory, myxoid stroma

Most are semi-pedunculated polyps arising in the submucosa
- Covered by mucosa or may be eroded
- Occasional tumors may be restricted to the lamina propria and muscularis mucosae
- Larger tumors may extend into muscularis propria
- Most <5 cm, rarely up to 20 cm
Composed of bland, uniform spindled and/or stellate cells
- The lesional cells may be lost in the background and difficult to identify
- Multinucleated giant cells in 1/3 of cases
Loose fibromyxoid background with regular vascular pattern
- Regular small to medium sized vessels throughout
- May have granulation tissue appearance
Eosinophil rich mixed inflammatory infiltrate
- Also includes lymphocytes, plasma cells, macrophages, mast cells
- Lymphoid aggregates may be seen
  - Germinal centers unusual
Frequent whorled, concentric “onion skin” pattern centered on blood vessels and glands
- 10% of cases may lack this pattern
  - May be accentuated by CD34 stain
  - It has been proposed that lack of this pattern correlates with large size but this is not supported by several studies
Most common in gastric antrum, followed by small intestine

Robert V Rouse MD
Department of Pathology
Stanford University School of Medicine
Stanford CA 94305-5342

Original posting/updates: 12/5/09, 11/27/11